Understanding Radiation, Radioactivity, and Ionizing Radiation

Understanding Radiation, Radioactivity, and Ionizing Radiation


All too often all that people know about radiation is its connection to the atom bomb and its massive destructive powers.  The terms Radiation and Radioactivity or Radioactive are used interchangeably, while not always technically correct, and most have never even heard of Ionizing Radiation.  In this article we will peer into this invisible part of our universe to better understand what they are, their relationship to one another, and how they are different.

What is Radiation?

Let’s begin by first understanding what Radiation is.  Radiation is the emission or transmission of energy in the form of waves or particles through space or through materials.  The two energy forms, waves and particles, are important to understand so let’s explore each of these beginning with energy in the form of waves.

The word radiation arises from the phenomenon of waves radiating meaning traveling in all directions, from a source.  One visible example of waves being radiated is when you drop an object onto a body of still water that produces waves emitted from the center and traveling outwards.  Another great example is our sun, which radiates its energy outward in all directions. 

When we think of the sun, we think of it radiating visible light, but in fact it also radiates infrared and ultraviolet light as well.  The infrared, visible, and ultraviolet energies are all part of what is called the Electromagnetic Spectrum. 

The Electromagnetic spectrum as represented on the accompanying chart is a range of energies measured by their frequency (in terms of Hertz or cycles per second), their wave lengths, and their photon energies.


Electromagnetic Spectrum

This chart shows the electromagnetic spectrum of waves and begins at the left side of the chart with low energy, long waves known to us as radio waves. Radio waves can be anywhere from one kilometer to 1,000 kilometers and more in length. As the energy increases, the wave frequency also increases with the wavelength becoming shorter and shorter until you arrive at the far-right side of the spectrum where the wave length is only a small fraction of the diameter of an atom and where the frequency and energy strength are both very high.

While we may not readily recognize these wavelengths, we do easily recognize the devices that operate at these different energy levels such as radios, microwave ovens, and infrared lamps. Going up in energy there is the very narrow visible energy band we humans are able to see with our eyes. After visible light, the energies progress on to ultraviolet, through x-rays, and ending with gamma-rays.

Man has been able to use the different frequencies to operate separate AM & FM radio broadcasting channels for our listening pleasure, navigation systems like LORAN, GPS, and beacons, communications for HAM radio, cell phones, walk i-talkies, secure military communications, emergency broadcasting, Morse code, Telecom and much much more.

What is Ionizing Radiation?

A primary concern is at what energy level across this entire spectrum do we begin to experience negative effects that cause damage to our bodies?  More specifically, at what energy point do we see cell damage occurring in the tissues that make up our body?  While this question continues to be vigorously debated today as in the case of cell phones, one clearer distinction is the energy level required that cause changes to the electrical charges within atoms.

Atoms as we know all have a delicate balance of protons, neutrons and electrons.   Any radiation energy with sufficient power to knock off electrons results in an imbalanced charged atom known as an ion.  Scientists have measured the radiation with enough power to knock off electrons at about 10 electron volts and higher and have classified them as ionizing radiation.  Any radiations with insufficient power to knock off electrons are classified as non-ionizing radiation.

The ionizing region begins in the midst of the ultraviolet range of energies and then proceeds through the increasingly higher x-ray and gamma regions.  That is why we see cautionary measures being exercised anytime we’re exposed to these type of ionizing radiations.  Studies have shown that Ion Atoms with missing electrons results in an electrical imbalance that cause chemistry changes to occur to the molecules and also our DNA that make up our tissues and can lead to harmful outcomes. 

Damage to cells vary by energy and the amount of exposure they receive.  Ultra-violet energy is relatively low and does not have much penetration capability so damage is limited.  X-rays and Gamma-rays on the other hand are both very powerful as they are more energetic and have deep penetrating power. 

When exposed to low or intermittent levels of ionizing radiation our bodies are able to handle it and repair themselves.  But when the exposures are too severe, our bodies cannot keep up with the rate of damage and we begin to experience radiation sickness, burns, and death in the most extreme cases.


What is Radioactivity?

This now leads us to the last term Radioactivity.  Radioactivity is when alpha, beta, and neutron particles from inside an atom’s interior are spontaneously being emitted or ejected either because they are:

  • Electrically unstable
  • Being bombarded by man made accelerators
  • Interacting with other radioactive materials as in the case of producing fission.

There exists a variety of radioactive elements that occur naturally here on earth like uranium, thorium, potassium, radium, and radon.  Added to this are man made radioactive elements like plutonium, americium, californium, and einsteinium to name a few.

All of these radioactive elements emit particles as they strive to neutralize their energy in a process we call decay.  Some elements will emit particles for fractions of a second before neutralizing and becoming non-radioactive; others can take up to millions of years.

While the particles types and energies will differ they are classified as ionizing type of radiation along with their higher energy electromagnetic wave counterparts.  The chart seen here gives us a good overview of radiation as a whole with distinction between particles and electromagnetic waves and between non-ionizing and ionizing classifications.

Radiation Chart


In conclusion radiation is energy being emitted or transmitted through space or materials like the tissue in our bodies.  We are most concerned with ionizing type of radiation where the radiation energy has sufficient power to knock off electrons that can cause harmful effects to our bodies if we receive excessive exposures.

Electromagnetic waves in the form of x-rays and gamma-rays are ionizing radiation.  So too are radioactive elements emitting alpha, beta, gamma and neutrons particles.

Knowing what these terms mean helps us to better understand the invisible realm all about us.

Radioactive Consumer Products

Radioactive Consumer Products

Radioactive Consumer Products Around Us

Most people are unaware of the fact that there are several radioactive consumer products in existence.  Radioactive materials ability to radiate its rays flawlessly over many years without an external power source has attracted manufactures to utilize them.  Other times they are utilized for their illumination properties.  In many cases the materials best suited to their purpose just so happened to also be naturally radioactive. 

Naturally radioactive materials have very low activity levels and present no threat to us or society.  They represent the most common type of radioactive consumer products still in existence.  Most others have fallen out of favor and have been replaced with substitute materials and means. While naturally radioactive materials pose no threat, they can present problems when grouped together in larger volumes reaching the size of a shipping container or a semi-truck.  The collective volume produces enough activity to trigger alarms whenever they are scanned by radiation detectors at shipping yards or border crossings. 

Here’s a list of the more common radioactive consumer products from the present, recent past, and even cray stuff from the long past.


Radioactive Clockface

Clocks & Watches

Some luminous watches and clocks contain a small quantity of hydrogen-3 (tritium) or promethium-147. Older watches and clocks (made before 1970) may contain radium-226 paint on dials and numbers to make them visible in the dark.

Smoke Detector

Smoke Detectors

This application probably wins the prize for the least expected radioactive consumer product.  Most smoke detectors used in our homes utilize americium-241, a radioactive element.

The radioactive material is positioned between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm. 

Unless tampered with, smoke detectors pose little to no health risk; a smoke detector’s ability to save lives far outweighs the health risks from the radioactive materials.  Visit RadTown to learn more.

Thorium Welding Rod

Thorium Welding Rods

Thoriated welding rods are really electrodes used in tungsten inert gas (TIG) welding.  This type of welding is typically used where high-quality welding is required like in the aircraft and petrochemical industries.  Thorium is added to the tungsten because it increases the current carrying capacity of the electrode and it reduces contamination of the weld. In addition, it is easier to start the arc and the latter is more stable. 

By weight, the rods are usually 1 or 2% thorium oxide although higher concentrations up to 4% have been used.  The rods are color coded to indicate the thoria content: yellow indicates 1 %, and red indicates 2 %. The color usually appears as a band at one end of the rod. While they range from 0.25 to 6.35 mm in diameter and 7.6 to 61 cm long, a “typical” rod would be about 2.4 mm in diameter, 15 cm long, and contain 0.23 grams of thorium. Estimates over the last two decades put the annual production at 1 to 5 million electrodes.

Radioactive Gas Mantle

Gas Lantern Mantles

Older, and some imported, gas lantern mantles generate light by heating thorium (primarily thorium-232). Unless gas lantern mantels are used as the primary light source, radiation exposure from thorium lantern mantles is not considered to have significant health impacts.  Because they were so readily available in the past, they were also frequently used to verify or demonstrate radiation meters!

CRT Monitor

CRT Computer Monitors

Older televisions and computer monitors that contain cathode ray tubes (CRTs) may emit x-rays. X-ray emissions from CRT monitors are not recognized as a significant health risk.

Radioactive Fertilizer


Commercial fertilizers are designed to provide varying levels of potassium, phosphorous, and nitrogen to support plant growth. Such fertilizers can be measurably radioactive for two reasons: potassium is naturally radioactive, and the phosphorous can be derived from phosphate ore that contains elevated levels of uranium.

Water Softner

Water Softner

A variety of materials can be used as the water softener salt, e.g., sodium chloride (NaCl) or potassium chloride (KCl). In the example shown here, the water softener salt is over 99% potassium chloride.

All potassium contains potassium-40, a naturally occurring beta gamma emitter, and in large enough quantities it is easily detected with a simple survey meter. This bag, for example, could not get through a monitor at a nuclear power plant without setting off an alarm.

Radioactive Ceramics


Ceramic materials such as tiles and pottery may contain elevated levels of naturally-occurring uranium, thorium, and/or potassium. In many cases, the activity is concentrated in the glaze. Unless there is a large quantity of the material, the amount of radioactivity in these products is unlikely to be greater than natural background levels. However, some older dishware (e.g., pre-1972 Fiesta®ware) can have radioactivity exceeding background levels; to minimize health risks, you may not want to use these pieces for eating or drinking.

Radioactive Glassware


Glassware, especially antique glassware with a yellow or greenish color, can contain easily detectable quantities of uranium. Such uranium-containing glass is often referred to as canary or vaseline glass. In part, collectors like uranium glass for the attractive glow that is produced when the glass is exposed to a black light. Even ordinary glass can contain high-enough levels of potassium-40 or thorium-232 to be detectable with a survey instrument. However, the radiation received when using glassware – even canary or vaseline glass – is unlikely to exceed background radiation levels.

Thorium Camera Lens

Camera Lenses

Older camera lenses from the 1950s-1970s incorporated thorium into the glass, allowing for a high refractive index while maintaining a low dispersion. The health risk from using older camera lenses is low; the radiation received when using a thoriated lens camera is approximately equal to natural background.

Radioactive Exit Signs

Exit Signs

Some EXIT signs contain the radioactive gas called tritium, allowing them to glow in the dark without electricity or batteries. The tritium used in EXIT signs gives off low-level beta radiation, causing a light-emitting compound to glow. Tritium EXIT signs do not pose a direct health hazard, as the beta radiation can be stopped by a sheet of paper or clothing. Tritium EXIT signs must not be disposed of in normal trash.  Learn more about tritium exit signs.

Brazil Nuts

Brazil Nuts

It has been known since the 1930s that Brazil nuts contain relatively large concentrations of barium (approximately 0.1 – 0.3% by weight).  That Brazil nuts also contain high levels of radium was first reported in the 1950s.

Brazil nuts are the seeds of Bertholletia excelsa, a large tree that is grown in various parts of world, not just Brazil.  The nuts, in groups of 12 to 25 much like the sections of an orange, form the globular (4-6” diameter) fruit of the tree.  It is not true, as is sometimes thought, that the high concentration of radium in Brazil nuts is due to elevated levels of the uranium and/or thorium series in the soil in which the tree grows. The accumulation of the radium (and barium) is due to the very extensive root system of the tree. For what its worth, measurements by Penna-Franca et al indicated that higher radium concentrations are found in the leaves and cork of the tree than in the nut.

Crookes Spintharscope

Crookes Spintharscope

The spinthariscope was invented in 1903 by William Crookes. These two photos show an example of the first commercially-available version of the spinthariscope. This particular spinthariscope came from Robert Millikan’s Laboratory at Cal Tech and dates from the 1920s or earlier.

After dark-adapting the eyes, the viewer looks through the lens of the spinthariscope and observes a screen of zinc sulfide where tiny flashes of light appear, an image Crookes described as a “turbulent luminous sea.” Each flash of light is produced by an alpha particle emitted from a tiny sample of radium on the tip of a pointer positioned just above the screen. The spinthariscope can be considered the first radiation counter, i.e., it is capable of recording individual events.

Crazy Radioactive Consumer Products & Services from Long Ago

Shortly after Wilhelm Roentgen discovered X-rays and Marie Curie’s discovery of radium, the world immediately recognized the powerful value in the field of medicine.  Not to be left behind, enterprising individuals introduced their own elixirs to remedy ailments of almost any kind.  It did not take too long, in most cases, to realize they did more harm than good.    With our current knowledge of radioactivity and the risks to health, we view these early adoptions with shock and horror; but back then, they simply had no idea.

Below are some of the more interesting innovations of the time.



A Thomas Radium C. R. (aka Thomas Radium Ore) jar promised good health to those who drank waters stored in them. 

A short note in the February 1921 issue of Popular Science Monthly written by him stated”

“Pottery is now manufactured which has in it a small percentage of radioactive material. This is mixed with the clay and baked in the kiln. Water left in the pottery of this nature for a short time will become radioactive by induction, and a health-giving drink is made. Such water may also be employed in the watering of plants with good results, since the presence of a radioactive compound near the roots of a plant is very helpful to its growth.”

Thomas placed the following advertisement in the November 5, 1921 issue of the El Paso Herald:

RADIUM ORE. that will keep you supplied with soft Radio Active Water for generations is the greatest remedy and cure ever discovered for each and every disease.

Degens Eye Glasses

Degnen's Radioactive Eye Applicator

Quoting the manufacturer’s literature: “the Radio-Active lenses will be found helpful in imperfect refraction, MYOPIA or Nearsight, HYPERMETROPIA or Farsight, PRESBYOPIA or Oldsight, HETROPHOBIA or difficulty in focussing.”

“Headaches, caused by eyestrain and other eye disorders, can be quickly relieved by the use of the lenses.”

“The best results are obtained by wearing the lenses for a period of from five to ten minutes twice a day, keeping the eyes closed during treatment.”

A brochure describing Degnen’s Radio-Active Eye Applicator includes testimonial letters that date from 1921 and 1922.

Exposure Rates:   10 – 15 uR/hr above background at one foot

Energized Golf Ball

Energized Golf Ball

The ENERGIZED Golf Ball, highest quality ball made in the USA, is treated with gamma rays from radioactive Cobalt 60 in our laboratories in Oak Ridge to give it greater distance and a tougher cover.  It has a steel center and carries an exclusive guarantee that compression will be a constant 95+.  Also the ENERGIZED Golf Ball conforms to USGA Rules.  Exclusively unique, this new golf ball creates interest, excitement, fun.

Frisky Whiskey

Frisky Whiskey

This one is not exactly a radiation consumer product, but fun and interesting at the same.  According to the label on the front of the bottle, it was produced by the fictitious Oak Ridge Distilling Company, aged by radiation and tested with a Geiger Counter. In reality, it is an empty plastic container with a battery powered motor inside that causes the bottle to shake violently when it is picked up. That’s what the label is referring to when it states “you will note its 150 proof strength from the moment you pour.” Since it comes empty, it is up to you to fill it with your favorite beverage.

The earliest reference for the “Frisky Whiskey” is a brief mention in the December 13, 1965 issue of the Odessa American. It was said to add laughs galore to a Christmas party – exploding cigars were also recommended. The following year, it was advertised as a great Father’s Day present (Cincinnati Enquirer, June 12, 1966):

“Frisky Whiskey bottle looks so innocent . . .watch the unsuspecting dad pick it up . . as he starts to pour, the bottle starts vibrating to shake his hand uncontrollably.”

Shoe Fitting Fluorscope

Shoe Fitting Fluoroscope

One of the most unexpected radioactive consumer products is the shoe fitting fluoroscope.  This was a common fixture in shoe stores during the 1930s, 1940s and 1950s. A typical unit, like the Adrian machine shown here, consisted of a vertical wooden cabinet with an opening near the bottom into which the feet were placed. When you looked through one of the three viewing ports on the top of the cabinet (e.g., one for the child being fitted, one for the child’s parent, and the third for the shoe salesman or saleswoman), you would see a fluorescent image of the bones of the feet and the outline of the shoes.

According to Duffin and Hayter, Dr. Jacob Lowe created his first fluoroscopic device for x-raying feet during World War I. By eliminating the need for his patients to remove their boots, the device sped up the processing of the large number of injured military personnel who were seeking his help. After the war, he modified the device for shoe-fitting and showed it for the first time at a shoe retailer’s convention in Boston in 1920.

If you wish to dispose of any of the radioactive items presented here or from industrial products, call Radiation Solutions at 208-206-3203.

Remembering the Harmful Effects of Ionizing Radiation

Remembering the Harmful Effects of Ionizing Radiation

Harmful Effects from Ionizing Radiation Known Since the Beginning

Scientists have known for a very long time now that exposure to ionizing radiation can have harmful effects in humans.  Awareness first manifested itself by radiation burns on the early experimenters who paid dearly for their work.  Fortunately, modern radioactive devices employ many well engineered safety measures to prevent this from ever happening when used properly.  Radiation induced injuries are relatively rare anymore which is a very good thing.  But it can also result in a lack of full appreciation for what damage can occur if ignored.  This article serves as a reminder of how harmful and painful radiation burns can be if we don’t take all safety precautions and procedures seriously.

The early pioneers investigating radioactivity in the late 1800’s and early 1900’s were not aware of the harmful effects until radiation burns began manifesting themselves.  Radiation burns were first noted in 1896, within just one month after Roentgen’s announcement of the discovery of what he called x-rays.  Within a year or two it became widely known that those working with x-ray devices had to take some precautions.

Early experimenters with natural radioactive sources were not immune from harmful effects and also received burns.  Most notable was Henri Becquerel who burned himself by carrying a sample of radium in his pocket.  The famous Marie Currie and her husband Pierre also received radiation burns on their skin from their work with radium and are believed to have also developed leukemia.  While Pierre was tragically killed relatively early and was largely spared long term suffering, Marie’s lifetime exposure resulted in a great deal of pain that she had to endure, especially to her hands.

By 1905 it was also known that excessive exposure to radiation could cause cancer.  Repeated large doses to the hands of workers frequently caused fatal skin cancer.  Many of the early medical radiologists either died of skin cancer or had to have their fingers or hands amputated. 

Immediate and Long-Term Effects of Ionizing Radiation

Very large doses of radiation can cause harmful health effects within just hours or weeks.  Such effects are called prompt effects because they appear relatively soon after the exposure.  The prompt effects result in radiation burns to the skin as well as radiation sickness, which can be fatal.

Other effects that manifest themselves years later are called delayed effects.  Cancer and genetic effects in offspring are examples of delayed effects

Radiation Burns

A radiation burn is not a temperature induced injury as the name would suggest; however, the cell damage appears in identical fashion; hence the name.  The severity of the cellular damage by ionizing radiation increases with dosage.  Lower one-time doses enable the body to heal itself over time.  As the dose levels increase, additional medical attention will be required to assist in recovery.  Eventually you reach a dose level where the damage becomes so great death becomes inevitable.  The chart below presents the prompt effects of one-time doses at increasing dose levels.

Effects to One-Shot Doses

600 rem

Radiation cell damage is equivalent to a first-degree heat burn or mild sunburn.  Within a few hours reddening occurs and often disappears over the next few days as the body does its healing work (assuming no further exposures occur). 

1000 rem

Results in serious tissue damage like a second-degree heat burn.  The initial inflammation is followed by swelling and tenderness.  Blisters will form within 1-3 weeks and break open leaving raw, painful wounds susceptible to infection.  Hands exposed to these dose levels become stiff and finger motion is often painful.  After several months the visible damage may heal but there will be some permanent damage to the surrounding tissue and make it more susceptible to injury in the future.

2000-3000 rem

An injury resembling a scalding or chemical burn is caused.  Medical treatment is immediately needed.  The injury may not heal without surgical removal of the exposed tissue.  Damage to blood vessels also occurs.  Future medical problems can be expected as this area will be more susceptible to pain, lower resistance to injury and reopening of the wound.

> 3000 rem

When more than 3000 rems are received at one time the tissue is completely killed and must be surgically removed. 

Prolonged Dose Effects

A radiation dose between 5000 to 10,000 rems received gradually over a period of several weeks will result in a chronic irritation, inflammation, dryness, and itching of the skin.  Once this condition has developed, it seldom heals completely.  Open sores may erupt and the regenerative and recuperative powers of the body are greatly reduced.  Malignant skin cancer occurs in a large percentage of these cases.

Severe Radiation Burn Cases

Back Pocket Carry

In 1979 a man found a 28-curie iridium radiography source that had accidently been left at the jobsite by a radiographer.  Not being a radiation worker or understanding what the material was he picked it up and put it in his back pocket for about 45 minutes. 

About an hour after the exposure he became nauseated, at 6 hours he noticed a burning feeling and a reddening of his right buttock.  The burning and reddening got worse and after 2 days went to a doctor.  The doctor not knowing what he was dealing with assumed the skin irritation was most likely caused by an insect bite.  But the burn got worse and worse until it became a large open sore.  After 17 days, the man was hospitalized and it took another three days of persistent questioning by doctors before they realized that he had a radiation burn.  By this time the man had an open wound about 4 inches in diameter and 1 inch deep.  Figure 1 shows the wound 31 days after the incident. 

It was later calculated that the radiation dose to the man’s right buttock exceeded 20,000 rems.  At a tissue depth of about 3 inches the dose still exceeded 1000 rems. 

To treat the burn, doctors surgically removed the dead tissue and a thick piece of skin from his thigh was sewn to close the wound, see Figure 2.  Six months later, the skin flap edge was not healing so at 10 months a second skin flap was sewn on.  At 19 months, the wound was still not healed, see figure 3 & 4, and further constructive surgery would be needed.  Two years after the accident, the man still walks with a limp and experiences pain where he was burned.

Figure 1
Figure 2
Figure 3
Figure 4

Front Pocket Carry

A similar incident occurred to a man in Argentina who placed a highly radioactive source in his front packet.  The front pocket location placed the source too close to his arteries that carried blood to his legs.  The arteries disintegrated because of the radiation damage and both legs had to be amputated.

Fatality Cases

Construction Watchman

The previous two cases were about those who survived, but there are also very sad fatalities that have been recorded.  In March of 1962 a construction watchman in Mexico was given a 5-curie Co-60 source for safekeeping by his employer.  Not understanding what he had, he took it home for safe-keeping where he, his wife, mother-in-law, son, and daughter were all exposed over a period of several months.  The employer retrieved the source in late July.  The damage was done, and one-by-one, members of his family began dying beginning in April and ending in Oct of that year.  Only the watchman survived because he was away so much of the time working.   

Scrap Yard in India

An incident in India more recently occurred whereby a university abandoned irradiator was taken to a metal scrap yard by individuals who had no idea what the device was.  The scrap yard placed the irradiator next to their worker bunk house.  A few days later several men became sick and at least one died. 


Fortunately, severe cases like those presented herein are rare.  Never-the-less, accidents and moments of forgetfulness do still occur.  Maintaining diligence is something Radiation Safety Officers and all those who work with or around radiation sources and devices cannot afford to ignore. 

The stealth properties of radiation make us vulnerable and so we each need to practice and follow procedures very carefully to avoid incidents of any kind.  It’s too easy to take safety for granted or to ignore when it comes to radiation exposure.  It’s much easier to think and act safely when climbing a ladder high above the ground.  It’s quite another mindset that is needed when you cannot see, smell, hear, taste or feel the impending danger.   Its stealthy nature all too often lure us into a false sense of security or a relaxed state of mind that typically exists at the beginning of any radiation incident.

While the incidents shown here are severe in nature, less severe exposures can still impact the quality of our lives, and we need to remember that too.  Sometimes we need a good dose of reality of what has already happened to others to fully appreciate the dangerous nature of the materials that are all about us in the industrial world.  Remembering the very real-life tragedies of others along with training and repeat training will hopefully keep your radiation safety program on guard at all times and in all places. 

Radiation safety should never be an after-thought, or just another item added to an already long list of duties.  It needs to be taken very, very seriously.  Let the tragic lessons of others be ever present on your mind as you strive to protect your fellow workers, friends and family.  Ionizing radiation is an excellent servant to mankind when contained and properly used and highly destructive and lethal when not carefully watched over and used properly. 


A Watered-Down Perspective to Radiation Measurement Units

A Watered-Down Perspective to Radiation Measurement Units

Relating Radiation Measurement Units to Water

If I were attempting to explain radiation measurement units to something even a child could understand, I would liken it to water which I feel really works well as a metaphor.  In many ways one can draw simple analogies using water to relate it to radiation. 

After completing my previous article Simplified Radiation Measurement for Radiation Safety Officers, I felt I had broken the subject down to its simplest form, but then I had this inspiration to relate water to radiation.  As ridiculous as it first sounds, in my mind, it worked surprisingly well.

In the previous article I had developed a chart that presents a great overview or map of the various radiation measurement units along with a more detailed explanation of each.  I have included the same chart below to use as a baseline reference for the water analogies I put forth. 

I hope this helps  those struggling to understand radiation measurement units more readily.  Here goes….

Physical Properties

Radiation is a physical property like water that requires different forms of measurement to describe it and to enable its use for our protection.  Water is measured by weight, volume, flow rate, temperature, pressure, acidity etc.  Similarly, radiation uses Roentgen, Rad, REM, Sieverts, etc.

Different Measurement Standards

Radiation measurements are described by different measurement systems, primarily US and International.  In the US we measure water volume in terms of gallons, whereas  internationally they use the  metric system and liters. So you’ll find two standards used interchangeably. 

Radiation Measurement Chart

Click to see larger image

Water Correlation to Radiation Measurement Units

Radiation measurements use different terms to describe the energy, rate, and accumulation in a very similar fashion to water. Here’s how the two relate:

Stationary Water Droplet

A droplet is a tiny measure of water.  If we forget the hydrogen/oxygen chemistry and science behind all its different forms and just call the droplet the base unit we could easily relate it to the Roentgen, which is a measure of energy in a volume of air.  

Streaming Water Droplets

If we take droplets dropping from an eye dropper, rain falling from the sky, or water flowing in a stream, it would represent different levels of our exposure to water droplets.  Water streaming from a hose represents one rate of exposure, rainfall another, and a raging stream another.  Likewise, radiation Exposure Rate is defined in units that enable us to better understand how much radiation we are receiving or are exposed to.  The US unit for exposure to radiation is described as Roentgens per hour (R/h).

Accumulated Water Droplets

As the water droplets accumulate you might receive enough to fill a glass of water, a small pond, or a lake.  The accumulated quantity referred to in radiation is called Dose.  The unit of dose in the US is called a RAD.

Accumulation of Water Droplet Energies

If water is hitting you with a greater force, the accumulated damage to you will be greater than if it were only trickling in for the same overall volume of water.  With radiation, there are different types of radiation, some more forceful than others so the dose type Equivalent Dose (rem) is used to adjust for the added energetic effects.

Water Droplet Absorption Properties

Water is absorbed differently by different materials.  Steel is largely impervious to water absorption, but a sponge will absorb many times its own weight.  Human absorption/effects/damage by radiation varies by the tissue type.  So to accurately describe the effective impact to each type of tissue a weighting factor is applied that results in an Effective Dose (Sv) measurement.

Methods of Measurement

Measurements of water and radiation fall into two categories, detectable and calculated.  It’s important to realize that most measurement units are not directly measurable and need to be calculated.  Here’s how the two relate.


The easiest way to measure the quantity of water droplets is visually count drops as they individually come out of an eye dropper.  If we wanted to do this in a more automated fashion without using any of our human senses, we could use a microphone and an electronic counter that listened for each droplet splashing into a container of water and register the number of times droplets fell (counts).  Since radiation is not detectable to human senses, we use an electronic counter like a Geiger counter.  These rad meters are outfitted with a detector that collect counts every time it senses an interaction with radiation. 


Some measurements are simply not possible using man-made sensors so they require a representative sample or an indirect measurement as a starting basis.  From that initial measurement, various factors and formulae are applied to derive various units of measurement.  A good example is determining the waterfall from a rainstorm or other periods of time.  A small water gauge in the form of a tube opened to the sky above collects a volume of water as it rains.  By measuring how many inches (or fractions of an inch) that is received, you can calculate the water collection in terms of inches/hour, inches/storm, millimeters/day, cc/month etc. 

If you wanted to know how much water was streaming inside a ditch, you could begin by measuring the flow rate directly using a flow type instrument.  Then by calculating the cross-sectional area of the ditch and multiplying it with the flow rate you arrive at a volumetric streaming rate of gallons/sec, acre-feet/min etc.  Radiation measurement units work in similar fashion whereby you can receive a rudimentary count measurement using a rad meter, that can then be applied to a series of factors and formulas to derive the desired measurement. 


I hope this brief article helps you to better understand the fundamentals of radiation measurement units.  To learn more be sure to also read these two articles:


Simplifying Radiation Measurement for Radiation Safety Officers

Simplifying Radiation Measurement for Radiation Safety Officers

Simplifying Radiation Measurement

Radiation measurement is a complex subject overall, but when working with nuclear gauges in industrial environments it can be simplified.  The purpose of this article to is give Radiation Safety Officers and Authorized Users who are new to the subject of Radiation and its measurement in industrial applications a simple overview to the extent possible.

There are many internet articles, scientific papers, and college level text books that cover radiation units and measurement very thoroughly, but sometimes it’s nice, even refreshing, to just get the basics so we can perform our jobs better.

If you’re one of those who don’t want to become physics professors, scientists, or experts on radiation measurement but prefer to just get a handle on the subject, this article is for you. 

Why are Radiation Measurement Units So Confusing?

To radiation neophytes, the subject of radiation measurement units can be a confusing topic.  All too often this topic is explained by taking you through complex set of physics, energy conversions, and mathematical formulas that only make this subject even more esoteric and confusing.


The confusion is not merely a function of physics and mathematics but is also be attributed to the evolving science and history of this subject.  Ever since Willhelm Roentgen first discovered X-rays in 1895 and the Roentgen unit was first established in 1902, the science has continued to evolve with refined definitions and added measurement units.  This refinement continues even today as we become more and more knowledgeable and continue our quest for absolute measurement certainty.

A second component of confusion is the duality of units with the US and the International community.  This is not any different than many other forms of measurement.  The International Commission of Radiation Units (ICRU) has established a set of standards to bring about world-wide uniformity, but here in the US, we cling on to past units and definitions as far as we can.  Overcoming past traditions, the huge number of perfectly functioning rad meters utilizing older measurement units that are still in use, and perhaps some of the American Revolutionary Independency all contribute to the US slow uptake to the newer measurement standards.

A third element adding to the confusion is the fact that most measurement units are not actually directly measurable.  What you say?  Yes, this means that many of the radiation measurement types are calculated values derived only after radiation detection events are collected by a rad meter.  For example, you cannot detect the REM or Sieverts of dose received by the lens of an eye; it has to be calculated based upon a number of factors once the radiation measurement by a rad meter like a Geiger counter has been made.

Added to this is a sub-level of added confusion whereby manufacturers of such instruments have purposefully ignored measurement technicalities in an effort to simplify radiation understanding for non-scientific users, extend the applications of a given instrument configuration, and indirectly sell more instruments.   To measurement purists, this is almost inexcusable, but tradition, economics, ignorance, and simplicity remain a formidable force yet to be overcome.

Comprehending all these factors and correctly applying all the physics and accompanying formulas are what Health Physicists are educated and trained to do.  But for the rest of us who do not have four or more years of study on this subject, there has to be a simpler way.  This article attempts to expose you (pun intended) to all the nuances in one simple elegant way.


Radiation Fundamentals

Here are a few fundamentals you need to understand before moving on.  You may wish to also read our blog  entitled: What is Radiation to gain a quick and better understanding as well. 

Is energy emanating from unstable atoms as they seek to reach equilibrium of its charges
Ionizing Radiation
Radiation is divided into lower energy and higher energy classifications. The higher end of the energy spectrum causes ionization interaction with matter that can alter matter structure.
Ionizing Radiation Properties - Part 1
Ionizing radiation strips electrons from atoms it interacts with causing atomic level changes to materials. The extent of material change depends on the material type and the accumulative amount of energy the material interacted with.
Ionizing Radiation Properties - Part 2
Radiation interaction and potential damage to living tissue varies for different types of tissue. This is significant to Radiation Safety Officers because the regulations differentiate between a conservative whole body radiation dose and more specific doses to skin, body extremities (hands and feet), lens of the eye and our organs.
Ionizing Radiation Properties - 3
Ionization interaction with materials including air causes the original x-ray or gamma radiation energy level to lose its strength the further it travels away from its originating source.
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Understanding Measurement Types

Like any other physical property, it can be measured in multiple ways.  Radiation is similar and can be broken down by classification, category, method, and type.  The chart in Figure 1 below provides a convenient overview that shows how these radiation measurement units all fit in relationship to each other.   It’s quite a broad view, but I believe it gives a beginner a full perspective or map that places everything in their proper order and relationship.  This map in combination with the explanations that follow should provide you with an adequate foundation. 

Figure 1

The Three Basic Categories of Ionizing Radiation


Activity measures the energy being emitted from unstable atoms until they reach equilibrium like other non-radioactive elements.  The activity levels vary by the type of radionuclide and the amount of material present.  The activity level is an important measurement to assess the amount of radioactive material being sold or just found.  It’s also the key measurement for any contamination that might be found or is present on persons, objects or the surrounding area.  Finally, it’s used to see if the activity level requires immediate corrective action to ensure safety of all involved.  


Over exposure to harmful rays is no good independent of whether you’re talking sun rays, x-rays, or gamma rays.  So knowing your exposure to these radiations anytime you enter into an environment with either known or unknown ionizing radiation is key to any radiation safety program.  Exposure type measurements determine the rate at which irradiation is impacting you.  The purpose of these measurements is to ensure work areas are below regulatory limits so accumulative doses are never exceeded.  When working in higher exposure rate areas, it also establishes how long one can safely remain in the radiation field before having to leave. 


The harmful effects of radiation exposure are pretty well known and are ultimately attributed to radiation dose values. Bombardment by higher energy, ionizing radiation over elapsed time causes fundamental changes to a materials structure.  When the material is living tissue, it can damage or even kill it if over-exposed.  Regulations are all keyed to annual dosage limits that have large built-in safety factors.   

Radiation dose is not uniform across all radiation types and materials.  Radiation dosage effects vary depending upon the radiation type and the material receiving the dose so they must be measured and noted separately. 

All doses are initially calculated by taking the exposure rate in air (which is all that radiation detectors can really measure), and multiplying it by the exposure time to arrive at a general-purpose dose value called Absorbed Dose.  In living tissue, not all radiations are equivalent; alpha producing radiations, for example, contribute 20 times more dose damage than gamma and x-rays.  So, multiplying your Absorbed Dose by 20 then gives you an appropriate Equivalent Dose.  Absorbed Dose effects on living tissue also varies by tissue type, so applying an appropriate dose factor for each type of tissue is required to arrive at what is known as the Effective Dose.

The Two Methods of Measuring Ionizing Radiation

Given all the measurement types and categories, it may be somewhat surprising that there really are only two measurement methods: Direct Measurement and Calculated.  It may also be surprising that the majority of measurement types all fall into the latter category.  I suspect most incorrectly believe that rad meter direct measurements tell the whole story and once you know how to read a rad meter, you’re good to go.  But fundamentally, that simply is not so, it’s just the beginning.  Here’s why….

Direct Measurement

Direct Measurement is the method whereby one acquires a radiation reading “DIRECTLY” from a radiation meter.  For simplicity sake, I am going to restrict the foregoing explanation to simple Geiger counters that are dominantly used throughout industry. 

All radiation meters function basically the same in that they electronically view the interaction of radiation within the detector medium and count the separate interactions.  There are several types of detector sensing materials each with their own set of  unique characteristics.   As such, not all radiation detectors are equal; each will have their sensitivities, advantages, and disadvantages.

Rad meters are inherently radiation unit agnostic, in that they natively can only report the number of interactions counted within their small detector volume per unit of time.  That’s all they see and know.  Thus natively, they can only report the raw counts per minute or raw counts per second.  They have no idea what type of radiation they are counting, the energy level, isotope, the  originating source activity, nor how far away or what direction the source is.  In other words, all the details you really want to measure cannot be inherently be obtained without additional knowledge.  Hence beyond raw counts, all radiation measurements need to be calculated.


Having established that gross counting radiation meters fundamentally only acquire relative count values based upon their inherent interaction characteristics, we recognize that in order to obtain meaningful radiation measurements more intelligence needs to be factored in. 

The factors required will be different for each type of measurement type but always begin with the known detection characteristics of the specific detector used, the overall system detection efficiency, time of measurement, exposure level and time, and where possible the radiation isotope, energy, and distance to the source.

For Geiger counters that display readings beyond other than just counts, which most do, many of these factors have to be assumed.  The most common assumption is that the energy is close to Cs-137 gamma energy of 660 keV. 

Radiation Measurement Units Definitions


The raw counts acquired by the radiation meter either as a count rate or accumulated counts over a given period of time.


Refers to the amount of ionizing radiation released by a material. Whether it emits alpha or beta particles, gamma rays, x-rays, or neutrons, a quantity of radioactive material is expressed in terms of its radioactivity (or simply its activity). This represents how many atoms in the material decay in a given time period.


Describes the amount of radiation traveling through the air. Many types of radiation monitors measure exposure. The units for exposure are the Roentgen (R, U.S. unit) and coulomb/kilogram (C/kg, international unit). The Roentgen was officially retired by the international community a long time ago but refuses to die in the US.


Describes the amount of radiation absorbed by an object or person. The unit for absorbed dose is the rad (U.S. unit) or the gray (Gy, international unit). One gray is equal to 100 rads.


A measure of the biological damage to living tissue as a result of radiation exposure. Also known as the " biological dose," the dose equivalent is calculated as the product of absorbed dose in tissue multiplied by a quality factor and then sometimes multiplied by other necessary modifying factors at the location of interest. The dose equivalent is expressed numerically in rems or sieverts (Sv)


Describes the amount of radiation absorbed by person, adjusted to account for the type of radiation received and the effect on particular organs. The unit used for effective dose is rem (U.S. unit) or sievert (Sv, international unit).

Fractional Units of Measurement Often Necessary

Many of the base radiation measurement units described above represent very large amounts of radiation.  It therefore becomes necessary quite often to describe these in fractional terms or scientific formats as presented in the table below.

Fractional Units

Practical Radiation Measurement Values

Here are some measurement values to better understand the environment we live in and the dose impact to our bodies:


Average background exposure rates:             10 uR/h     (0.1 uSv/h)

Daily dose (using exposure rates above):      240 urem  (2.4 uSv)

Yearly dose (using exposure rates above):     88 mrem   (0.88 mSv)


Transatlantic Airplane Flight:                            7 mrem     (0.07 mSv)

European Airline Crew Annual Limit:              2 rem        (20 mSv)

6 month flight on Int. Space Station:             7.5 rem     (75 mSv)

180 days transit to Mars:                                     13.3 rem   (133 mSv)


Chest X-ray:                                                              6 mrem      (0.06 mSv)

Panoramic Dental X-ray:                                     9 mrem     (.09 mSv)

Mammogram:                                                        70 mrem   (0.7 mSv)

Full Body CT Scan                                                  1 rem         (10 mSv)


Annual Public Dose Limit:                                100 mrem (1 mSv)

US Annual Rad Worker Occupational Dose Limit:      5 rem (50 mSv)

Body Effects

Radiation Effects when doses occur in short period:

  • Dose causing symptoms:     40 mrem  (0.4 Sv)
  • Letha Dose (50% death):      400 rem ( 4 Sv)
  • Certain death:                           800 rem    ( 8 Sv)


Believe it or not we have hardly scratched the surface when it comes to radiation measurement units.  The chart in Figure 1 should prove helpful anytime you need to cross reference units and standards, or better understand what type of dose is being measured or referenced.  If you’re interested in an even simpler explanation, see our other blog Watered-Down Perspective to Radiation Measurement Units.

Radiation measurement becomes very exciting when you have a Geiger meter in hand and have different radio-isotopes available for lab experimentation.  Watching the meter behavior to invisible rays and particles streaming from different isotopes, source activities, and varying distances can be a lot of fun and put you in touch with the invisible realm of radiation and its ability to be measured.  When measuring contamination, or calculating doses for given exposure rates you also get a better understanding of the different dose types and how they relate to the activities you counted with  your rad meter. 

Radiation Measurement Units make a lot of sense once you take just a little time to grasp it.  Like any other measurement units, there’s a lot of history and science behind them, but we need not understand all of that to benefit from the measurements.

What is Radiation?

What is Radiation?

To many, the term radiation is a confusing and even a terrifying subject, but it need not be so.  Like any other subject, once its better understood, it’s not as mysterious or frightening.

The purpose of this article is to present this subject as simply as possible by avoiding nuclear physics, mathematical formulas, and complex scientific explanations.   I’ve also added some great YouTube video links that further support the basic concepts presented.

While the term radiation is commonly associated with radioactivity, in the purest sense, it can be any type of energy radiating from its source. 

Different kinds of radiation would include thermal radiation from the sun, acoustical radiation such as ultrasound or music from a radio speaker, and nuclear radiation resulting from naturally radioactive materials or man-made processes, etc. 

For the purpose of this article I will focus on the nuclear type of energy, and more specifically, the kind that can cause bodily harm.  Let’s begin with a high-level definition as follows:

Radiation is defined as the emission of energy in the form of electromagnetic waves or subatomic particles that cause ionization.

So let’s break this definition down into its separate 4 parts so we can attempt to better understand what this really means:

1. Emmission of Energy - a simple analogy
We live in a world and universe immersed in energy; it’s all about us. Examples include radio, microwave, ultraviolet and more. All energy begins with a source that radiates outwardly. A good visual I use to comprehend the emission of energy is that of the sun radiating its rays in all directions and at all times. Like the sun, the energy level at the origination point is always the most energetic. When surrounded by empty space, the radiating energy loses its potency over distance as the unit of contained energy leaving its point of origin is rapidly dispersed across an ever-increasing volume of space the further it travels. This behavior acts just like hot water or electric heating radiators that delivers a nice comfortable heat up close but becomes noticeably less warm the further away we are from the heat source.
3. Subatomic Particles
The second way energy is manifested is via subatomic particles. These include alpha, beta, and gamma emissions that emanate from atoms that have been influenced by a nuclear reaction. Alpha’s are large in size, slow moving, and while packed with lots of energy lose their energy in only a few centimeters of air. A thin piece of paper will stop alpha’s and are not too worrisome unless ingested in which case they can be fatal. Beta’s are electrons that can penetrate skin but are relatively weak. Gammas (behave like waves and particles) are very penetrating, can travel great distances, and can cause great harm to human tissue. Gamma radiation is used in most industrial applications to measure the density and level of materials being processed. Irradiators are another beneficial application used to sterilize food, pharmaceuticals, cosmetics, packaging, blood products, medical products and more. Medical diagnostics and therapy also use gamma radiation to treat cancer and other diseases.
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Background Radiation

This does not mean that all ionizing radiation is bad or going to kill us. We are surrounded by ionizing radiation rising from the earth’s geological formations, some of the foods we eat, and from the cosmos above.  Even our bodies contain some elements that are radioactive, albeit very miniscule amounts. 

Radiation is a natural part of the universe

Background radiation is what we hear whenever we hear the clicking sounds coming from a Geiger counter even when no extraneous or known radiation source is present.  The background ionizing radiation varies from one location to another depending upon the geological formation.  Granite for instance, emanates a fair amount of natural radiation that results in higher background radiation readings. 

Likewise, cosmic radiation streaming from the heavens above are continually filtered by the earth’s atmosphere until it reaches the surface.  Those living at sea level typically have the lowest background levels when compared to those living at higher altitudes like Denver.  When traveling at 35,000 feet in an airliner, passengers will experience radiation levels 40 to 60 times higher than when at sea level.  Astronauts traveling in space are the most vulnerable since they are not being shielded by the earth’s atmosphere.

Another natural radiation source is radon which is released from the ground into the atmosphere.  This inert type of radioactive gas is odorless, colorless, and tasteless so like other radiation types it cannot be detected by our human senses.  When radon becomes trapped inside home basements the concentration levels can rise to dangerous levels.  Studies have linked breathing high concentrations of radon to lung cancer.   

While some fear any kind of radiation natural or not, others have reason to believe that the cacophony of ionizing radiations surrounding us is beneficial to sustaining life here on the earth.  They conclude that the energy field we are cocooned in is perfectly tuned to protect us from deadly germs and bacteria that would otherwise flourish and kill us. 

Radiation Behavior

Our radiating sun makes a great metaphor for how radiation behaves

The sun is a great teacher to better help us understand how Radiation behaves.  If we traveled inside a spaceship and got too close to the sun we would certainly die.  Yet, back on earth simple shielding can soften or even eliminate its adverse effects.  If we limit the time we are exposed to the sun’s brilliant rays, we can avoid sunburns.  And sometime in the distant future, the sun will eventually burn up all its fuel and will no longer radiate.

Radioactive materials we typically see in industrial applications all follow these same three principles of distance, shielding, and time.  When radioactive materials like Cs-137 and Co-60 are properly shielded and kept at a safe distance, their purposeful design ensures we remain safe.  Even when we are in close proximity while performing maintenance, by limiting our time, we can still remain safe.   Distance, shielding, and time are the three corner stones to any radiation safety program and when applied properly will ensure everyone’s dose is well below regulatory limits.

 Another well-known behavior is that radioactive materials give up all their energy over time through a decay process until they become stabilized and are no longer radioactive.  The time to stabilization or equilibrium varies by element and ranges from fractions of a second to billions of years.  A measurement of time used in the nuclear field to clock the decay process is called the half-life, or the time it takes to decay half of its activity.  Cs-137 has a half-life of 30 years, so after 30 years, the radiation being emitted is only half of what it was when measured at the time it was installed in the device.  After about 7 half-lives, the material reaches its equilibrium state.  Thanks to modern-day microprocessors and memory, modern radiation devices can compute the decayed value on a daily basis and re-calibrate itself to compensate for the ever-decreasing output of the radioactive source.  Never-the-less, at some point well before its total demise, the radiation output becomes too weak to perform its primary function and must be replaced either by a new source or device.

Beneficial Uses of Radiation Go Largely Ignored

Mankind has found many truly beneficial uses for radiation in enhancing our lives.  Unfortunately, radiation gets a lot of bad press resulting from the use of atom bombs in WWII,  the nuclear reactor disasters at Chernobyl and more recently at Fukushima, and the prospects of dirty bombs by terrorists.  Early adoption of radioactive products and elixirs shortly after radioactivity was discovered and before its harmful effects were known also did not help its cause.  We hardly ever hear about positive uses of radiation outside of nuclear medicine and nuclear power; and even those are controversial in their own ways.

Thanks to the properties of radiation, mankind has found numerous other beneficial uses that include:

Nuclear Gauges

Nuclear gauges that measure materials being processed for density, moisture, flow rate, and material levels in a wide variety of industries including paper & pulp, chemical/petrochemical, steel, food, packaging, roofing products, mining, fertilizer, construction and many more.


Products including smoke detectors, x-ray machines used in non-medical applications like those built to perform quality inspections on welds, CT scanners, exit signs, static eliminators, depleted uranium penetrators

Calibrator for Radiation Meters and Dosimeters


Irradiators that sterilize fruits, vegetables, and other food products, medical and pharmaceutical supplies, eradicating insects through sterile male release programs, calibrating dosimeters and radiation detection instruments, security applications


Research for discovering material age via carbon dating, tracking living organisms by injecting radioactive tracer materials, studying environmental pathways in a similar manner, changing material composition

Most of us are touched in one way or another on almost a daily basis by some process or product that employs radiation.  Despite what many might think, the uses of radiation are expanding as new technologies and materials continue to evolve. 


We need not look beyond our own sun to grasp the basic principles of radiation.  While ionizing radiation is fundamentally simple to grasp, it becomes immensely complex and is still being studied at research institutes world-over.  Pin-pointing the precise radiation level at which radiation is beneficial and where it becomes harmful has been a point of great debate for many decades with no clear ending in sight. 

The discovery of radiation at the end of the 19th century opened our eyes to the understanding of elements here on earth and enables us to detect distant galaxies far beyond our natural eye-sight.  It is amazing, powerful, dangerous, and beautiful all at the same time.  Harnessing this great power has changed our world forever and will undoubtedly continue to open new vistas far into the future.