The Ultimate Dosimeter and Geiger Counter Guide

The Ultimate Dosimeter and Geiger Counter Guide

by Matt Collins

When is the time to ask questions about a dosimeter, including what it does, and how it functions? Is it when your phone makes emits bizarre noise, indicating that an ICBM is coming, and that you must seek shelter immediately? Or is it well before this event ever occurs?

You probably know the answer to this question.

And if so, you've probably already given some thought to how to avoid falling into the former camp. This, as always, entails a lot of preparation.

But what exactly must you do? And how do you use a dosimeter to survive a nuclear attack?

We'll lay it all out for you.


  • 01

    What is a Dosimeter Used For?

  • 02

    A Note on Nuclear Emergency Measurements

  • 03

    How Does a Dosimeter Work?

  • 04

    Why Should You Consider Adding a Dosimeter to Your Nuclear Preparedness Kits?

  • 05

    What is the Difference Between a Geiger Counter and a Dosimeter?

  • 06

    Frequently Asked Questions

What is a Dosimeter Used For?

Whether there is a nuclear strike, Chernobyl-like meltdown, or dirty bomb attack, a great deal of lethal radiation is going to be pushed out into the atmosphere. And as you already know, this radiation will either kill you outright or give you a terminal form of cancer, so you want to ensure that you're not absorbing too high of radiation levels.

Nuclear-capable MIRVs separate as the warheads head to their respective targets.

This is where a dosimeter comes into play.

X-ray technicians, nuclear plant workers, and the like all carry dosimeters on their person to ensure that they are not taking in dangerously high levels of radiation as they go about their day. That, at its essence, is what a dosimeter does.

Worn or carried about by the person for a long time, the dosimeter will absorb radiation the entire time. That means that when the user looks at the dosimeter, they can obtain a reading on the total amount of radiation they have been exposed to since entering the "danger zone."

An X-ray technician's hand, circa 1900, after regular work around the machine. Excellent photographic proof of why dosimetry is so vital. (Image courtesy of the Wellcome Collection at Wikimedia Commons. )

Note that for a nuclear plant worker, the "danger zone" is essentially the entire facility. By keeping a dosimeter on his person throughout his entire shift, however, the employee is able to quickly discover if there is a dangerous radiation leak somewhere.

There are other instruments in use to detect this throughout the facility as well, to be sure, but having a personal dosimeter not only serves as a functional backup for this man, but also allows him to know with a high level of certainty exactly how much radiation he has absorbed.

Within a nuclear disaster, the purpose is very much the same.

If you're not killed in the nuclear blast, the radioactive fallout that will soon blanket the surrounding region of Ground Zero (and well beyond) will do the job unless you take decisive measures. Part of the problem, however, is that radiation is invisible. You cannot see, smell, hear, or taste it, but it can kill you all the same. This is where a scientific instrument needs to come into play–something that can do what your body cannot.

While you may have a fallout shelter already established and well-stocked with provisions, you need a means of detecting how much radiation is in the environment above you to know how safe it is to be out of the shelter.

While nuclear war expert Cresson Kearny of Nuclear War Survival Skills fame notes that after two weeks, one can safely begin to leave their fallout shelter for limited amounts of time, this raises the question: how do you know what the proper amount of time is? What's the point of spending two weeks under the ground and all that time preparing before the war ever started if you're only going to kill yourself by walking around like nothing ever happened on Day 15? This is why you would need some means of measuring the radiation levels around you.

Grand Canyon Caverns fallout shelter area. (Image courtesy of Lauri Vain at Wikimedia Commons. )

And a dosimeter is an excellent, easy-to-use means of doing just that. But if you're going to use a dosimeter, you need to make sure you know what it's trying to say to you, and to do that, we need to know a thing or two about the units of measurement used for radiation.


Bananas contain Potassium-40, a radioactive substance. Simply eating one banana will expose you to 0.1 microsieverts of radiation.

A Note on Nuclear Emergency Measurements

Understandably, the world of nuclear science can be somewhat confusing. Most understand that the splitting of an atom results in a massive amount of energy being released, uranium is essential for developing nuclear weapons, and the like, but few of us tend to understand the basics of radiation measurements.

If you want to keep yourself safe with a dosimeter, you need to have some inkling of what the numbers you're looking at on the screen actually mean. To fully understand a car, a mechanic must know about PSI, miles per gallon, and other specific units. For our purposes? All you need to know about is the sievert. (If you're used to using rems, just know that rem is essentially the same as a sievert.)

A sievert is a unit used to measure the amount of radiation that a human body has absorbed. A millisievert is 1/1000 of a sievert and a microsievert is 1/1000 of a millisievert. So a microsievert is smaller than a millisievert which is smaller than a sievert.

Sievert > Millisievert > Microsievert

The more sieverts of radiation a person absorbs through his body in any given period, the greater his chances of experiencing some negative health outcome. Once this reaches past a particular threshold (typically one sievert), you have an acute radiation sickness (ARS) case on your hands. The end results can often be lethal. This is why it's so important to be able to measure environmental radiation – particularly after some type of nuclear event.

X-ray burns on a technician's hand from unshielded equipment. (Image courtesy of Otis Historical Archives National Museum of Health and Medicine at Wikimedia Commons. )

While the sievert is the unit of choice for measuring absorbed radiation, doctors, researchers, and policymakers like to stick to the smaller microsieverts and millisieverts when discussing safe levels of absorbed radiation. This is because a sievert is a tremendous and rare find in nature. It would be the equivalent of using tons to measure how big your steak was last night.

You ate an 8 oz. steak, but if you measured that as 2.5e-4 tons, things would quickly grow to be more complicated than they need to be. Both measurements are precisely the same, but one is much easier to work with than the other.

On an annual basis, a human being is typically exposed to 2400 microsieverts. There's always some degree of background radiation in the world around us no matter where we go, so this amount is both expected and safe. When we start to be exposed to levels drastically above that annual rating of 2400 microsieverts, we begin to see health problems develop.

After a nuclear emergency, however, you'll see microsievert radiation levels jump into the millions.

    • 30,000,000 microsieverts = Seizures and tremors until death 48 hours later.

    • 10,000,000 microsieverts = death within two weeks.

    • 10,000,000 microsieverts = death within two weeks.

    • 4,000,000 microsieverts = Bleeding and hair loss until possible death within 4-6 weeks. A miserable existence until that point.

    • 5,000,000 microsieverts = Will kill 50% of those who absorb this amount. So if two people each absorb 5,000,000 microsieverts, one is guaranteed to die within 30 days. The other one may pass on day 31 or beyond.

    • 1,000,000 microsieverts – Causes ARS. Not immediately fatal, but it will cause terminal cancer in 5% of its victims years into the future.

    • 100,000 microsieverts – Increased cancer risk in the future

*Data from this and this link.

If you have a good idea of the risks of absorbing so many microsieverts of radiation, however, you can make a more informed decision on how safe it is for you and your family to leave your fallout shelter and for how long, if so.


The Chernobyl cleanup crew that was hospitalized in 1986 were each exposed to 1-6 sieverts of radiation.

How Does a Dosimeter Work?

While several different types of dosimeters are on the market, each uses essentially the same process to measure radiation.

If you remember back to your high school chemistry class, we see that individual atoms are orbited by electrons at the atomic level. When radiation hits those atoms, it does so with much force and can knock those electrons out of orbit.

Think of the electron as being the moon orbiting earth. Radiation would be a massive meteor that sends the moon hurtling off through space. And just like an Earth without a moon could, an atom without its electron can also cause problems.

Those asteroids would represent radiation hitting the electrons from an atom.

A dosimeter takes advantage of this "missing moon" by using phosphor crystals to trap these electrons that have been shot out from the atom. When these crystals are hit by electrons, they heat up, and when this happens, they put out a little bit of light. The more they're heated up by these electrons, the more light they put out. This light can then be measured to determine how much radiation the dosimeter has been exposed to. Because a dosimeter is typically worn on one's person, this measurement can also be used to tell how much radiation that person has absorbed.

With a card, ring, or bracelet-style dosimeter, the user simply has to look at the color of their dosimeter and compare it with a radiation chart. They then match up the colors on the two and see how much radiation they've absorbed.

A ring dosimeter. (Image courtesy of Image Thermoluminescence Dosimeter at Wikimedia Commons. )

A digital dosimeter makes this process easier, faster, and more foolproof. Here, the dosimeter will precisely measure how much has been absorbed, so the user doesn't risk judging the color incorrectly.

Of the two, digital methods are the preferred first-line dosimetry means.

Why Should You Consider Adding a Dosimeter to Your Nuclear Preparedness Kits?

If you are concerned about the risk of nuclear war or some form of a terrorist strike and have begun to stock food, water, and gear, then it would make sense to also prep with a dosimeter. You want to know how much radiation your body absorbs after a nuke. Otherwise, you're literally playing a guessing game.

While there are biometric signals that your body creates that the skilled scientist can use to determine how much radiation a human has absorbed in a given amount of time, these require special equipment and training to measure. After a nuclear weapon has been dropped, odds are you won't find somebody who knows how to use your urine to judge how much radiation you've absorbed.

Not to mention, biometric signals don't save lives. They're what's measured well after potentially lethal doses of radiation have been absorbed.

This is where a dosimeter comes into play.

Let's say you're traveling on the subway in New York when you hear that there's been a nuclear attack in Boston. You're worried about the potential of radiation being blown by the wind to where you are, but you have a pen dosimeter you always carry in your pocket.

Measuring the radiation at Chernobyl. (Image courtesy of Gabriella Clare Marino at Wikimedia Commons. )

You could then pull out your dosimeter, turn it on, and carry it with you as you head for shelter. When you have found your shelter, you can look at your dosimeter to see precisely how much radiation you have absorbed. Whether you had your family with you or not, it would be a massive mental relief to know that you aren't going to die from one of the most miserable deaths imaginable over the next few weeks.

But what if you're already in your nuclear fallout shelter when you hear that the bombs are coming?

A dosimeter would still prove beneficial.

Imagine you have been forced to dig an ad hoc nuclear fallout shelter akin to what American scientist Cresson Kearny advocates for in the classic text Nuclear War Survival Skills. You've built everything to his specifications, but now you've been in a hole in the ground for four days, and you're worried about how much radiation people are absorbing still – mainly if they sit near the main entrance.

A dosimeter would give you a precise measurement of inner shelter radiation, helping you make crucial decisions or setting your mind at ease.

Now, consider that it's been two weeks since the bombs fell. From your research on nuclear war survival, you know that you should be able to safely exit your fallout shelter for brief amounts of time at this point. You're lacking a lot of information, though. You don't know where precisely the bombs hit, on what date they hit, how large they are, if there are other survivors – in short, there's a lot you don't know.

MIRV ICBM. (Image courtesy of Leonidl at Wikimedia Commons. )

Nobody enjoys living in a dank hole in the ground for weeks on time, especially in crowded circumstances in a perpetual state of fear, and so you really want to know what a safe exposure time is back up on the surface. A dosimeter would give you this information.

As we pointed out above, spending time, money, and energy building a shelter and doing everything else that goes along with surviving a nuclear strike is a fruitless endeavor if you're not going to take the simple step of figuring out how much radiation you're absorbing.

What happens if you don’t have a dosimeter after a nuclear attack?

Aside from playing a guessing game, as mentioned above, you depend on signs and symptoms to determine how much radiation one has absorbed after the fact.

You will measure the time from detonation to when individuals begin to experience nausea, vomiting, diarrhea, and malaise. If the individual starts to convulse, develops a fever or headache, becomes dizzy, or becomes disoriented within 24 hours after the explosion, they likely received a fatal dose of radiation.

You'll know how much they've absorbed via a general rule of thumb, but it will be too late for them – and likely for you too.


In 1953, the National Academy of Science Advisory Committee on Civil Defense said, "The final effectiveness of shelter depends upon the occupants of any shelter having simple, rugged, and reliable dose rate meters to measure the fallout dose rate outside the shelter."

You’re not going to be able to rely on the government for accurate readings here, either.

(Image courtesy of Michael Perekas at Wikimedia Commons. )

At least as of 1987, most civil defense shelters throughout the United States were stocked with CDV-742 pocket dosimeters. After these dosimeters were studied, it was found that not only were they "not suitable for use in a neutron or mixed radiation field," but shelter occupants couldn't trust their use whatsoever.

You may think to yourself that there's no need to have a dosimeter that can handle neutron radiation, but keep in mind as far back as 1968, the US Army was actively looking for "tactical dosimeters" that could measure neutron radiation for deployment with troops while out in the field.

Knowing this, these are the questions you need to ask yourself:

  • Do you think those dosimeters were ever replaced?

  • Do you even know where your local civil defense shelter is?

  • Have you heard of your politicians in the past 40 years discussing using funds to update existing civil defense shelters?

The answer to these questions further points towards why individuals need to be prepared to get their own safety.

Fallout shelter in Guam. (Image courtesy of Lance Vanlewen at Wikimedia Commons. )

The MIRA Safety Geiger-2 Counter/Dosimeter

If you're looking for one of the most portable and easy-to-use means of detecting high radiation levels on the market, look no further than the MIRA Safety Geiger-2 Counter/Dosimeter. Capable of measuring radiation down to the 0.999 microsievert/hour level, this device can easily be stowed away in a purse, backpack, or pocket with minimal fuss, as it's slightly larger than a ballpoint pen.

When the time comes to use it, nobody will know that you’re actively reading the radiation levels in the air as they would if you were walking around with the traditional Geiger counter concept. Within 20 seconds of being turned on, you’ll have a radiation reading alerting you whether or not you are in a dangerous area or not.

Thanks to its two-button operation, even a child could use this device. Should your child spend a lot of time away from home for various reasons and you're concerned about something happening while you are separated, the MIRA Safety Geiger-2 Counter/Dosimeter could help give you some added peace of mind. There's no need for calibration; it runs off a rechargeable battery, and an integrated alarm will go off, alerting the user once 0.3 microsieverts/hour is detected.

What is the Difference Between a Geiger Counter and a Dosimeter?

While both instruments will measure radiation, they are used for slightly different purposes. A Geiger counter is used to detect if there is radiation present right now on something. If you're in a fallout shelter and another family has just run in from the outside, you could use a Geiger counter to see if they're covered in radioactive fallout.

If they were, you could then have them toss their clothes in the trash and take a shower.A dosimeter can’t do that. What a dosimeter does is tell you how much you personally have absorbed in a given period of time.

This is why X-ray technicians and other medical personnel carry these on their person throughout their shifts. They can look at them whenever and see if they absorb more than the usual radiation dose. If so, they know they must head for safety quickly.

The cool thing about a dosimeter is that it can also be a silent and passive means of measurement. A Geiger counter generates noise and has to be turned on to work, and walking around all day with a clicking electrical device on your person all day would be incredibly annoying.

In contrast, a dosimeter will do its job silently and with minimal fuss while still helping to keep you safe.

Easy Dose It

The modern world contains weapons with unprecedented destructive potential, and war now possesses the ability to impact far more of the globe than it ever has before. With this in mind, it makes sense to do what you can to protect your family from some of these modern forms of weaponry.

The ancient man kept a sword and a shield to protect himself from the state-of-the-art technology of his day. Why not do the same thing with a dosimeter to protect your family against nuclear weapons?

What are your thoughts? Let us know in the comment section below.

Frequently Asked Questions

What is a dosimeter?
Can a dosimeter save your life?
Wouldn’t a fallout shelter in my area have a dosimeter?
Why can’t I just use a radiation card?
Do soldiers use dosimeters?
Are dosimeters still used?
When should you wear a dosimeter?
How often are dosimeters read?
How accurate are dosimeters?
How long can a dosimeter be used?
What is a dosimeter badge?
What is a noise dosimeter?
What is medical dosimetry?
How is dosimetry reported?