Radiation Units

Radiation Units & Conversions

Intended for clarifying the various measurement units for radioactivity
this page covers:

the Curie (Ci)
the Becquerel (Bq, used to report soil and food contamination, for instance)
the rad   (rad)
the Gray (Gy – also used in the media:  nGy/h = nanoGray per hour)
the rem   (rem)
the Sievert (Sv, also in the media: millieSievert (mSv& microSievert (µSv) per hour)
the Roentgen (R)
– the Coulomb/kilogram (C/Kg)
– CPM (CPMCounts Per Minute, or CPS = Counts Per Second – are common
Differences between Alpha, Beta and Gamma ionizing radiation:  http://www.s-cool.co.uk/a-level/physics/radioactivity/revise-it/what-is-ionising-radiation
A basic Radiation Units converter: http://www.convert-me.com/en/convert/radiation/.  
Another easy-to-use Radiation Units converter:  http://www.translatorscafe.com/cafe/EN/units-converter/radiation/
!!–> For more complicated calculated “conversions”, see the excellent http://www.radprocalculator.com/ described further below (under Becquerel).  
UC Berkeley’s dose calculation page, http://www.nuc.berkeley.edu/UCBAirSampling/DoseCalculation, can be helpful too to clarify specific aspects of this complex field of study.
For decay calculations (in various units and for all isotopes), see this handy DECAY CALCULATOR: http://ordose.ornl.gov/decay.cfm (->  Search for “DLC-0202 ZZ-NUCDECAYCALC” or newer version. ;-/
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Note:  Easy Conversion table, at bottom of page.

(Another absolutely excellent helpful site for conversions WAS http://www.nuclearcrimes.org/conversions.php)

Another helpful table (though here with the smallest at the top-beware)  for undoing confusion around prefixes (kilo, mega, giga, tera, peta, exa, etc.) I found:

RADIATION UNITS – extra explanation

  • Curie & Becquerel

The curie (Ci) was replaced by the becquerel (Bq). In this case Wikipedia is actually quite useful to explain what it “is” (though not how to work with it):  http://en.wikipedia.org/wiki/Becquerel

1 Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. That’s why there’s a quantity indicated:  becquerel…  per liter (Bq/L), per kilogram (Bq/Kg), per square meter(Bq/m2), per cubic meter (Bq/m3), etc.

Bq is always PER SECOND.   In contrast to ‘activity’, ‘dose rates’ and ‘absorbed dose rates’ (in Sievert (Sv), rem, or Gray (Gy)) can be for an event/instant (like a medical X-ray or CT-scan), for a period (annual dose from normal background radiation), or for a flow (usually per hour), such as for common sea level normal background radiation: 0.07 µSv/h

The becquerel is named for Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie for their work in discovering radioactivity.

The curie (Ci), an older unit of radioactivity, is defined as radioactivity equal to the activity of 1 gram of radium-226. The conversion factors are:

1 Ci = 37,000,000,000 Bq,  meaning: that many decays occur in a gram of radium-226 per second

1 μCi = 37,000 Bq

1 Bq =  0.0000000000270 Ci

1 GBq = 0.0270 Ci

The US government offer reports food contamination in picoCurie (pCi) per volume or weight:

 1 pCi = 0.037 Bq

100 pCi = 3.7 Bq

For exampleVegetation from private garden in San Luis Obispo, sampled on April 14, 2011 measured “Cesium-137 @ 154.10 pCi/kg” (picoCurie per kilogram).  Using the below unit converter, 154.1 pCi = 5.7 Bq, so 5.7 Bq/kg of Cs-137 in that sample.  

! –> The http://www.radprocalculator.com/, which is super handy to calculate values for dose rates for certain isotopes for a number of Becquerels and vise vera.  It also includes a really convenient radiation units converter:  ! –> http://www.radprocalculator.com/Conversion.aspx.

–> Click image or here for description:  http://www.radprocalculator.com.

It’s useful for many conversions, but it’s particularly handy to do the complicated calculation for you to figure out the relation between ACTIVITY (Bq or Ci) and DOSE RATE (Sv, rem, etc.).   Go to the site to learn why you can’t simply convert Bq (activity)  measurements into dose rates (in µSv/h, etc.), where its FAQ section (on http://www.radprocalculator.com) clears up much:

Also, Regarding ‘Converting gamma or beta radiation ACTIVITY to EQUIVALENT DOSE rates’, see also this (more complicated) explanation:  http://hps.org/publicinformation/ate/faqs/gammaandexposure.html 

Play around with the calculator (adjust settings to your preferences: gamma, beta, disnatnce from isoptope, which isotope, which units, values,…):


See also UC Berkeley’s formula @ http://www.nuc.berkeley.edu/UCBAirSampling/DoseCalculation

An important thing to remember (IMO) is that “The language of dose is the language of deception”.

All in all, I must admit, I still actually don’t know how to gauge fallout measurements accurately and confidently.  Regardless of the formula used, there remains a psychological factor that leaves the ultimate assessment largely up to the weight given to the used formula (which by their nature contain some assumptions and generalizations), plus nuances that can’t easily be quantified, from personal sensitivities to dietary aspects, etc.

Many experts have stated that what changes the risk landscape is accumulations in food, which can magnify risks through accumulated higher concentrations of tissue-stored radionuclides.

!-> To see isotopes in their decay chainshttp://periodictable.com/Isotopes/084.210/index2.full.prod.html  –> Just click on an element, pick an isotope. Indicate to also to show the decay chains before and after the isotope. Then you can see what which isotope can turn into, look up its half life and dominant decay modes. (link is for Polonium-210)

  • Rad  &  Gray

The rad (rad) or Radiation Absorbed Dose recognizes that different materials that receive the same exposure may not absorb the same amount of energy. A rad measures the amount of radiation energy transferred to some mass of material, typically humans. One Roentgen of gamma radiation exposure results in about one rad of absorbed dose. The rad thus represents a certain dose of energy absorbed by 1 gram of (human) tissue.  Expressed in SI Units, 100 rads = 1 Gray. Both are a unit of concentration. So if we could uniformly expose the entire body to radiation, the number of rads received would be the same (when expressed in rads or Grays) whether we were speaking of a single cell, an organ (e.g., an ovary) or the entire body (just as the concentration of salt in sea water is the same whether we consider a cupful or an entire ocean).  The International Commission on Radiation Units and Measurements wants aims for standardized use of units, for which they want us to give up the rad in favor of the gray (Gy).     1 Gy =100 rad

The Gray (Gy) approximates the “absorbed dose” of ionizing radiation (a.k.a. radioactivity).  The Gray replaced the rad; 1 Gray equals 100 rads.

1 Gy corresponds with 1 Sievert absorbed (for humans). Since some sites report in nGy/hr (nanoGray/hour; 1 Gy = 1,000,000,000 nGy), the easy key to convert Grays to Sieverts is: 1 Gy = 100 rad ; With Q=1 for gamma rays & human tissue (see rem), 100 rad x 1 = 100 rem ; and 100 rem = 1 Sv.

For easy conversion:   1 nGy/hr ≈ 0.001 µSv/hr.

For example, a reporting of  631 nGy/hr corresponds with
631 / 1000 =>            0.631 µSv/hr.
0.631 / 1000  =>        0.000631 mSv/hr ≈ 63 CPM (depending on the Geiger Counter)

  • Rem & Sievert

rem or ‘Roentgen Equivalent Man’ is a unit that relates the dose of any radiation (in rad or Gray) to the biological effect of that dose, in rem or Sievert).  To relate the absorbed dose of specific types of radiation to their biological effect, a “quality factor, Q” must be multiplied by the dose in rad, which then shows the dose in rems. For gamma rays and beta particles, 1 rad of exposure results in 1 rem of dose.  Interpretation of rems depends on what kind of radiation we’re speaking of. Some forms of radiation are more efficient than others transferring their energy to the cell.  To have a level playing field, it is convenient to multiply the dose in rads by a quality factor (Q) for each type of radiation to arrive at the “absorbed dose”. The resulting unit is the rem (“roentgen-equivalent man”). Thus, rem = rad x Q.  X-rays and gamma rays have a Q ≈ 1, so the absorbed dose in rads is the same number in rems.  (For contrast: Neutrons have a Q of about 5 and alpha particles have a Q of about 20. An absorbed dose of, say, 1 rad of these is equivalent to 5 rem and 20 rem respectively.)

[Source: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Radiation.html, ]

If it wasn’t confusing enough yet, despite the years of high-quality research reported in rems and millirems (1 rem = 1000 mrem), the International Commission on Radiation Units and Measurements has replaced the rem by the Sievert (Sv):

100 rem = 1 Sv.

The Sievert (Sv) – is the same as the rem (albeit 100 rem = 1 Sv.): a unit measuring absorption of radiation by tissue (equivalent doses).  Like the rem, the Sievert takes into account the relative biologic effectiveness (RBE) of ionizing radiation, since each form of such radiation — e.g., X rays, gamma rays, neutrons — has a slightly different effect on living tissue.  Accordingly, one Sievert is generally defined as the amount of radiation roughly equivalent in biologic effectiveness to one gray (or 100 rads) of gamma radiation. I aim to to express all radiation doses in a single unit, the microsievert (µSv) to make comparisons easier (when possible).  Reporting is often done in millieSievert (mSv), which is 1,000 times bigger than a microSievert.

  • Roentgen  & Coulomb/kilogram

Roentgen (R) – The roentgen measures the energy produced by gamma radiation in a cubic centimeter of air. It is usually abbreviated with the capital letter “R”. A milliroentgen, or “mR”, is equal to one one-thousandth of a roentgen. An exposure of 50 roentgens would be written “50 R”.  See also  Wikipedia – HERE. For easy conversion:

1 microsievert (µSv) = 100 microroentgens (µR)

As an example in time-warped realities: even in 2011 you may still get reporting about radiation in Roentgen: “In Primorye, including Vladivostok, Russia’s largest city on the Pacific, exposure rates varied from 10 to 15 micro-roentgen per hour, while in Sakhalin they ranged from 5 to 15 micro-roentgen per hour. Exposure rates of up to 30 micro-roentgen per hour are considered normal.”, was reported in RiaNovosti, HERE (06:19 18/03/2011).  Conversion:

1 microsievert (µSv) = 100 microroentgens (µR)

1 µR/hr = 0.01 µSv/hr

10  µR = 0.1 µSv  = completely normal, on the low side of the natural range

Coulomb/kilogram (C/Kg) – not discussed here; See Wikipedia – Coulomb

  • CPM = COUNTS PER MINUTE is a very clear measure of how many gamma rays hit a gamma ray sensor per minute.  The reading of course depends on the sensitivity of the Geiger Counter you’re using.   For many Geiger Counters, the conversion rule “100 CPM = about 1 µSv/hr” or vise versa: 1,000 µSv/hr would give readings of about 100,000 CPM (less on older or less sensitive models) is no longer valid.  You have to check the calibration/conversion for your specific monitor.  [See also comments Dec 2015] For a technical look at the differences in Geiger Counter sensitivity, see here.

Reference: Normal USA CPM level:   10 to 50 CPM   (0.1 – 0.5 µSv/ hr),or up to 90 CPM in places like Denver, Colorado.

Baseline in Tokyo pre-accident: 10 to 20 CPM  Here’s an example of a CPM Geiger Counter streaming live data from Hino, Japan (near Tokyo):  http://park30.wakwak.com/~weather/geiger_index.html  See my RADIOACTIVITY page (tab) for many more options and global radiation monitoring stations online.


– The “Alert level” set for the US grassroots radiation network, for instance, of which the US Geiger Counter network seems an expanded and improved (also independent) version, is a mere 130 CPM or about 1.3 µSv/ hr, which, going solely by comparison to many radiation levels (see “Health Expose Effects”, would be little reason for alarm if it were originating from distant radiation sources only.  Most places wouldn’t reach such high readings naturally, thus it would be a clear signal that something has gone awefully wrong somewhere.  Another thing to keep in mind is that fallout tends to accumulate on the ground (especially with precipitation), and radiation monitors are usually high above the ground, sometimes even on top of buildings.

– Accumulative effects from built-up in cell tissue is not accounted for in simple comparisons between exposure to amounts of radiation, and thus they are a bit deceiving, downplaying the dangers.

– In many locations measurements are generally below 0.15µSv/hr, or on common Geiger Counters that would give readings somewhere between 5 and 30 CPM.

– Some more sensitive Geiger (gamma ray) Counters will give readings corresponding with ‘100 CPM = 5 µSv/ hr’.

–>  For a technical look at the differences in Geiger Counter sensitivity, see HERE.

– Exposures can be expressed as totals, or as flows (units/time, such as mSv/hr).  Common prefixes are milliSievert (one-thousand of a SIevert, mSv) and microSievert (one-millionth of a Sievert), as well as hecto-gray (one-hundredth of a Gray, hGy).

– The various kinds of radiation units & how to convert them are als covered in this table at:  http://www.albert-cordova.com/iso/Units.htm (CAUTION, though: In this Table instead of the usual “µ” for micro, they used another “m” than for the m that abbreviates milli; along the same vein: u is sometimes used as an abbreviation for micro, instead of the more correct µ  (option m on a Mac)). Also at: http://orise.orau.gov/reacts/guide/measure.htm

– For reporting: Because for living organisms 1 Sv is such a large amount of radiation, generally measurements are given in milliSievert (mSv) or microSievert,  (µSv):

1 Sv = 1,000 mSv = 1,000,000 µSv

rems/mrems (millirems) are still seen in media reports too:    1 mrem = 10 µSv

1 rem = 0.01 Sv= 10 mSv = 10,000 µSv

Remember: In the Standard International (SI) units the rem has been replaced by the Sievert, and the rad has been replaced by the Gray:

– the Sievert (Sv)  -> 1Sv = 100 rem

– the Gray (Gy).   -> 1Gy = 100 rad

CAUTION: Comparing dose rates is NOT a dependable way to gauge dangers from fallout.

If you spot an error, please immediately leave a comment, I’ll fix it asap.  Tx!

Additional SOURCES:

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2 Responses to Radiation Units

  1. Scott says:

    Hello, first of all thank you taking the time to write this blog. You pulled to gather a great amount of information and tools on radiation conversions.

    We are looking for a way to convert beta particle counts into radon levels in picocuries per liter.

    From what I can tell there is no way to do this “mathematically“ as it’s not a direct conversion, yet they’re absolutely has to be a relationship.

    Assuming we know the energy level of the beta particle, and it matches the energy level in the Bricktown process of uranium, let’s say that we have 1 L of volume and we detect one beta particle. Is there anyway to quit that into a Ci per liter number?

    Thank you, Any help would be appreciated.

    • MVB says:

      I doubt that can be done with only knowing beta counts, u,less you’re certain they’re beta counts specifically from radon, then maybe an approximation is possible, but I wouldn’t know how.

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