Friday, December 20, 2013

Radioactive Units - Do Not Use Them Incorrectly!

Geiger counters count ionizing radiation events.

To measure a detected reading, the energy of the detected radiation must be known. If the detected radiation has an unknown energy, there can be no measure, but merely the detection.

Examples of different energies from common isotopes released by Fukushima (approx):
Cs137 -- 0.5 MeV beta
Cs137 -- 1.1 MeV beta
Cs137 --Ba137m -- 0.6 MeV gamma (often used to calibrate GM's)
Sr90 -- 0.5 MeV beta + weak gamma
I131 -- 333 KeV beta
I131 -- 606 KeV beta
U238 -- 4MeV alpha

As you can see, the energies very quit allot and cannot be assumed.

Here are some energy dependent units:
1 Gray = 1 joule / 1kg
1 Seivert = 1Gy x RadiationFactor x BodyPartFactor
1 RAD = 0.01 joule / 1kg
1 REM = 1 Rad x RadiationFactor
1 Roentgen = = 2.58×10^-4 Coulomb / 1kg

As you can see... each of these units uses a degree of energy. You do not know the energy unless you know the exact nature of your source. As a result, you cannot use them.

In short: If and only if you know the exact energy of your source and a specific calibration and calibrated geometry, you cannot accurately use any energy dependent unit. All such unit measures are meaningless in these cases.

Use Counts Per Minute (CPM) or Counts Per Second (CPS)

Have fun!

Bonus: Links to radiation risk charts:

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