B Quick Question about emitted radiation and Geiger counter accuracy

Abu

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Hi everyone.
I read from:
https://www.nucleonica.com/Applet/NaturalRA/Button5/page5.html
that inside the human body, 4400 of K40 atoms disintegrate every second through radioactive decay. Of this decay, 11% (480) results in gamma radiation, and 50% of that 11% (240) escapes the body.

My question is that since your body is emitting 240 Bq every second, if you stood next to a geiger counter, would the geiger counter detect your radiation? Would that be a source of error when using the counter?

Or is it so insignificant that it is negligible? Because the 240 Bq would be divided since the radiation is spreading in all directions from yourself, and the geiger would take only a small fraction of that?

Thank you!
 

kuruman

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Yes, the 240 estimated gamma rays that escape the body are emitted in all directions and only a small fraction of them will enter the counter. You should also consider the efficiency of the counter; not all gamma rays entering the counter result in a "click".
 
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Once in a while it will trigger a Geiger counter. But so does everything else. The floor, the walls, ... even the material of the Geiger counter itself. This is natural background that has to be taken into account for measurements of low activity.
 
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Abu

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Once in a while it will trigger a Geiger counter. But so does everything else. The floor, the walls, ... even the material of the Geiger counter itself. This is natural background that has to be taken into account for measurements of low activity.
Ah okay, so it's part of the background radiation technically. Thank you two very much!
 

kuruman

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Ah okay, so it's part of the background radiation technically.
It doesn't have to be. You can record background counts with and without you in the room and see if your presence makes a difference.
 
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see if your presence makes a difference
Ah, the good old existential question.


No, seriously: Background measurements should be done under the same conditions as the measurements with source, if it is relevant this includes the same people nearby.
 
Hi everyone.
I read from:
https://www.nucleonica.com/Applet/NaturalRA/Button5/page5.html
that inside the human body, 4400 of K40 atoms disintegrate every second through radioactive decay. Of this decay, 11% (480) results in gamma radiation, and 50% of that 11% (240) escapes the body.

My question is that since your body is emitting 240 Bq every second, if you stood next to a geiger counter, would the geiger counter detect your radiation? Would that be a source of error when using the counter?

Or is it so insignificant that it is negligible? Because the 240 Bq would be divided since the radiation is spreading in all directions from yourself, and the geiger would take only a small fraction of that?

Thank you!
"My question is that since your body is emitting 240 Bq every second, if you stood next to a geiger counter, would the geiger counter detect your radiation? "

Definitely.
Would it be a source of error? Again: Definitely.
We spend a great deal of time and money on complex shielding to deal with all sources of background radiation! The more sensitive is your sensor, the more mass quantity and complex the shield needs to be.
Will your bones affect a CDV-700 Civil Defense Geiger Counter- no not really, it's not sensitive enough, but a great deal of the counts it gives with no radioactive sample present do come from the tons of K-40 in the soil surrounding your location.

For the record some facts;
K-40 decays 89% of the time by Beta-minus Emission Decay eventually yielding a stable Ca-40 daughter atom,
while 11% of the time K-40 decays by EC (Electron Capture) Decay, eventually yielding a stable Ar-40 daughter.

Beta Emission Products: K-40>Ca40 Decay
Maximum Average
Fraction Energy(MeV) Energy(Mev)
0.893300 1.311600 0.508540

Photon Emission Products: K-40 >Ar-40
Fraction Energy(MeV)
0.009376 0.002958
0.106700 1.460800

1460 keV is rather strong among elemental Gamma Rays, and is a major constituent of earthly "background" radiation. Since it is so prevalent everywhere on earth, it is used as a key calibration marker for Nuclear Metrology calibrations.

Notice the stray 0.002958 MeV photon in the chart. This is
actually a K-alpha (K-a) Chracteristic X-Ray of 2.96 keV generated in the K-a electron shell as the emitted 1460 keV leaves and excites the K-a electron out of its shell. When it is replaced by another electron from a higher shell, that electron emits an energy equivalent to its orbital binding energy.

The 1460 keV (1.46 MeV on the chart above is the IT (Isomeric Transistion) Gamma Ray that is emitted by the excited daughter nucleus, Ar-40.

Thanks
George Dowell
 

DEvens

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Yes. It can even produce a dose of radiation. In the linked graph, it's the very smallest dose, at the very top left. And it's about half what you would get from eating one banana.

 

gleem

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For what it is worth the contribution to the radiation survey count rate from the surveyor is of the order of 0.3 cpm. assuming a solid angle for the detector of 0.02 strd ( detector intercepts only about 0.2% of gammas) and an intrinsic efficiency of 1% and neglecting any absorption or scattering by the body or inverse square law corrections for a non point source.

So unless you are performing a very low activity measurement where your presence would affect the results you need not be concerned. Additionally if you were performing such a measurement you would not be using GM counter.
 
For what it is worth the contribution to the radiation survey count rate from the surveyor is of the order of 0.3 cpm. assuming a solid angle for the detector of 0.02 strd ( detector intercepts only about 0.2% of gammas) and an intrinsic efficiency of 1% and neglecting any absorption or scattering by the body or inverse square law corrections for a non point source.

So unless you are performing a very low activity measurement where your presence would affect the results you need not be concerned. Additionally if you were performing such a measurement you would not be using GM counter.
100% Correct, you would be using a whole body counter. Here are 3 at the school for nuclear reactor operators, pictured with my assistant Mat Hazard getting his thyroid scan, whole body, and deep chest scans before going home for the day. These are all large volume, highly shielded Gamma Scintillator counters.

Thyroid scanner, tests for concentration of radioiodine in the thyroid, the natural biological sponge for iodine (I had to get one every day when doing certain tasks not to mention the wearing ring film, the TLD, the graduated chest film and the two ionization chamber dosimeters)


Here Mat sits in a heavy lead chair facing a very large disc of lead shielding with a hole in the middle for the scintillator:


and same scanner from the rear, looking through the lead shield before installing the sensor:


These can read you bone's natural radiation, plus anything unusual.

George Dowell
 

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