Can GM gamma meter be sensitive for neutron radiation?

[LeonT]

Hi, I'm a new member in the forum.

I own two similar GM military grade meters with calibration certificates, calibrated for gamma-rays metering and each one has two tubes filled with helium, argon (or neon), halogen (or quenching) gases. When I am exposed to some radiation source, my GM meter shows dose rate of about 300 microR per hour, but scientific proportional gamma-rays dose-meter (also has calibration certificate), at the same moment is following to display background's gamma radiation numbers of about 7 microRentgen per hour.

I suspect, that my GM meters are measuring secondary gamma radiation caused by neutron radiation, born in their own tubes by the process of thermal neutron capture (or recoil) in helium-argon gas and then, the exposure radiation must be built of neutrons.

Here in forum I saw discussion in the following thread:

Neutrons and neutron "beams" are very hard to detect with portable instruments. The most common portable instruments are gas proportional counters using thermal neutron capture in BF₃ (boron tri-fluoride) or He³ gas.

Is it possible, that my GM gamma-meter is sensitive to neutron radiation too?
If yes, which physical mechanism should give GM gamma meter sensitivity for neutron radiation?

Thank you.

 

[Bob S]

Any water or other hydrogenous material in the vicinity could absorb thermal neutrons and emit capture gammas (~2.2 MeV) on hydrogen, but the sensitivity of a GM tube to these high energy gammas is low. (gamma detection is only via Compton scattering). GM tubes are most sensitive to charged particles (betas, alphas, cosmic rays). Alphas have a very short range, and cannot get through the wall of the GM tube. Neutron capture on some elements can lead to short half life beta emitters (e.g., Ag¹⁰⁹). This reaction is used for a pulsed neutron detector developed at Fermilab. Other reactions are He³n.p (see http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=14963&mf=3&mt=103&nsub=10) and B¹⁰ n, α (see http://www.nndc.bnl.gov/sigma/getPlot.jsp?evalid=14969&mf=3&mt=107&nsub=10).. Running a GM tube in the proportional mode is usually better for pulse amplitude discrimination, but this requires better electronics.