# Can GM gamma meter be sensitive for neutron radiation?

1. Jun 2, 2012

### 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:

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.

2. Jun 2, 2012

### 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.