Dear colleagues,
recently there was a question here on RG about a mysterious high energy shoulder of a gamma peak.The real reason for that is unknown up to now.
https://www.researchgate.net/post/Why_does_a_shoulder_appear_in_full-enegy_peak_in_HPGe_gamma-spectrum_of_certain_sample.
One of my ideas is EMI interference with cell phone radiation.
It is well known, that cell phone (handy) radiation affects/irritates sensitive electronic equipment.
A HPGe detector is such a sensitive device.
Does anybody of you have performed tests about that issue; are there any experiences?
Any contributions are welcome...
Thanks in advance and best regards
G.M.
I dont have much experience on this topic and cannot add evidence based facts. I thought at first that a mobile phone would just create interference on the electronics of the detector i.e. high voltage amplifier...
Then I thought that to produce an electron-hole pair you need 3eV in Ge semiconductor crystal, can we have photoelettric effect from a normal mobile phone signal? I don't think so, a GSM 1600MhZ wave has an energy in the range of nano-eV unlikely to produce any electron-hole in the detector crystal. Am I missing something?
Dear Enrico Corniani , thanks for feed back.
You are right, electron-hole pairs cannot be created by the cell phone radiation, and I do not think that the high voltage is affected strong enough to produce a ripple in the amplification.
My thoughts touch the noise level of the signals entering the preamplifier e.g. by noise on the ground line(s), especially when groundline loops are accidently present. Beats of cell phone radiation may cause such noise, when the cell phone is close to the detector; but I am not expert in these things.
Any amplified noise which (in amplitude) is nearly equivalent to a 3keV detector signal may add to the gamma peaks (at the above mentioned gamma spectrum) via pile up at high incidence rates.
Unfortunately I am retired now; so I have no access to HPGe detectors anymore.
Otherwise I would have been checked that issue experimentally by myself....
Yes, such interferences do appear and I did experience one myself in the microBq lab from.the Unirea salt mine in Slănic Prahova (the low background lab brlonging to IFIN-HH). We were investigating a strange peak appearing at low energies (below 10 keV) in a system 120% efficiency HPGe detector and we were not able to obtain reproducible results. Is was pure serendipity that one of the mobile phones on the desk started ringing and simultaneously with that the strange peak appeared in the spectrum. We then experimented several times and the conclusion was clear: the low energy peak was, in fact, interference from the mobile phone RF signal. The mine had GSM antennae installed and one was close enough to the lab. As soon as extra shielding was added to all cables and to the MCA, the problem disappeared.
Dr. Romul Mărgineanu might add some details, he was the head of the lab at the time of the incident.
But bear in mind this happened in a very low background lab (approx. 2 nSv/h bckg dose rate). I am not sure such phenomenon could be observed in normal background.
Thanks Radu A. Vasilache ,
for feed back.
I appreciate your answer, which shows that shiedling also for EMI is very essential and has to be performed very carefully.
In the meantime the gamma-shoulder issue seems to be solved. It is most propably pile up from L-fluorescent lines of the sample which is excited by the multiply Compton scattered gammas and Compton recoiled electrons within the sample.
You may have a look a my recent answer in:
https://www.researchgate.net/post/Why_does_a_shoulder_appear_in_full-enegy_peak_in_HPGe_gamma-spectrum_of_certain_sample
I guess the second page of this document may describe the problem (multi-pulse saturation in the preamplifier ) https://www.science.mcmaster.ca/radgrad/images/6R06CourseResources/4RA34RB3_Lecture_Note_6_Pulse-Processing.pdf
Dear Nikolay Pavlov ,
thanks for your contribution.
Does the pulse saturation really lead to a high energy shoulder? I think we will in that case have a low energy shoulder or tail.
But how one can test that the high enery shoulder issue is due to multi-pulse saturation and not due to pile up via quite a high count rate low pulse series?
Lowering the countrate via a smaller amount of sample material will affect both scenarios.
X-ray filtration will mainly reduce the flow of low energy photons and thus will lower the pile up propabilty with them.
In the thread mentioned above, I recently suggested the filtration option. You may have seen it.
Gerhard Martens I think we need just to reduce the activity of the source, e.g. cut a piece of it if possible or let it decay a bit.
Hi sir
Microwave and electromagnetic radiation may both induce phonon vibration in HPGe crystal which leads to weak detectable signals like what is detected from low energy gamma ray
does the shoulder appear in the total energy peak in the HPGe gamma spectrum of certain samples, there are two probabilities, if the problem in the HPGE detector, adjust it if not it is problem due to the high activity of the sample therefore it is necessary to remove the sample at the level of the detector to eliminate the peak sum phonomene
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