About selecting energy range on the spectrometer

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Discussion Overview

The discussion revolves around the selection of energy ranges on a spectrometer, specifically in the context of measuring alpha and gamma spectra using different types of detectors. Participants explore the implications of energy range settings on count rates and peak detection, as well as the suitability of specific detectors for alpha spectroscopy.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant reports a significant difference in time to reach 3000 counts when measuring alpha spectrum at different energy ranges (3-8 MeV vs. 4-6 MeV) and seeks explanations.
  • Another participant questions whether the peak was fully contained within the selected energy range and whether the counts represented only the peak, suggesting potential issues with the setup.
  • Concerns are raised about the suitability of a NaI(Tl) detector for alpha measurements, with suggestions that alpha particles may not penetrate the detector's endcap and that semiconductor detectors are typically preferred in vacuum chambers.
  • A participant confirms that the peak was fully contained and that the count was just from the peak, but expresses uncertainty about the detector type initially mentioned.
  • Clarification is provided that a charged silicon detector was used for measuring Po-210 in a vacuum chamber, rather than NaI(Tl).
  • Further questions arise regarding the use of NaI(Tl) for measuring gamma spectra, particularly about the effects of selecting a large COARSE value on the MCA, leading to almost no counts and potential dead time issues.
  • One participant notes unexpected counts in the spectrum when the NaI(Tl) was measuring nothing, raising questions about the source of these counts.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the NaI(Tl) detector for alpha spectroscopy, with some agreeing on its limitations while others provide alternative suggestions. The discussion remains unresolved regarding the reasons for the observed counting discrepancies and the unexpected peaks in the gamma spectrum.

Contextual Notes

Participants mention various assumptions about detector capabilities and measurement conditions, but these assumptions are not fully explored or validated within the discussion.

toex
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Hi everyone, I am doing an experiment about alpha spectrum. I am using Model P-2000/1 (don't know if this matters), a NaI(Tl) scintillation probe. I selected energy range 3-8 MeV at the front panel and waited for 3000 counts at the peak, it took ~800 seconds. But when I selected energy range 4-6 MeV and did the same measurement, it took me ~17000 seconds to have 3000 counts at the peak! Does anyone know why? Thanks a lot!
 
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Was the peak fully contained within 4-6MeV?
Are you sure that the count was just the peak, not events in the whole range?
If it is not one of these things: No idea. Might be some strange effect from the setup.
 
I'm not sure if I'm right but NaI(Tl) detector isn't good choice for alpha. IMHO its in endcap made by some metal maybe Al (hygroscopic material) so alpha particles cannot penetrate through this "cover". Alpha is mostly measured (spectrometry measurement) in vacuum chambers with some kind of semiconductor detectors. Are u sure u have NaI(Tl)? There are another scintilitor Zn(S)which is used for some kind of alpha spectroscopy. And regarding your question have to agree with mfb, u have narrower window so its possible that part of peak is out of your rang. BTW do u know what nuclide are u measuring?
 
mfb said:
Was the peak fully contained within 4-6MeV?
Are you sure that the count was just the peak, not events in the whole range?
If it is not one of these things: No idea. Might be some strange effect from the setup.

1. Yes, the peak was fully contained in 4-6 MeV.
2. Yes, the count was just the peak.
3. Thanks for your reply :)

ramses22 said:
I'm not sure if I'm right but NaI(Tl) detector isn't good choice for alpha. IMHO its in endcap made by some metal maybe Al (hygroscopic material) so alpha particles cannot penetrate through this "cover". Alpha is mostly measured (spectrometry measurement) in vacuum chambers with some kind of semiconductor detectors. Are u sure u have NaI(Tl)? There are another scintilitor Zn(S)which is used for some kind of alpha spectroscopy. And regarding your question have to agree with mfb, u have narrower window so its possible that part of peak is out of your rang. BTW do u know what nuclide are u measuring?

Sorry, I mixed them up. I was not using NaI(Tl), I was using a charged silicon detector to measure Po-210 inside a vacuum chamber. Thank you for replying!
Another question, this time I was using a NaI(Tl) to measure the gamma spectrum of Cd-109. As it has two very nearby peaks(22.1 & 24.9 keV), I selected a very big COARSE value on the MCA so that the two peaks can be resolved. But when I chose the maximum COARSE value, the counting almost stop (I assume it is very long dead time?), what was happening? Also, when the Na(Tl) was measuring nothing, the spectrum showed two significant peaks and there were 10000 counts in 10 seconds! I don't think this comes from the background. Anyone know what was it?
 
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