Gamma spectroscopy- Fine Gain Coarse Gain factors

In summary, the conversation discusses the use of a scintillator and Cs-137 to obtain a Cs-137 spectrum in a spectroscopy lab. The spectrum is then calibrated using the known gamma energy for Cs-137 at 662 Kev at the photo peak. The problem arises when trying to use this calibration for a Co-60 spectrum due to adjustments in the coarse and fine gain. The conversation delves into the role of fine gain in adjusting the factor and suggests that a good approximation for calibration would be to solve for the fine gain and redo the calibration.
  • #1
Tito_Tileto
4
0
I'm currently doing a spectroscopy lab where you use a scintillator and Cs-137 to obtain a Cs-137 spectrum. I calibrated this spectrum using the known gamma energy for Cs-137 at 662 Kev at the photo peak. I am now trying to use this calibration for a Co-60 spectrum. The problem is that when I obtained my Cs-137 Spectrum I had the coarse gain at x16 and fine gain at x5. When I was taking data for the Co-60 I had to adjust the coarse gain to x8 and fine gain to x3.5. I understand the coarse gain is half that of the Cs-137 but how would I factor in the fine gain? For example for Cs-137 the photo peak was on channel 935 at 662Kev. So if I adjust the gain by half then 662Kev should correspond to channel 467.5 for the Co-60 spectrum. How does the fine gain adjust the factor?
 
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  • #2
Hi,

I know this is a little late for a reply, but perhaps someone else is wondering the same thing.

This is good question, and Iam not sure there really is correct answer regarding fine gain.
I once heared from a wise man, that coarse gain is what you would expect to be, a pure amplification, and I would say you are correct on using half the coarse gain, nothing major should affect the spectrum.

However, the wise man told me that, fine gain somehow takes a percentage from the input signal and passes this on to the coarse gain, this would mean that messing with fine gain should be done carefully.

E.g. the less you take from a signal the less noise you would amplify, so I am pretty sure you would receive different values for the FWHM depending on what fine gain value you use. So even if you "fine tune" the fine gain to match a certain channel, I would think that the spectrum would not be the same, because you have messed with the amount of signal you are using.

However, this depends on what kind of information you are wanting for from the spectrum.

If you simply just want to find out the calibration factor, I would guess you could view like this:

Now that the coarse gain is half, this means the correction factor should be 0.5-something.

The fine gain would be the last remaining digits, like 87.

So the correction factor would be 0.587 to divide or multiply (not sure which one, too tired :P) with the calibration value.

It would be like two simple equations where you solve the parameter "fine gain".

I could of course be wrong :)
 
  • #3
Old thread is old!

This of course assumes that the amplifier is "perfect". Which is not something you can assume, well, ever. Halving the gain will almost certainly not put the peak exactly half way down the spectrum. In reality, you'd have to pick your one gain setting for the entire experiment - pick it such that you can see the highest energy peak, and then calibrate the spectrum.

Also, by the way, using only one point (the 662 keV line for 137Cs) to calibrate an energy spectrum is extremely incorrect. The OP should have taken uncalibrated spectra for several sources, and then made a decent calibration.
 
  • #4
e.bar.goum said:
Old thread is old!

Also, by the way, using only one point (the 662 keV line for 137Cs) to calibrate an energy spectrum is extremely incorrect.

Well, it was a "lab" (not so serious) and he was using a scintillator, which is known for it's linearity. So I would not say its extremely incorrect, but a good approximation :)
 
  • #5
abotiz said:
Well, it was a "lab" (not so serious) and he was using a scintillator, which is known for it's linearity. So I would not say its extremely incorrect, but a good approximation :)

Huh. I actually teach a Compton scattering lab for undergrads, and I'd fail someone so hard if they handed me something with a one point calibration - the point of labs is to learn good lab skills, after all.

ETA: And you really won't get the positions of the peaks to particularly good accuracy.
 
  • #6
Well, he/she wanted to calibrate with Cs and Co, there was just an unexpected problem.


e.bar.goum said:
I actually teach a Compton scattering lab for undergrads,

So do I :) and I would commend the student for trying to solve the problem by using the amplifier gain.

However, a better option would be to redo the calibration.
 

Related to Gamma spectroscopy- Fine Gain Coarse Gain factors

What is gamma spectroscopy?

Gamma spectroscopy is a scientific method used to measure the energy and intensity of gamma rays emitted from a radioactive source. It involves the use of a gamma ray detector and a spectroscopic analysis system to identify the energies of the detected gamma rays.

What is the purpose of fine gain and coarse gain factors in gamma spectroscopy?

Fine gain and coarse gain factors are used to adjust the sensitivity of the gamma ray detector. Fine gain adjusts the sensitivity at low energies, while coarse gain adjusts it at high energies. These factors are important for accurately measuring the energy of gamma rays and differentiating between them.

How do fine gain and coarse gain factors affect the results of a gamma spectroscopy experiment?

The fine gain and coarse gain factors can affect the resolution and accuracy of the gamma spectroscopy results. If the gain factors are not properly calibrated, it can lead to incorrect identification and quantification of gamma rays in the sample.

How are fine gain and coarse gain factors calibrated?

The fine gain and coarse gain factors are typically calibrated using known radioactive sources with well-defined gamma ray energies. The detector response to these sources is then used to determine the appropriate gain factors for accurate measurements.

Can fine gain and coarse gain factors be adjusted during a gamma spectroscopy experiment?

Yes, the fine gain and coarse gain factors can be adjusted during a gamma spectroscopy experiment to improve the accuracy and resolution of the results. This is especially important when analyzing samples with a wide range of gamma ray energies.

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