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Shaping time on my amplifier alters the gamma energy registered?

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abotiz
#1
Aug28-13, 11:00 AM
P: 59
Hi,

My understanding of shaping time on amplifiers is that its the amount of time the capacitor has to collect charge. I would say that the longer the time the better energy resolution you would have due to that all the charge created from the photon is collected. However, if the time is long enough, that would mean that another electrons energy created from another photon interaction could add up. Following this, the amount of counts (or pulses I can seperate) decreases. Almost like the effects of dead time on a GM-tube.

But when I tried this to prove that this was the case, I got somewhat different results.

Sure I registered more counts with shorter shaping time, 0.5usec, when compared to 12usec. And the FWHM was better with a longer shaping time.

But the energy for the peak was affacted.

With 0.5usec the peak was at 345keV (kilo electron volts) and with 12usec the peak was at 280keV. My guess was that with longer shape time the photons would add up, so the peak would be like 600keV.

Any ideas?
Thank you very much!

Iam working with a scintillation detector btw.
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mfb
#2
Aug28-13, 03:28 PM
Mentor
P: 11,580
How did you modify this time?
How did you get your energy value?

I would expect some calibration issue.
abotiz
#3
Aug29-13, 08:07 AM
P: 59
I have what some calls a NIM-Bin which supplies electricity to some units, I used a High Voltage supply and amplifier wich can be seen in the attached image.

I got my energy through an MCA connected to a software on my laptop, a gamma spectrometry software.

Thank you
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IMG_20130829_150117.jpg  


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