Gamma Spectrometry Forum

Hi,

When you use a 3-points calibration, the three energies used for calibration will be exactly at their place. But since NaI are not 100% linear, some measured energies will be off by a certain amount compared to real energies. In your opinion, what should be the max difference in keV between measured energy and real energy for a NaI detector when calibrating for a region between 32 keV and 2614 keV ?

Hello Sebastian,
NaI(Tl) is only non linear <100KeV so never use a calibration point lower <100KeV.
Above 100KeV is is fairly linear but linearity is also strongly depending on used pmt, voltage divider and room temperature.
So if you use a mca and make a three point (or better five or more points) calibrate and use wide range calibration sources with energies >100KeV It will be near 100% accurate for energies from100KeV up to 3MeV.
Luuk

Very interesting to hear about the "not under 100 keV" rule, I did not know this and I have not read this previosuly. I have almost always used my Eu-152 source for calibration, and the results have been good, but I will now skip the low point of 39.9 keV which I have been using, and try the 121,8 keV peak instead.

Do you have any kind of reference regarding this "100 keV" statement ,or is it based on your professional experience?

But as for calibration in general, I assume the largest uncertainty of the calibration will be in the middle of two calibration points, whatever they may be...

Are you sur about the 100 keV threshold ? because today I was reading this : [broken link removed - Steven]

In page 4, figure 3 I see a lack of linearity under 1000 keV, not 100 ? (I may misinterpret the graph since I am still a newbie in gamma spectrometry)

NaI(Tl) is non linear under 100KeV that is common knowledge, (all info availabe on the www) in that area the linearity is there really bad, but above 100KeV it is also not completely linear but much better, from about 300-400 KeV then it is really linear!
So never try to calibrate NaI(Tl)with energies <100KeV.
High resolution crystals e.g. LaBr3/CeBr3 etc. are very linear also in the low energy area.
Luuk

Ok thanks Luuk :)