Gamma Spectrometry Forum

I wasn't seeing much on the higher end energies at 700v so I moved it up to 850v where I know where 59.5 is located on the scale. I found this to be quite a surprise!

ROI from left to right - 63 & 93 from 234-Th, 186 from 226-Ra, 569 from 207-Bi (or 583 from 208-Th?), and 1001 from 234-Pa. Maybe one at 405 from 211-Pb?

Am I wrong? If so, where? Help.

I'm also befuddled on how to label peaks on the graph.

Daryl,

I can see a couple of problems here..

By moving the voltage up you have moved the whole spectrum to the left, this has a) introduced the tall peak on the left hand side which is electronic noise and b) hit the limit of your sound card at 100 arb.u. You can check this by turning off the calibration.

That big peak on the right is not a previously unknown source that's going to cook the world, it's more likely to be the sum o f all the gamma rays which exceeded the sound card limit.

Back off on the voltage and try to calibrate with K40 at 50 arb.u then run the spectrum again. Fiestaware often give high count rates on a pancake detector but are not very impressive on a gamma spectrum.

Steven

Steven,

Thank you! Okay here is one at 700v where K40 sits around 79 arb.u.
If I go down to 650v, K40 will sit around the 34 arb.u mark.

BTW, is the above spectrum pretty much okay up to 700KeV?

Daryl

Daryl wrote:Steven,

Thank you! Okay here is one at 700v where K40 sits around 79 arb.u.
If I go down to 650v, K40 will sit around the 34 arb.u mark.

BTW, is the above spectrum pretty much okay up to 700KeV?

Daryl

Much more realistic looking spectrum, and yes, the first spectrum is fine as long as you ignore the left and right peaks which are artefacts of the system.

In recent versions of PRA you have the advanced pulse filter, which lets you discriminate the LLD and ULD post recording.

Steven

Thanks for sharing. All these spectrume are great for comparison :)