Gamma Spectrometry Forum

Hi all,

I am working on a proposal to supply a Compton experiment for a University, so I have been teaching myself to use Fusion 360 CAD design software. As always it takes some time to master the various commands of a new software package, but I am slowly getting the hang of it and enjoying it (although the red SHV cable was tricky).

This experiment shines a collimated Cs-137 beam onto a BC412 plastic scintillation detector, and uses a NaI(Tl) or Csi(Tl) detector to record a spectrum of the scattered photons. The objective of the experiment is to show that the resulting energy peak from scattered photons (after colliding with an electron) are predictable and follows a given equation.

To achieve better resolution this experiment uses PRA with two detectors in coincidence mode, but it still takes 10-15 minutes before you see a good peak.

Anyone interested in trying this experiment or having one of these built can PM me above..

Steven

Interesting ! How does one collimate photons ? A simple hole in a lead plate is enough, or should the hole be long enough like a tunnel to form a "cannon" ?

Holy crap that's cool!

Sebastien,

The simple way to collimate photons is to use two lead bricks with holes that are aligned. The problem is obviously the strength of the source, as the count rate falls off at 1/r^2.

For this experiment you need a fairly high count rate, if you only have a single 0.1 µC Cs137 source you are going to struggle or it will take a long time, but I guess one could stack 4-5 sources together and get a high enough count rate.

Steven

Hi Steven,

the setup looks quite nice! I think such a setup could also be use to measure gamma-gamm angular correlations (the change in the coincidence count rate of two detectors, if the angle detector1-source-detector2 is changed).

One can see two GS-USB-PRO in the picture, and I'm wondering how well a coincidence measurement with two independent sound chips will work. The two sound chips might not have the exact same sampling frequency. Can it happen that the time bases of the two sound chips drift away from each other after a while?

Michael

Michael,

miree wrote: ↑

08 Feb 2019, 03:01

One can see two GS-USB-PRO in the picture, and I'm wondering how well a coincidence measurement with two independent sound chips will work. The two sound chips might not have the exact same sampling frequency. Can it happen that the time bases of the two sound chips drift away from each other after a while?

It is correct that you see two GS-USB-PRO being used for coincidence counting, but only one stereo CODEC is used for Left-Right channel coincidence counting.

The GS-PRO has a clever TRRS port (Tip-Ring-Ring-Sleeve jack) where the tip is left channel analogue output and the first ring is right channel analogue input.

Two GS modules can now be connected together with a Stereo crossover cable, so right goes to left and left goes to right.

This way the second GS is connected to the primary GS right channel by analogue connection.

Normally you would connect the better resolution detector to the primary GS.

Works well..

Steven