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NaI/Tl Gamma spectroscopy - New kit with new sources.

Seoul_lasers

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I have been on this topic for a while now so please bear with me. I do amature gamma spectroscopy among many other things as a hobby... I am one of these people who seldom finds anything boring/tiresome. Late last year, (Spring of 2019) I finally acquired a very well built Scionix 1.5" dia NaI/Tl detector along with a GS-USB-PRO from Gamma spectacular in Australia. For those of you who are not familiar with this product it has a built in ADC which samples incoming pulses as audio.
The binning of the pulses in done in PRA, Theremino MCA or Berqeulmoni (Japanese MCA software).

Along with equipment I got 2 very strong calibrated sources ( a 10uCi Mn54 disk source as well as a 5uCi Cs137 source). The Cs137 source does nearly 200KCPM on my LND7317 geiger tube. It is highly active! The 2 sources combine to nearly 365KCPM ~110uSv/hr Hence to say, they are both stored in a Lead isotope storage container. They are both considered mid-energy gamma emitters and require much paperwork to obtain in Canada.


Anyways... Here are some pictures of my setup. I am in the process of building a spectroscopy lead pig to shield the background. 0.25" Inner copper layer, followed by Cadmium foil, the followed by ~2-3" of Pb. The shield is meant to block the ambient background as much as possible to have only the measured sample show in the collected output spectrum.

All my spectra taken thus far has been at 550V over 2-4hours periods. Stronger sources require a few seconds up to 5 minutes to produce a useful spectrum. High count rate samples are NOT something you want when doing spectroscopy as they cause pulse pileups.

An added benefit of the GS-USB-PRO is the ability for it to hook up to an iPhone or Android phone to do portable Isotope identification.





Picture insert here




I had posted my pictures here but there seems to be an issue with the server.......
 
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paul1598419

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Cool! I had wondered if you had still been working on gamma ray spectroscopy. I look forward to your photos of the new detector.
 

RedCowboy

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Would either of your sources be energetic enough to drive a layer of phosphor in order to produce a visible glow ?
I am also interested in seeing your device, it sounds interesting.
 

Seoul_lasers

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Here are the pics..

Lead pig for the Cs137 and Mn54 (mid-energy gamma storage container) Knocks ~60% of the emissions down.
Still ~100KPM at the surface of the pig.

IMG_5463.jpeg


Exposed Caesium 137 source (toasty warm) :)

IMG_5464.jpeg



Gamma spectrometer running at 651V.. Note the SHV HV connector on the right is in a single wire mode here. The output is decoupled into an ADC inside the spectrometer.


IMG_4802.jpeg



This is the sweet spot for my probe (550V) - This is the most linear of the voltage settings and produces best results with 10x gain in software. (pictures of incoming pulses coming up)
IMG_4823.jpeg


A 0.3uCi (Cs137 source) - Front of 1.5" Scionix NaI/Tl Scintillation detector - detector set at 550V input gain at 10x
IMG_4805.jpeg


Here is the spectrum generated in ~10 minutes. Note the Gamma peak at 662KeV is due to Beta decay of Ba137m ( m being metasable) ... The 32keV X-ray is due to the two K α-lines of Ba. The compton scatter peak, plateau and edges are also quite visible in the graph.
Resolution is about 6.5% FWHM here, pretty much maximum as you'll get from a NaI/Tl detector.

IMG_4270.jpeg

Scionix NaI/Tl detector with a T bias splitter/filter going into a high resolution audio recorder. Pulses are stretched out between 50-100uSec so they can be processed by a desktop sound card.
IMG_4273.jpeg


This spectrum was generated by a 0.2uCi Ra226 sample ( a watch hand) after about 2 hrs.
The collection of pulses to generate this histogram is around 13.8 million pulses total. There are probably 100x this many that were filtered out. Note the Pb214 peaks and the very prominent 609.3KeV Bi214 peak. This is common to U series decay which Ra226 is part of. The smaller 186.1KeV peak belongs to our target isotope ( Radium 226) The majority of Radium's energy is ejected as alpha particles (He4 nuclei)
while decaying into Ra222 through alpha decay.

This spectrum was captured as a .CSV and then brought into numbers for MacOS 10.15.2

Ra226.png


Portable iPhone Gamma spectroscopy. No computer, no problem. :)
This time we are dealing with Uranium Dioxide ( note the 609.3KeV - Uranium decay chain)
Also can see extra spikes near where Ra226 is.. These belong to numerous U238 and U235 gamma energies.
The iPhone can just barely resolve the peaks due to the crappy ADC sampling rate. Uraninite sample used to generate this is around 27.8KCPS and is only 2cmx1.5cmx1.23cm --tiny but screaming hot sample from a Uranium hotspot in B.C. --or so I've been told.

IMG_4490.png
 
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Seoul_lasers

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Here is a discrimination of Cs137 and Mn54 being done off an iPhone 6S+ Peaks are resolved well 661.7KeV Cs137 and 834.8KeV for the Mn54. Total time for resolution was only 2.5 minutes. Very useful.

IMG_4492.png


A smallish 10Ah Miniso battery bank powers the spectrometer for portable use. In this configuration the spectrometer could run for 62.5hrs without needing a charge.

IMG_4497.jpeg
 
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