Introduction to gamma spectroscopy on a budget. Daniel Emes SA Radiation

Transcription

1 Introduction to gamma spectroscopy on a budget. Daniel Emes SA Radiation

2 Outline What is gamma spectroscopy, what is the point? What is required to set up a gamma spec system? Soundcard spectroscopy My experience setting up the Gammaspectacular Some spectra of sources and materials Uses and limitations

3 Disclaimer We have no affiliation with any of the companies, products or software mentioned within this presentation. This presentation reviews the Gammaspectacular system to compare to conventional gamma spectroscopy systems.

4 Gamma Spectroscopy Gamma spectroscopy is the science of identifying radionuclides based on their gamma ray energy spectrum. Most radionuclides have their own fingerprint gamma spectrum.

5 Gamma Spectroscopy By looking at the fingerprint (the location and relative size of peaks), the radionuclides in a sample can be determined. With enough information (knowledge of gamma yields, efficiency of detector, geometry, and some calibrated samples), the approximate activity or activity concentrations of samples can be determined. The next few slides show some gamma spectra for specific radionuclides. Prizes for correct answers.

6 Am keV

7 Co keV 1333keV

8 Disneyland!!!!

9 Cs keV

10 Gammaspectacular kit Came with a detector (2 inch sodium iodide), signal processing box, and all required cables.

11 Kit positives and negatives Compared to a commercial gamma spec laboratory with a high purity germanium (HPGe) detector setup Gamma spectacular HPGe Relatively very cheap!! Better counting efficiency Much greater resolution (easy to determine peaks) Possible to use in field Room temperature operation* Poor resolution in comparison (can be difficult to interpret) Cooling required Expensive Longer count times required

12 Shielding Shielding is used to reduce the amount of background radiation reaching the detector (mainly from terrestrial and cosmic sources). It can create more problems (mainly due to x-ray fluorescence) than it solves if you are not careful.

13 Shielding I used lead shot within a PVC tower (graded shielding with high pressure PVC at core to reduce lead x-rays). If lead surrounds your sample completely the gamma spectrum can become over shadowed by lead x-rays.

14 Signal processing You need a way to process the signal from the detector to create a gamma spectrum. Typically this is done with a multi channel analyser (Very expensive!) The Gammaspectacular uses your computer s sound card to do part of the signal processing for you (a good quality USB sound card is even better!) The result is a spectrum of different frequency gamma sounds heard by your sound card, output in a program that is capable of organizing the spectrum. (if you get into it enough you can start to pick radionuclides based on the sound alone!)

15 Software There are a few versions of free software available to organize your spectrum. Essentially all of them allow you to do some analysis of signal pulses and reject pulses that don t meet your criteria. I mainly used a program called PRA (shown in my screenshots). Other programs will give similar results (BeqMoni, Thermino, and even an iphone app)

16 Identification of peaks The next few slides are to demonstrate that the Gammaspectacular kit is capable of detecting radionuclides within things that you don t even need a licence to handle.

17 Smoke detector Americium keV Americium keV

18 Low sodium salt Potassium keV

19 Brazil nuts.. extra nutty

20 Brazil nuts vs background

21 Brazil nuts background compensated Lead keV Radium keV Lead keV 295keV 352keV Bismuth keV Actinium keV 969keV Potassium keV

22 Uranium glass Thorium keV 93keV Uranium keV

23 Radium clock Lead keV Radium keV Lead keV 295keV 352keV Bismuth keV

24 Uses and further investigation The gammaspectacular can clearly distinguish most radionuclides if you know what peaks you are looking for. It is therefore very useful when trying to identify an unknown source. It is also useful for wipe test analysis (leak test of a sealed source) due to its surprisingly good sensitivity. With enough effort it could determine approximate activity concentrations. Oversaturation issues??

25 Wipe test positive result Cs keV slightly above background at 0.2Bq

26 Conclusions It is clear that the Gammaspectacular kit can serve as a reasonable basic gamma spectroscopy system. The kit can be used to identify unknown gamma emitters. It can identify small quantities of radionuclides within samples, which is useful for wipe test result/contamination determination. It does have limitations particularly in terms of resolution when gamma peaks are close. Activity determination is difficult but can be accomplished with some good calibration samples in the appropriate geometry.

27 Questions?