NaI Kristall

[Lposter]

As you are interested in the low energy part of the spectrum, here is a standard 2" model of a NaI detector with both Al and Stainless Steel housings. In both cases, the housing is 0.5mm thick.

The sample is a 5cm diameter, 1 cm thick disk of material - in this case simply described chemically as "water" was then placed on the housing face. So it will not be entirely relevant for a soil sample.

12356 Bq of 238U and 568 Bq of U235 were placed in the container. These were aged by 500 000 years to bring the majority of the daughters into equilibrium.

A resolution for HPGe was used to make the peaks clearer - the material was NaI so the efficiency of it is consistent with that material but the resolution is just a confection to enable easier area calculations. 2048 channels, 0.25 keV/channel.

The sample was then "counted" for 1000 s. Not really long enough for good statistics but perhaps OK for purpose.

Comparison of the two should give some idea of the impact choice of detector housing has on the efficiency at low energy. Given that the thickness I used was only 0.5 mm...it may not be that much at all.

Spectra in .n42 format. Rename to such. If there are "anomalies" in terms of peak energies or intensities...probably my fault as such data is entered "by hand" and it is tedious in the extreme and prone to errors just by it being so tedious.

[Rob Tayloe]

The results posted by Lars Poster are quite interesting when the spectra are viewed graphically. I imported the files (pdf extensions renamed to n42) into interspec. The first image is of the results with resolution (in green) and without (in black). Next are the results of the NaI detector with an Al endcap and then with the Stainless Steel endcap; these results are similar.

[Lposter]

That looks nice....thanks for plotting! Given the simulated endcap is only .5 mm thick, I would have guessed the difference in efficiency would only manifest itself at very low energies. Things would probably be different if it went up to 1mm thick.

It always impresses me to see the complexity of what lies beneath NaI peaks in actuality. Lots of physics and minor interactions and little peaks.

Thanks agian!

Lars