ZnS:Ag is a pretty bright scintillator, with the ability to be loaded with Li-6. We bought some sheets of ZnS:Ag loaded with 6-LiF, and fabricated them in a layered configuration.
First a single film was measured, in order to benchmark the samples. This film was measured in the upright (vertical position), as well as horizontally on the PMT (not shown).
I'm getting pretty good at taping stuff together. The sponge is my favorite part.
After the individual film was measured (results below), four sheets of ZnS:Ag where layered together.
The upright film had significantly more counts*, but a lower light yield as seen by the lower peak position. The higher count rate comes from collecting light from both sides of the film; having two sides exposed to the PMT eliminates some of the self-shielding. The response of the multiple films exposed to the neutron source yielded a much higher count rate, but not to the extent expected (expected 4 times a single film, or ~1,000 cps).
This could be due to the attenuation of neutrons (a single film would attenuate a beam ~12%), or effects from the LLD, where low energy (low channel number) counts are lost. For the most part the gamma response was unaffected by adding layers (or the orientation).
When plotting the intrinsic efficiency (what really matters) the separation between the trials becomes more evident (but keep in mind that the error on the intrinsic efficiency is 30%, and we are interested in 1 in a million (1E-6)). There are 7.6 cps above the necessary gamma LLD for the stacked films, and 6.9 cps for the single vertical film. Needless to say we have improvements to make.
*This might not be significant; measurements made using a glass spacing
material had a count rate similar to 250 cps horizontally on the PMT.
Randomly (I found it and I really like Charlie Parker), this is what I want to imagine the next time I have an argument:
No comments:
Post a Comment