Gayo 2021 Update

[Joe Gayo]

I've been very reluctant to add neutron shielding "close" to the device since I have an array of neutron detectors (at various angles and distances) to better characterize total output and any distribution bias. These detectors have been calibrated with a point source and I don't want excessive moderators changing the distribution of neutrons. In addition, I can't place any detector closer than 100cm or the counts are overwhelming and x-ray pile-up becomes a risk (the latest runs are at 10mA+).

[Joe Gayo]

In other news, after a short run I decided to bring my Geiger counter to check to see if I activated any material near the moderated detector tubes. The aluminum plates that electronically shield the detector assembly give about 10k cpm! It fades fairly quickly in agreement with the 2.2min half life of aluminum.

[Richard Hull]

It's nice to see that the 5 folks who bought my 5 copies of the table of the isotopes at HEAS 31-2020 have been using them. That glorious aid and reference is a must have item for those doing any activation.

Yes, any form of neutron shielding will scatter like a big bear. That is the beauty of the shield!.... To turn any direct fast neutrons heading for a human bag of water, operator into a big sphere of thermals. It does screw with critical neutron counting trying to determine any beaming. Of course wooden structures, building materials, etc., will also send neutrons a-flying in tortured directions if the flux is high enough.

Richard Hull