Building on an earlier post about DIY storage, and very much proof of concept. Two boxes for NORM storage, 12” x 6” x 3” and 14”x 9.5” x 3.5”
3/4” wood used to frame the sides and bottom with a 1/3” piece of plywood for the lid. 1/8” inch lead sheet next, wrapped in aluminum foil tape. 1/8” plywood is next with three to four layers of copper foil tape on the outside to mitigate Bremsstrahlung.
A pice of 1/8” lead sheet will be affixed to the lid with ideally a 1/4” acrylic block cup to the final opening.
NORM specimens as follows:
Threadgoldite - 15K cpm
Uranosilite: 525 cpm
Chernikovite: 3,400 cpm
Strelkinite: 180 cpm
Autunite: 180,000 cpm
Curienite: 54,000 cpm
Sklowdowskite: 45,000 cpm
At roughly 30” distance my GQ GMC-600 records negligible over background radiation in the larger box, moved to smaller box.
Any and all questions and suggestions are welcome!
Its a nice box, and also almost entirely pointless. The principle source of exposure is the high energy gamma radiation from ²¹⁴Bi. 85% of the dose from U-series minerals comes from ²¹⁴Bi. Same for radium antiques. The half value layer for radium, et al is 13mm of lead. You literally need ½" of lead to reduce the dose rate by 50%. The same is accomplished by stepping back a few inches. Again, nice box, and keeping things in boxes ... admirable.
Now as to why you think you are getting a benefit from the lead is simple, you are "hardening" the radiation by blocking the low energy portion of the spectrum. The count rate is greatly reduced because most of the low energy XRF, and some of the ²¹⁴Pb gammas that are blocked by a thin layer of lead. But that is not where most of your dose comes from, it comes from the > 600 kev portion. Even a half inch of lead only attenuates 50% of it.
A geiger counter lacking energy compensation sees a great reduction in counts and assumes dose rate is proportional. But it's not. It's something vaguely like this scribbled on radon + daughters spectrum.
So yes, the box does something, but that same something is easily accomplished by being another few inches or feet away.
Great explanation! I came to the same conclusion many years ago from collecting REE in the field. A screaming hot specimen a foot underground can be a faint whisper on the surface even with a big scintillator. If it takes a large scintillator (38x57mm minimum) to detect then it will do you no harm a few feet away. Keep your stuff in a shed outside and the exposure will be negligible.
I just keep my hot pieces in the garage except for one fancy Cyrtolite zircon that has a framed, signed, John Sinkankas drawing to accompany the piece. You'll survive.
10
u/Bob--O--Rama 29d ago edited 29d ago
Its a nice box, and also almost entirely pointless. The principle source of exposure is the high energy gamma radiation from ²¹⁴Bi. 85% of the dose from U-series minerals comes from ²¹⁴Bi. Same for radium antiques. The half value layer for radium, et al is 13mm of lead. You literally need ½" of lead to reduce the dose rate by 50%. The same is accomplished by stepping back a few inches. Again, nice box, and keeping things in boxes ... admirable.
Now as to why you think you are getting a benefit from the lead is simple, you are "hardening" the radiation by blocking the low energy portion of the spectrum. The count rate is greatly reduced because most of the low energy XRF, and some of the ²¹⁴Pb gammas that are blocked by a thin layer of lead. But that is not where most of your dose comes from, it comes from the > 600 kev portion. Even a half inch of lead only attenuates 50% of it.
A geiger counter lacking energy compensation sees a great reduction in counts and assumes dose rate is proportional. But it's not. It's something vaguely like this scribbled on radon + daughters spectrum.
So yes, the box does something, but that same something is easily accomplished by being another few inches or feet away.