The old 1970 Rad Health Handbook [from the Public Health Service] has some handy thumb rules for characterization of a contained Sr-90/Y-90 source based upon external gamma exposure rates resulting from bremsstrahlung generated from those big powerful betas. I've seen these thumb rules used and abused over the years [myself guilty of both on a few occasions]. Is anyone aware of a similar thumb rule or equation for the considerably weaker Tc-99 beta? Any experience on the topic or a reference to a good article on Tc-99 Brehm would also be greatly appreciated.
Thanks,
mgm
Brem radiation is not produced by weak betas. Requires high Z target, high energy beta.
That was always my misconception too, but after experiencing it first hand, I've done further research and found several technical papers discussing Brehm from Tc-99 and other mid energy beta emitters [I wouldn't call Tc-99 a weak beta emitter, reserving that classification to the likes of H-3, C-14, and Ni-63]. We encounter a lot more Brehm from contained (e.g., in steel) Sr-90 sources because of the high emission energies, but it turns out that in sufficient quantities (e.g., hundreds of Curies) you'll also see Brehm from contained Tc-99 sources [Although not at the levels that you'd see from a strong beta emitter].
I have some right now that it'd be handy to make some preliminary characterization assumptions prior to sampling. I was just wondering if anyone else had any experience with it.
Thanks,
mgm
Any beta particle can lose energy and produce bremsstrahlung x-rays. The difference is the maximum energy of the x-ray. If you can measure low energy photons, you will even see x-rays from those so-called hard to detect. It will be a skin dose largely.
http://www.iop.org/EJ/abstract/0305-4616/9/6/013
cupla others research lines are listed here two.
Found it!
There are detailed calculations for Brehm production [based upon beta energy and absorber Z] in the Cember book. I hadn't thought to look in such an obvious reference [didn't have a copy handy and hadn't read it in years]. I just thought that I'd close the thread.
Thanks,
mgm
Quote from: Khak-Hater on Jul 08, 2009, 12:38
The old 1970 Rad Health Handbook [from the Public Health Service] has some handy thumb rules for characterization of a contained Sr-90/Y-90 source based upon external gamma exposure rates resulting from bremsstrahlung generated from those big powerful betas. I've seen these thumb rules used and abused over the years [myself guilty of both on a few occasions]. Is anyone aware of a similar thumb rule or equation for the considerably weaker Tc-99 beta? Any experience on the topic or a reference to a good article on Tc-99 Brehm would also be greatly appreciated.
Thanks,
mgm
I have a 15m Ci plastic bottle of Tc-99 and I am seeing a TON of brem coming off of it with our HPGe detector. I was very surprised to see this too considering the Tc-99 is not in any kind of High-Z material, no shielding is present, and it Tc-99 is contained in an epoxy packaged in a plastic vial. Did you learn anything interesting about brem from Tc-99? I actually have a total of .17 Ci, and it is saturating my detector with X-rays!
Tc-99 ( I have seen at DOE facilities) is a beta emitter with a long half life, Tc-99m emits alot of gamma and is used in imaging studies at hospitals with a 6 hour half life. Sometimes people look at these and think apples to apples but it really is apples to oranges when looking at emmisions from these.
Here is a Wikipedia on Tc-99, It does mention soft X-rays from Laboratory glass. I did not know that. So the comment on X-rays seems valid.
Technetium-99
From Wikipedia, the free encyclopedia
Technetium-99 (99Tc) is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting soft beta rays[1], but no gamma rays.
Technetium-99 has a fission product yield of 6.0507% for thermal neutron fission of uranium-235, making it the most significant long-lived fission product of uranium fission, with a half-life over 2000 times as long as the next longest-lived fission product.
The weak beta emission is stopped by the walls of laboratory glassware. Soft X-rays are emitted when the beta particles are stopped, but as long as the body is kept more than 30 cm away these should pose no problem. The primary hazard when working with technetium is inhalation of dust; such radioactive contamination in the lungs can pose a significant cancer risk.
Technetium-99m is a short-lived (half-life about 6 hours) metastable nuclear isomer used in nuclear medicine, produced from molybdenum-99. It decays by isomeric transition to technetium-99, a desirable characteristic, since the very long half-life and type of decay of technetium-99 imposes little further radiation burden on the body.
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99Tc NuDat database
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Z 43
Decay mode B-
Half life 2.11E+5 y
Half life (s) 6.661809E+12
Atomic mass 98.906253640951 u
Jp 9/2+
Q-value 0.294 MeV
Production Thermal neutron activation
Fission product
Parent 99Mo
99mTc
Branching
Daughter 99Ru 1
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Gamma radiation
Energy (keV) Intensity Remarks
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2.56 0 X L
19.1504 1.75E-06 X KA2
19.2792 3.33E-06 X KA1
21.7 1.02E-06 X KB
89.5 0.0000065
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Beta radiation
Endpoint energy (keV) Intensity Average energy (keV)
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204 0.000016 81.7
293.5 0.999984 84.6
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as info
sf