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A large slab of DU metal, "DU slab" 4" X 4 1/8" is used as a semi-infinite or PLANE source of beta radiation to test and calibrate probes.
A known contact dose rate is available from such a slab and is the standard for calculating "Beta Factors".
(a semi-infinite slab of depleted uranium has a contact dose rate of 237 + 19% mRad/h, mostly from beta)
These test sources are sold right along side of Cs-137 Tc-99 and all the other rad test samples. Naturally they are quite expensive:
http://www.eberlineservices.com/rad.htm (search DNS-26)
"Measurements of the surface dose rates from a slab of uranium have been reported by a number of investigators in the scientific literature, and recently calculated by Fetter and von Hippel (Global Security 8:125-161, 1999) for a slab of DU. The calculated value for DU was 250 mrad/h which was in good agreement with the measured value of 233 mrad/h of beta radiation plus an additional 23 mrad/h from from photons (i.e., x and gamma radiation) for a total of about 255 mrad/h for a slab of natural uranium, made through a 7 mg per square centimeter filter to mimic the cornified (i.e., dead) layer of the skin (Health Phys. 29:143-152, 1975). The beta dose rate from a uranium slab is quite constant for the first few millimeters away from the slab and then drops off rapidly. At 10 cm (approximately 4") from the slab, the dose rate is only about 11.5 mrad/h, about 80 percent of which is from beta radiation. "
see
My particular "large chunk" of DU is actually a shield/collimator from a radiographic camera. It shielded the operator fro the 10TBq of Ir-192 inside.It id not nearly 4" x 4", but it IS large enough to cover the entire beta window on the probes that I work with mostly.
Trivia: DU was once called:Q-metal, depletalloy, and D-38.
Any serious rad lab that can afford one has a DU slab. The others just *want* one:
(for a real hoot also click on the message AFTER this one!):
Geo
George Dowell
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