RE: Natural Thorium

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

Elizabeth,

Eisenbud and Gesell give a specific activity of 0.11 pCi/gm for Th-232.
However, Stannard's book notes in Chapter 4 that "...in the strict sense,
there is really no specific entity with more of less constant and
predictable isotopic composition present in thorium ores that we can call
'natural thorium.'"  This is because of varying amounts of U3O8 present in
these ores.  He concludes by saying that the U series thorium isotopes
"...obviously should vary in activity with time after preparation and there
is no 'natural thorium' analogous to 'natural uranium.'"

In this section he also cites a reference by Hursh, published in 1974 in
Health Physics (volume 27, pp 147-152).

Andy
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