Control dosimeters and background

["Cook, Lew (LCOO)" <LCOO@chevron.com>]

As someone who works with background and near background exposures, I have
become quite aware of the differences in "background" exposures caused by
different types of building materials - especially different types of stone.
For the Natural Radiation Environment III Symposium (in 1978) in Texas we
established intercalibration sites over limestone and a metamorphic rock
called the Valley Spring Gneiss - referred to locally as "pink granite". The
pink granite is used extensively in Texas for building materials - as is
limestone.

The exposure over the limestone was less than 6 micro R per hour but over
the gneiss it was 25 micro R per hour. Cosmic ray background was
approximately the same at both sites. The difference amounts to about 166
milliR per year, or about 14 mR/month.

No one makes a big deal about the use of either type of stone for
construction regarding radiation protection aspects. For a control
dosimeter, however, it would matter if the control was kept in one type of
building while the user has his/hers in the other.

Lew
510 242-7040
lcoo@chevron.com


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