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The Gamma Source
Thermo Fisher Scientific
The source head contains the gamma source. The gamma radiation is
emitted naturally by a radioactive material. Mostly Cesium-137 (Cs-137) is
used for this application. The radioactive material is first bound in a glass
or ceramic matrix and encapsulated in a stainless steel cylinder that is
welded closed and tested for leakage. This capsule is placed inside another
cylinder of stainless steel that is also welded closed. This double
encapsulation ensures that the source material will remain contained even
under extreme conditions of use. The source capsule is then secured in the
center of the housing.
The radiation hazard of the gauge is minimized by its construction. The
source housing is a rugged, circular steel cylinder that is filled with lead
except in the direction of the beam path. The lead is designed to reduce the
radiation level outside the housing to a relatively low level. The gamma ray
beam is therefore collimated in the direction of the detector.
There are two source housing models primarily used for this application:
Model 5192: This source housing typically does not have a shutter. It is
welded to a high pressure pipe and designed to handle high vibration
applications. For the source head without a shutter, the back of the
detector is designed with extra metal thickness to allow the radiation
beam to be reduced to a safe level outside the detector assembly for
transportation purposes.
Model 5190: This source housing has a sliding shutter with three
positions: ON, OFF, and CAL. The purpose of the shutter is to block
the radiation beam when it is placed in the OFF position.
Due to the precautions taken during manufacture, the chance of leakage is
remote. However, the United States Nuclear Regulatory Commission
(NRC) requires that the source housing be leak tested at regular intervals,
not to exceed three years. Canadian regulations require that leak test
intervals not exceed one year. Refer to the Gamma Radiation Safety Guide
(p/n 717904) for further information. Thermo Fisher is licensed to
perform these tests and can do so through contract services. The first test or
"wipe" is done by licensed personnel or prior to shipment from the factory.
If the source housing is damaged or the system is abandoned, the source
housing must be disposed of properly. Regulations for the NRC, U.S.
Department of Transportation, and the Canadian Nuclear Safety
Commission are continuously being updated; contact Thermo Fisher
Scientific for information on proper source disposal.
Product Overview
Introduction
SGD-O User Guide
1-3
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