Model 3440 D-7
Shielding
Shielding is any material used to reduce the radiation exposure
rate from a radioactive source. The gauge has some built-in
shielding, which reduces the exposure rate. When gauges are in
storage, additional shielding may be necessary to keep exposure
to personnel in adjacent areas below the dose limits for
members of the public.
The thickness of any material that reduces the incident
radiation intensity by one-half is known as the half-value layer
(HVL). The HVL of a material varies with the type and energy of
radiation. The HVL values of certain common shielding
materials are shown below for gamma and fast neutron
radiation.
Cs-137 Gamma
Half-Value Layer
Am-241:Be Neutrons
Half-Value Layer
Personnel Monitoring
In the United States, anyone working with or near radioactive
materials is subject to occupational dose limits. Individual
monitoring of each authorized user is recommended in order to
demonstrate compliance with these dose limits.
The most common types of individual monitoring devices used
by licensees are film badges and thermoluminescent dosimeter
(TLD) badges. Film badges are typically exchanged and
processed monthly due to concerns about film fading. TLD
badges are usually exchanged quarterly. Troxler offers NVLAP-
certified personnel monitoring services using TLD badges.
In Canada, nuclear gauge users are not normally classified as
Atomic Radiation Workers. In such cases, the general public
Lead does not provide any effective shielding of fast neutrons.
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