Operating Manual

Also greatly depleted uranium (with the highest radiation absorption) is used for shielding,
resulting in very compact exposure containers. A disadvantage of this material, however, is
that it has a certain minimal radioactivity, which is reason that in some countries the use of
depleted uranium is not allowed.
Regardless of the shielding material used, all containers have a considerable weight in
common.
There are several solutions to the problem of safely storing a source on the one hand, and
of putting it in a simple but absolutely safe manner in its radiation position on the other
hand. Two regularly used constructions for this purpose are: source S is situated in a rota-
ting cylinder, as shown in figure 11-5, or in an S-channel container as shown in figure 12-5.
The S-channel container is usually provided with a means to move the source out from a
distance (after all, distance is the safest protection from radiation). This may be done by
means of a flexible cable in a hose (Teleflex design) as shown in figures 13-5 and 14-5.
With this construction it is possible to extend the flexible hose in such a way that the source
can safely be moved several metres out of the container to the most favourable exposure
position.
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5.5 Source holders (capsules)
All gamma-ray sources for radiography are supplied in hermetically sealed, corrosion
resistant source holders (capsules), made out of monel, vanadium or titanium.
The Atomic Energy Authority in the country of origin encapsulates the radioactive materi-
al. The supplier will supply the source with a certificate which indicates the type of source,
its serial number, the activity at a certain date, and a disintegration graph.
The radiation material proper, also called the source or pellet, ranges in size from
1 to 4 mm. The size is dictated by the specific radiation activity of the source material.
The outside dimensions of the cylindrical capsule are approximately 5.5 x 15 mm, as shown
in figure 9-5.
5.6 Transport- and exposure containers
Transportation and handling of sealed sources are subject to strict international safety
regulations, as a source is continuously emitting radiation in all directions, in contrast to an
X-ray tube which can be switched off. During transportation and use the source must be
surrounded by a volume of radiation absorbing material, which in turn is encapsulated in
a container. The level of radioactivity at the outside surface of the container shall not
exceed the legally established maximum limit.
Like the transport container, the exposure container needs to be robust and must function
safely at all times. The exposure container, also called camera, must be fail-safe and water-
and dirt proof. It must also not be effected by impact.
Moreover, if the radiation-absorbing material, for example lead, melts (in a fire) the radia-
tion absorbing qualities must not be lost.
This requires a casing made of a material with a high melting point, for example steel.
Besides lead, increasingly a new sintered material with very high tungsten content (97%)
is used as shielding material. This material is easily worked and finished and not prone
to melting.
Fig. 9-5. Cross-section of a capsule for a radioactive source
15 mm
5.5 O
/
Fig. 10-5. Sealed capsule
handling / operation side
flexible connection
storage position
of the source
casing/container
exposure position
of the source
shielding
Fig 11-5. Exposure container with source S in a rotating inner cylinder
Fig. 12-5. S-channel container with
source S in storage position
Fig. 13-5. Exposure container
with S-channel and flexible
operating hose ad cable
open
SS
S
closed