Page 39 - Winter 2026

Kr 85 is dispensed into borosilicate glass ampoules adopted to check how frequently each egg in each tray
using the apparatus illustrated in Fig. 3. This illustrates in an incubator received a change of air, so that
the use of localised shielding and of a remote controlled modifications could be made to the design of the venti-
valve. The ampoules are evacuated while the Kr 85 lator to increase its efficiency. Unfortunately, the gap
remains in the storage pot, which can hold 20 curies. between the eggs and the tray above was so small that
The valves of the storage pot are then opened and the no Geiger probe at present designed in this country
gas slowly allowed to fill the ampoules to the appropri- could be placed in the correct position for recording
ate pressure by operating the remote control valve. The the presence of the radioactive tracer gas.
ampoules can then be sealed off, and the unused gas Allied with ventilation experiments is the use of a
absorbed on the charcoal finger and then re-transferred radioactive gas to follow the flow of gas underground in
to the storage pot. an oil field. Using I curie of T 2, Kr 85 or CH 3T,
At present the cost of Kr 85 is E5 per curie, but technicians in America have proved that each is equally
within a few years when more advanced purification effective in tracing methane in a 10 acre oil field .
4
equipment has been constructed, the cost shouId be From such information it is possible to discern how oil
considerably reduced. wells are interconnected and the size of gas space below
Xenon 133 sources are prepared by dissolving a the Earth's surface. The experiment on the small oil
uranium slug, which has been irradiated for about 14 field was so successful that we were asked to provide
days, in nitric acid solution, and purifying the gases in 250 curies Kr 85 for a large scale experiment in
a high vacuum glass apparatus shielded by ¼-inch lead . Venezuela. The information gained from the use of
2
Remote control solenoid valves similar to the one illus- radioactive gases in this way can save oil companies
trated in Fig. 3 are employed instead of stop-cocks. many months of time and money.
The gas is available in small glass ampoules or ad-
sorbed on charcoal in a glass capillary tube, the final (b) Leak Detection
volume of a source which may be as high as 15 curies Many conventional methods of leak detection are
being less than 1 cc. NTP. more sensitive than the radioactive methods. Helium
Argon 37, in addition to being prepared in microcurie leak detection in fact is the most sensitive method of
quantities by irradiation of argon gas in the reactor for all, but requires expensive equipment, and is not always
a few weeks, is prepared in a more enriched form by practicable especially for experiments conducted in the
irradiating calcium in a reactor. The reaction involves field. For instance, we were asked recently for a radio-
the bombardment of calcium by fast neutrons and the active gas method of estimating the size and position of
ejection of an alpha particle from the calcium nucleus. a leak during underground gasification of coal experi-
Up to 1 mc can be prepared from 2 gm. Ca irradiated ments. In the process, air or oxygen is pumped at high
for 6 weeks, at a flux of 10 ns/cm /sec. velocity through a long pipe leading into a coal seam.
2
12
By melting the calcium under vacuum the argon is At the end of the pipe the coal is fired and the resultant
released and purified from traces of quantities of gases from the combustion returns along the air space
Fig. 2. A simple Krypton 85 Source Filling System. occluded gases which are gettered by the molten and between the ingoing pipe and the seam, entering another
evaporated calcium. The yield can be calculated by pipe before returning to the surface (Fig. 4).*
removing a minute aliquot and counting it in a gas
counter. The radioisotope is supplied in a glass ampoule,
or absorbed on charcoal also in a glass ampoule. The
cost is E12 per mc.
INDUSTRIAL APPLICATIONS
(a) Ventilation Experiments
The siting of plenum fans and air inlets in factories
and other buildings is an important factor of modern
building. In order to ensure that the air is frequently
changed in all parts of the building and that equipment
can be positioned correctly to prevent the accumulation
of pockets of stagnant air, something can be added to
the incoming air to follow its course through the build-
ing. One method would be the introduction of smoke
or some other gas which can be checked by detectors
at various positions.
Much the simpler technique is the introduction of a Fig. 4. Leak detection in Underground Gasification
few millicuries of an inert gas which will disappear System using Krypton 85.
through the normal extract and leave no trace. Geiger
counters positioned in the suspected parts of the build- When 100 mc Kr 85 was injected into the ingoing air
ing will provide a rapid means of checking the efficiency stream, a Geiger counter fitted into the return pipe
of the extract system. quite easily differentiated between a small leak which
There are naturally limitations to the technique. For *Kr 85 is now being used to determine leaks in transistors
Fig. 3. Kr 85 Dispensing Apparatus. instance, it was anticipated that the method could be down to cc/s.
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