Page 39 - Spring Summer 2026

Institution of Electronics News

Institution of

The Use of Gamma-Ray Level Detectors in
Electronics the Chemical Industry

by E. W. JONES*, B.Sc., A.Inst.P.
(A lecture demonstration delivered at the Thirteenth Annual Electronics Exhibition and
Convention of the Northern Division of the Institution of Electronics).
News The conventional methods of level detection are outlined and the outstanding advantages of gamma-ray level
detectors and switches are considered. The radiation safety aspects are discussed, and a typical installation of
the detector to a glass-melting furnace is described.
INTRODUCTION dipsticks or floats), hydrostatic systems measuring
In almost all aspects of chemical manufacture, there differences in pressure head or buoyancy, electrical con-
is a need for indication or control of the level of vessel ductivity detectors, electrical capacitance measuring
contents. systems, optical systems depending on the interruption
of light beams, pneumatic systems which detect in-
Where manufacture is carried out on a large scale, it creases of back pressure as the liquid surface approaches
is essential to have storage space in the form of bunk- an air jet, etc., etc. Each of these systems has its own
ers, hoppers, or tanks, to receive the incoming raw peculiar advantages and disadvantages, and it is, of
materials and to hold the outgoing product before ship- course, good practice to select the instrument best suited
ment. The operation of loading fairly large quantities to the process conditions.
of bulk materials into such storage vessels calls for The outstanding property of the gamma-ray method,
some form of instrumentation to indicate contents level compared with all the other systems, is that it can
and the instruments can also give information which is operate entirely from outside the vessel and usually
essential for the planning and utilisation of storage requires no special ports, diaphragms, windows, lenses,
capacity. or probes to be fitted into the vessel walls. This implies
In continuous flow processes it is often necessary to at least four useful advantages:
employ reservoirs or surge tanks to take up short-term
differences in flow rate between stages of the system, 1. The design and construction of the vessel can be
simplified-an important consideration for high
and it may be important to initiate an alarm or auto- pressure vessels, glass-lined tanks, etc.
matic control action when the content level in a surge
tank exceeds the working limits. In the reaction vessel 2. The installation of the measuring element on
itself it may be desirable, in the interests of process existing plant is simple, even under working con-
efficiency, to control the contents level to fine limits by ditions, so that the instrument units can, if neces-
automatic regulation of the input or output flow rates in sary, be installed, and subsequently serviced,
response to signals from a level detecting element. without causing any ''down-time" to plant which
Batch processes call for accurate measurement of in- is running.
gredients by volume or by weight into the reaction 3. Satisfactory instrument performance is almost
vessel, and in the vessel itself it may be important to entirely independent of the nature of the contents
ensure that over-flow or boiling-over does not occur. provided that they have sufficient mass to absorb
At the end of the reaction, it may be useful to have an appreciable proportion of the gamma-rays.
automatic indication of the point at which the vessel is The system can, therefore, be used with very
completely emptied ready for the next batch. viscous fluids, bubbling or agitated liquids, froth,
Apart from the normal raw materials of a process, it granular solids, fluidised powders, explosive
may be important to control the level of a continuously materials, etc.
replenished or regenerated catalyst, e.g. in a cracking 4. The instrument components themselves are not
column or synthesis plant. subjected to mechanical or chemical damage due
The vessels themselves vary enormously in size and to drastic conditions within the vessel, such as
construction and may range from glass-lined steel severe vibration, abrasion, corrosive action, high
temperature, etc.
drums to refractory-walled furnace tanks or gasifiers.
Different contents and chemical processes may give rise ESSENTIAL COMPONENTS
to a wide diversity of working conditions: for example, A gamma-ray level measuring or detection system
the contents may include corrosive chemicals under consists of:
high pressure, slurries which set like cement on settling,
molten metals or glass at temperatures above 1000ºC, (a) A long-lived radio-active source in a suitable
viscous liquids such as latex, tar, etc., abrasive lump shield. The isotope is usually Cobalt 60 (half-
life 5.3 years), Caesium 137 (half-life 33 years)
INSTITUTION OF ELECTRONICS NEWS: solids, or powders which do not flow in a uniform or Radium (half-life 1,600 years). The last-
manner. With such a wide range of conditions to be
FROM THE ARCHIVES 39 met, it is natural that a wide variety of level measuring named is very expensive.
techniques has been evolved. The more conventional (b) A gamma-ray detector. This is usually a Geiger
VOLUNTEER OPPORTUNITY 45 methods include purely mechanical devices (such as Müller Tube but may be an Ionisation Chamber
MAKE YOUR BUSINESS THE FIRST TO BE FOUND ON GOOGLE 46 *Isotope Developments Ltd. or a Scintillation Counter.
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