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2. MEAT INSPECTION IN THE PORT OF LONDON, WITH SPECIAL REFERENCE TO THE
USE OF IONIZING .RADIATION*
(Published in The Medical Officer - Volume CXVIII No.19)
10th November 1967
The recent announcement that a new regulation has been introduced which controls the use
of ionizing radiation for the treatment of food was headlined in the Press as "Irradiation of Food
Now Banned". To those not familiar with developments in this field this appeared to mean the
the end of a new technology, whereas in fact a step forward has been taken in that we now have
the machinery to gain official approval for radiation processes as they are required. Official
approval was seen to be necessary at an early stage of research into this subject. Industry would
not be prepared to initiate something so new involving high capital investment without the
blessing of central and local health authorities. It is also important from the public viewpoint in
that this use of radiation is so easily confused in people's minds with the non-peaceful application
of atomic energy and the problems of fall-out and possible radioactivity in foods.
I have been personally interested in these developments and have been keeping in touch with
developments in food irradiation, especially its use in the treatment of certain imported foods.
With the introduction of atomic power and its development has come the facility to produce
radioactive isotopes in extremely large quantities. Over the last four years in the United Kingdom
alone many millions of curies of isotope cobalt 60, the same isotope that is being used in
hospitals for therapy, have been produced in our atomic reactors for industrial use.
This isotope is produced by bombarding the non-radioactive cobalt 59 with neutrons in the
core of certain power reactors. After the inactive cobalt has been left in the neutron field for
perhaps a year or more it is converted into the radioactive form cobalt 60. Depending on the time
it is exposed to the neutrons the cobalt will have a certain number of curies per gram.
The Choice of Cobalt 60
Cobalt 60 has been chosen as the most useful isotope for industrial processing because it
has certain attractive properties: —
(1) It emits gamma radiation of an energy which does not cause radioactivity to be induced
in the material which is treated. Gamma radiation is electromagnetic radiation and is the
same as X-rays.
(2) Cobalt 60 has a half life of 5.3 years. In other words replacement of it can be done
at convenient time intervals (there is about 1 per cent "throughput" per month radioactive
power lost).
(3) It is convenient to produce in large amounts according to demand, in the atomic reactors.
Properties of Gamma Radiation of Particular Interest lor Food Treatment
Apart from the fact that gamma radiation from this isotope produces no radioactive activity
in the material treated, it has other properties which make it attractive for industrial processing.
(a) It has a high penetrating power, in fact it would take a thickness of 12 in. of water
before the absorbed radiation is reduced by half; so it is ideal for treating blocks of material
even after they have been packaged.
(b) This radiation has a lethal effect on micro-organisms, insects and parasites. The dose
to bring about this lethal effect will vary with the species involved. We all appreciate this
effect .on man, where the dose required in cancer therapy varies from the lethal dose.
(c) It is most important that it produces this lethal effect without causing a rise of
temperature in the material treated, which may be in a frozen state, or if it does it is not
more than a few degrees centigrade.
In other words we have a penetrating lethal cold process in an advanced stage of technological
development ready to be applied if required.
How has this Process been Applied so far?
These properties have been used to advantage already in industry for the purpose of
sterilizing medical supplies. Four large radiation plants are already operating in commercial
hands in this country and others have been built abroad. The United Kingdom has taken the
lead in introducing this process to industry, and many plants being built are British.
In medical practice disposable equipment, made of heat-sensitive plastic material and cheap
enough to be disposable after one use, has assisted in avoiding cross-infection problems in
hospital. The dose of radiation used for the purpose of sterilizing this equipment is 2.5
megarad (that is 2.5 million rad). The lethal dose for man is regarded as about 600 rad, so this
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