first stage, specialized materials of high 
intrinsic value when treated will be 
processed on a limited scale. Par- 
ticularly, this method will be used to 
treat materials whose properties can- 
not readily be suitably modified by 
other techniques. In the second stage, 
irradiation may be in direct competi- 
tion with existing chemical techniques. 
The time scale will be determined 
mainly by the availability and com- 
parative costs of the various methods of 
obtaining high-energy radiation. 
Sources. Since the phenomena ob- 
served occur equally well whatever the 
source of primary high-energy radia- 
tion (electrons, X-rays, y-rays, fast 
neutrons, etc.), the most suitable form 
of radiation will depend on the cost 
of the source and its ability to produce 
radiation of the most useful penetrat- 
ing power. High-energy electrons ob- 
tained from linear accelerators have 
penetrations of only a few millimeters 
and, thus, seem most suitable for 
thin specimens. Gamma radiation is 
so penetrating that fairly considerable 
thicknesses of material are necessary 
if full use is to be made of the energy 
available. The use of reactors appears 
feasible. Irradiations can be carried 
out in the shield, thus making use of 
energy otherwise wasted. However, 
installation of conveyor belts or similar 
methods of feeding specimens into 
reactors, and post-irradiation storage 
in the immediate vicinity of the reactor 
might raise engineering objections. 
Economics. Use of high-energy ra- 
diation on a commercial scale appears 
to be promising in a number of fields. 
In many cases the required radiation 
doses run into at least several million 
roentgens. It is too early to make any 
reliable calculations of costs, but very 
rough estimates concerned with the 
use of fission products may be of inter- 
est as an order-of-magnitude indication. 
Assume that fission products will be 
available at d dollars per curie (includ- 
ing cost of mstallation and operation) 
and have a half-life of y years. Fur- 
thermore, consider a radiation treat- 
ment needing 7 million roentgens, and 
consider that the plant is designed to 
have an efficiency  (i.e., the proportion 
of emitted radiation captured by 
the irradiated specimens). A gamma 
source of 10° curies, emitting -rays 
of E Mev, will emit (3.7 X 10!° xX FE 
X 10® X 105) ev/sec, or (2.3 E X 10°) 
ergs/sec. This is equivalent to about 
(3 E X 107) roentgen/sec for the 
materials generally dealt with, and 
will process (30 En/r) gm/sec, or 
about (1,000 En/r) tons/yr in full 
operation. The cost of treatment will 
be 105 d/y, or (100 dr/yEn) per ton. 
For example, if we assume an in- 
stalled and operating cost of $1/curie 
(d = 1), a treatment needing 1-million 
roentgens (r = 1), a source of half-life 
10 years (y = 10), a gamma source 
emitting 1-Mev y-rays (HZ = 1), and 
an over-all efficiency of 10%, the cost 
of processing will be $100/ton, or 
5¢/lb. 
This estimate is very rough indeed; 
somewhat higher radiation doses are 
needed for many polymers. About 
2- to 3-million roentgens are required 
to initiate gel formation in many types 
of polyethylene. The cost of produc- 
ing, installing, and operating fission- 
product sources is not known, nor is the 
efficiency with which radiation can be 
absorbed. However, these figures in- 
dicate that costs are not necessarily 
exhorbitant for certain modifications 
in plastics. 
In the cases of oils or shorter chain 
compounds in which several units of 
pile radiation are needed to produce 
useful changes, the costs are much 
higher. Two units of reactor radiation 
(or 100-million roentgens) would, on 
these bases, cost about $5/lb. It is for 
this reason that the more promising 
commercial applications of crosslinking 
lie in the field of long-chain polymers. 
This is where small degrees of cross- 
linking result in marked and often 
desirable changes in physical properties. 
A considerable need for sources of 
high-energy radiation appears to be 
arising for a variety of industrial pur- 
poses. Design of equipment to pro- 
vide such sources at an economical cost 
is most desirable. The modification 
of polymer properties is only one of the 
possible applications of such sources. 
They also could be used for sterilizing 
pharmaceuticals and foodstuffs. 
CONCLUSIONS 
The ability to crosslink or degrade 
long-chain polymers by high-energy 
radiation (under accurately controlla- 
ble physical conditions) offers many 
interesting lines of research. The 
amount of information obtained to 
date is limited mainly by the effort 
devoted to this interesting new sub- 
ject. Large-scale industrial use de- 
pends on the availability of suitable 
sources of radiation. The many appli- 
cations possible can be discovered best 
by close collaboration between indus- 
trial scientists and radiation physicists 
and chemists. 
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