Page 204 - Radiochemistry and nuclear chemistry

188 Radiochemistry and Nuclear Chemistry

Ionizing radiation is an expensive form of energy, whether the radiation source is 60Co
or an accelerator, and generally at least one of the following criteria are fulfilled in the
established radiation processes:

o A small amount of chemical change causes a marked change in physical
properties (e.g. for polymers or biological systems).
o The radiation induced reaction has a high yield (e.g. polymerization, chain
reaction).
o The radiation has a specific effect or process technical advantages which not
easily can be obtained by other methods (e.g. staining of glass).

About 80% of ongoing radiation processes can be ascribed to the first category. Some
examples of radiation processing are briefly described in the remainder of this chapter.

7.11.3. Radiation induced synthesis

A great number of reaction types have been investigated, the majority involve radical
initiated organic chain reactions. A limited number of radiation induced synthesis has,
however, been developed to the pilot plant or industrial scale. Examples of reported
industrial synthesis are sulfoxidation and sulfochlorination of hydrocarbons for detergent
production and polymerization of ethene.
The bromoethane process, which from 1963 and a number of years onwards, was used
by the Dow Chemical Company to produce 500 tons bromoethane per year is of especial
interest. In the process a 67 GBq 6~ was utilized to irradiate hydrogen
bromide-ethane mixtures and initiate the reaction sequence

Initiation HBr .... ~ H" + Br-

C2H 4 .... ~ C2H 2 + 2 H.
H-+ HBr ~ H 2 + Br-

Propagation Br- + C2H 4 -~ .CH2CH2Br

9 CH2CH2Br + HBr ~ CH3CH2Br + Br-

Termination 2 Br---, Br 2

2 .CH2CH2Br ~ BrCH2CH2CH2CH2Br

The chemical yield was, depending on reaction conditions, in the range 0.001 - 0.01 mol/J.