932 
GENETIC AND BIOLOGICAL EFFECTS OF RADIATION 
duced as a by-product of uranium-fueled re- 
actors. It decays by alpha particle and gamma 
ray emission to -^*U with a half-life of 85 years, 
and it also undergoes spontaneous nuclear fis- 
sion with a half-life of 4.9 X 10^° years. The 
alpha decay results in the production of heat as 
the high energy heavy alpha particles are de- 
cellerated. The thermal power density of -"^^Pu 
in the metallic form is 0.55 watts/gram or 32.1 
watts /kilocurie, making it a suitable implant- 
able heat source. Plutonium is not only a source 
of heat, but also a source of potentially danger- 
ous neutrons and photons. These are from the 
following six sources r^^ (a) Neutrons from 
spontaneous fission; (b) Neutrons produced by 
alpha particle reactions ia,n) with low atomic 
number impurities; (c) Fast fission neutrons; 
(d) Photons from -^^Pu decay; (e) Photons and 
neutrons from other plutonium isotope contami- 
nants and their daughters; and (f) Photons 
produced by alpha particle ia,y) reactions with 
light impurities. 
In order to permit study of the biological ef- 
fects of chronic intracorporeal exposure to 
-^^Pu, an implantable aortic heat exchanger was 
designed. An. insulated solid aluminum carrier 
containing the radioisotope capsule is attached 
to a metallic tube which is interposed in place 
of an excised segment of either thoracic or ab- 
dominal aorta.ii (Figure 1) Heat from the fuel 
capsule is conducted by the carrier to the blood 
which carries it away to be dissipated by the re- 
cipient's thermoregulatory mechanisms. The re- 
cipient is also exposed to neutron and gamma 
radiation. Total tissue neutron plus gamma 
dose rates fall off from the order of 10^ mrem/ 
hr at the source surfaces to 20.0 and 34.3 mrem/ 
hr 8cm from the 16 and 24 watt capsules re- 
spectively. 
Eleven dogs were implanted with heat ex- 
changers fueled with either 16 watt or 24 watt 
-•■'^Pu capsules. At maximum, this represented 
a thermal dose of 0.4 watts/kg. The acute ther- 
moregulatory responses of all animals to the 
heat load were observed. A long-term survivor 
of implantation of both the 16 and 24 watt cap- 
Aorta 
Figure 1. — Drawing showing design of ^Pu-fueled lieat exchanger which is interposed in either 
the thoracic or abdominal canine aorta. 
