Page 179 - Radiochemistry and nuclear chemistry

Absorption of Nuclear Radiation 163

-- J

FIG. 6.29. A - 9~ B- thermoeouples; C - radiation shield (depleted U); D -capsule;
E - 23SPu; F - secondary containment; G - thermal insulation; H - thermopile; J - insulator.

9~ is the preferred radionuclide for terrestrial uses. Its power density is relatively high,
0.93 W g- 1, as compared to some other possible radionuclides as 137Cs (0.26 W g- 1) and
238pu (0.55 W g-l), but it is lower than 244Cm (2.8 W g-l) and 245Cm (121 W g-l).
Recently 6~ has come into use; the heating mainly comes from absorption of the 7's in
a uranium shielding.
238pu has been used as an energy source in space. Several satellites with radioisotope
generators of 25 W have been placed in space, and the Apollo project employed a generator
"SNAP-27" containing 238pu with a total weight of 14 kg and producing 50 W power. The
Viking landers on the planet Mars used 238pu as the main energy source. It was used also
to power the Pioneer vehicles which gave us the first close pictures of the planet Jupiter and
in the Voyager missions to the outer planets (in August 1989 one of them passed Neptunus
at - 5000 km altitude, taking remarkable close-up pictures) where the 238pu power source
produced 450 W. One will reach the star Sirius in about 300 000 years!

6.10. Exercises

6.1. In w two equations are given for calculating the range of cx-particles in air and in other material from the
particle energy as well as a curve for the range in aluminum. How different are the values from the equations and
from the curve for a 5 MeV o~?