18.08.2015   NUCLEAR CHEMICAL ENGINEERING

Neutrons from Spontaneous Fission

Another radiation problem arises from fast neutrons produced in spontaneous fission of the even-mass plutonium isotopes. Half-lives and specific activities for spontaneous fission of the plutonium isotopes are listed in Table 8.17.

In determining the biological hazard from spontaneous fission, it is assumed that each fission produces an average of three neutrons, each with an energy of 2 MeV. Estimated surface fluxes and dose rates are given in Table 8.18.

Table 8.17 Half-lives for spontaneous fission

Spontaneous fission

half-life, у г

238 Pu

4.9 X Ю10

240 Pu

1.4 X 1011

242 Pu

7.1 X 1010

Table 8.18 Dose rates from spontaneous fission of plutonhunt

Spontaneous fission neutrons per min

Spontaneous fission dose rate, mrem/h

Surface flux of spontaneous fission neutrons, «/(cm2 — s)

Surface

1 m

239 Pu 239 Pu plus

1.82 X 103

8.6 X 10’2

2.4 X 10"s

0.67

1000 ppm 238 Pu

2.1 X 10s

9.8

2.7 X 10‘3

76

t Basis: 1-kg sphere of plutonium; 3 л/fission, 2 MeV/n; 58 л/(cm2 *s) = 7.5 mrem/h.