Table 6.7.1 Spontaneous Fission Neutron Yields

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Table 6.7.1 Spontaneous Fission Neutron Yields

Spontaneous

Spontaneous Fission

Fission Yield,

Half-Life,

n/sec-gram

years

Isotope

Total Half-Life

232

1.41 x 1010 y

>1 x 1021

>6 x 10-8

8 x 1013

232

71.7 y

1.3

233

1.59 x 105 y

1.2 x 1017

8.6 x 10-4

2.45 x 105 y

2.1 x 1016

5.02 x 10-3

234

7.04 x 108 y

3.5 x 1017

2.99 x 10-4

235

236

2.34 x 107 y

1.95 x 1016

5.49 x 10-3

4.47 x 109 y

8.20 x 1015

1.36 x 10-2

238

2.14 x 106 y

1.0 x 1018

1.14 x 10-4

237

4.77 x 1010

2.59 x 103

238

87.74 y

2.41 x 104 y

5.48 x 1015

2.18 x 10-2

239

6.56 x 103 y

1.16 x 1011

1.02 x 103

240

2.5 x 1015

5 x 10-2

241

14.35 y

3.76 x 105 y

6.84 x 1010

1.72 x 103

242

1.05 x 1014

241

433.6 y

1.18

242

6.56 x 106

2.10 x 107

163 days

1.35 x 107

1.08 x 107

244

18.1 y

1.90 x 109

1.0 x 105

249

320 days

2.34 x 1012

252

2.646 y

85.5

Adapted from NUREG/CR-5550 (Reilly et al., 1991)

Energetic alpha particles can overcome coulomb barriers in low-atomic-number

elements and create an unstable nucleus that emits neutrons. Because of the high alpha

activity of plutonium, this can be a significant source of neutrons. There are two nuclear

reactions that are of importance:

" + 18O 6 21Ne + n

(6.6)

" + 19F 6 22Na + n.

(6.7)

Table 6.8 contains the alpha-neutron yields for oxides and fluorides for the most

common plutonium and transuranic nuclides. Note that the neutron yields are

normalized per gram of nuclide, not per gram of compound. To obtain the yields per

6-15