Fission Product Yield Data for the Transmutation of Minor Actinide ...

P
LD
È Ê * E - 44. 7ˆ
˘
= Í1
+ exp
Ë
Á
¯
˜ ˙
ÎÍ
91. 2 ˚˙
(4.4.33)
The data of Maslov were used for the transmission
coefficients (T l ) [4.4.28]. These coefficients
provide a good description of the cross-sections for
the fission of 238 U by neutrons and take into account
pre-fission neutron emission up to incident neutron
energies of 200 MeV.
Zöller data [4.4.27] for pre-neutron emission
fragment mass distributions from 238 U fission by
neutrons with energies from 2 to 200 MeV are
summarized in Figs 4.4.12–4.4.14. As can be seen
from these figures, the assumption made in the
present work results in satisfactory agreement
between the experimental data and calculations
over the whole energy range.
The following expressions were obtained from
an analysis of Zöller data [4.4.27] to describe the
post-neutron emission fragment mass distributions
of 238 U fission by neutrons in this energy range:
A
ÏÔ
A
= Ì
ÓÔ A
(4.4.34)
(4.4.35)
where v – i L,H are the average values of the neutrons
emitted from fragments for the corresponding
fission modes:
(4.4.36)
Descriptions of the post-neutron emission fragment
mass distributions for 238 U fission by neutrons in the
energy range from 2 to 200 MeV are summarized in
Figs 4.4.15–4.4.17 and compared with the experimental
data [4.4.27].
4.4.7. Fragment mass distribution
for spontaneous fission
We have performed an analysis of the
evaluated data on fragment mass distributions from
spontaneous fission of nuclei [4.4.25] in order to
determine the dependence of the model parameters
on the mass and charge of the fissioning nuclei at
zero excitation energy and angular momentum.
-1
I f
I
2∓1718 . - n L, H £ cr
LH ,
f 2 - n S > cr
II
II
LH , f L, H
A = A 2∓20. 56-n
I
I
n L = 326 . , n H = 388 . ,
II n L = 026 . , II n H = 36 . ln( 0039 . En
+ 167 . ),
n = 364 .
S
The following equations were obtained for the
parameters appearing in Eq. (4.4.5):
I
H
I
L
A = 140, A = A -A
II
H
II
L
(4.4.37)
(4.4.38)
(4.4.39)
Af = A0-v, (4.4.40)
v = 5. 355 -0. 644( Z - 96) + 0. 386( A -252)
W II = 100 – W I – W III
I
f H
II
f H
A = 140, A = A -A
III
H
III
L
III
f H
A = 146, A = A -A
s AI
s AII
s AIII
0 0
= 2. 472 + 0. 005( A -252)
0
(4.4.41)
= 4. 140 + 0. 041( Z - 96) + 0. 082( A -252)
(4.4.42)
(4.4.43)
(4.4.44)
(4.4.45)
(4.4.46)
The fragment mass distributions for the
spontaneous fission of 252 Cf nuclei are shown in
Fig. 4.4.18, where our calculations are also
compared with the evaluated data [4.4.25] and
calculations of Wahl [4.4.29]. Figure 4.4.19
compares evaluated data [4.4.25] with our calculations
of fragment mass distribution for the
spontaneous fission of nuclei from 240 Pu up to 256 Fm.
Results of the analysis of the fragment mass
distributions from spontaneous fission show the
absence of the symmetric fission contribution, in
agreement with the results of Wahl [4.4.29].
However, at least three asymmetric modes need to
be taken into account for a satisfactory description
of fragment mass distributions from the
spontaneous fission of nuclei with Z > 94.
4.4.8. Description of fission fragment mass
and charge distributions
0
= 6. 166 + 0. 027( Z - 96) + 0. 150( A -252)
W = 14. 0 -2. 993 Z - 96 + 2. 694 A -252
I
0
0 0
W = 34. 222 -1. 445 Z - 96 + 2. 427 A -252
III
A phenomenological approach has been
developed in the present study to describe the
2
2
0 0
0
0
171