**56-Ba-135 Review**

By V.G. Pronyaev, NDS, IAEA

13 March 2004

**General Comment:**

Taking into account that the accuracy of nuclear data for fission
products is most important in neutron transport and nuclear
transmutation calculations, the following priority to the quality of the
data can be given when we compare different evaluations:

1.  Most important energy region is a region of spectrum with maximum
    neutron fluxes in thermal and fast fission reactors, namely around
    0.0253 eV and below 5 MeV.

2.  Most important cross sections in order of reducing of their
    importance are integral cross sections: capture, total, elastic,
    inelastic with excitation of levels and other threshold cross
    sections; differential cross sections: secondary neutron spectrum
    from inelastic scattering and elastic scattering differential cross
    sections, gamma production cross section and spectra.

Abbreviations: E-6 -- ENDF/B-VI, J-3 -- JENDL-3, F-2 -- JEF-2, B-2 --
BROND-2, C-3 -- CENDL-3,

CS -- cross section, RRR -- resolved resonance region, URR -- unresolved
resonance region SOM -- spherical optical model, SM -- statistical
model, reaction mechanism, PEQ -- pre-equilibrium decay model, reaction
mechanism.

##### 

##### **Files**

ENDF/B-VI -- old and obsolete ENDF/B-V evaluation was revised in the RRR
by R.Q. Wright (1988). 29 MLBW s-resonances are given in the RRR for
E~n~ 10^-5^ to 1.65 keV. No unresolved resonance region is given.
Results of optical and statistical model calculations without account of
contribution of the pre-equilibrium and direct processes are given for
energy above 1.65 keV. 9 discrete levels with excitation energy up to
0.980 MeV were evaluated in statistical model.

JEF-2 file: identical to old and obsolete ENDF/B-V evaluation without
revision made by R.Q. Wright in 1988. 13 SLBW s-resonances in the RRR
for E~n~ 10^-5^ to 0.486 keV. No URR is given. Results of optical and
statistical model calculations without account of contribution of the
pre-equilibrium and direct processes are given for energy above 1.65
keV. 9 discrete levels with excitation energy up to 0.980 MeV were
evaluated in statistical model.

JENDL-3.2 -- 1990 JNDC FPND working group evaluation. The resolved
resonances (204 positive and 1 negative MLBW s-resonances and 44
p-resonances) are given for En up to 5.96 keV. In the energy range below
3 keV, many artificial levels were generated with STAT code by assuming
D~0~=39.3 eV, S~0~=0.8E-4, S~1~=0.48E-4 and average radiation width 0.15
eV. URR from 5.96 keV to 100 keV. Parameters were adjusted to describe
the cross sections predicted by SM code GASTHY below 40 keV and
experimental data by Musgrove above 40 keV. For energy above 100 keV the
results of optical, statistical and pre-equilibrium decay reaction
models were used in the evaluation. Direct-semi-direct nuclear reaction
mechanisms were accounted in capture cross section evaluation. 7
discrete levels to 0.980 MeV excitation energy were included in the
statistical model calculations of inelastic scattering. No direct
excitation was accounted.

CENDL-3 evaluation in the RRR and URR is taken from JENDL-3.2 library.
OM and SM calculations with account of contribution of PEQ and DR (for
inelastic scattering) mechanisms were used for high-energy evaluation. 4
discrete levels to 0.588 MeV excitation energy were included in the
statistical model calculations of inelastic scattering. MF=4 and MF=5
files used for energy-angular distributions with excitation of continuum
of the states.

###### Thermal and resonance region

Table below shows the thermal cross section values (barns at 0.0253 eV),
resonance integral RI (barns) and position and width of negative
resonance for all libraries. JEF-2 as old and obsolete evaluation in the
RRR was not included in the comparison.

Large difference in total and elastic scattering cross section in the
thermal energy point and in resonance energy range is due to the
position, neutron width of the negative resonance and potential
scattering radius. The position of the negative resonance in B-6 and J-3
library (-51 eV) is probably too low.

J-3 resonances in the RRR are s-resonances and p-resonances with
random-statistical assignment of positions and widths to missed
resonances. Due to this the RI in J-3 is higher than in B-6 and in S.F.
Mughabghab evaluation, that looks very reasonable.

+-------------+------------+-------------+-----------------------------+
| Cross       | ENDF/B-VI  | JENDL-3.2   | Experiment, if relevant and |
| section ,   |            |             | exists                      |
|             |            | =CENDL-3    |                             |
| parameter   |            |             | Comments                    |
|             |            |             |                             |
|             |            |             | Partial conclusions         |
+-------------+------------+-------------+-----------------------------+
| E~min~,     | 1.0E-5     | 1.0E-5      |                             |
| RRR, eV     |            |             |                             |
+-------------+------------+-------------+-----------------------------+
| E~max~,     | 1.65       | 5.96        |                             |
| RRR, keV    |            |             |                             |
+-------------+------------+-------------+-----------------------------+
| N~res~      | 29         | 205         | J-3 widths are based on exp |
|             | s-         | s           | data. Above 3 keV positions |
|             | resonances | -resonances | and widths for many         |
|             |            |             | resonances were assigned by |
|             | (1         | (1          | Kikuchi                     |
|             | negative)  | negative)   | random-statistically basing |
|             |            |             | on average parameters.      |
|             |            | 44          |                             |
|             |            | p           |                             |
|             |            | -resonances |                             |
+-------------+------------+-------------+-----------------------------+
| Total cs, b | 10.1       | 7.594       | No exp data                 |
+-------------+------------+-------------+-----------------------------+
| Elastic cs, | 4.284      | 1.798       | No exp data, probably too   |
| b           |            |             | low in J-3, because of low  |
|             |            |             | R' and neutron width of     |
|             |            |             | negative resonance          |
+-------------+------------+-------------+-----------------------------+
| Capture cs, | 5.816      | 5.796       | 5.8±0.9(S.F.Mughabghab,     |
| b           |            |             | 2003)                       |
|             |            |             |                             |
|             |            |             | 5.6±0.8(X4=11507)           |
+-------------+------------+-------------+-----------------------------+
| RI, b       | 99.34      | 131\.       | 97±7(S.F.Mughabghab, 2003)  |
|             |            |             |                             |
|             |            |             | No direct exp data.         |
|             |            |             | Mughabghab evaluation is    |
|             |            |             | obtained probably from      |
|             |            |             | resonances and CS known.    |
|             |            |             |                             |
|             |            |             | J-3 with assignment of      |
|             |            |             | possible missed resonances  |
|             |            |             | is more reliable            |
+-------------+------------+-------------+-----------------------------+
| R', RRR, fm | 6.188      | 5.15        | 5.8±0.8 (X4=20688)          |
+-------------+------------+-------------+-----------------------------+
| E~r~(-), eV | -51.       | -51.        | For D~0~=21.25 eV, -51 eV   |
|             |            |             | is too large                |
+-------------+------------+-------------+-----------------------------+
| Γ~n~(-), eV | 0.1824     | 0.136       | Probably slightly low in    |
|             |            |             | J-3                         |
+-------------+------------+-------------+-----------------------------+
| Γ~γ~(-), eV | 0.14       | 0.147       | Probably slightly high in   |
|             |            |             | J-3                         |
+-------------+------------+-------------+-----------------------------+
| E~min~,     | \-         | 5.96        |                             |
| URR, keV    |            |             |                             |
+-------------+------------+-------------+-----------------------------+
| E~max~,     | \-         | 100\.       |                             |
| URR, keV    |            |             |                             |
+-------------+------------+-------------+-----------------------------+
| R', URR, fm | \-         | 5.2315      | 5.8±0.8 (X4=20688)          |
|             |            |             |                             |
|             |            |             | Possibly slightly low in    |
|             |            |             | J-3, what can lead to       |
|             |            |             | slightly low elastic        |
|             |            |             | scattering cross section.   |
+-------------+------------+-------------+-----------------------------+
| D~0~, min,  | \-         | 21.25       |                             |
| eV          |            |             |                             |
+-------------+------------+-------------+-----------------------------+
| FAST        | 0.362      | 0.538       | J-3 is close to the         |
| capture, b  |            |             | experimental data           |
|             |            | 0.528 (C-3) |                             |
+-------------+------------+-------------+-----------------------------+
| Capture, b, | \~0.3      | 0.4386      | 0.4286 (X4=22307, at        |
| E~n~=37.5   |            |             | \<30-40\> keV)              |
| keV         |            |             |                             |
+-------------+------------+-------------+-----------------------------+

**Fast region**

Table below describes major characteristics of evaluations in the fast
neutron energy region (E~n~ \> 100 keV).

+------------+---------+--------+--------+---------------------------+
| Cross      | EN      | JEN    | C      | Experiment, if relevant   |
| section,   | DF/B-VI | DL-3.2 | ENDL-3 | and exists                |
|            |         |        |        |                           |
| parameter  |         |        |        | Comments                  |
|            |         |        |        |                           |
|            |         |        |        | Partial conclusions       |
+------------+---------+--------+--------+---------------------------+
| Begin of   | 1.65    | 100\.  | 100\.  | The use of OM and SM      |
| OM and SM  |         |        |        | calculations starting     |
| ca         |         |        |        | from 1.65 keV in B-6 is   |
| lculations |         |        |        | not reliable. But B-6     |
|            |         |        |        | result for total and      |
| E~min~,    |         |        |        | elastic looks more        |
| FAST, keV  |         |        |        | reliable (P. Moldauer OMP |
|            |         |        |        | is one of the best for    |
|            |         |        |        | low energies)             |
+------------+---------+--------+--------+---------------------------+
| Total      | \~5.    | 4.68   | \~4.9  | 6.45 b ( \<En\>=0.1 --    |
|            | 55(0.15 | (0.15  | 7(0.15 | 0.2 MeV, X4=22307), 5.6 b |
|            | MeV)    | MeV)   | MeV)   | ( \<En\>=0.15 -- 0.2 MeV, |
|            |         |        |        | X4=22307)                 |
|            | 4.      | \~5.   | \~4.65 |                           |
|            | 94(19.5 | 0(19.5 | (19.5  |                           |
|            | MeV)    | MeV)   | MeV)   |                           |
+------------+---------+--------+--------+---------------------------+
| Elastic    | 5.50 b  | 4.47b  | 4.75 b | B-6 is too high above 10  |
|            | at 0.15 | at     | at     | MeV because has no (n,2n) |
|            | MeV     | 0.15   | 0.15   |                           |
|            |         | MeV    | MeV    |                           |
|            | \~2.43  |        |        |                           |
|            | b at 5  | 2.48 b | 2.174  |                           |
|            | MeV     | at 5   | b at 5 |                           |
|            |         | MeV    | MeV    |                           |
+------------+---------+--------+--------+---------------------------+
| Capture    |         |        |        | B-6 is below experimental |
|            |         |        |        | data. C-3 is slightly low |
|            |         |        |        | in MeV range(?).          |
+------------+---------+--------+--------+---------------------------+
| Discrete   | 9       | 7      | 4      | 3 missed levels in J-3    |
| levels     | levels  | levels | levels | according latest ENSDF.   |
| inelastic  | to      | to     | to     | No account of DR in J-3.  |
| scat.      | 0.980   | 0.980  | 0.59   | DR is accounted in C-3.   |
|            | MeV     | MeV    | MeV    |                           |
+------------+---------+--------+--------+---------------------------+
| Continuum  | E~cont  | E~cont | E~cont | PEQ model contribution    |
| levels     | ~=0.983 | ~=1.17 | ~=0.59 | accounted in J-3, C-3 but |
| inelastic  | MeV     | MeV    | MeV    | not in B-6.               |
| scattering |         |        |        |                           |
+------------+---------+--------+--------+---------------------------+
| Total      | 1.896 b | \      | 2.38 b | B-6 gives as total        |
| inelastic  | at 5    | ~2.028 | at 5   | inelastic -- the first    |
| cross      | MeV     | b at 5 | MeV    | neutron emission cross    |
| section    |         | MeV    |        | section.                  |
|            | \~1.2 b |        | \      |                           |
|            | at 20   | \      | ~0.297 | Average experimental      |
|            | MeV     | ~0.343 | b at   | value for non-elastic     |
|            |         | b at   | 20 MeV | cross section (50 \<Z\<   |
|            |         | 20 MeV |        | 60, 4 \<E~n~\< 6 MeV) is  |
|            |         |        |        | 2.12 b. B-6               |
|            |         |        |        | underestimates and C-3    |
|            |         |        |        | overestimates slightly    |
|            |         |        |        | the inelastic scattering  |
|            |         |        |        | CS at 5 MeV.              |
+------------+---------+--------+--------+---------------------------+
| (n,2n)     | absent  | 1.61 b | 1.635  | J-3 normalized to         |
|            |         | at 14  | b at   | systematics at 14 MeV.    |
|            |         | MeV    | 14MeV  |                           |
+------------+---------+--------+--------+---------------------------+
| (n,p),     |         |        |        | Minor cross sections.     |
| (n,a) and  |         |        |        | J-3, C-3 are more         |
| other      |         |        |        | reliable.                 |
+------------+---------+--------+--------+---------------------------+
| Elastic    | is      | SOM+SM | SOM+SM |                           |
| scattering | otropic | calcul | calcul |                           |
| angular    |         | ations | ations |                           |
| distr.     |         |        |        |                           |
+------------+---------+--------+--------+---------------------------+
| Inelastic  | Is      | SM     | SM+    | MF=4, MT=91 symmetric in  |
| scattering | otropic | calcul | PEQ+DR | J-3 in CMS. MF=4, MT=91   |
| angular    |         | ations |        | in CENDL-3 has no sense.  |
| distr.     |         |        | calcul | MF=6 should be used.      |
|            |         |        | ations |                           |
+------------+---------+--------+--------+---------------------------+
| Secondary  | Temp    | Proba  | Proba  | B-6 gives wrong spectra   |
| neutron    | erature | bility | bility | for E~n~ above (n,2n)     |
| spectra    | prese   | tables | table  | threshold.                |
|            | ntation | with   | with   |                           |
|            |         | SM and | SM and | J-3 has no contribution   |
|            |         | PEQ    | PEQ    | of direct processes.      |
|            |         | mech   | mech   |                           |
|            |         | anisms | anisms |                           |
+------------+---------+--------+--------+---------------------------+

B-6 is very old evaluation in the FAST energy region and cannot compete
with other evaluations. J-3 and C-3 evaluations are rather similar. As
seems the imaginary part of optical potential is slightly low than
needed in C-3 at low energies, what leads to the overestimation of
non-elastic cross section. Non-elastic cross sections for neighboring
nuclei should be considered when OM parameters are adjusted.

Direct reaction mechanism with excitation of collective levels in the
inelastic scattering should be accounted in the evaluations for larger
number of low-laying levels. Energy-angular distributions for secondary
particles should be calculated with SM, PEQ and direct reaction
mechanisms contributions and presented in the file MF=6.

No secondary gamma spectra are given in files of all libraries.

###### 

###### Recommendation and conclusion

JENDL-3.2 evaluation with newly adjusted position and width of negative
resonance, and R' in the RRR and JENDL-3.2 evaluation in the URR with
slightly revised parameters (adjusted better to the experimental total
cross section) can be selected. JENDL-3.2 can be recommended for
high-energy range after some improvements.

###### Further possible improvements

To revise parameters of negative resonance and R' in JENDL-3.2 library
to fit evaluated thermal capture cross section value with gamma width of
negative resonance close to average gamma width in RRR. To revise R' in
URR in JENDL-3.2 by adjusting total CS to existing experimental data but
not to the results of OM+SM calculations. Use non-SOM model to account
for direct process. Use MF=6 file for energy-angular distributions of
secondary particles with account of SM, PEQ and direct reaction
mechanisms.