**56-Ba-136 Review**

By V.G. Pronyaev, NDS, IAEA

20 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: B-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). 4 MLBW s-resonances are given in the RRR for
E~n~ 10^-5^ to 1.644 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 3.177 keV.

JEF-2 file: identical to old and obsolete ENDF/B-V evaluation without
revision made by R.Q. Wright in 1988. 2 MLBW s-resonances and 1
p-resonance in the RRR for E~n~ 10^-5^ to 3.177 keV. No URR is given.
For energy above 3.177 keV J-2 is the same as B-6.

JENDL-3.2 -- 1990 JNDC FPND working group evaluation. The resolved
resonances (15 positive and 1 negative MLBW s-resonances and 76
p-resonances) are given for En up to 34.49 keV. In the energy range
below 3 keV, 4 artificial levels were generated with STAT code by
assuming D~0~=225 eV, S~0~=0.8E-4, S~1~=0.8E-4 and average radiation
width 0.125 eV. URR from 34.49 keV to 100 keV. Parameters were adjusted
to describe the cross sections predicted by SM code GASTHY. Capture
cross section was adjusted to experimental data by adjusting average
distance between levels. 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. 10 discrete levels to
2.2071 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
with small modification to fit new thermal capture cross section
evaluation. Results of OM and SM calculations with account of
contribution of PEQ and DR (for inelastic scattering) mechanisms. 3
discrete levels to 1.579 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.

+------------+------------+------------+------------------------------+
| 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     | New ORELA set of parameters  |
| RRR, eV    |            |            | (27 s- and 65 p-) by P.E     |
|            |            |            | Koehler et al. (1996) is     |
|            |            |            | available but not            |
|            |            |            | incorporated in any          |
|            |            |            | evaluation.                  |
+------------+------------+------------+------------------------------+
| E~max~,    | 3.177      | 34.49      |                              |
| RRR, keV   |            |            |                              |
+------------+------------+------------+------------------------------+
| N~res~     | 4          | 16         | Ratio of numbers of p- to    |
|            | s-         | s-         | s-resonances in RRR J-3 is   |
|            | resonances | resonances | about 5; it should be 3. J-3 |
|            |            |            | positions and widths for     |
|            | (1         | (1         | some resonances were         |
|            | negative)  | negative)  | assigned by Kikuchi          |
|            |            |            | random-statistically basing  |
|            |            | 76         | on average parameters.       |
|            |            | p-         |                              |
|            |            | resonances |                              |
+------------+------------+------------+------------------------------+
| Total cs,  | 5.924      | 2.9        | 3.17 b for \<E\>=1.26 --     |
| b          | (therm.)   | 74(therm.) | 18.8 eV (X4=21992).          |
|            |            |            |                              |
|            | \~5.5 at   | \~2.56 at  | J-3 is closer to exp data    |
|            | 10 eV      | 10 eV      |                              |
|            |            |            |                              |
|            |            | 2.457      |                              |
|            |            | (C-3)      |                              |
+------------+------------+------------+------------------------------+
| Elastic    | 5.511      | 2.574      | No exp data, probably too    |
| cs, b      |            |            | low in C-3, and too high in  |
|            |            | 1.78 (C-3) | B-6                          |
+------------+------------+------------+------------------------------+
| Capture    | 0.413      | 0.4        | 0.4±0.4(S.F.Mughabghab,      |
| cs, b      |            |            | 1981)                        |
|            |            | 0.68 (C-3) |                              |
|            |            |            | 0.68±0.17(S.F.Mughabghab,    |
|            |            |            | 2003)                        |
|            |            |            |                              |
|            |            |            | Parameters of negative       |
|            |            |            | resonance in C-3 are         |
|            |            |            | adjusted to new thermal      |
|            |            |            | capture CS                   |
+------------+------------+------------+------------------------------+
| RI, b      | 1.72       | 2.06       | 1.7±0.3(S.F.Mughabghab,      |
|            |            |            | 2003)                        |
|            |            | 13.42(C-3) |                              |
|            |            |            | 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. First      |
|            |            |            | positive resonance in C-3 is |
|            |            |            | wrong (non-existent)         |
+------------+------------+------------+------------------------------+
| R', RRR,   | 6.203      | 5.15       | Possibly slightly low in J-3 |
| fm         |            |            |                              |
+------------+------------+------------+------------------------------+
| E~r~(-),   | -250.      | -250.      | As seems there is error in   |
| eV         |            |            | C-3 where negative 250 eV    |
|            |            | No (C-3)   | resonance was introduced as  |
|            |            |            | positive one.                |
+------------+------------+------------+------------------------------+
| ~n~(-), eV | 0.759      | 0.653      |                              |
+------------+------------+------------+------------------------------+
| (-), eV    | 0.125      | 0.125      |                              |
+------------+------------+------------+------------------------------+
| E~min~,    | \-         | 34.49      |                              |
| URR, keV   |            |            |                              |
+------------+------------+------------+------------------------------+
| E~max~,    | \-         | 100\.      |                              |
| URR, keV   |            |            |                              |
+------------+------------+------------+------------------------------+
| R', URR,   | \-         | 5.288      | Possibly slightly low in     |
| fm         |            |            | J-3, what can lead to        |
|            |            |            | slightly low elastic         |
|            |            |            | scattering cross section.    |
+------------+------------+------------+------------------------------+
| D~0~, min, | \-         | 790        |                              |
| eV         |            |            |                              |
+------------+------------+------------+------------------------------+
| FAST       | 0.0482     | 0.0706     | J-3, C-3 is close to the     |
| capture, b |            |            | experimental data            |
|            |            | 0.101      |                              |
|            |            | (C-3)      |                              |
+------------+------------+------------+------------------------------+
| Capture,   | \~0.043    | \~0.063    | 0.0585 (X4=22307, at         |
| b,         |            |            | \<30-40\> keV) 0.065±0.009   |
| E~n~=37.5  |            |            | (X4=30328, at \<30-40\>      |
| keV        |            |            | keV), 0.07±0.01 (X4=30328,   |
|            |            |            | 45 keV)                      |
+------------+------------+------------+------------------------------+

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 J-3 library gives values in eV region much closer
to experimental values than other libraries.

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, but this looks very reasonable.

**Fast region**

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

+------------+---------+---------+---------+-------------------------+
| Cross      | EN      | JE      | CENDL-3 | Experiment, if relevant |
| section,   | DF/B-VI | NDL-3.2 |         | and exists              |
|            |         |         |         |                         |
| parameter  | =JEF-2  |         |         | Comments                |
|            |         |         |         |                         |
|            |         |         |         | Partial conclusions     |
+------------+---------+---------+---------+-------------------------+
| Begin of   | 3.177   | 100\.   | 100\.   | The use of OM and SM    |
| OM and SM  |         |         |         | calculations starting   |
| ca         |         |         |         | from 3.177 keV in B-6   |
| lculations |         |         |         | is not reliable.        |
|            |         |         |         |                         |
| E~min~,    |         |         |         |                         |
| FAST, keV  |         |         |         |                         |
+------------+---------+---------+---------+-------------------------+
| Total      | \~5.    | 4.67    | \~4.    | 4.9 b ( \<En\>=0.1 --   |
|            | 55(0.15 | (0.15   | 97(0.15 | 0.2 MeV, X4=22307)      |
|            | MeV)    | MeV)    | MeV)    |                         |
|            |         |         |         |                         |
|            | 4.      | \~5     | \~4.65  |                         |
|            | 98(19.5 | .0(19.5 | (19.5   |                         |
|            | MeV)    | MeV)    | MeV)    |                         |
+------------+---------+---------+---------+-------------------------+
| Elastic    | 5.52 b  | 4.63 b  | 4.93 b  | B-6 is too high above   |
|            | at 0.15 | at 0.15 | at 0.15 | 10 MeV because has no   |
|            | MeV     | MeV     | MeV     | (n,2n)                  |
|            |         |         |         |                         |
|            | \~2.48  | 2.39 b  | 2.181 b |                         |
|            | b at 5  | at 5    | at 5    |                         |
|            | MeV     | MeV     | MeV     |                         |
+------------+---------+---------+---------+-------------------------+
| Capture    | 0.025 b | 0.038 b | 0.037 b | B-6 is below            |
|            | at 150  | at 150  | at 150  | experimental data.      |
|            | keV     | keV     | keV     |                         |
+------------+---------+---------+---------+-------------------------+
| Discrete   | 10      | 10      | 3       | Contribution of DR in 2 |
| levels     | levels  | levels  | levels  | low-lying levels in C-3 |
| inelastic  | to 2.21 | to 2.21 | to 1.58 | is equal(?).            |
| scat.      | MeV     | MeV     | MeV     |                         |
+------------+---------+---------+---------+-------------------------+
| Continuum  | E~cont  | E~con   | E~con   | PEQ model contribution  |
| levels     | ~=2.204 | t~=2.28 | t~=1.58 | accounted in J-3, C-3   |
| inelastic  | MeV     | MeV     | MeV     | but not in B-6.         |
| scattering |         |         |         |                         |
+------------+---------+---------+---------+-------------------------+
| Total      | 1.866 b | \~2.12  | 2.374 b | B-6: total inelastic =  |
| inelastic  | at 5    | b at 5  | at 5    | the first neutron       |
| cross      | MeV     | MeV     | MeV     | emission cross section. |
| section    |         |         |         | Average experimental    |
|            | 1.176 b | \~0.333 | \~0.254 | value for non-elastic   |
|            | at 20   | b at 20 | b at 20 | cross section (50 \<Z\< |
|            | MeV     | MeV     | MeV     | 60, 4 \<E~n~\< 6 MeV)   |
|            |         |         |         | is 2.12 b. Probably B-6 |
|            |         |         |         | underestimates and C-3  |
|            |         |         |         | overestimates slightly  |
|            |         |         |         | the inelastic           |
|            |         |         |         | scattering CS at 5 MeV. |
+------------+---------+---------+---------+-------------------------+
| (n,2n)     | absent  | 1.64 b  | 1.534 b | J-3 normalized to       |
|            |         | at 14   | at 14   | systematics at 14 MeV.  |
|            |         | MeV     | MeV     |                         |
+------------+---------+---------+---------+-------------------------+
| (n,p),     |         |         |         | Minor cross sections.   |
| (n,a) and  |         |         |         | J-3, C-3 are more       |
| other      |         |         |         | reliable.               |
+------------+---------+---------+---------+-------------------------+
| Elastic    | is      | SOM+SM  | SOM+SM  |                         |
| scattering | otropic | calcu   | calcu   |                         |
| angular    |         | lations | lations |                         |
| distr.     |         |         |         |                         |
+------------+---------+---------+---------+-------------------------+
| Inelastic  | is      | SM + DR | SM      | MF=4, MT=91 symmetric   |
| scattering | otropic | calcu   | +PEQ+DR | in J-3 in CMS. MF=4,    |
| angular    |         | lations | calcu   | MT=91 in CENDL-3 has no |
| distr.     |         |         | lations | sense, MF=6 should be   |
|            |         |         |         | used.                   |
+------------+---------+---------+---------+-------------------------+
| Secondary  | Temp    | Prob    | Prob    | B-6 gives wrong spectra |
| neutron    | erature | ability | ability | for E~n~ above (n,2n)   |
| spectra    | prese   | tables  | tables  | threshold.              |
|            | ntation | with SM | with SM |                         |
|            |         | and PEQ | and PEQ |                         |
|            |         | mec     | mec     |                         |
|            |         | hanisms | hanisms |                         |
+------------+---------+---------+---------+-------------------------+

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-lying 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 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 new S.F. Mughabghab evaluated thermal capture cross section value
with gamma width of negative resonance close to average gamma width in
RRR. New ORELA results by P.E. Koehler et al. (1996) for RRR with 27
s-resonanses and 65 p-resonances should be included. To revise R' and
neutron width of negative resonance in JENDL-3.2 by adjusting also to
existing experimental data on total CS in eV region. 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.