**56-Ba-138 Review**

By V.G. Pronyaev, NDS, IAEA

23 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 ENDF/B-V evaluation was revised in the RRR by R.Q.
Wright (1994). 11 MLBW s-resonances and 49 p-resonances are given in the
RRR for E~n~ 0.4 to 198 keV. Below 0.4 keV total cross section was
adjusted to fit existing experimental total cross sections in eV region.
No unresolved resonance region is given. Results of optical and
statistical model calculations without account of contribution of the
pre-equilibrium and direct processes and consideration of discrete
levels in inelastic scattering are given for energy above 198 keV. (n,p)
and (n,) cross sections are taken from J-3.

JEF-2 file: Bologna 1982 evaluation extended up to 20 MeV in 1985 and
added by charged particle production data in 1989. 12 MLBW s-, 19 p- and
8 d-resonances in the RRR for E~n~ from 10^-5^ eV to 90 keV. No URR is
given. Results of OM and SM calculations in the energy region above 198
keV. No PEQ or DR mechanisms accounted.

JENDL-3.2 -- 1990 JNDC FPND working group evaluation. The resolved
resonances (27 positive and 1 negative MLBW s-resonances and 29
p-resonances) contribute in the RRR from 1.0E-5 eV to 100 keV.
Parameters are based on experimental data available. Spins of some
resonances were assigned by random-number method. No URR is given. For
energy above 100 keV the optical, statistical, pre-equilibrium decay and
direct reaction models were used in the evaluation. Direct-semi-direct
nuclear reaction mechanisms were accounted in capture cross section
evaluation. 19 discrete levels to 3.156 MeV excitation energy were
included in the statistical model calculations of inelastic scattering.
DR mechanism with excitation of collective levels of vibrational nature
in inelastic scattering was accounted for 2 levels.

CENDL-3 1999 evaluation in the RRR is taken from JENDL-3.2 library with
(clearly wrong, -- sign of negative resonance was lost) modification of
parameters of first resonance in the RRR. Results of OM and SM
calculations with account of contribution of PEQ and DR (for inelastic
scattering) mechanisms. 3 discrete levels to 2.091 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     | E        | JEF-2    | JENDL-3.2 | Experiment, if        |
| section , | NDF/B-VI |          |           | relevant and exists   |
|           |          |          | =CENDL-3  |                       |
| parameter |          |          |           | Comments              |
|           |          |          |           |                       |
|           |          |          |           | Partial conclusions   |
+-----------+----------+----------+-----------+-----------------------+
| E~min~,   | 4.0E+2   | 1.0E-05  | 1.0E-5    |                       |
| RRR, eV   |          |          |           |                       |
+-----------+----------+----------+-----------+-----------------------+
| E~max~,   | 198\.    | 90\.     | 100\.     |                       |
| RRR, keV  |          |          |           |                       |
+-----------+----------+----------+-----------+-----------------------+
| N~res~    | 11 s-    | 12 s- (1 | 28        | Ratio of numbers of   |
|           | and 49   | ne       | s-r       | p- to s-resonances in |
|           | p-re     | gative), | esonances | RRR in B-6 deviates   |
|           | sonances | 19 p-,   | (1        | from 3. Negative      |
|           | (MLBW    | and 8    | negative) | energy resonance is   |
|           | fo       | d-re     | 29 p-     | wrongly placed as     |
|           | rmalism) | sonances | r         | positive in C-3.      |
|           |          |          | esonances |                       |
|           |          |          | (MLBW)    |                       |
+-----------+----------+----------+-----------+-----------------------+
| Total cs, | 3.36     | 7.416    | 5.9       | 3.27 b for \<E\>=1.26 |
| b         | (therm.) | (therm.) | 3(therm.) | -- 18.8 eV            |
|           |          |          |           | (X4=21992).           |
|           | \~3.00   | 7.05 at  | 5.56 at   |                       |
|           | at 10 eV | 10 eV    | 10 eV     | B-6 is best relative  |
|           |          |          |           | exp. data             |
|           |          |          | 1.226(th  |                       |
|           |          |          | erm.)C-3, |                       |
|           |          |          | 8.31      |                       |
|           |          |          | (C-3) at  |                       |
|           |          |          | 10 eV     |                       |
+-----------+----------+----------+-----------+-----------------------+
| Elastic   | 3.00     | 7.066    | 5.57      | No exp data, probably |
| cs, b     |          |          |           | too low in C-3, and   |
|           |          |          | 0         | too high in F-2       |
|           |          |          | .816(C-3) |                       |
+-----------+----------+----------+-----------+-----------------------+
| Capture   | 0.36     | 0.35     | 0.359     | 0.360±                |
| cs, b     |          |          |           | 0.036(S.F.Mughabghab, |
|           |          |          | 0.410     | 1981), 0.404±0.04     |
|           |          |          | (C-3)     | (S.F.Mughabghab,      |
|           |          |          |           | 2003)                 |
|           |          |          |           |                       |
|           |          |          |           | Parameters of         |
|           |          |          |           | fictitious "positive" |
|           |          |          |           | resonance in C-3 are  |
|           |          |          |           | adjusted to new       |
|           |          |          |           | thermal capture CS    |
+-----------+----------+----------+-----------+-----------------------+
| RI, b     | 0.267    | 0.183    | 0.265     | 0.32                  |
|           |          |          |           | ±0.04(S.F.Mughabghab, |
|           |          |          | 0         | 2003). No direct exp  |
|           |          |          | .357(C-3) | data. Mughabghab      |
|           |          |          |           | evaluation is         |
|           |          |          |           | obtained probably     |
|           |          |          |           | from known            |
|           |          |          |           | resonances. J-3 with  |
|           |          |          |           | assignment of         |
|           |          |          |           | possible missed       |
|           |          |          |           | resonances is most    |
|           |          |          |           | reliable. First       |
|           |          |          |           | positive resonance in |
|           |          |          |           | C-3 is wrong          |
|           |          |          |           | (non-existent). This  |
|           |          |          |           | leads to high RI      |
+-----------+----------+----------+-----------+-----------------------+
| R', RRR,  | 5.083    | 6.234    | 5.14      | Possibly slightly low |
| fm        |          |          |           | in J-3 and B-6        |
+-----------+----------+----------+-----------+-----------------------+
| E~r~(-),  | Po       | -2524.   | -6220.    | There is an error in  |
| eV        | int-wise |          |           | C-3 where negative    |
|           | data     |          | No (C-3), | 6220 eV resonance was |
|           | given    |          | +6220.    | introduced as         |
|           |          |          |           | positive one.         |
+-----------+----------+----------+-----------+-----------------------+
| ~n~(-),   | Po       | 86\.     | 477.5     |                       |
| eV        | int-wise |          |           |                       |
|           | data     |          |           |                       |
|           | given    |          |           |                       |
+-----------+----------+----------+-----------+-----------------------+
| (-), eV   | Po       | 0.31     | 0.55      |                       |
|           | int-wise |          |           |                       |
|           | data     |          | 0         |                       |
|           | given    |          | .629(C-3) |                       |
+-----------+----------+----------+-----------+-----------------------+
| D~0~,     | 18.7     | \-       | \-        |                       |
| min, keV  | (RRR)    |          |           |                       |
+-----------+----------+----------+-----------+-----------------------+
| FAST      | 5.25     | 3.42     | 5.38      | J-3, C-3 is close to  |
| capture,  |          |          |           | the experimental data |
| mb        |          |          | 9.1 (C-3) |                       |
+-----------+----------+----------+-----------+-----------------------+

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 F-2 and J-3 libraries give values in eV region
above the experimental values. B-6 gives best fit in eV region but still
does not fit at "cold" neutron point. C-3 with wrong sign of energy of
first resonance gives wrong behavior of CS and highest RI. Capture cross
section at thermal point is adjusted to new S.F. Mughabghab evaluation
only in C-3 library. 1/V part in RI is dominating. With adjustment to
new thermal capture value, the consistency with new RI S.F. Mughabghab
evaluation will be improved.

**Fast region**

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

F-2 is wrong above 15 MeV due to simplified method of energy extension.
Capture cross section in F-2 is below the experimental data. B-6, J-3
and C-3 evaluations are rather similar for many reactions (B-6 uses 3
reactions taken from J-3). 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
neutron inelastic scattering is accounted in J-3 and C-3 files but not
in other files. No MF=6 is given in all libraries. should be accounted
in the evaluations for larger number of low-lying levels. Secondary
gamma spectra are given in files of all libraries.

###### Recommendation and conclusion

B-6 evaluation with newly adjusted position and width of negative
resonance to fit new 2003 S.F. Mughabghab thermal capture value can be
selected. CENDL-3 evaluation after some improvements can be recommended
for fast neutron energy region.

###### Further possible improvements

To revise parameters of negative resonance in B-6 library to fit new
S.F. Mughabghab evaluated thermal capture cross section value. C-3
evaluation will require the adjusting of OM potential in MeV region with
account of experimental non-elastic cross sections, the use of more
discrete levels of inelastic scattering for SM and DR calculations, the
use of MF=6 for presentation of secondary energy-angular distributions.

+------------+--------+-------+---------+---------+-------------------+
| Cross      | END    | JEF-2 | JE      | CENDL-3 | Exp. data         |
| section,   | F/B-VI |       | NDL-3.2 |         |                   |
|            |        |       |         |         | Comments          |
| parameter  |        |       |         |         |                   |
|            |        |       |         |         | Partial           |
|            |        |       |         |         | conclusions       |
+------------+--------+-------+---------+---------+-------------------+
| Begin of   | 198    | 90    | 100\.   | 100\.   |                   |
| OM and SM  |        |       |         |         |                   |
| ca         |        |       |         |         |                   |
| lculations |        |       |         |         |                   |
|            |        |       |         |         |                   |
| E~min~,    |        |       |         |         |                   |
| FAST, keV  |        |       |         |         |                   |
+------------+--------+-------+---------+---------+-------------------+
| Total at   | 5.267  | 5.414 | \~4.8   | 5.01    | Data are rather   |
| 0.2        |        |       |         |         | consistent.       |
|            | 6.56   | 6.27  | \~6.6   | \~6.3   | ^nat^Ba: 6.39 b   |
| and 2.5    |        |       |         |         | at 2.5 MeV        |
| MeV, b     |        |       |         |         | (X4=10047)        |
+------------+--------+-------+---------+---------+-------------------+
| Elastic at | \~3.0  | \~2.8 | \~3.0   | \~2.7   | ^nat^Ba: 2.5±0.3  |
| 4.1 MeV    |        |       |         |         | b at 4.1 MeV      |
|            |        |       |         |         | (X4=11621)        |
+------------+--------+-------+---------+---------+-------------------+
| Capture    |        |       |         |         | B-6 and C-3 give  |
|            |        |       |         |         | the best fit of   |
|            |        |       |         |         | exp. data         |
+------------+--------+-------+---------+---------+-------------------+
| Discrete   | No     | 10    | 19      | 3       | Contribution of   |
| levels     | di     | l     | levels  | levels  | DR in 2           |
| inelastic  | screte | evels | to      | to      | vibrational       |
| scat.      | in     | to    | 3.156   | 0.662   | levels in J-3.    |
|            | eval.  | 2.446 | MeV     | MeV     |                   |
|            |        | MeV   |         |         | Contribution of   |
|            |        |       |         |         | DR in low-lying   |
|            |        |       |         |         | levels of g.s.    |
|            |        |       |         |         | rotat. band(?) in |
|            |        |       |         |         | C-3.              |
+------------+--------+-------+---------+---------+-------------------+
| Continuum  | E~cont | E~    | E~cont  | E~cont  | PEQ model         |
| levels     | ~=1.43 | cont~ | ~=3.164 | ~=2.091 | contribution      |
| inelastic  | MeV    | =2.46 | MeV     | MeV     | accounted in J-3, |
| scattering |        | MeV   |         |         | C-3 but not in    |
|            |        |       |         |         | F-2. B-6 gives    |
|            |        |       |         |         | the same MT=4     |
|            |        |       |         |         | (and MT=91) cross |
|            |        |       |         |         | sections as MT=4  |
|            |        |       |         |         | in J-3.           |
+------------+--------+-------+---------+---------+-------------------+
| Total      | Taken  | 2.168 | 2.06 b  | 2.329 b | Average           |
| inelastic  | from   | b at  | at 5    | at 5    | experimental      |
| cross      | J-3    | 5 MeV | MeV     | MeV     | value for         |
| section    |        |       |         |         | non-elastic cross |
|            | 2.06 b | 0     | 0.208 b | 0.191 b | section (50 \<Z\< |
|            | at 5   | .0303 | at 20   | at 20   | 60, 4 \<E~n~\< 6  |
|            | MeV    | b at  | MeV     | MeV     | MeV) is 2.12 b.   |
|            |        | 20    |         |         | C-3 overestimates |
|            | 0.208  | MeV   |         |         | slightly the      |
|            | b at   |       |         |         | inelastic         |
|            | 20 MeV |       |         |         | scattering CS at  |
|            |        |       |         |         | 5 MeV.            |
+------------+--------+-------+---------+---------+-------------------+
| (n,2n)     | Taken  | \~2.0 | 1.731 b | 1.623 b | J-3 normalized to |
|            | from   | b at  | at 14   | at 14   | systematics at 14 |
|            | J-3    | 14    | MeV     | MeV     | MeV.              |
|            |        | MeV   |         |         |                   |
+------------+--------+-------+---------+---------+-------------------+
| (n,p),     | Taken  |       |         |         | Minor cross       |
| (n,a) and  | from   |       |         |         | sections. J-3,    |
| other      | J-3    |       |         |         | C-3 are more      |
|            |        |       |         |         | reliable.         |
+------------+--------+-------+---------+---------+-------------------+
| Elastic    | SOM+SM | S     | SOM+SM  | SOM+SM  |                   |
| scattering | calcul | OM+SM | calcu   | calcu   |                   |
| angular    | ations | ca    | lations | lations |                   |
| distr.     |        | lcul. |         |         |                   |
+------------+--------+-------+---------+---------+-------------------+
| Inelastic  | iso    | isot  | SM + DR | SM+PEQ  | MF=4, MT=91 in    |
| scattering | tropic | ropic | calcu   |         | CENDL-3 has no    |
| angular    |        |       | lations | +DR     | sense, MF=6       |
| distr.     |        |       | (no PEQ | calc.   | should be used.   |
|            |        |       | for     |         |                   |
|            |        |       | a       |         |                   |
|            |        |       | ngular) |         |                   |
+------------+--------+-------+---------+---------+-------------------+
| Secondary  | Proba  | Temp. | Prob    | Prob    | F-2 gives wrong   |
| neutron    | bility | pre   | ability | ability | spectra for E~n~  |
| spectra    | tables | sent. | tables  | table   | above (n,2n)      |
|            | with   |       | with SM | with SM | threshold.        |
|            | empiri |       | and PEQ | and PEQ |                   |
|            | cal(?) |       | mec     | mec     |                   |
|            | data   |       | hanisms | hanisms |                   |
+------------+--------+-------+---------+---------+-------------------+
| Secondary  | Given  | No    | No      | No      |                   |
| gamma      | for    |       |         |         |                   |
| spectra    | all    |       |         |         |                   |
|            | non-e  |       |         |         |                   |
|            | lastic |       |         |         |                   |
|            | pro    |       |         |         |                   |
|            | cesses |       |         |         |                   |
+------------+--------+-------+---------+---------+-------------------+

######