**WPEC SG 21: Assessment of Neutron Cross-Section Evaluations for the
Bulk of Fission Products**

**56-Ba-140 Review**

I. Sirakov, INRNE, March 17, 2003

######## **[Files]{.underline}**

***ENDF/B-VI:*** Year of origin 1974, taken from ENDF/B-V, no revision
since then

***JEF-2:*** Year of origin 1982, data taken from ENEA/CEA evaluation
(1977), last revision 1989

***JENDL-3:*** Year of origin 1990, revised (non-essentially) in 2002
when transformed to JENDL-3.3

######## **[Thermal and resonance region]{.underline}**

***ENDF/B-VI:*** No resonance parameters; pointwise data; scattering
radius 6.26 fm, constant (4.93 b) form assumed for elastic cross
section; 1/v form assumed for capture so that to reproduce the thermal
capture cross section from BNL-325 (1973). Computed resonance integral
of 12.74 b agrees (to within 1 sigma) with BNL-325.

*** ***

***JEF-2:*** Resolved resonance parameters up to 23 keV; MLBW
representation of 8 artificial s-wave resonances with parameters
randomly generated by PSEUDO code; scattering radius 6.23 fm. Unresolved
region up to 100 keV with energy independent parameters. Computed
resonance integral 13.7 b.

***JENDL-3*:** No resolved resonance parameters, pointwise data up to 14
keV; 1/v and constant (3.3 b) form assumed for capture and elastic cross
sections respectively; thermal capture cross section taken from BNL-325
(1981). Unresolved region up to 100 keV; S0, S1 and S2 strength
functions calculated with CASTHY; the effective scattering radius of 5.3
fm determined from fitting to the calculated total cross section at 100
keV. Level spacing determined to reproduce the capture cross section
from CASTHY. Average radiative width of 75 meV based on systematics for
neighbouring nuclides. Computed resonance integral 0.728 b.

**Note on the resonance region**: The different values of the one-group
capture cross sections (1E-5 eV - 20 MeV) over fast-reactor weighting
spectrum (<http://www.nndc.bnl.gov/sg21/nucl/acs/accs.htm>) for
***ENDF/B-VI*** (69.0 mb), ***JEF-2*** (20.5 mb) and ***JENDL-3*** (2.4
mb) are due to the higher ***ENDF/B-VI*** and lower ***JENDL-3***
capture cross section in the interval \~100 eV- 100 keV, where the
fast-reactor flux is predominant.

**Experimental data** -- Halperin1967
([EXFOR10348](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=10348&DatType=H&RetType=byAccNum&ReDo=N)
002, 003) data giving 1.57(30) b for the thermal capture cross section
and 13.6(14) b for the resonance integral. ***JEF-2*** values of 1.59 b
and 13.7 b respectively are in full agreement with Halperin's
experimental results.

**Recommendation/Conclusion**: ***JEF-2*** recommended in the resonance
region up to 100 keV for its best agreement with the experimental data
(Halperin1967) on thermal capture cross section and resonance integral.
In addition, ***JEF-2*** covers the whole region with a resonance
representation. ***JENDL-3*** gives too low resonance integral and,
therefore, its (n,g) cross section can not be recommended. A preference
for the (n,tot) and, consequently, (n,el) evaluations of ***JEF-2***
could be assumed from the better ***JEF-2*** fit to the experimental
total cross section for natural Ba at 100 keV.

######## **[Fast neutron region]{.underline}**

-   Methodology

***ENDF/B-VI:*** The optical potential of Moldauer used for MT=1. MT=4,
91 calculated with COMNUC-3 code, no discrete inelastic scattering
considered; MT=102 evaluated with NCAP code; elastic cross section
obtained as (MT1-MT102-MT4); Isotropic angular distribution for MF=4,
MT=2 in CM system. Evaporation spectrum (NCAP code) presented in MF=5
for the continuum inelastic scattering. Account taken of MT=1, 2, 4, 91,
102.

***JEF-2:*** Spherical OM and statistical model code CERBERO used for
the continuum cross section region. The OM code ERINNI applied for the
high energy region. No discrete inelastic scattering considered; no
charge particle production cross sections were first considered; in 1989
they were included from REAC-ECN-4 Library. Legendre coefficients from
CERBERO to get anisotropic angular distribution for MF=4, MT=2 in CM
system. Evaporation spectrum assumed in MF=5 for the continuum inelastic
scattering. MT=1, 2, 4, 16, 17, 91, 102, 103, 104, 105, 106, 107, 111.

***JENDL-3:*** Spherical OM and statistical model code CASTHY for MT=1,
4, 51-91, 102 by taking into account competing reactions MT=16, 17, 103,
107, etc, calculated with the preeq and multi-step evaporation model
code PEGASUS. The gamma-ray strength function adjusted to measured
capture cross section for Ba-138 at 25 keV. Direct and semi-direct
capture estimated; 7 levels up to 1.99 MeV adopted for the inelastic
scattering. MT=103 and MT=107 normalized to recommended by Forrest
(1986) values at 14.5 MeV; elastic calculated as (MT1 -- sum of partial
cross sections); Legendre coefficients from CASTHY to get anisotropic
angular distribution for MF=4, MT=2, 51-57 in CM system. Energy
distributions in MF=5 calculated with PEGASUS. MT=1, 2, 4, 16, 17, 22,
28, 32, 33, 51-57, 91, 102, 103, 104, 105, 107.

-   MT=1

Since no experimental data are available for the total cross section of
Ba-140, the comparison with experimental (EXFOR) cross sections for
natural Ba shows that all evaluations are reasonable. Especially well
fitted look ***JEF-2*** (0.1-20 MeV) and ***JENDL-3*** (0.4-20 MeV) for
their adjustment to available experimental data for natural Ba, except
the recent data of Koehler (1996). Merging the URR and fast energy
region in ***JEF-2*** is not very smooth because of the small skip of
0.1 b at 100 keV. The discrepancies between ***JEF-2*** and
***JENDL-3*** are 2 b at 100 keV (where ***JEF-2*** is preferable for it
merges the recommended resonance evaluation) and -0.4 b at \~2 MeV
(which is the biggest discrepancy above 0.4 MeV).

-   MT=2

***ENDF/B-VI:*** Too high in the region 2 -- 20 MeV, since not only
(n,2n) reaction is neglected, but also (n,n') is practically negligible
(30 times less than ***JEF-2*** and ***JENDL-3***).

***JEF-2*** and ***JENDL-3*** are almost the same except around 100 keV
where ***JEF-2*** is preferable for it merges the recommended resonance
evaluation, in spite of the small skip of 0.1 b that appears at the
boundary. The small unreasonable peak at 6.5 MeV, in ***JENDL-3***
curve, arises since the sharp slope of the (n,inl)-decrease starts at 6
MeV while the (n,2n)-rise starts at 6.5 MeV.

 

-   MT=4

***ENDF/B-VI:*** The maximum of the curve (70 mb at 3-5 MeV) is too low
compared to the 2 b-values of JEF-2 and JENDL-3. In addition, the trend
of (n,n\') cross section is unrealistic for neglecting (n,2n) reaction.

***JEF-2*** and ***JENDL-3:*** Close and reasonable in shape. The
difference of 0.4 b at 2 MeV leads to the 0.4 b-discrepancy in MT=1.

-   MT=16

***ENDF/B-VI:*** No (n,2n) in File 3, assumed to be zero.

***JEF-2*** and ***JENDL-3:*** Close and reasonable in shape.

-   MT=102

All three evaluations are below 10 mb. ***JEF-2*** and ***JENDL-3*** are
very close above 7 MeV. Preference should be given to ***JEF-2*** for it
merges the recommended (n,g) resonance evaluation at the boundary of 100
keV.

-   MT=103

***ENDF/B-VI:*** No (n,p) in File 3, assumed to be zero.

***JEF-2*** and ***JENDL-3*** are reasonable as can be seen from
comparison with experimental results for Ba-138,137,136 (n,α) reactions.
In addition both evaluations are very close up to 20 MeV and almost the
same at 14.7 MeV.

-   MT=107

***ENDF/B-VI:*** No (n,α) in File 3, assumed to be zero.

***JEF-2*** and ***JENDL-3*** are reasonable as can be seen from
comparison with experimental results for Ba138(n,α) reaction. In
addition they are almost the same at 14.7 MeV.

**Recommendation/Conclusion**: ***JEF-2*** and ***JENDL-3*** recommended
in the fast energy region 100 keV - 20 MeV; ***JEF-2*** seems more
reasonable than ***JENDL-3*** for MT=1, 2, 102, since besides being very
close to ***JENDL-3*** at high energies, it merges the recommended
resonance evaluation at the boundary of 100 keV. Both ***JEF-2*** and
***JENDL-3*** can be recommended for MT=4, 16, 103, 107.

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

**[Table 1]{.underline}.** Summary for Resolved and Unresolved Resonance
Region: Ba-140

+---------+---+---------+-------+----+-------------------------------+
| Library | Y | First   | RRR   | U  | Remarks                       |
|         | e | Authors |       | RR |                               |
|         | a |         |       |    |                               |
|         | r |         |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| EN      | 1 | S       | 1     | \- | No resonance parameters;      |
| DF/B-VI | 9 | chenter | 0.683 |    | pointwise data; scattering    |
|         | 7 | (HEDL)  | keV   |    | radius 6.26 fm, constant      |
|         | 4 | Schm    |       |    | (4.93 b) form assumed for     |
|         |   | ittroth | Poin  |    | elastic cross section; 1/v    |
|         |   | (HEDL)  | twise |    | form assumed for capture so   |
|         |   |         |       |    | that to reproduce the thermal |
|         |   |         |       |    | capture cross section from    |
|         |   |         |       |    | BNL-325 (1973). Computed      |
|         |   |         |       |    | resonance integral of 12.74 b |
|         |   |         |       |    | agrees (to within 1 sigma)    |
|         |   |         |       |    | with BNL-325.                 |
+---------+---+---------+-------+----+-------------------------------+
| JEF-2   | 1 | Gru     | 23    | 1  | MLBW representation of 8      |
|         | 9 | ppelaar | keV\  | 00 | artificial s-wave resonances  |
|         | 8 | (ECN)\  | \     | k  | with parameters randomly      |
|         | 2 | M       | MLBW  | eV | generated by the PSEUDO code; |
|         |   | enapace |       |    | scattering radius 6.23 fm.    |
|         |   | (ENEA)  |       |    |                               |
|         |   |         |       |    | URR: Energy independent       |
|         |   |         |       |    | parameters; scattering radius |
|         |   |         |       |    | 6.23 fm.                      |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 13.7 b.                       |
+---------+---+---------+-------+----+-------------------------------+
| JENDL-3 | 1 | JNDC FP | 14    | 1  | New evaluation.\              |
|         | 9 | Nuclear | keV\  | 00 | No resolved resonance         |
|         | 9 | Data    | \     | k  | parameters, 1/v and constant  |
|         | 0 | Working | Point | eV | (3.3 b) form assumed for      |
|         |   | Group\  | wise\ |    | capture and elastic cross     |
|         |   |         |       |    | sections respectively;        |
|         |   |         |       |    | thermal capture cross section |
|         |   |         |       |    | taken from BNL-325 (1981).    |
|         |   |         |       |    |                               |
|         |   |         |       |    | URR: S0, S1 and S2 strength   |
|         |   |         |       |    | functions calculated with     |
|         |   |         |       |    | CASTHY; the effective         |
|         |   |         |       |    | scattering radius of 5.3 fm   |
|         |   |         |       |    | determined from fitting to    |
|         |   |         |       |    | the calculated total cross    |
|         |   |         |       |    | section at 100 keV. Level     |
|         |   |         |       |    | spacing determined to         |
|         |   |         |       |    | reproduce the capture cross   |
|         |   |         |       |    | section from CASTHY. Average  |
|         |   |         |       |    | radiative width of 75 meV     |
|         |   |         |       |    | based on systematics for      |
|         |   |         |       |    | neighbouring nuclides.        |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 0.728 b.                      |
+---------+---+---------+-------+----+-------------------------------+

**[Table 2]{.underline}.** Thermal Cross Sections for Ba-40

  -------------------------------- ------------- ------------- -----------
  Library / Experiment             Total         Capture       Elastic

  ENDF/B-VI                        6.55 b        1.60 b        4.95 b

  JEF-2                            3.49 b        1.59 b        1.90 b

  JENDL-3                          4.92 b        1.60 b        3.32 b

  Halperin (1967)                                1.57(30) b    
  -------------------------------- ------------- ------------- -----------