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

**34-Se-82 Review**

I. Sirakov, INRNE, February 20, 2004

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

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

***JEF-2:*** Year of origin 1982, data taken from ENDF/B-V, last
revision 1989

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

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

***ENDF/B-VI, JEF-2:*** Resolved resonance region up to 31.118 keV with
resonance parameters from BNL-325 (1973) based on Good experiment
(1966); SLBW representation for 4 s-wave resonances (at 6.58, 13.8,
22.7, and 26.55 keV) with neutron widths of the order of 100 eV; a 1/v
component added to give the thermal capture cross section from BNL-325
(1973); scattering radius 5.24 fm. No unresolved resonance region (Table
1). Computed resonance integral 93 mb. ***JEF-2*** changed the flag to
the MLBW representation.

***JENDL-3*:** Resolved resonance region up to 18 keV with resonance
parameters based on experimental resonance energies by Browne and Berman
(1982) and on reduced s-wave neutron widths from BNL-325 (1981); MLBW
representation for 7 s-wave resonances (at 0.579, 1.154, 3.63, 7.105,
9.508, 13.54, and 16.5 keV) and a bound resonance level at -120 eV;
Reduced neutron widths normalized so as to reproduce the experimental
thermal scattering length (Koester, 1980). Average radiation width of
46.7 meV determined for all resonances so as to reproduce the thermal
capture cross section from BNL-325 (Table 2). Scattering radius of 7.5
fm from BNL-325. Unresolved region up to 100 keV; S0 and S1 strength
functions based on Mughabghab's compilation and systematics; S2
calculated with CASTHY; radiation width of 190 meV determined from a
systematic trend of measured values for neighboring nuclides. Level
spacing determined to reproduce the capture cross section from CASTHY;
the effective scattering radius of 7.07 fm fitted to the calculated MT=1
at 100 keV. Computed resonance integral 799 mb.

**Note on the resonance region** (up to 100 keV for JENDL)**:**

***ENDF/B-VI*** evaluation does not show the negative elastic and total
cross sections in the derived files (T=0K, T=300K) since it changes the
MT=2 negative output to zero through an 'optionally' chosen procedure
embedded in the preprocessing codes. Without this change, 2 ranges of
negative elastic cross sections (up to -0.53 b) come out and result in
negative total cross sections throughout the region 6200-6407 eV, with
lowest values of about -0.5 b. The arbitrary procedure of changing the
negative output, followed by recalculation of the imbalanced total cross
section, is equivalent to and could have rigorously been organized as a
background in MF=3, MT=2 (and MT=1) of the basic evaluated file.

The capture cross section from about hundred eV to several hundred keV
has a predominant contribution to the one-group capture cross section
(1E-5 eV - 20 MeV) over fast-reactor weighting spectrum
(<http://www.nndc.bnl.gov/sg21/nucl/acs/accs.htm>) and accounts for the
one-group values of ***ENDF/B-VI*** (9.43 mb), ***JEF-2*** (9.42 mb) and
***JENDL-3*** (28.64 mb). The higher value of ***JENDL-3*** is related
to its higher capture cross section from 18 keV to \~1 MeV and, to some
extent, to the higher contribution of the resolved resonances.

The factor-of-nine higher value of the capture resonance integral for
***JENDL-3*** (0.799 b) compared to ***ENDF/B-VI/JEF-2*** (0.093 b) is
mainly due to the dominant contribution of the ***JENDL-3*** resolved
resonances at 579.4 and 1154 eV, not available in
***ENDF/B-VI/***(***JEF-2***).

Disadvantage of ***ENDF/B-VI***(***JEF-2***) is the lack of unresolved
resonance region.

**Experimental data** -- ***ENDF/B-VI/JEF-2*** evaluation is based on
Good experiment (1966, ORNL data), until ***JENDL-3*** takes into
account the resonance energies from the experiment of Browne and Berman
(1982), who did not observed the previously assigned resonances by Good
at 6.58, 22.7, and 26.55 keV and declared them as not belonging to
Se-82.

Since Browne and Berman carried out capture measurements and did not
report neutron widths for the resonances they observed, alternative
explanation (suggested, to some extent, by Mughabghab) could be given
for the different observations in the keV region. The capture
measurement could miss the observed by Good broad s-wave resonances
(~n~\~100 eV, \~0.1 eV) of low maximum capture cross section
4k^-2^g(J)/~n~ ≈ 4k^-2^.1E-3 and detect only sharp p-wave resonances
(~n~ from \~0.01 to \~1 eV, \~0.1 eV), of at least 100 times larger
maximum capture cross section 4k^-2^g(J)~n~/(~n~+≈ 4k^-2^.1E-1, which
subsequently were assigned s-wave properties. It is to be hoped that
such a hypothesis has been considered and excluded by the
experimentalists and evaluators.

The recommendation for the thermal capture cross section of 43(3) mb
(Mughabghab 2003,
[INDC(NDS)-440](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf))
fully agrees with the identical values of all evaluations (Table 2).

No resonance integral data are available in EXFOR. The discrepancy
between the RI recommendation of 30(4) mb (Mughabghab 2003,
[INDC(NDS)-440](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf)) and
the computed RI values of ***JENDL-3*** (799 mb) and
***ENDF/B-VI***(***JEF-2***) (93 mb) should be explained. The misprint
'b' instead of 'mb' in the recommended value was confirmed by
Mughabghab. It was calculated, for the purpose of this review, that the
RR region of ***JENDL-3*** contributes 86% to the resonance capture
integral and the RR region of ***ENDF/B-VI***(***JEF-2***) 53%. The
inconsistency between the average capture width of 190 meV in the
unresolved and of 46.7 meV in the resolved region of ***JENDL-3***,
should also be noted.

The Chaubey-1966
([EXFOR30079](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=30079&DatType=H&RetType=byAccNum&ReDo=N)
001) partial capture cross section data of 45(15) mb at 24 keV for
production of a meta-stable state (I=1/2^-^) fully agree with the
unresolved capture cross section of ***JENDL-3*** (46.5 mb), if assumed
that the ground-state (I=9/2^+^) production is not larger than 15 mb.

As the elastic scattering is concerned, Koester's 1980 data
([EXFOR21653](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=21653&DatType=H&RetType=byAccNum&ReDo=N)
009) for a bound coherent scattering length of 6.34(8) fm give a
zero-energy scattering cross section, for the free atom, of 5.00(13) b.
This value is in full agreement with the ***JENDL-3*** evaluation of
5.00 b for the zero-energy scattering cross section, in contrast to the
***ENDF/B-VI*** and ***JEF-2*** values of 2.88 and 2.90 b, which are too
low and lead to rather low elastic and total cross sections in the
thermal and low-energy regions. The resolved
***ENDF/B-VI***(***JEF-2***) elastic cross section between the
resonances is also affected by the low effective scattering radius.

***JENDL-3*** total cross section in the URR shows a reasonable trend of
agreement with the total cross section data of Muselyan (1983, 1987),
available in the fast energy region above 265 keV, and this is also an
argument for a reasonable unresolved elastic cross section.

**Recommendation/Conclusion**: ***JENDL-3*** is recommended in its
resonance region up to 100 keV. ***JENDL-3*** agrees not only with the
suggested thermal capture and the experimental thermal scattering data
in the RR region, but also with the experimental capture data of Chaubey
(1966) in the URR.

***ENDF/B-VI*** and ***JEF-2*** have unacceptably low elastic and total
cross sections in the region up to several keV. In addition,
***ENDF/B-VI*** shows negative elastic and total cross sections unless
an optional procedure for changing the negative output is used in the
preprocessing codes.

The RI recommendation of Mughabghab 2003
([INDC(NDS)-440](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf)),
infers a RI overestimation of a factor of 30 toward the ***JENDL-3***
and of a factor of 3 toward the ***ENDF/B-VI***(***JEF-2***), and this
difference should be explained.

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

-   Methodology

***ENDF/B-VI, JEF-2:*** Spherical OM (Moldauer potential) for MT=1;
capture from NCAP code; inelastic cross sections (MF=3, MT=4, 51-53, 91)
from COMNUC-3 code, no preeq corrections; 3 discrete levels (at 0.655,
1.49, and 1.75 MeV) adopted for the inelastic scattering; elastic cross
section obtained as (MT1-MT102-MT4); isotropic angular distribution
assumed for MF=4, MT=2 in CM system. Account taken of MT=1, 2, 4, 51-53,
91, 102. ***JEF-2*** includes charge particle production data (MT=103,
104, 105, 106, 107, 111) from REAC-ECN-4 Library.

***JENDL-3:*** Spherical OM and statistical model code CASTHY for MT=1,
4, 51-56, 91, 102 by taking into account competing reactions MT=16, 17,
22, 28, 103, 104, 105, 107 which were calculated with the preeq and
multi-step evaporation model code PEGASUS. The gamma-ray strength
function (5.46E-5) adjusted to reproduce a capture cross section of 45
mb at 25 keV. Direct and semi-direct capture estimated; 6 discrete
levels (from 654.8 keV to 2.894 MeV) adopted for the inelastic
scattering. MT=16 normalized to measured by Frehaut (1980) and MT=103 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 and
MT=51-56 in CM system. MT=1, 2, 4, 16, 17, 22, 28, 51-56, 91, 102, 103,
104, 105, 107.

-   MT=1

In comparison with ***ENDF/B-VI**(**JEF-2**)*, ***JENDL-3*** shows a
slightly better fit to the rather scattered experimental data (Muselyan
1983, 1987), available in the region 265 keV - 2.59 MeV. A drawback of
***JENDL-3***, to some extent, is the non-smooth merging between the UR
and the continuous region at 100 keV. ***ENDF/B-VI**(**JEF-2**)* do not
merge into the recommended URR. The evaluations are almost close with
maximum differences of 0.8 b at 300 keV and 0.55 b at 8 MeV.

-   MT=2

***ENDF/B-VI*** and ***JEF-2*** are in a better agreement, compared to
***JENDL-3***, with the experimental data available from 1.18 MeV to 10
MeV (Konobeevskij-1984,
[EXFOR40845](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40845&DatType=H&RetType=byAccNum&ReDo=N)
01; Korzh-1983,
[EXFOR40859](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40859&DatType=H&RetType=byAccNum&ReDo=N)
005; and Lachkar-1976
[EXFOR20426](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=20426&DatType=H&RetType=byAccNum&ReDo=N)
020) and almost merge into the recommended ***JENDL-3*** at 100 keV.

Similarly to MT=1, ***JENDL-3*** does not merge smoothly into the upper
boundary of the URR (100 keV) and does not follow the trend of the URR,
which hinders a better agreement with the experimental elastic
scattering data. In addition, the small peaks (of \~0.1 b) at 9.4 and 12
MeV are not reasonable on the ***JENDL-3*** curve. They appear since the
beginning (9 MeV) and end (12 MeV) of the steep (n,inl)-decrease are not
consistent with the beginning (9.4 MeV) and end (11 MeV) of the sharp
(n,2n)-rise.

The evaluations are almost close with maximum differences of 0.8 b at
300 keV and 0.6 b at 20 MeV.

-   MT=4

***ENDF/B-VI**(**JEF-2**)*: Unrealistic trend at high energies; (n,2n)
reaction neglected.

***JENDL-3*** shows a reasonable shape and higher than
***ENDF/B-VI**(**JEF-2**)* values up to \~10 MeV. Although closer to the
experimental data of Konobeevskij-1984 at 1.18 MeV
([EXFOR40845](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40845&DatType=H&RetType=byAccNum&ReDo=N)
017), ***JENDL-3*** is 46% lower the measured values. The additional
***JENDL-3*** problem that concerns MT4 and MT2, was described above
(see MT=2). The (n,2n) threshold is 9.4 MeV.

-   MT=16

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

***JENDL-3***: Shows a reasonable shape and a good agreement with the
experimental data of Frehaut, 1980
([EXFOR20416](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=20416&DatType=H&RetType=byAccNum&ReDo=N)
010) and Hasan, 1972
([EXFOR30041](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=30041&DatType=H&RetType=byAccNum&ReDo=N)
004) available from 9.93 to 14.8 MeV. The Frehaut's (1980) data are
overestimated in the region 10-12.5 MeV with a maximum discrepancy of
0.2 b at 10.9 MeV. The (n,3n) threshold is 16.2 MeV.

-   MT=102

***JENDL-3*** disregards Trofimov-1987
([EXFOR40975](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40975&DatType=H&RetType=byAccNum&ReDo=N)
003,
[EXFOR41001](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=41001&DatType=H&RetType=byAccNum&ReDo=N)
006) experimental capture cross section data at 1 and 2 MeV, probably
for being below the partial capture cross section data for Se-83
ground-state production (Herman 1981,
[EXFOR30567](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=30567&DatType=H&RetType=byAccNum&ReDo=N)
004). With the value of 0.98 mb, ***JENDL-3*** is close above the
similar (Perkin-1958) partial capture cross section measurement of
0.65(20) mb at 14.5 MeV
([EXFOR21438](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=21438&DatType=H&RetType=byAccNum&ReDo=N)
012).

***ENDF/B-VI**(**JEF-2**)* is several times smaller than ***JENDL-3***
up to 4 MeV, but still above the Herman's (1981) data.
***ENDF/B-VI**(**JEF-2**)* does not merge into the recommended
unresolved region at 100 keV. In addition, the steep descent that starts
at 364 keV is not reasonable on the ***ENDF/B-VI**(**JEF-2**)* curve,
since it is supposed to start at the inelastic scattering threshold of
663 keV (see ***JENDL-3*** curve).

-   MT=103

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

***JENDL-3*** and ***JEF-2*** show reasonable shapes shifted in a way
that both libraries present the value of 2.4 mb at 14.5 MeV. The
evaluations, however, differ substantially (10 times) at 20 MeV being
12.2 mb and 1.26 mb respectively.

-   MT=107

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

***JEF-2*** and ***JENDL-3*** show reasonable shapes but quite different
values around 14 MeV. According to \[1\], the deduced 82Se(n,) cross
section, on the basis of \[2\] and \[3\], is 1.2(3) mb at 14.7 MeV. This
value gives preference to ***JEF-2*** (0.87 mb) in contrast to
***JENDL-3*** (0.30 mb).

**Recommendation/Conclusion** in the fast energy region 100 keV - 20
MeV: A reasonable recommendation that practically retains the cross
section balance, could be ***JENDL-3*** for all cross sections except
MT=107 and ***JEF-2*** for MT=107.

More precisely, ***JENDL-3*** is preferable for MT=1, 4, 16, and 102, in
spite of some shortcomings described above. ***ENDF/B-VI*** and
***JEF-2*** perform best for MT=2, in the region 0.4-10 MeV; ***JEF-2***
is the best for MT=107. Both ***JENDL-3*** and ***JEF-2*** should be
taken into account for MT=103.

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

**[Table 1]{.underline}.** Summary for Resolved and Unresolved Resonance
Region: Se-82

+---------+---+---------+-------+----+-------------------------------+
| Library | Y | First   | RRR   | U  | Remarks                       |
|         | e | Authors |       | RR |                               |
|         | a |         |       |    |                               |
|         | r |         |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| EN      | 1 | S       | 3     | \- | RR parameters from BNL-325    |
| DF/B-VI | 9 | chenter | 1.118 |    | (1973) based on Good          |
|         | 7 | (HEDL), | keV\  |    | experiment (1966); Four       |
|         | 4 | Schm    | \     |    | s-wave resonances (at 6.58,   |
|         |   | ittroth | SLBW  |    | 13.8, 22.7, and 26.55 keV)    |
|         |   | (HEDL)  |       |    | with neutron widths of the    |
|         |   |         |       |    | order of 100 eV; a 1/v        |
|         |   |         |       |    | component added to give the   |
|         |   |         |       |    | thermal capture cross section |
|         |   |         |       |    | from BNL-325 (1973);          |
|         |   |         |       |    | scattering radius 5.24 fm.    |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 93 mb.                        |
+---------+---+---------+-------+----+-------------------------------+
| JEF-2   | 1 | Sci     | 3     | \- | RR parameters taken from      |
|         | 9 | entific | 1.118 |    | ENDF/B-V. Flag changed to     |
|         | 8 |         | keV\  |    | MLBW.                         |
|         | 2 | Co-ord  | \     |    |                               |
|         |   | ination | MLBW  |    |                               |
|         |   |         |       |    |                               |
|         |   | Group   |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| JENDL-3 | 1 | JNDC FP | 18    | 1  | RR parameters based on        |
|         | 9 | Nuclear | keV\  | 00 | experimental resonance        |
|         | 9 | Data    | \     | k  | energies by Browne and Berman |
|         | 0 | Working | MLBW  | eV | (1982) and on reduced s-wave  |
|         |   | Group   |       |    | neutron widths from BNL-325   |
|         |   |         |       |    | (1981); 7 s-wave resonances   |
|         |   |         |       |    | (at 0.579, 1.154, 3.63,       |
|         |   |         |       |    | 7.105, 9.508, 13.54, and 16.5 |
|         |   |         |       |    | keV) and a bound resonance    |
|         |   |         |       |    | level at -120 eV; Reduced     |
|         |   |         |       |    | neutron widths normalized so  |
|         |   |         |       |    | as to reproduce the           |
|         |   |         |       |    | experimental thermal          |
|         |   |         |       |    | scattering length (Koester,   |
|         |   |         |       |    | 1980). Average radiation      |
|         |   |         |       |    | width of 46.7 meV determined  |
|         |   |         |       |    | for all resonances so as to   |
|         |   |         |       |    | reproduce the thermal capture |
|         |   |         |       |    | cross section from BNL-325    |
|         |   |         |       |    | (Table 2). Scattering radius  |
|         |   |         |       |    | of 7.5 fm from BNL-325.       |
|         |   |         |       |    |                               |
|         |   |         |       |    | URR: S0 and S1 strength       |
|         |   |         |       |    | functions based on            |
|         |   |         |       |    | Mughabghab's compilation and  |
|         |   |         |       |    | systematics; S2 calculated    |
|         |   |         |       |    | with CASTHY; Radiation width  |
|         |   |         |       |    | of 190 meV determined from a  |
|         |   |         |       |    | systematic trend of measured  |
|         |   |         |       |    | values for neighboring        |
|         |   |         |       |    | nuclides. Level spacing       |
|         |   |         |       |    | determined to reproduce the   |
|         |   |         |       |    | capture cross section from    |
|         |   |         |       |    | CASTHY; the effective         |
|         |   |         |       |    | scattering radius of 7.07 fm  |
|         |   |         |       |    | fitted to the calculated MT=1 |
|         |   |         |       |    | at 100 keV.                   |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 799 mb.                       |
+---------+---+---------+-------+----+-------------------------------+

**[Table 2]{.underline}.** Thermal (2200 m/s) Cross Sections for Se-82

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

  ENDF/B-VI                                                              2.927 b       45 mb          2.882 b

  JEF-2                                                                  2.943 b       45 mb          2.898 b

  JENDL-3                                                                5.044 b       44.2 mb        5.000 b

  BNL-325 (1981)                                                                       43(3) mb       

  S.F.Mughabghab,                                                                      43(3) mb       
  [INDC(NDS)-424](http://www-nds.iaea.or.at/reports/indc-nds-424.pdf),                                
  p.73 (2001)                                                                                         

  S.F.Mughabghab,                                                                      43(3) mb       
  [INDC(NDS)-440,](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf)                                
  p.11 (2003)                                                                                         
  ---------------------------------------------------------------------- ------------- -------------- ----------

**References:**

**1.** A.Majdeddin et al., INDC(HUN)-031, Distr. L, IAEA (1997).

**2.** R.A.Forrest, AERE-R 12419, Harwell Laboratory, (1986).

**3.** J.Csikai et al., Fusion Engineering and Design **37**, 65 (1997).