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

**34-Se-80 Review**

I. Sirakov, INRNE, January 23, 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, revisions in 1993 (JENDL-3.2) and
2002 (trivial) when transformed to JENDL-3.3

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

***ENDF/B-VI, JEF-2:*** Resolved resonance region up to 6.707 keV with
resonance parameters from BNL-325 (1973); SLBW representation for five
s-wave and two p-wave resonances; artificial value of J=L=1 given to the
unknown spins J from the p-wave; a 1/v component added to give the
thermal capture cross section of BNL-325 (1973); scattering radius 5.197
fm. No unresolved resonance region (Table 1). Computed resonance
integral 1.08 b. ***JEF-2*** changed the flag to the MLBW representation
and randomly assigned the spin J for L=1 by the code RNDSPIN.

***JENDL-3*:** Resolved resonance region up to 10 keV with resonance
parameters based on BNL-325 (1981); MLBW representation for 12 s-wave
resonances (7 of them being background or out of range) and 4 p-wave
resonances; a bound resonance level at -3.69 keV added to reproduce the
thermal capture and scattering cross sections according to BNL-325
(Table 2); unknown spins J tentatively assigned by the random number
method. Scattering radius 7.5 fm. 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 230 meV from
Mughabghab's compilation. Level spacing determined to reproduce the
capture cross section from CASTHY; the effective scattering radius of
6.99 fm fitted to the calculated MT=1 at 100 keV. Computed resonance
integral 0.976 b.

**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, 3 ranges of
negative elastic cross sections (up to -1.74 b) come out and result in
negative total cross sections throughout the regions 595-1467 eV,
1473-1681 eV and 3796-4037 eV with lowest values of about -1.7 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*** (57.7 mb), ***JEF-2*** (57.7 mb) and
***JENDL-3*** (41.7 mb). The higher value of
***ENDF/B-VI/***(***JEF-2***) is related to their higher capture cross
section from \~ 10 keV to \~1 MeV.

The 10%-larger capture resonance integral for ***ENDF/B-VI/JEF-2***
(1.08 b) compared to ***JENDL-3*** (0.976 b) is mainly due to its higher
capture cross section above 6.7 keV, which contributes more than the
***JENDL-3*** p-wave resonances at 6120 eV and 8150 eV.

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

**Experimental data** -- The recommendation for the thermal capture
cross section of 0.61(5) b (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).
Also, the rather scattered capture cross section data of Walter, 1984
([EXFOR22037](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22037&DatType=H&RetType=byAccNum&ReDo=N)
006) above 3 keV, generally agree with all evaluations. The capture
cross section data of Tolstikov 1968
([EXFOR40007](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22037&DatType=H&RetType=byAccNum&ReDo=N)
005) above 10 keV, however, are only in favor of ***JENDL-3***.

The resonance integral data of Nakamura 1998
([EXFOR22632](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22632&DatType=H&RetType=byAccNum&ReDo=N)
005) do not contradict the library values. The other RI data, however,
like those of Ricabarra 1968,
([EXFOR30129](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=30129&DatType=H&RetType=byAccNum&ReDo=N)
004), and Heft 1978,
([EXFOR12866](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=12866&DatType=H&RetType=byAccNum&ReDo=N)
051, 053), with values of 1.43(16) b and 1.80(11) b respectively as well
as the RI recommendation of 1.6(2) b (Mughabghab 2003,
[INDC(NDS)-440](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf))
infer substantial underestimation (\~40%) in the evaluated RI values and
are not in favor of the libraries.

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)
008) for a bound coherent scattering length of 7.48(3) fm gives a
zero-energy scattering cross section, for the free atom, of 6.95(5) b.
This value is in full agreement with the ***JENDL-3*** evaluation of
6.95 b for the zero-energy scattering cross section, in contrast to the
***ENDF/B-VI*** and ***JEF-2*** values of 0.675 b and 1.064 b, which are
too low and lead to rather low elastic and total cross sections in the
thermal region and in the region up to \~1 keV. The resolved
***ENDF/B-VI***(***JEF-2***) elastic cross section between the
resonances is also affected by the low effective scattering radius.

**Recommendation/Conclusion**: ***JENDL-3*** is recommended up to 100
keV for its better agreement with the experimental data for capture and
elastic cross sections in the thermal region and in the regions below 1
and above 10 keV.

***ENDF/B-VI*** and ***JEF-2*** have unacceptably low elastic and total
cross sections in the region up to 1 keV and do not show agreement with
the capture data above 10 keV (Tolstikov 1968,
[EXFOR40007](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22037&DatType=H&RetType=byAccNum&ReDo=N)
005). In addition, ***ENDF/B-VI*** presents negative elastic and total
cross sections unless an optional procedure for changing the negative
output is used in the preprocessing codes.

Some RI data, as well as the RI recommendation of Mughabghab 2003
([INDC(NDS)-440](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf)),
show a discrepancy of \~40% with the RI values of all libraries and
imply a substantial underestimation of the evaluated capture cross
sections in the resolved resonance region (1-10 keV).

######## **[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, 51-58, 91)
from COMNUC-3 code, no preeq corrections; 8 discrete levels (from 666
keV to 1.96 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, 51-58,
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, 51-79, 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 (4.66E-5) adjusted at 100 keV to the measured capture cross
section (Walter 1984). Direct and semi-direct capture estimated; 29
discrete levels (from 666 keV to 3.35 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 and MT=51-79 in CM system. MT=1, 2,
4, 16, 17, 22, 28, 51-79, 91, 102, 103, 104, 105, 107.

-   MT=1

***JENDL-3*** presents a worse than ***ENDF/B-VI**(**JEF-2**)* fit to
the rather scattered experimental data (Muselyan 1983, 1987) between 250
and 650 keV. ***JENDL-3*** does not merge smoothly into the upper
boundary of the URR (100 keV) and does not follow the trend of the URR.
It can be noticed that, around 200 keV, ***ENDF/B-VI**(**JEF-2**)*
follows the trend of the recommended URR.

***JENDL-3***, however, shows better agreement with the experimental
data (Muselyan 1983, 1987) in the region 750 keV - 2.5 MeV. The largest
discrepancies between ***JENDL-3*** and ***ENDF/B-VI**(**JEF-2**)* are 1
b at 300 keV and 0.55 b at 8 MeV.

-   MT=2

***ENDF/B-VI*** and ***JEF-2*** show a better agreement, compared to
***JENDL-3***, with the experimental data available from 1.2 MeV to 8
MeV (Lachkar-1976,
[EXFOR20426](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=20426&DatType=H&RetType=byAccNum&ReDo=N)
014; Gorlov-1964,
[EXFOR40221](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40221&DatType=H&RetType=byAccNum&ReDo=N)
015; Konobeevskij-1984,
[EXFOR40845](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40845&DatType=H&RetType=byAccNum&ReDo=N)
014; and Korzh-1983,
[EXFOR40859](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40859&DatType=H&RetType=byAccNum&ReDo=N)
004). It should again be noticed that, around 200-300 keV,
***ENDF/B-VI**(**JEF-2**)* follows the trend of the recommended URR.

Following 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.

***ENDF/B-VI*** and ***JEF-2*** are, generally, not as smooth as
***JENDL-3***. The biggest discrepancies between ***JENDL-3*** and
***ENDF/B-VI**(**JEF-2**)* are 1.1 b at 300 keV, 0.55 b at 8 MeV and
-0.65 b at 20 MeV.

-   MT=4

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

***JENDL-3*** is higher than ***ENDF/B-VI**(**JEF-2**)* up to 10.3 MeV.
Although closer to the experimental data of Konobeevskij 1984 at 1.19
MeV
([EXFOR40845](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=40845&DatType=H&RetType=byAccNum&ReDo=N)
015), ***JENDL-3*** is 35% lower the measured values. The (n,2n)
threshold is 10 MeV

-   MT=16

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

***JENDL-3***: Shows a reasonable shape, being systematically higher but
close to the experimental data of Frehaut, 1980
([EXFOR20416](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=20416&DatType=H&RetType=byAccNum&ReDo=N)
009). The maximum difference is 0.22 b at 12 MeV. The (n,3n) threshold
is 17.1 MeV.

-   MT=102

Compared to ***ENDF/B-VI**(**JEF-2**)*, ***JENDL-3*** is in better
agreement with the experimental data of Walter, 1984
([EXFOR22037](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22037&DatType=H&RetType=byAccNum&ReDo=N)
006) and Tolstikov 1968
([EXFOR40007](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=22037&DatType=H&RetType=byAccNum&ReDo=N)
005) in the region 100 keV -- 3.1 MeV. Above 300 keV, it slightly
overestimates the measured values.

***ENDF/B-VI*** and ***JEF-2*** are systematically high compared to the
experimental data and ***JENDL-3***. In addition, the descent that
starts at 370 keV is not reasonable on the ***ENDF/B-VI**(**JEF-2**)*
curve, since it is supposed to start at the inelastic scattering
threshold of 674 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 and full agreement
with experimental data of Minetti, 1967
([EXFOR21107](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=21107&DatType=H&RetType=byAccNum&ReDo=N)
021) at 14.7 MeV, but differ substantially (9 times) at 20 MeV being 41
mb and 4.56 mb respectively.

-   MT=107

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

***JENDL-3*** and ***JEF-2*** show reasonable shapes among the
inconsistent experimental data found between 2.6(3) mb (Hoang 1989,
[EXFOR32108](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=32108&DatType=H&RetType=byAccNum&ReDo=N)
007) and 32(4) mb (Casanova 1976,
[EXFOR20748](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=20748&DatType=H&RetType=byAccNum&ReDo=N)
032) at around 14 MeV. Differ substantially at 20 MeV being 43 mb and
9.6 mb respectively.

**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, along
with ***JEF-2*** for MT=103 and 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=1 in the region 250-650 keV, and for
MT=2 in the region 0.25-10 MeV; Both ***JENDL-3*** and ***JEF-2***
should be taken into account for MT=103 and 107.

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

**[Table 1]{.underline}.** Summary for Resolved and Unresolved Resonance
Region: Se-80

+---------+---+---------+-------+----+-------------------------------+
| Library | Y | First   | RRR   | U  | Remarks                       |
|         | e | Authors |       | RR |                               |
|         | a |         |       |    |                               |
|         | r |         |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| EN      | 1 | S       | 6.707 | \- | RR parameters from BNL-325    |
| DF/B-VI | 9 | chenter | keV\  |    | (1973); Five s-wave and two   |
|         | 7 | (HEDL), | \     |    | p-wave resonances; artificial |
|         | 4 | Schm    | SLBW  |    | value of J=L=1 given to the   |
|         |   | ittroth |       |    | unknown spins J from the      |
|         |   | (HEDL)  |       |    | p-wave; a 1/v component added |
|         |   |         |       |    | to give the thermal capture   |
|         |   |         |       |    | cross section of BNL-325      |
|         |   |         |       |    | (1973); scattering radius     |
|         |   |         |       |    | 5.197 fm.                     |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 1.08 b.                       |
+---------+---+---------+-------+----+-------------------------------+
| JEF-2   | 1 | Sci     | 6.707 | \- | RR parameters taken from      |
|         | 9 | entific | keV\  |    | ENDF/B-V. Flag changed to     |
|         | 8 |         | \     |    | MLBW. Spin J, for L=1,        |
|         | 2 | Co-ord  | MLBW  |    | assigned randomly by the code |
|         |   | ination |       |    | RNDSPIN.                      |
|         |   |         |       |    |                               |
|         |   | Group   |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| JENDL-3 | 1 | JNDC FP | 10    | 1  | RR parameters based on        |
|         | 9 | Nuclear | keV\  | 00 | BNL-325 (1981); 12 s-wave     |
|         | 9 | Data    | \     | k  | resonances (7 of them being   |
|         | 0 | Working | MLBW  | eV | background or out of range)   |
|         |   | Group   |       |    | and 4 p-wave resonances; a    |
|         |   |         |       |    | bound resonance level at      |
|         |   |         |       |    | -3.69 keV added to reproduce  |
|         |   |         |       |    | the thermal capture and       |
|         |   |         |       |    | scattering cross sections     |
|         |   |         |       |    | according to BNL-325 (Table   |
|         |   |         |       |    | 2). Unknown spins J           |
|         |   |         |       |    | tentatively assigned by the   |
|         |   |         |       |    | random number method;         |
|         |   |         |       |    | Scattering radius 7.5 fm.     |
|         |   |         |       |    |                               |
|         |   |         |       |    | URR: S0 and S1 strength       |
|         |   |         |       |    | functions based on            |
|         |   |         |       |    | Mughabghab's compilation and  |
|         |   |         |       |    | systematics; S2 calculated    |
|         |   |         |       |    | with CASTHY; radiation width  |
|         |   |         |       |    | of 230 meV from Mughabghab's  |
|         |   |         |       |    | compilation. Level spacing    |
|         |   |         |       |    | determined to reproduce the   |
|         |   |         |       |    | capture cross section from    |
|         |   |         |       |    | CASTHY; the effective         |
|         |   |         |       |    | scattering radius of 6.989 fm |
|         |   |         |       |    | fitted to the calculated MT=1 |
|         |   |         |       |    | at 100 keV. Computed          |
|         |   |         |       |    | resonance integral 0.976 b.   |
+---------+---+---------+-------+----+-------------------------------+

**[Table 2]{.underline}.** Thermal (2200 m/s) Cross Sections for Se-80

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

  ENDF/B-VI                                                              1.29 b        0.61 b         0.68 b

  JEF-2                                                                  1.67 b        0.61 b         1.06 b

  JENDL-3                                                                7.56 b        0.61 b         6.95 b

  BNL-325 (1981)                                                                       0.61(5) b      

  S.F.Mughabghab,                                                                      0.61(5) b      
  [INDC(NDS)-424](http://www-nds.iaea.or.at/reports/indc-nds-424.pdf),                                
  p.73 (2001)                                                                                         

  S.F.Mughabghab,                                                                      0.61(5) b      
  [INDC(NDS)-440,](http://www.nndc.bnl.gov/sg21/nucl/indc-nds-440.pdf)                                
  p.11 (2003)                                                                                         
  ---------------------------------------------------------------------- ------------- -------------- ----------