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

**37-Rb-85 Review**

I. Sirakov, INRNE, February 28, 2003

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

***ENDF/B-VI:*** Year of origin 1979, 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 1984, taken from JENDL-2, last revisions
1990, 2002

***CENDL-3:*** Year of origin 1999, last revision 2001

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

***ENDF/B-VI:*** Resolved resonance parameters up to 20.0 keV; MLBW
representation for the 76 s- and 12 p-wave resonances with resonance
parameters based on BNL-325; scattering radius 7.0 fm. No unresolved
resonance region (Table 1). Computed resonance integral 5.5 b.

***JEF-2:*** Resolved resonance parameters up to 9.227 keV; MLBW
representation for the 55 s- and 12 p-wave resonances with resonance
parameters based on BNL-325 (1973); scattering radius 7.2 fm. No
unresolved resonance region. Computed resonance integral 6.37 b.

***JENDL-3*:** Modified JENDL-2 resolved resonance parameters up to
8.468 keV, which were obtained from data measured by Ohkubo (1984); MLBW
for 117 s- and 22 p-wave resonances; Unknown spins J assigned randomly;
Average radiative width of 328 meV adopted for 128 levels; A negative
resonance added at -943 eV to reproduce the thermal capture cross
section (Table 2) from BNL-325 (1981); scattering radius 7.06 fm from
BNL-325 (1981). Unresolved resonance parameters up to 100 keV adopted
from JENDL-2. S0 taken as recommended in BNL-325 (1973), S1 and S2
strength functions from CASTHY and the effective scattering radius of
6.83 fm 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 205 meV adopted. Computed resonance
integral 8.73 b.

 

***CENDL-3:*** Resonance parameters taken from JENDL-3.2. Computed
resonance integral 8.63 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*** (198 mb), ***JEF-2*** (224 mb) and ***JENDL-3*** (276
mb) are due to the lower ***ENDF/B-VI*** and ***JEF-2*** capture cross
sections in the interval \~100 eV- 100 keV, where the fast-reactor flux
is predominant.

**Experimental data** -- The available EXFOR data on total and capture
cross sections are above 100 eV, of bad resolution and are useful mainly
in the unresolved resonance region (n,g; Dovbenko 1967, Beer 1989). The
resonance integral data of 8.34(42) b measured by Heft (1978), and of
8.0(9) b measured by Steinness (1972), are in favor of ***JENDL-3***
(***CENDL-3***). Koester's 1981 data
([EXFOR21842](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=21842&DatType=H&RetType=byAccNum&ReDo=N)
005) for a bound coherent scattering length of 7.07(10) fm, however,
give 7.04(10) fm free coherent scattering length and 6.23(18) b coherent
scattering cross section. Due to spin incoherent component, the
zero-energy scattering cross section has to be higher than the coherent
scattering cross section. Therefore, only the ***JEF-2*** potential
scattering radius of 7.2 fm and thermal scattering cross section of 6.3
b can be recommended. The thermal scattering cross sections of the other
evaluations are low (Table 2).

 

**Recommendation/Conclusion**: ***JENDL-3*** (***CENDL-3***) recommended
in the resonance region up to 100 keV except for the potential
scattering radius in the thermal and resolved resonance region. The
scattering radius should be adopted from ***JEF-2*** on the basis of
Koester's 1981 data for a bound coherent scattering length of 7.07(10)
fm.

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

-   Methodology

***ENDF/B-VI:*** Spherical OM code SCAT2 for MT=1 with experimental data
of Barnard (1973) and Foster (1971); Elastic cross section obtained as
(total -- non-elastic); COMNUC for MT=4 and 102. MT=22, 28, 104, 105,
106 from THRESH code; Hauser-Feshbach approach for MT=103, 107, with
width fluctuation corrections for MT=51 to 55; 5 discrete levels up to
868 keV considered for the inelastic scattering. MT91 calculated as
MT4-sum discrete inelastic cross sections. Legendre coefficients from
COMNUC code to get anisotropic angular distribution for MF=4, MT=2 in CM
system. Account taken of MT=1, 2, 4, 16, 22, 28, 51-55, 91, 102, 103,
104, 105, 106, 107.

***JEF-2:*** The optical potential of Moldauer used for MT=1; inelastic
cross sections (MF=3, MT=4, 51-53, 91) from COMNUC-3 code, no preeq
corrections; 3 discrete levels up to 870 keV considered for the
inelastic scattering; MT=102 from COMNUC code; elastic cross section
obtained as (MT1-MT102-MT4); no charge particle production cross
sections were first considered. In 1989 they were included from
REAC-ECN-4 Library. Isotropic angular distribution assumed for MF=4,
MT=2 in CM system. Evaporation spectrum (NCAP code) presented in MF=5
for the continuum inelastic scattering. MT=1, 2, 4, 51-53, 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 at 25 keV. Direct and semi-direct capture
estimated; 8 levels up to 1.18 MeV adopted for the inelastic scattering.
MT=16 normalized to recommended by Bychkov (1980) value at 14.5 MeV;
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, 51-58 in CM system. MT=1, 2, 4, 16, 17, 22,
28, 51-58, 91, 102, 103, 104, 105, 107.

***CENDL-3:*** Spherical OM and unified preeq-statistical model code
SUNF; 17 levels up to 1.63 MeV adopted for the inelastic scattering.
MT=4, 51-57, 91 calculated with SUNF. Elastic calculated as (MT1 -- sum
of partial cross sections); Legendre coefficients obtained to present
anisotropic angular distribution for MF=4, MT=2 in CM system. MT=1, 2,
4, 16, 17, 22, 28, 51-67, 91, 102, 103, 104, 105, 106, 107, 111.

-   MT=1

Since no experimental data are available for the total cross section of
Rb-85, the comparison with experimental (EXFOR) data for natural Rb
shows that all evaluations are reasonable, except maybe ***JEF-2***.
Especially well fitted looks ***ENDF/B-VI*** for its adjustment to
available experimental data for natural Rb like those of Foster (1971)
and Barnard (1969). The maximum difference between ***JENDL-3*** and
***CENDL-3*** is 0.45 b at 200 keV. The discrepancy between any of them
and ***ENDF/B-VI*** is smaller.

-   MT=2

***JEF-2:*** Too high above 12 MeV since (n,2n) reaction is neglected.

The maximum difference between ***JENDL-3*** and ***CENDL-3*** is 0.6 b
at 10 MeV, and between ***CENDL-3*** and ***ENDF/B-VI*** -- 0.6 b at 1
MeV. The small unreasonable peak at 10-11 MeV, in ***JENDL-3*** curve,
appears since the sharp slope of the (n,inl)-decrease starts at 10 MeV
while the (n,2n)-rise starts actually at 11 MeV. Similar peak appears
also in ***ENDF/B-VI***. ***CENDL-3*** curve has the advantage of being
smoother.

 

-   MT=4

***JEF-2:*** Unrealistic trend of (n,n\') cross section; (n,2n) reaction
neglected.

The difference of 0.3 b at 3 MeV between ***CENDL-3*** and ***JENDL-3***
leads to the same magnitude of difference in MT=1. The same discrepancy
of 0.3 b at 10 MeV partly compensates the 0.5 b lower ***CENDL-3***
values in MT=2 and results in 0.2 b higher ***JENDL-3*** values in MT=1.

-   MT=16

***JEF-2:*** No (n,2n) in File 3, assumed to be zero.

The available evaluations ***ENDF/B-VI,*** ***JENDL-3*** and
***CENDL-3*** are almost the same and in good agreement with the
experimental data. The maximum difference between ***CENDL-3*** and
***JENDL-3*** is 0.1 b at 20 MeV.

-   MT=102

All evaluations are in agreement with the experimental data of Stupegia
(1968) and Beer (1989), with some preference for ***JENDL-3*** because
of the data of Stupegia (1968) above 0.5 MeV.

-   MT=103

From systematics it follows that, far from the thresholds, (n,p) cross
sections for different isotopes of a given element become smaller as the
isotope mass A increases. Natural Rb has a higher atomic mass A than
85Rb. Comparison between 85Rb(n,p) evaluations and experimental data for
Rb-Nat(n,p) reaction
([EXFOR21319](http://www.nndc.bnl.gov/htbin/csisrs.cgi?AccNum=21319&DatType=H&RetType=byAccNum&ReDo=N)
006, Koenig 1965) shows that only ***ENDF/B-VI*** follows this trend and
can be recommended.

-   MT=107

***CENDL-*3** is in best agreement with the experimental data after
rejecting the data of Augustyniak (1976) which have an unreasonable dip
at 15.4 MeV.

**Recommendation/Conclusion**: ***ENDF/B-VI, CENDL-3*** and
***JENDL-3*** recommended in fast energy region 100 keV - 20 MeV.
***ENDF/B-VI*** is mostly recommended for MT=1, 103 on the basis of
EXFOR data for natural Rb; ***JENDL-3*** is mostly recommended for
MT=102 and ***CENDL-3*** for MT=107. ***JEF-2*** is not acceptable
mainly for the neutron channels MT=2, 4, 16.

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

**[Table 1]{.underline}.** Summary for Resolved and Unresolved Resonance
Region: Rb-85

+---------+---+---------+-------+----+-------------------------------+
| Library | Y | First   | RRR   | U  | Remarks                       |
|         | e | Authors |       | RR |                               |
|         | a |         |       |    |                               |
|         | r |         |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| EN      | 1 | A.      | 20.0  | \- | 76 s- and 12 p-wave           |
| DF/B-VI | 9 | Prince  | keV\  |    | resonances with resonance     |
|         | 7 | (BNL)   | \     |    | parameters based on BNL-325;  |
|         | 9 |         | MLBW  |    | scattering radius 7.0 fm.     |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 5.5 b.                        |
+---------+---+---------+-------+----+-------------------------------+
| JEF-2   | 1 | H.      | 9.227 | \- | 55 s- and 12 p-wave           |
|         | 9 | Gru     | keV\  |    | resonances with resonance     |
|         | 8 | ppelaar | \     |    | parameters based on BNL-325   |
|         | 2 |         | MLBW  |    | (1973); scattering radius 7.2 |
|         |   | (ECN)   |       |    | fm. Computed resonance        |
|         |   |         |       |    | integral 6.37 b.              |
|         |   | E.      |       |    |                               |
|         |   | M       |       |    |                               |
|         |   | enapace |       |    |                               |
|         |   |         |       |    |                               |
|         |   | (ENEA)  |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+
| JENDL-3 | 1 | JNDC FP | 8.468 | 1  | RRR: Modified JENDL-2         |
|         | 9 | Nuclear | keV\  | 00 | resonance parameters obtained |
|         | 9 | Data    | \     | k  | from data measured by Ohkubo  |
|         | 0 | Working | MLBW  | eV | (1984); 117 s- and 22 p-wave  |
|         |   | Group   |       |    | resonances. Unknown spins J   |
|         |   |         |       |    | assigned randomly. Average    |
|         |   |         |       |    | radiative width adopted for   |
|         |   |         |       |    | 128 levels; scattering radius |
|         |   |         |       |    | 7.06 fm from BNL-325 (1981).  |
|         |   |         |       |    |                               |
|         |   |         |       |    | URR: S0 taken as recommended  |
|         |   |         |       |    | in BNL-325, S1 and S2         |
|         |   |         |       |    | strength functions and the    |
|         |   |         |       |    | effective scattering radius   |
|         |   |         |       |    | determined using optical      |
|         |   |         |       |    | model calculations. Level     |
|         |   |         |       |    | spacing determined to         |
|         |   |         |       |    | reproduce the capture cross   |
|         |   |         |       |    | section from CASTHY.          |
|         |   |         |       |    |                               |
|         |   |         |       |    | Computed resonance integral   |
|         |   |         |       |    | 8.73 b.                       |
+---------+---+---------+-------+----+-------------------------------+
| CENDL-3 | 1 | J       | 8.468 | 1  | Resonance parameters taken    |
|         | 9 | .W.Zhao | keV\  | 00 | from JENDL-3.2. Computed      |
|         | 9 | W.N.Su  | \     | k  | resonance integral 8.63 b.    |
|         | 9 |         | MLBW  | eV |                               |
|         |   | (NJU),  |       |    |                               |
|         |   |         |       |    |                               |
|         |   | C.H.    |       |    |                               |
|         |   | Cai     |       |    |                               |
|         |   | (NKU)   |       |    |                               |
+---------+---+---------+-------+----+-------------------------------+

**[Table 2]{.underline}.** Thermal Cross Sections for Rb-85

+--------------------------------+------------+------------+----------+
| Library / Experiment           | Total      | Capture    | Elastic  |
+--------------------------------+------------+------------+----------+
| ENDF/B-VI                      | 6.2219 b   | 480.6 mb   | 5.7413 b |
+--------------------------------+------------+------------+----------+
| JEF-2                          | 6.8119 b   | 476.5 mb   | 6.3354 b |
+--------------------------------+------------+------------+----------+
| JENDL-3                        | 6.3697 b   | 480.1 mb   | 5.8896 b |
+--------------------------------+------------+------------+----------+
| CENDL-3                        | 6.3697 b   | 480.1 mb   | 5.8896 b |
+--------------------------------+------------+------------+----------+
| BNL-325 (1981)                 |            | 480(10) mb |          |
+--------------------------------+------------+------------+----------+
| S.F.Mughabghab, INDC(NDS)-     |            | 480(10) mb |          |
|                                |            |            |          |
| 424, p.69 (2001)               |            |            |          |
+--------------------------------+------------+------------+----------+