Contribution to Subgroup 21

Eu-156

Reviewed by A.Ignatyuk, March, 2004

**1. Files**

***ENDF/B-VI***: Evaluation was made in 1974 for ENDF/B-V and
transformed to ENDF/B-VI in 1989.

***JENDL-3.3***: Evaluation was made for JENDL-2 in 1984. JENDL-2 data
were revised in 1990 for JENDL-3.1, modified for JENDL-3.2 in 1993 and
transformed to JENDL-3.3 in 2001 with minor corrections.

***JEF-3.0***: ENDF/B-V was adopted for JEF-2 in 1982. The missing
charged-particle emission cross sections were included from REAC-ECN-4
in 1989. JEF-2.2 was transformed to JEF-3.0 in 2002.

**2. Thermal and resonance region**

***(1) Resolved resonance parameters***

***ENDF/B-VI*** (1.0e-5 -- 257.36 eV): No resonance parameters included
except the scattering radius of 6.494 fm.

***JENDL-3.3***: There are no resolved resonance parameters.

***(2) Unresolved resonance parameters***

***ENDF/B-VI***: There are no unresolved resonance parameters.

***JENDL-3.3*** (1.0 eV -- 100 keV): Energy dependent parameters were
used. The neutron strength functions S0=2.3, S1=0.52, S2=2.4 were
estimated from the optical model calculations. The average radiative
width of 100 meV was taken in accordance with the systematics for
neighbouring nuclei. The resonance spacing and the effective radius were
determined to reproduce the total and capture cross section at 100 keV
calculated with the CASTHY code.

***(3) Thermal cross sections and resonance integrals*** (in barns)
calculated for the corresponding files are compared in the following
table:

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

Library/Experiment Total Elastic Capture Cap.Res.Integ.

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

ENDF/B-VI 487.9 5.3 482.6 1486

JENDL-3.3 106.7 6.6 100.1 1430

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

***(4) Recommendation/conclusion for resonance region***

There are no any experimental data for the given nucleus. Both
independent evaluations ENDF/B-VI and JENDL-3.3 are similar enough. Some
preference can be given to JENDL-3.3 due to an estimation of unresolved
resonance parameters at energies below 100 keV.

**3. Fast neutron region**

***(1) Methodology***

Statistical model calculations were widely used for all evaluations.
However the optical potential parameters and the corresponding
statistical codes were rather different that reflected into the obtained
results.

***ENDF/B-VI***

The total and the elastic scattering cross sections were calculated for
the Moldauer's optical potential parameters \[Mo63\]. Inelastic
scattering and capture cross sections were calculated with the COMNUC-3
code. Angular distributions for elastic and inelastic neutron scattering
were assumed isotropic. The temperature approximation was used for
neutron evaporation spectra. The threshold reaction cross sections were
not considered.

## JENDL-3.3

The total, elastic and inelastic scattering, and capture cross sections
were calculated with the spherical optical model and the statistical
model code CASTHY. The contribution of preequilibrium processes was
taken into account through the PEGASUS code. Capture cross sections at
high energies were estimated according to the direct-collective capture
model of Benzi and Reffo \[Be69\] and normalized to 1 mb at 14 MeV. The
threshold reaction cross sections were calculated with the PEGASUS code.
The (n,p) and (n,) reaction cross sections were normalized to the
systematics of Forrest \[Fo86\] at 14.5 MeV. PEGUSUS calculations were
also used for evaluations of secondary neutron energy spectra.

***(2) Intercomparison of evaluations***

**Total cross section** (MT=1, Fig:
http://www.nndc.bnl.gov/sg21/fp/nucl/Eu156/Eu156tot.htm):

Both evaluations are rather similar. JENDL-3.3 seems preferable due to
more consistent description of elastic and inelastic cross sections.

**Capture cross section** (MT=102, Fig.:
http://www.nndc.bnl.gov/sg21/fp/nucl//Eu156/Eu156cap.htm):

Capture cross sections is most important for practical applications.
There are no direct experimental data to test the available evaluations.
Nevertheless, JENDL-3.3 seems preferable taking into account the
systematics of capture cross sections for neighbouring nuclei.

**Inelastic scattering** (MT=4, Fig.
http://www.nndc.bnl.gov/sg21/fp/nucl//Eu156/Eu156inl.htm):

ENDF/B-VI is certainly wrong above 9 MeV. JENDL-3.3 looks preferable for
the whole energy region.

**(n,2n) cross section** (MT=16, Fig:
http://www.nndc.bnl.gov/sg21/fp/nucl//Eu156/Eu156n2n.htm):

JENDL-3.3 is alone and it looks reasonable enough.

**(n,p) and (n,) cross sections** (Figs.
http://www.nndc.bnl.gov/sg21/fp/nucl//Eu156/Eu156np.htm ,
http://www.nndc.bnl.gov/sg21/nucl//Eu156/Eu156na.htm): JENDL-3.3 looks
acceptable for both cross sections.

***(3) Recommendation/conclusions for fast neutron region***

JENDL-3.3 should be considered as preferable ones on the basis of a
comparison with evaluations and available experimental data for
neighbouring nuclei.

**References**

\[Be69\] V.Benzi, G.Reffo, Report CCDN-NW/10 (1969).

\[Fo86\] Forrest R.A.: Report AERE-12419 (1986).

\[Mo63\] P.Moldauer. Nucl. Phys., 47 (1963) 65.