WPEC SG21: Assessment of Neutron Cross-Section Evaluations for the Bulk
of Fission Products

> 35-Br-81 Review

Pavel Oblozinsky, BNL, March 2003

### 

### **1. General**

### 

### **Properties:** Stable nucleus, natural abundance 49.31%.

### 

**EXFOR data**

Total not measured except of resonances; capture data fairly sufficient;
(n,p), (n,) and (n,2n) at 14 MeV only; other reaction channels not
measured.

### **Evaluations**

-   ENDF/B-VI year of origin 1974, by Schenter & Schmittroth (ORNL)

-   JEF-2 year of origin 1982, by Gruppelaar (Petten) and Menapace
    (Bologna)

-   BROND-2 none

-   JENDL-3 year of origin 1990, author M. Kawai et al (JNDC FP Working
    Group)

-   CENDL-3 none

### **2. Thermal and resonance region**

**ENDF/B-VI**

-   Thermal capture cross-section from BNL-325 (1973).

-   Resolved resonance (RR) region -- parameters from BNL-325 (1973).

-   Unresolved resonance (UR) region - no data.

**JEF-2**

-   Thermal cross sections based on BNL-325 (1981).

-   RR region -- parameters taken from BNL-325 (1981).

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-   UR region - no data.

**JENDL-3**

-   Thermal capture cross section based on BNL-325 (1981).

-   RR region up to 13 keV, MLBW formula used with parameters from
    BNL-325 (1981).

-   UR region (13 keV -- 100 keV) based on BNL-325 (1981)

**Recommendation/Conclusion**

In the thermal and resonance region, JENDL-3 is the most recent and most
up-to-date complete evaluation. It is well documented. We note that 2003
evaluation of thermal cross sections and resonance integrals by
Mughabghab \[1\] indicates certain preference towards ENDF/B-VI.
**JENDL-3 is recommended**.

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

#### ENDF/B-VI methodology

-   In general, methodology clearly obsolete.

#### JENDL-3 methodology

-   Methodology fairly up-to-date, all important nuclear reaction
    processes taken into account.

-   Above 100 keV spherical optical model and statistical model code
    CASTHY used.

-   Pre-equilibrium effects included using code PEGASUS.

-   (n, p) and (n,) normalized at 14 MeV using systematic values by
    Forrest.

-   Angular distributions are provided, either based on CASTHY or
    considered isotropic.

##### JEF-2 methodology

-   Data mostly taken from ENDF/B-VI that in general judged to be
    obsolete.

-   Charged-particle production data taken from REAC-ECN-4 library.

**Comparison of evaluations**

-   MT=1 Lack of experimental data does not allow to make a qualified
    conclusion.

-   MT= 4 Unrealistic shape for both ENDF/B-VI and JEF-2, while JENDL-3
    looks ok.

-   MT=16 Only JENDL-3 evaluation is available.

-   MT=102 JENDL-3 reproduces experimental data well. Both ENDF/B-VI and
    JEF-2

> evaluations clearly overestimate experimental data.

-   MT=103,107 ENDF/B-VI not available, JENDL-3 normalized to
    systematic.

**Recommendation/Conclusion**

In the fast energy region, JENDL-3 is the only evaluation based on
up-to-date methodology, it is the most complete evaluation and it is
well documented. **JENDL-3 is recommended**.

Table 1. Thermal cross sections for Br-81

+----------------+------+--------+-------+--------------+-----------+
| **\            | # T  | # C    | # El  | # Re         | # O       |
| Source**       | otal | apture | astic | sonance Capt | ne-group  |
|                |      |        |       | ure Integral |           |
|                | **   | **(b   | **(ba |              | # Capture |
|                | (bar | arn)** | rn)** | **(barn)**   |           |
|                | n)** |        |       |              | **(barn)  |
|                |      |        |       |              | \[2\]**   |
+----------------+------+--------+-------+--------------+-----------+
| ENDF/B-VI      |      | 2.69   |       | 50.2         | 3.931E-1  |
+----------------+------+--------+-------+--------------+-----------+
| JEF-2          | 4.14 | 2.77   |       | 54.1         | 4.318E-1  |
+----------------+------+--------+-------+--------------+-----------+
| JENDL-3        | 6.31 | 2.69   | 3.62  | 46.7         | 2.742E-1  |
+----------------+------+--------+-------+--------------+-----------+
| Mughabghab     |      | 2      |       | 50(5)        |           |
| 2003 \[1\]     |      | .36(7) |       |              |           |
+----------------+------+--------+-------+--------------+-----------+

**Table 2**. Summary of resolved and unresolved resonance region for
Br-81

+----------+---+----+---------+---+-------+------+---------------------------+
| **L      | * |    | **First | * |       | #    | **Remarks**               |
| ibrary** | * |    | Author\ | * |       |  URR |                           |
|          | Y |    | **      | R |       |      |                           |
|          | e |    |         | R |       |      |                           |
|          | a |    |         | R |       |      |                           |
|          | r |    |         | \ |       |      |                           |
|          | * |    |         | * |       |      |                           |
|          | * |    |         | * |       |      |                           |
+----------+---+----+---------+---+-------+------+---------------------------+
| ENDF/    | S |    |         | # |       | B    |                           |
| B-VI1974 | c |    |         |   |       | ased |                           |
|          | h |    |         |   |       | on   |                           |
|          | e |    |         |   |       | BNL  |                           |
|          | n |    |         |   |       | -325 |                           |
|          | t |    |         |   |       | (1   |                           |
|          | e |    |         |   |       | 973) |                           |
|          | r |    |         |   |       |      |                           |
+----------+---+----+---------+---+-------+------+---------------------------+
| JEF-2    | 1 |    | Gru     |   |       | #    | Based on BNL-325 (1981)   |
|          | 9 |    | ppelaar |   |       |      |                           |
|          | 8 |    |         |   |       |      |                           |
|          | 2 |    |         |   |       |      |                           |
+----------+---+----+---------+---+-------+------+---------------------------+
| JENDL-3  |   | 19 | M.      |   | 13    | 13   | MLBW formalism adopted.   |
|          |   | 90 | Kawai   |   | keV\  | keV  | Based on                  |
|          |   |    |         |   | MLBW  | --   |                           |
|          |   |    |         |   |       | 100  | BNL-325 (1981).           |
|          |   |    |         |   |       | keV  |                           |
+----------+---+----+---------+---+-------+------+---------------------------+

#### References

1.  S.F. Mughabghab, Thermal neutron capture cross sections, resonance
    integrals and g-factors, Report INDC (NDS)-440 (IAEA, Vienna,
    February 2003).

2.  H. Gruppelaar et al, Status of pseudo-fission-product cross sections
    for fast reactors, Final Report of Subgroup 17, Report NEA/WPEC-17,
    ECN-R-98-014 (NEA, Paris, 1998). Recalculated systematically for all
    211 FP and all 5 evaluated libraries by I. Sirakov (BNL, 2002), see
    <http://www.nndc.bnl.gov/sg21/nucl/acs/accs.htm>.