Formal Specifications for File 2


The following is based on ENDF-102,
Data Formats and Procedures for the
Evaluated Nuclear Data File ENDF-6.

Resonance parameters for resolved and unresolved resonance ranges are given in File 2. It has only one section, with the reaction type number MT=151. The resonance parameters for a material are obtained by specifying the parameters for each isotope in the material. The data for the various isotopes are ordered by increasing ZAI values. The resonance data for each isotope may be divided into several incident neutron energy ranges, given in order of increasing energy. The energy ranges for an isotope should not overlap; each may contain a different representation of the cross sections. File 3 may contain "background" cross sections" in the resonance ranges resulting from inadequacies in the resonance representation (e.g., SLBW), the effects of resonances outside the resonance range, the average effects of missed resonances, or competing cross sections. These backgrounds are to be added to the contributions computed from File 2. In the unresolved range, the File 3 section may optionally contain an "infinitely dilute" cross section. Self shielding factors are to be computed from File 2 and multiplied against the values in File 3. There must be double energy points corresponding to each resonance range boundary (except 1e-5 eV).

General Format for File 2

The following quantities are defined:

ZA,AWR
standard material charge and mass parameters
NIS
number of isotopes in the material (up to 10).
ZAI
1000*Z+A designation for an isotope.
ABN
abundance of an isotope in the material (this is a number fraction, not a weight fraction, nor a percent).
LFW
flag indicating whether average fission widths are given in the unresolved resonance region for this isotope (0=no, 1=yes).
NER
number of resonance energy ranges for this isotope.
EL
lower energy limit for an energy range.
EH
upper energy limit for an energy range.
LRU
flag indicating whether this enrgy range contains resolved or unresolved resonance parameters:
  • LRU=0, only the scattering radius is given (for information) and no resonance contributions are calculated for File 3.
  • LRU=1, resolved resonance parameters are given.
  • LRU=2, unresolved resonance parameters are given.
LRF
flag indicating which representation has been used for the energy range (the definition of LRF depend on the value of LRU):
  • If LRU=1 (resolved parameters), then
    • LRF=1, single-level Breit-Wigner (SLBW);
    • LRF=2, multi-level Breit-Wigner (MLBW);
    • LRF=3, Reich-Moore (RM);
    • LRF=3, Adler-Adler (AA);
    • LRF=4, General R-matrix (GRM);
    • LRF=4, Hybrid R-function (HRF);
  • If LRU=2 (unresolved parameters), then
    • LRF=1, only average fission widths are energy dependent;
    • LRF=2, all parameters are energy dependent.
NRO
flag designating possible energy dependence of the scattering radius (0=no, 1=yes).
NAPS
flag controlling the use of the two radii, the channel radius a and the scattering radius AP.
  • If NRO=0 (AP energy independent), then
    • NAPS=0: calculate a from AWRI and read AP. Use a in the penetrabilities and shift factors, but use AP in the hard-sphere phase shifts.
    • NAPS=1: read AP and use it in the penetrabilities, shift factors, and phase shifts.
  • If NRO=1 (AP energy dependent), then
    • NAPS=0: calculate a from AWRI and read AP(E). Use a in the penetrabilities and shift factors, but use AP(E) in the hard-sphere phase shifts.
    • NAPS=1: read AP(E) and use it in the penetrabilities, shift factors, and phase shifts.
    • NAPS=2: read AP(E) and use it in the phase shifts. In addition, read the constant AP from the range card and use it for penetrabilities and shift factors.

The structure of a section for the special case, in which just a scattering radius is specified (no resolved or unresolved resonance parameters are given) is as follows: (such a material is not permitted to have multiple isotopes or an energy-dependent scattering radius) 

        [MAT, 2, 151/ ZA, AWR, 0, 0, 1, 0] HEAD
        [MAT, 2, 151/ ZA, 1., 0, 0, 1, 0] CONT
        [MAT, 2, 151/ EL, EH, 0, 0, 0, 0] CONT
        [MAT, 2, 151/ SPI, AP, 0, 0, 0, 0] CONT
        [MAT, 2, 0/ 0., 0., 0, 0, 0, 0] SEND

If resonance parameters are given, the structure of a section is 
        [MAT, 2, 151/ ZA, AWR, 0, 0, NIS, 0] HEAD
        [MAT, 2, 151/ ZAI, ABN, 0, LFW, NER, 0] CONT
        [MAT, 2, 151/ EL, EH, LRU, LRF, NRO, NAPS] CONT
           subsection for the first energy range
           of the first isotope
        [MAT, 2, 151/ EL, EH, LRU, LRF, NRO, NAPS] CONT
           subsection for the second energy range
           of the first isotope
         ...
        [MAT, 2, 151/ ZAI, ABN, 0, LFW, NER, 0] CONT
        [MAT, 2, 151/ EL, EH, LRU, LRF, NRO, NAPS] CONT
           subsection for the first energy range
           of the second isotope
         ...
        [MAT, 2, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND

If NRO is not equal to zero, at TAB1 record giving AP(E) is inserted just after the energy range card.

More information on the formats and methods used for the various resonance representations will be found on the following pages:


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15 December 2012 T-2 Nuclear Information Service ryxm@lanl.gov