
The following is based on ENDF102, Data Formats and Procedures for the Evaluated Nuclear Data File ENDF6. This page describes MT=452, 456, and 455 from File 1. Number of Neutrons per Fission, nubar (MT=452) If the material fissions, then a section specifying the average total number of neutrons per fission, nubar (MT=452), must be given. This format applies to both particleinduced and spontaneous fission, each in its designated sublibrary. Values of nubar may be tabulated a function of energy or represented by coefficients provided for the following polynomial expansion of nubar(E): 
where
Formats The structure of this section depends on whether the data are given in tabulated form or as a polynomial expansion. The following quantities are defined:
If LNU=1, the structure of a section is 
[MAT, 1, 452/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=1 [MAT, 1, 452/ 0., 0., 0, 0, NC, 0/ C1, C2, ... CNC] LIST [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
If LNU=2, the structure of the section is 
[MAT, 1, 452/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=2 [MAT, 1, 452/ 0., 0., 0, 0, NR, NP/ Eint/ nubar(E)] TAB1 [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
For spontaneous fission, the polynomial representation (LNU=1)
is used with NC=1. There is no energy dependence. The polynomial form for particleinduced nubar is only used when neither prompt nor delayed nubar values are given. Delayed Neutron Data, nubard (MT=455) This section describes the delayed neutrons resulting from either particle induced or spontaneous fission. The average total number of delayed neutron precursors emitted per fission, nubard, is given, along with the decay constants lambda_{i} for each precursor family. The fraction of delayed neutrons generated for each family is given in MT=455 of File 5. The energy distribution of the neutrons associated with each precursor family are also given in File 5. For particle induced fission, the total number of delayed neutrons is given as a function of energy in tabulated form (LNU=2), just as for MT=452. For spontaneous fission, the polynomial representation (LNU=1) is used with NC=1, just as for MT=452. Formats The following quantities are defined:

[MAT, 1, 455/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=2 [MAT, 1, 455/ 0., 0., 0, 0, NNF, 0/ lambda1, lambda2, ...] LIST [MAT, 1, 455/ 0., 0., 0, 0, NR, NP/ Eint/ nubard(E)] TAB1 [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
If LNU=1 (spontaneous fission), the structure of the section is: 
[MAT, 1, 455/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=1 [MAT, 1, 455/ 0., 0., 0, 0, NNF, 0/ lambda1, lambda2, ...] LIST [MAT, 1, 455/ 0., 0., 0, 0, NC, 0/ nubard] TAB1 NC=1 [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
If MT=455 is used, then MT=456 must also be used, as well as MT=452. Number of Prompt Neutrons per Fission, nubarp (MT=456) If the material fissions, a section specifying the average number of prompt neutrons per fission, nubarp (MT=456), can be given using formats identical to MT=452. For particleinduced fission, nubarp is given as a function of incident particle energy. The prompt nubar for spontaneous fission can also be given using MT=456, but there is no energy dependence. The following quantities are defined:
If LNU=2, the structure of the section is 
[MAT, 1, 456/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=2 [MAT, 1, 456/ 0., 0., 0, 0, NR, NP/ Eint/ nubarp(E)] TAB1 [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
If LNU=1 (spontaneous fission), the structure of a section is 
[MAT, 1, 456/ ZA, AWR, 0, LNU, 0, 0] HEAD LNU=1 [MAT, 1, 456/ 0., 0., 0, 0, NC, 0/ nubarp] LIST NC=1 [MAT, 1, 0/ 0.0, 0.0, 0, 0, 0, 0] SEND
For spontaneous fission, the polynomial representation (LNU=1)
is used with NC=1. There is no energy dependence. If MT=456 is specified, then MT=455 must also be specified, as well as MT=452.

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15 December 2012  T2 Nuclear Information Service  ryxm@lanl.gov 