THERXS S(α,β)

Released: 2002-07-25

General information concerning ENDF/B-V and ENDF/B-VI S(α,β) data

Information on the current supported S(α,β) neutron data libraries for MCNP® is listed in Appendix G of the MCNP® manual. The ENDF/B-V based S(α,β) data are available in the data library TMCCS (note that ENDF/B-V thermal data have be carried over from ENDF/B-III). An initial set of Los Alamos cold moderator data are available on the THERXS library. ENDF/B-VI (Release 3) based data are available in the SAB2002 library [1].

The ENDF/B-VI thermal neutron scattering files (through Release 2) that contained the S(α,β) data were simply translations from the ENDF/B-V evaluations. When the translations were done, some problems were introduced due to the new formatting. No new MCNP data libraries were produced using these translated data. Substantial updating of the S(α,β) evaluations was completed by R. MacFarlane and made available in Release 3 of ENDF/B-VI [2]. There will be no noticeable improvement in lwtr and hwtr, as there has been no new 'physics' implemented. The incoherent approximation is still used for heavy water.

Each S(α,β) table includes a list of integer ZAIDs indicating for those nuclides the S(α,β) data may be used. See Table G-1 of the MCNP® Manual for a complete mapping. As an example, all lwtr tables include only 1001 in this list, indicating that the S(α,β) scattering data are to be used in the appropriate energy range for H-1 only. Another example is for beo tables: the list of integer ZAIDs includes both 4009 and 8016, indicating that the S(α,β) scattering data are to be used in the appropriate energy range for both Be-9 and O-16.

For information regarding MCNP® treatment of the S(α,β) data, see "MCNP S(α,β) Detector Scheme", LA-11952 [3].

If further information is required contact a member of the Data Team by e-mail at nucldata@lanl.gov

Documentation

1. "SAB2002 - An S(a,b ) Library for MCNP," Little, R.C, MacFarlane, R.E, (2003), LA-UR-03-808

2. "New Thermal Neutron Scattering Files for ENDF/B-VI Release 2," MacFarlane, R.E, (1994), LA-12693

3. "MCNP S(α,β) Detector Scheme," Hendricks, J.S, Prael, R.E, LA-11952