Created attachment 105 [details] Excel sheet with the result of modeling The energy spectrum of thermal neutrons doesn't have Maxwellian form. We studied the following problem. The source of the neutrons was point isotropic. The initial energy was 0.4 eV. The medium was uniform and infinite. The composition of the media was pure oxygen with density 1.0 g/cc. The energy distribution of the neutrons phase density was computed. The neutrons were registered after 500 microsec after their birth and then summarized over all times. The expected energy distribution should have Maxwellian spectrum but the computed spectrum doesn't fit to the shape of it.
Hi Unfortunately we could not identify where the problem comes from. This is likely connecting on flight Doppler broadening which is one of key features of NeutronHP. We think current difference of spectrum does not cause real problem in most calculations. Therefore we decide codes left as this at this moment. In case, you have serious trouble caused by this, please let us know. Then we reconsider the decision. FYI In thermal scattering S(alpha, beta) model, we have pretty similar shape of thermal peak to MCNP. Tatsumi
