The calculation of the neutron transmission through the access way of a high-energy accelerator installation (using the MORSE code)

The MORSE code (Multigroup Oak Ridge Stochastic Experiment) was used to calculate the attenuation of radiation in an access tunnel of a high-energy proton accelerator (NIMROD). A monoenergetic isotropic neutron point source was used to simulate the radiation source produced by the interaction of high-energy protons with a copper target. Different source energies (1.5MeV, 10MeV, 20MeV) were chosen for the calculation. The results of these calculations agree well with measurements and with a ''universal attenuation curve'' for the second leg of the tunnel. It seems that the MORSE code can be used to simulate the transport of neutrons in the second leg and onwards in a tunnel of a high-energy accelerator installation, independently of the source energy (when the source energy is above 4MeV). From the calculated spectra it can be seen that a quasi-equilibrium neutron spectrum appears from about 2.5m onwards in the second leg, and up to 45% of the total dose equivalent in the second leg comes from the neutrons with energies ranging from 0.15MeV to 2MeV. (author)