ANALOG NEUTRON TRANSPORT FOR NUCLEAR INSTRUMENTATION APPLICATIONS WITH THE MONTE CARLO CODE TRIPOLI-4.

Monte Carlo simulations of nuclear instrumentation configurations generally need to be run in a full analog transport mode. Up to Version 9 of the Monte Carlo code TRIPOLI-4®, the transport between two consecutive neutron collisions is analog if no variance reduction technique is requested by the user, but the collision itself is sampled in a nonanalog way. This paper presents the first implementation of a full analog neutron transport mode in TRIPOLI-4. This option concerns only fixedsource simulations. Details on the modifications implemented in the code are provided: The analog sampling of neutron interactions and the particular cases of fission and scattering reactions with multiple outgoing neutrons are addressed. Preliminary verification tests are provided, and results from nonanalog and analog neutron transport in a simple configuration of a pressurized water reactor fuel assembly are compared. An example of application to the simulation of the NUCIFER detector is also provided. This experiment, located in Saclay, France, next to the OSIRIS experimental reactor, is dedicated to reactor antineutrino detection, addressing both nonproliferation considerations and fundamental physics concerns. Antineutrinos emitted by fission reactions in OSIRIS are detected through the inverse beta decay reaction, producing a positron and a neutron. An analog TRIPOLI-4 simulation allowed us to calculate the distribution of neutron capture times on gadolinium nuclei. [ABSTRACT FROM AUTHOR]