FaNGaS: a New Instrument for Fast Neutron Gamma Spectroscopy at FRM II Research Reactor at Garching

摘要

For the identication and quantication of actinides in radioactive packages,the non-destructive method of Prompt-Gamma Activation Analysis (PGAA)is applied. To investigate the inelastic (n; n0) scattering, a new instrumen-tation was installed at the FRM II research reactor. It is designed to exploitthe 108 cm2s1 neutrons at an average neutron energy of 1:9 MeV deliveredby the SR10 beam line. The outgoing prompt -rays are measured utilizinga 50% eciency HPGe detector. Since the cross sections are expected to below for such a process, two related factors had to be taken into account for thedesign of the instrumentation: the high beam intensity at the sample positionand the high signal-to-background ratio seen by the detector. Eventual lowenergy neutrons due to the multiple scatterings through the beam line can beminimized using collimators in the beam tube. This has also an eect to a priorneutrons and photons background reduction of the experimental environment.A higher eciency of the counting can be achieved by the lowering of back-ground at the detector. In this case, a heavy shielding for both neutrons andphotons, is designed around the detector while optimizing the sample-detectordistance. Monte-Carlo simulation studies were conducted to eectively designthe fast neutron beam collimators and the detector shield. A detailed descrip-tion of the setup characterization and results from simulations and experimentalmeasurements will be discussed through this contribution.