(Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering)

The GENESIS project aims to support the next generation of nuclear data needs for neutron scattering cross sections by providing energy and angle differential neutron and gamma ray detection capabilities on an energy tunable collimated neutron beamline at the 88-Inch Cyclotron. Inelastic scattering cross sections play a critical role in modeling nuclear systems undergoing fission, and the current nuclear data assessments disagree on the balance between elastic and inelastic cross section necessitating modern differential measurement.

GENESIS is currently constructed on the Cave 5 beamline of the 88-Inch Cyclotron. The neutron production is managed via deuteron breakup, and collimation of the neutron beam occurs in the cyclotron vault. The beam spot size and energy spectrum can be adjusted to match the target size and desired energy range. The spectrometer is constructed modularly with inclusion of single crystal and segmented HPGe detectors located near neutron scattering targets of interest. Up to 28 2” right cylinders of pulse shape discriminating EJ-309 can be included with average flight paths of 0.5m allowing for simultaneous neutron gamma singles measurements as well as coincident event construction for angle differential measurements.

Acquisition for the array is currently being managed by MESYTEC MDPP-16 VME based digital pulse processing boards. Boards are readout using the MESYTEC mvme open source acquisition software while data reduction and analysis is being handled by internally developed C++ algorithms leveraging the ROOT data analysis framework for file I/O and histogram accumulations.

The GENESIS Array populated with 2 segmented Eurosys HPGe Clovers, two Ortec 90% single crystal HPGe detectors and 20 2” right cylinders of EJ-309 all awaiting cabling.

View of the GENESIS array from the perspective of an incident neutron.

The GENESIS array fully cabled and instrumented viewed from the beam side.

Adjustable collimation in the cyclotron vault leads to a well defined neutron beam spot size in the adjacent cave. Scattered neutrons from the collimator are separated from the GENESIS array by ˜4ft of concrete shielding.

Results of a raster scan of the collimated neutron beam in cave 5 using a 1” right cylinder of EJ309 and a 2d stage system.

GENESIS’s VME based MESYTEC acquisition system capable of managing up to 48 signal channels of mixed solid state and scintillation detector signals.