Characterization of a Tunable Quasi-Monoenergetic Neutron Beamfrom Deuteron Breakup

A neutron irradiation facility is being developed at the88-Inch Cyclotron at Lawrence Berkeley National Laboratory for thepurposes of measuring neutron reaction cross sections on radioactivetargets and for radiation effects testing. Applications are of benefit tostockpile stewardship, nuclear astrophysics, next generation advancedfuel reactors, and cosmic radiation biology and electronics in space. Thefacility will supply a tunable, quasi-monoenergetic neutron beam in therange of 10-30 MeV or a white neutron source, produced by deuteronbreakup reactions on thin and thick targets, respectively. Because thedeuteron breakup reaction has not been well studied at intermediateincident deuteron energies, above the target Coulomb barrier and below 56MeV, a detailed characterization was necessary of the neutron spectraproduced by thin targets.Neutron time of flight (TOF) methods have beenused to measure the neutron spectra produced on thin targets of low-Z(titanium) and high-Z (tantalum) materials at incident deuteron energiesof 20 MeV and 29 MeV at 0 deg. Breakup neutrons at both energies fromlow-Z targets appear to peak at roughly half of the available kineticenergy, while neutrons from high-Z interactions peak somewhat lower inenergy, owing to the increased proton energy due to breakup within theCoulomb field. Furthermore, neutron spectra appear narrower for high-Ztargets. These centroids are consistent with recent preliminary protonenergy measurements using silicon telescope detectors conducted at LBNL,though there is a notable discrepancy with spectral widths

Neutron Beams from Deuteron Breakup at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory

Accelerator-based neutron sources offer many advantages, in particular tunability of the neutron beam in energy and width to match the needs of the application. Using a recently constructed neutron beam line at the 88-Inch Cyclotron at LBNL, tunable high-intensity sources of quasi-monoenergetic and broad spectrum neutrons from deuteron breakup are under development for a variety of applications