A Quadrupole Band-Pass Filter for LANSCE protons

Neutrons are produced for many purposes at the LANSCE facility by 800 MeV protons into a thick tungsten target. The reactions also yield a continuum of protons, emerging at energies up to about 700 MeV; these protons are currently absorbed to allow neutron experiments. We have designed a quadrupole doublet band-pass filter to focus a narrow range of proton energies onto small samples, for instance the size of electronic circuit elements. Wrong proton energies are spread over a wider area and diluted. One may thus irradiate such small samples with protons from about 50 to 700 MeV by adjuting the quadrupole current. For a typical example with an existing doublet, a one cm diameter sample could receive protons at 470 MeV with 38 MeV FWHM energy resolution at a flux of 1.9x107 protons per second within that energy band, using the 30 degree port of the WNR facility. The flux of protons below 440 MeV or above 530 MeV is reduced by a factor of ten or more. Since the produced range of proton energies is similar to that of protons above the atmosphere, such a band-pass system would be of great use to study proton-induced processes in the components of orbiting systems.