2.5 MeV NEUTRON SOURCE FOR FISSION CROSS SECTION MEASUREMENT
National Bureau of Standards
Gaithersburg, MD 20899, USA
A 2.5-MeV neutron source has been established on the beamline of a 100-kV, 0.5-ma ion accelerator. The ion accelerator provides a 100-kV deuteron beam of about 200 μa into a 3-mm beam spot at the target position. The neutron source is produced by the D(d,n)3He reaction with a yield of about 107 n/sec. The time-correlated associated particle method (TCAP) is utilized for the neutron fluence determination and for neutron background elimination. The 3He associated particles are detected at 90 degrees behind a thin aluminum foil and the corresponding neutrons are emitted at 73.5 degrees with an energy near 2.5 MeV. Also, the protons from the competing D(d,p)T reaction are monitored at 135 degrees for normalization and diagnostic purposes. A fission chamber containing six uranium tetrafluoride deposits has been designed for use in the 235U(n,f) cross section measurement at 2.5 MeV. The 5-cm diameter deposits range in thickness from 230-300 μg/cm2 and are expected to have good uniformity. A description of the 2.5-MeV neutron source facility is presented along with details of the associated particle detection and neutron beam characteristics. Preparations for the fission cross section measurement are discussed.
KEYWORDS: associated particle, D(d,n)3He, 2.5-MeV neutrons, neutron fluence determinations, 235U(n,f) cross section, TCAP