DETECTION OF NEUTRONS BY LYMAN-ALPHA RADIATION
Patrick P. Hughes1, Alan K. Thompson1 , Michael A. Coplan2, John W. Cooper2, Robert E. Vest3 and Charles Clark3
1Ionizing Radiation Division, NIST Gaithersburg, MD 20899
2Institue for Physical Sciences and Technology, University of Maryland College Park, MD 20742
3Electron and Optical Physics Division, NIST Gaithersburg, MD 20899
Lyman-alpha radiation has been detected as a result of the n(3He, t)p reaction occurring in a 3He gas cell. We have found that under our experimental conditions, multiple photons are produced for each neutron absorbed in the gas cell volume . The photon production appears to be the result of charge exchange and excitation collisions between the triton and ambient gas atoms. Decay from the 2p to the ground state of the triton produces 121.6 nm light that is collected in a solar-blind photomultiplier tube connected to the gas cell. This result suggests the possibility of utilizing these photons to detect cold and thermal neutrons with a compact device without the need for a quench gas or pressure limitations imposed by proportional counter designs. Recent results of measurements performed on pure 3He gas, at pressures between 7 and 100 kPa, show between 6 and 13 photons produced per absorbed neutron. Additional measurements show enhanced photon production when 3He is mixed with different concentrations of noble gases.
 A. K. Thompson, et al., J. Res. Natl. Inst. Stan. Technol., 113, 69, (2008)