Blocking effect in CsI(Tl) crystal by neutron

Abstract

To detect WIMP directly, which is strong candidate for dark matter, KIMS collaboration used CsI(Tl) crystal as a scintillation detector. To increase the detector`s sensitivity, we studied channeling and blocking effect in the CsI(Tl) crystal, which refer to the orientation dependence of charged ion`s penetration in crystals. It results in modulation of scintillation or ionization yield in the CsI(Tl) crystal. In order to measure the channeling and blocking effect in CsI(Tl) crystal, we used a CsI(Tl) crystal, a neutron generator, and three neutron detectors, with making the directions of recoil ions induced by the neutron-nucleus scatterings to be aligned along one of the symmetry axis or plane in the CsI(Tl) crystal. Also, we did simulations to compare their results with the data obtained from our experimental setup, by two kinds of computer simulations, MARLOWE and Geant4. To confirm the affection of the blocking effect in the CsI(Tl) crystal, we compared the light yields of recoil ions moving along the symmetry axis, [110], and those of recoil ions moving along random directions, and compared mean decay time of signals from each recoil direction. By comparing those from experiments and simulations, we could find a clue for the blocking effect which is expected to result in less scintillation light yields.