Calibration of a CsI(Tl) crystal with nuclear recoils and pulse shape measurements for dark matter detection

The quenching factor of cesium and iodine nuclei recoiling in a CsI(Tl) sci ntillator is measured by scattering of 3 to 6 MeV neutrons. This Factor inc reases when recoil energy decreases, from 7% at 150 keV to 15% at 25 keV. T his relatively high efficiency could be useful in experiments dealing with very low recoil energies like the WIMP direct detection. These values are w ell explained by the Birks model. Pulse shape discrimination between electr on and nuclei recoils is also investigated. Results are sufficiently good t o allow a significant statistical rejection of radioactive background. This rejection capability is shown to be better than for NaI(TI), at the same e lectron equivalent energy. (C) 1999 Elsevier Science B.V. All rights reserv ed.