Proceedings of the DAE Symp. on Nucl. Phys. 59 (2014) 994

GEANT4 simulation of scintillation response of Xenon gas to low energy γ-rays S. Roy1, I. Mazumdar1,∗ P.B. Chavan1, M. Dhibar2, and G. Anil Kumar2 1Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Mumbai - 400005, and 2Dept. of Physics, IIT-Roorkee, Roorkee 247667,

Introduction Simulation and results

Noble gases, namely, Helium, Argon, Kryp- We have initiated a programme to carry out ton and Xenon have long been used for ra- in-depth studies of Xe as ionization and scin- diation detection. They are used to operate tillator detector. Xe gas scintillator detector either as ionization detector or as scintillation is much simpler to construct and operate com- detector. Liquefied noble gases have been used pared to liquid Xe counter that requires con- in ionization detectors since early 1950s. The siderable cryogenic arrangement. As a first performance of Liquid Xenon has been found step we want to carry out a comparative study to be most satisfactory both as an conven- of the efficiency of Xe gas as scintillator with tional ionization detector and also in propor- Xe ionization chamber. We have designed tional mode. Xenon counters have variety of and constructed a a Xe gas scintillator cham- applications, namely, low energy gamma-ray ber that can operate up to 5 Atm pressure. spectroscopy, X-ray astronomy, medical imag- The chamber has been couple to 2” PMT ing etc. [1]. The high atomic number (Z=54) (ET9266QB) that can operate at 175 nm with of Xenon makes it an ideal choice for detection high quantum efficiency. Special glass win- of gamma-rays due to very large photo-electric dows have been used for transmission of the absorption. In more recent time Xenon coun- scintillation photons to the PMT. ters are widely considered for detection of dark In order to have better understanding of the matter and neutrino less double beta decay response of Xe gas as scintillator we have car- [2]. The real challenge in using liquid Xenon ried out very detailed, realistic GEANT4 sim- counter is the attainment of a very high level ulations for low energy gamma-rays from 10 of purity. Xenon can also be used to build to 100 keV. In the preliminary simulations we scintillation counters. The primary emission have considered a cubical Aluminium cham- of Xe due to scintillation is at 175 nm in the ber of dimensions 16cm X 40cm X 100cm filled very Ultra Violet region. It is to be noted that with Xe gas at 2 Atm pressure. The gamma- considerably more work has been reported in rays enter the main volume through a .05mm literature about the working of Xenon ion- thick mylar window. The gamma rays are al- ization chambers than Xenon gas scintillation lowed to fall vertically all over the entrance detector. It has also been reported that the window. For each energy we consider hundred energy resolution in Xenon gas proportional thousand events to generate the final spec- chamber is much better than what is achieved trum. Figures 1 and 2 show the response of in liquid Xenon [3]. It is therefore, quite inter- the detector to 100, 70, 50 and 30 keV gamma- esting to have better understanding of Xenon rays. The initial GEANT4 outputs have been as scintillator vis-a-vis as an ionization detec- folded with finite resolutions to get the final tor in both liquid and gaseous forms. spectra. The photo-peak efficiency increases from 18% at 100 keV to 74% at 30 keV. The photo-peak efficiency at 50 keV is higher than at 30 keV. This can be understood in terms ∗Electronic address: [email protected] of the variation of the photo-electric cross sec-

Available online at www.sympnp.org/proceedings Proceedings of the DAE Symp. on Nucl. Phys. 59 (2014) 995

tion of Xe with photon energy. The initial 8000 50 keV results are encouraging enough to carry out 6000

more realistic simulations for the exact design 4000 Counts of our detector chamber. The data taking and 2000 further analysis are underway and will be pre- 0 sented in the meeting. 0 25 50 75 15000 30 keV

10000

Counts 5000

4000 0 0 25 50 75 100 keV Energy (keV) 3000 FIG. 2: The GEANT4 simulated spectra for 50 2000 (top) and 30 keV (bottom) gamma-rays. Counts 1000

0 0 50 100 150 4000 70 keV 3000

2000

Counts References 1000 [1] F. Resnati et al., Nucl. Instr. Meth. A 715, 0 87, (2013) 0 50 100 150 Energy (keV) [2] E. Aprile et al., Phys. Rev. Lett. 107, 131302 (2011) FIG. 1: The GEANT4 simulated spectra for 100 [3] A. Bolotnikov et al., Nucl. Instr. Meth. A 396 (top) and 70 keV (bottom) gamma-rays. , 360 (1997)

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