Presented by Jianghua Kyungpook National University 5 th Seminar on Dark Matter Search and Double beta decay, Sept 22-23, 2011, Yangyang, Korea

  Motivation  Properties of an ideal scintillation crystal for DBD  Crystal growth systems (Czochralski and Bridgman)  Scintillation properties measurement system  Crystal growth and Scintillation properties of SrMoO 4 single crystal  Summary Outline

  Scintillation method is a promising tool to search for double beta decay processes.  Molybdenum-containing single crystals attract attention as a potential cryogenic scintillating bolometers for DBD.  Mainly molybdenum containing crystals, such as ZnMoO 4, PbMoO 4, and CaMoO 4,were studied as candidates for DBD. The most promising of them is calcium molybdate (CaMoO 4 ).  However, the scintillation crystal of CaMoO 4 has one essential drawback: the unavoidable background caused by the presence of 48 Ca  background unless depletion of 48 Ca.  SrMoO 4 single crystal is one of the candidates to overcome such drawback. Motivation

 Why SrMoO 4 crystal? Mo Mo Bi-214 Tl-208 Ca-48 2 Ca-48 2

 Crystal Growth Techniques

  The bigger system is about 10 times of the smaller. Czochralski Technique Pt bar & Pt wire Seed Alumina tube Window Crystal R.F. coil Thermo couple Pt crucible Fire-brick

 Crystal grown process WeighingGrowing Grown crystal Cutting Polishing Prepared sample

 Bridgman Technique Two Bridgman system Vacuum machine Used to sealing ampoule

 Crystal grown process Weighing powder Putting powder into ampoule Sealing ampoule Measuring melting point Putting ampoule into furnace Starting grow crystal

 Scintillation properties measurement system X-ray generator QE65000 (spectrometer ) Power X-ray tube Crystal Optic spectrometer PC X-ray induced emission spectrum Crystal PMT Amplifier FADC 25/400 PC HV γ source Pulse height spectrum and fluorescence decay time

  The crystal is placed in a vacuum environment of Torr.  The temperature can be decreased to 10 K. Experimental setup for measuring the scintillation properties at low temperature

 Grown crystals using Czochralski method at KNU Bi 4 Si 3 O 12 Bi 4 (Ge 1-x Si x ) 3 O 12 SrWO 4 SrMoO 4

  Powder XRD pattern shows that the SrMoO 4 single crystal has a tetragonal structure. X-ray diffraction (XRD)

  The spectrum consists of a broad band spanning form 350 to 700 nm wavelength with a peak at 496 nm. X-ray induced emission spectrum

  The excitation peak is around 317 nm and the emission peak is at 500 nm. Photoluminescence spectrum

  The decay time curve shows two decay components, a short component with a decay time constant of 18 ns and 48% intensity and a long component with a 631 ns decay time constant and intensity of 52%. Fluorescence decay time spectrum

  The light yield is increased by changing temperature from 250 to 10 K.  The light yield at 70 K is about three times of that at 250 K. Temperature dependence of the scintillation light yield

  The decay time gets slower as the temperature decreases.  The mean decay time of the SrMoO4 crystal at 70 K is about 26 µs. Temperature dependence of the mean decay time

  SrMoO4 single crystal was successfully grown in KNU.  The grown sample is transparent and crack free, but cracks appeared during cutting process.  The scintillation properties of the SrMoO 4 single crystal show that it can be used for neutrino-less double beta decay search of 100 Mo at low temperature. Summary

 Thanks for your attention ！