Can Solid Xenon be useful for search of Dark Matter and neutrinoless double beta decay? Kirill Pushkin Department of Physics and Astronomy, University of Alabama, Tuscaloosa Workshop on Xenon-Based detectors Lawrence Berkley National Laboratory November 16-18, 2009

Attractions of solid xenon Compactness of the detector (high density ~ 3.64 g/cm 3 ). Both drift velocity of electrons and their elastic losses are the same in solid xenon as in gas, v~1.3×10 5 cm/s at 5 kV/cm according to the latest measurements. Drift velocity of the electrons varies with the crystal temperature and higher than in liquid xenon. Primary scintillation light yield is HIGHER than in both gas and liquid xenon. Hot electrons reach energy of ~8 eV which might result in creation of secondary scintillation – electroluminescence. Small W i and W s values. No breakdowns even in the fields ~100 kV/cm Ions will freeze in the crystal – can Ba + ions be detected with laser!? Disadvantages of solid xenon Diffusion coefficients vs Electric field in solid xenon appear to be greater than in liquid xenon though the knowledge is still limited! May be some mechanical tensions in the crystalline xenon resulting in distortion of internal parts of the detector (You should really watch out!).

Drift velocity and mobility of electrons in solid xenon The data were taken back in 1967 and As it is seen from above the mobility results are inconsistent measured at the same temperature [1, 2]. Assumption! The cause could have been in the purity of the gases! [1] [2]

Drift velocities of electrons in liquid and solid xenon Reproduced from [2] The drift velocity of the electrons in solid xenon is dependent on temperature and considerably exceeds the drift velocity of electrons in liquid phase at E~300 V/cm. It tends to saturate at 5 kV/cm. The latest results indicate that v~1.3×10 5 cm/s at 5 kV/cm [see 3,4]

The drift velocity of electrons in SXe is greater than both in liquid and gas xenon at moderate electric fields and eventually converge the same drift velocity, v~1.3×10 5 cm/s, as in gas at 5 kV/cm (reproduced from [3,4]).

Diffusion coefficients in liquid and solid xenon HOWEVER, the diffusion coefficients varied with the temperature vs electric field are greater in solid than in liquid xenon [2].

Purification technique 1. Oil free pumping – turbomolecular + scroll pumps 2. Absence of any plastics and soldering even by silver (due to flux presence), HV valves, sapphire, glass, and ceramics as materials 3. Embedded system of xenon deep ( ) purification

Embedded system of xenon deep ( ) purification (electrospark technique) Electro spark sputtering of blade-shaped titanium cathode. Хе contamination removal down to 0.2 ppb proceeds in in scm volume in a few hours E.B. Gordon et al., Optics and Spectroscopy, 106, (2009),

Mobility of ions in crystalline xenon Mobility of Xe + ions in SXe at 157 K, ~0.02 cm 2 /Vcm Neither mobility nor diffusion have been measured carefully in solid gases. Mobility of Ba + ions in solid xenon has not been measured. BUT the mobility of Ba + ions has been recently measured in liquid phase, ~ cm 2 /Vs [5]. Interestingly, diffusion coefficient of Ba atom in solid xenon has been estimated, 1.458× cm 2 /s at 91 K [6].

Scintillation light in SXe and also in LXe 1) High scintillation efficiency (0.7 – gas, 0.9 – liquid, 1.0 – solid) [8] 2) Long attenuation length 3) Fast decay time ~2 nsec 4) Refractive index, n~1.5 [9] Important! Electrons in SXe might only achieve energy not greater than ~8.4 eV, which would allow exciting the first metastable levels, 3 P 2, 3 P 1, with subsequent developing of excimer molecules (excitons), A 2 * [10,11]. In 6 years the Gordon’s theory [10] was confirmed by A.S. Schussler et al., that proportional scintillation (electroluminescence) may be achieved in in both Liquid and Solid xenon mediums applying high electric fields, E cr ~5.4 kV/cm. In other words, low energy electrons become “hot” under the high electric fields and produce electroluminescence. (Before it has been claimed that either electroluminescence does not exist in condensed gases or there is a very small signal depends on purity) [12].

Two phase solid xenon detector 1.If the temperature is 77 K then one could use Ne or Ar as a second phase which are good scintillating gases in the visible range nm wavelength region [15]. Otherwise xenon can be used at higher temperatures. 2. Ne or Ar scintillation lights can only be detected with PMTs as the QE of CsI photodiodes is low (see next slide). 3. TAE or TMAE CsI photodetectors might be used to Detect VUV proportional light - electroluminescence.

Summary 1. High electron drift velocity (like in gas at 30 kPa). 2. High scintillation efficiency (primary and secondary) (more than both in gas and liquid). Compactness of the detector. No breakdowns even at extremely high electric fields. Ba atoms are frozen in the crystal. It stays a question whether the solid xenon can be useful for DBD.

References 1) L.S. Miller, S. Howe and W.E. Spear, Phys. Rev., 166, (1968), ) E.M. Gushchin, A.A. Kruglov and I.M. Obodovski, Sov.Phys.-JETP, 55, (1982), ) S.S.-S. Huang and G.R. Freeman, J. Chem.Phys., 68, (1978), ) E.B. Gordon, A.F. Shestakov, Low Temp.Phys., 27, (2001), ) S.-C. Jeng, W.M. Fairbank Jr and M. Miyajima, J. Phys. D: Appl. Phys., 42, (2009), ) B.M. Smirnov, Soviet Physics Uspekhi, 21, (1978), ) A.E. Ezwam and J. Billowes, A solid xenon catcher for rare isotope laser spectroscopy, Hyperfine Interactions, (2005) (available on Web). 8) A.I. Bolozdynya, Private communication, July, ) H. Nawa, Y. Tamagawa and M. Miyajima, ICDL 1999, Nara, Japan, ) E.B. Gordon, V.V. Khmelenko and O.S. Rzhevsky, Chem. Phys. Lett., 217, (1994), ) E.B. Gordon, Private communication, July, ) A.S. Schussler, J. Burghorn, P. Wyder et al., Appl. Phys. Lett. 77, (2000), ) A. Usenko, G. Frossati and E.B. Gordon, Phys.Rev.Lett., 90, (2003), ) E.B. Gordon, G. Frossati and A. Usenko, JETP, 96, (2003), ) P. Lindblom, O. Solin, Nucl. Instr. And Meth. in Phys. Res. A268, (1988), ) A.F. Buzulutskov, Phys. of Part. and Nucl., 39, (2008),

THANK YOU VERY MUCH FOR YOUR ATTENTION!

The figures have been reproduced from [15] Quantum efficiency of CsI and K-Cs-Sb photocathodes

The W – values seem to be unclear…