1. Yong-Hamb Kim Development of cryogenic CaMoO 4 detector 2nd International Workshop on double beta decay search Oct. 7~8 2010 Oct. 8, 2010

2. 2 Outline Introduction to cryogenic particle detectors –Basic principle, Why? –Measurement chains –Temperature sensors Cryogenic CMO detectors –Experiment with a small CMO –New sensor for large absorber

3. 3 Basic idea: Calorimetric detection Absorber Thermometer Thermal link Heat sink < 100 mK , , , etc. Energy absorption  Heat (Temperature) Choice of thermometers Thermistors (doped Ge, Si) TES (Transition Edge Sensor) MMC (Metallic Magnetic Calorimeter ) STJ, KID etc.

4. 4 Why cryogenics? Advantages of using cryogenic calorimeters Extreme sensitivity of energy resolution (ΔE/E < 1/1000) Ultra low energy threshold ( < 1 eV) Active for Charge, Light, Phonon(Temperature) chains NIST Al-Ag TES Si(Li) (NIST 2002)(KRISS 2007) SBD MMC (KRISS 2010) 241 Am

5. 5 Low temperature detectors for rare events Low threshold, high resolution Active background rejection Advantages of using cryogenic detectors Thermometer Charge collector Semiconductor Light detector Thermometer Scintillator

6. 6 Measurement Chains in LTDs Events Phonon Light Charge Measurement methods (Charge, Light, Phonon(Temperature)) “Low temperature favorable” CRESST, ROSEBUD CDMS, EDELWEISS COURE examples

7. 7 Thermistors Neutron transmuted doped Ge thermistors Ion implantation doped Si thermistors Near metal-insulator transition R(T) : 1 M  100 M  Operated with conventional electronics Slow due to poor coupling between conduction electrons and lattice of the thermistor NASA GSFC

8. 8 Transition Edge Sensor (TES) Superconducting strip at T c (W, Ir/Au, Mo/Au, Mo/Cu,Al/Ag, etc.) R N : 10 m  1  Proximity effect : Tunable T c (20~200mK) Voltage Bias  negative feedback working point ( 초전도상전이센서 )

9. 9 Metallic Magnetic Calorimeter (MMC) ( 자기양자센서 ) Magnetic material (Au:Er) in dc SQUID junctions Field coil Au:Er(10~1000ppm) weakly-interacting paramagnetic system metallic host: fast thermalization ( ~ 1  s) g = 6.8 5 mT  Δε = 1.5  eV 1 keV  10 9 spin flips U. of Heidelberg

10. 10 Different sensors for rare event searches TESMMC Thermistor Conventional electronics Absorber friendly Slow at low temp. Fast, Most sensitive MUX possible Narrow working temp. Fast, Wide working temp. Absorber friendly MUX being developed

11. 11 Bolometer and Calorimeter Absorber (Heat capacity C) Thermometer (  T) Thermal conductance G Heat sink Incident radiation P, E Bolometer : time Calorimeter : time Cryogenic micro calorimeters: T < 1 K, C, G are small,  ~ ms

12. 12 R & D with CaMoO 4 CMO (CaMoO 4 ) - Scintillating crystal - High Debye temperature: T D = 438 K, C ~ (T/T D ) 3 - 48 Ca, 100 Mo 0ν  candidates - O(light), Ca(middle), Mo(heavy) elements CaMoO 4 Phonon sensor w. TES or MMC Additional light sensor Si or Ge Two detection channels : phonon + light TES

13. 13 First trial with CMO detector ~ 500  m thick brass base temperature : 30 ~ 100 mK crystal size ~ 1 cm  1 cm  0.6 cm 241 Am

14. 14 Full spectrum 60 keV gamma (20 cps) typical signal 5.5 MeV alpha (1 cps) gamma peak alpha peak ~1/64 as expected by the heat capacity “5.5 MeV alpha and 60 keV gamma signals were measured at the same time.”

15. 15 Alpha spectrum of 241 Am on CMO three major peaks E  + 60 keV 11.2 keV FWHM 60 keV gamma pileups, low energy coincidences Too big alpha signals at optimal condition (factor of 3~4) 11.2 keV FWHM 60 keV gamma pileups Low energy coincidences

16. 16 Baseline noise Noise spectrum from optimal filtering method FWHM = 1/1750 4.2 keV at 5.5 MeV Electronic noise and signal size will determine  E for mono-energetic electron source. Why 11.2 keV FWHM for alphas ? - Source straggling effect for E  :  E ~ 5 keV - frequent low energy pileups : 6~8 keV - Temperature stability of cryostat: 3~4 keV - Radiation damage : 1~2 keV

17. 17 Gamma spectrum of 241 Am 1.7 keV 1.7 keV FWHM for 60 keV gammas matches with noise spectrum in the condition Mo x-ray escape peak 60 keV region Measured with higher field and finer range of digitizer

18. 18 Future experiment Future experiment CaMoO 4 Phonon sensor Si or Ge TES Crystal size: 0.6 cm 3 Energy resolution 2 ~11 keV Crystal size: ~ 60 cm 3, 250 g Energy resolution 1~2 @ 3 MeV Additional light sensor (Quenching) Time constant of phonon signal (Shaping)  60 cm 3 CMO C = 0.17 nJ/K at 10 mK 1.4 nJ/K at 20 mK

19. 19 New sensor for large heat capacity 2.5 x 2.5 x 0.07 mm 3 gold foil C = 0.6 nJ/K at 20 mK Meander is made in U. of Heidelberg. 60 cm 3 CMO C = 0.17 nJ/K at 10 mK 1.4 nJ/K at 20 mK

20. 20 Full spectrum of 241 Am with meander sensor

21. 21 241 Am Alpha spectrum FWHM : 2.8 keV  emissions (from nndc) 5388 1.66% 5416.5 0.0100% 5442.8 13.1% 5469 0.020 % 5485.56 84.8% 5511.5 0.225% 5544.5 0.37%

22. 22 MMC vs SBD SBD MMC

23. 23 Resolution of  spectrometer FWHM : 2.8 keV for alpha particles from 241 Am : 1.2 keV from baseline (signal to noise ratio) - Temperature fluctuations : 10  K  ~1 keV - Lattice damage : 1~2 keV - Coincidence with low energy radiations  May be the major contribution

24. 24 Low energy spectrum FWHM: 0.8 keV for 60 keV gammas Measured with the same field and finer range of digitizer 1.5 keV Conversion electrons

25. 25 Summary of using meander MMC Suitable for absorbers with large heat capacity. Works for wide energy range –2.8 keV (1/2000) FWHM for 5.5 MeV alphas –1.2 keV FWHM for baseline noise. –1.2 keV FWHM for 60 keV gamma with same dynamic range of 12 bit digitizer –0.8 keV FWHM for 60 keV gamma with finer range.  May require higher precision AD conversion or two digitizers  This sensor will be employed for 250 g CMO crystals.

26. 26 Gironi’s work on CMO Gironi NIMA617, 478 (2010) Alpha, gamma separation w/o light detection. Rise time is not universal! - Crystal dependant - Sensor dependant Long decay process  scintillations and phonons

27. 27 Phonon-light coincidence experiment T c of a TES device was measured.

28. 28 LTD people at KRISS (Daejeon, 大田 ) Kim, Yong-Hamb (Staff) Lee, Kyoung Beom (Staff) Lee, Min Kyu (Staff) Kim, Il Hwan Yoon, Won Sik Lee, Junesur (Kongju N.U.) (Korea Research Institute of Standards and Science) Jang, Yong Sik (KNU) Kim, Min Sung (KNU) Lee, Sang-Jun (SNU) Yuryev, Yury (SNU) Other Amore collaborators at KRISS Kim, Jungho ; Lee, Jong Man; Park, Hyeon Seo

29. 29 Thank you ( 감사합니다 )