Scin/lla/on of liquid neon Photon Detec/on at 27 K

Transcription

1 Scin/lla/on of liquid neon Photon Detec/on at 27 K Hugh Lippinco, Fermilab Jin Ping Solar Neutrino Workshop June 9,

2 Why neon? Scin?llates efficiently (of order 20 photons/kev or more) No long lived isotopes Easily purified of radioac?ve contaminants Charcoal extremely effec?ve at liquid neon temperatures (Harrison et al., NIM A 570 (2007) ) 1.2 g/liter Not cheap, although not as expensive as xenon (~few hundred USD/kg) Can detect neutrino- electron and neutrino- nucleus sca\ering Property He Ne Ar Kr Xe Atomic number (Z) Atomic mass (A) Boiling point T b at 1 atm [K] Melting point T m at 1 atm [K] Gas density at 1 atm, 298 K [g/l] Gas density at 1 atm, T b [g/l] Liquid density at 1 atm, T b [g/cm 3 ] Critical temperatre T c [K] Critical pressure p c [atm] Critical density ρ c [g/cm 3 ] Liquid dielectric constant Jin Ping Workshop, June 9-,

3 Why neon? Property He Ne Ar Kr Xe Atomic number (Z) Atomic mass (A) Boiling point T b at 1 atm [K] Melting point T m at 1 atm [K] Gas density at 1 atm, 298 K [g/l] Gas density at 1 atm, T b [g/l] Liquid density at 1 atm, T b [g/cm 3 ] Critical temperatre T c [K] Critical pressure p c [atm] Critical density ρ c [g/cm 3 ] Liquid dielectric constant Jin Ping Workshop, June 9-,

4 Liquid noble gas detectors reminder Radia?on (gamma, electron, neutron, neutrino) collides with electron or nucleus, deposi?ng energy Recoiling electrons or nuclei excite other atoms Leads to scin?lla?on via metastable molecules (in two states, singlet and triplet) and ioniza?on electron recoil nuclear recoil atomic motion Xe2 * +Xe excitation + ionization Xe+ + e- Xe * +Xe Xe2 + + e - escaping electrons ionization electrons 2Xe + hν scintillation light (175 nm) recombination Xe ** +Xe S1 S2 4

5 History Packard, Surko and Reif measure scin?lla?on spectrum in solid and liquid neon Suemoto and Kanzaki measure absorp?on spectra in liquid and solid neon, and observe both molecular and atomic transi?ons Atomic states have very long radia?ve life?mes (~600 us), but also have non- radia?ve decays Michniak et al. observe 7.4 photons/kev for electrons and a life?me of 4 us Yale group (James Nikkel) observes 15 us life?me, disagreement a\ributed to purity, first observa?on of pulse shape discrimina?on (PSD) MicroCLEAN measurements at Yale Jin Ping Workshop, June 9-,

6 Neon scin/lla/on probably more complicated than standard picture Small hump in molecular poten?als could lead to longer lived atomic species Free electrons form bubble states (as in helium) If molecules do as well (as in helium), that can change interac?ons From Cohen and Schneider, J. Chem Phys., 61, 3230 (1970) 6

7 MicroCLEAN 3.14 liter detector Op?mize light collec?on Two 20 cm Hamamatsu R MOD PMTs Inner surfaces of ac?ve region are coated with TPB Neon data comes primarily from run Jin Ping Workshop, June 9-,

8 MicroCLEAN Jin Ping Workshop, June 9-,

9 MicroCLEAN Sample scin?lla?on trace in neon (significant slow component) Voltage (V) Time (µs) Jin Ping Workshop, June 9-,

10 MicroCLEAN 83 Kr m source calibra?on - some krypton does diffuse into the bulk Counts/2 kev Energy (kev) Jin Ping Workshop, June 9-, 2014

11 Light yield (photoelectrons/kev) MicroCLEAN Maximum light yield of (3.5 +/- 0.4) pe/kev (ajer circula?on through internal charcoal trap that could not be purged) Iden?cal detector saw 6 pe/kev in argon Light scavenging impuri?es may be more of an issue than in argon Days since April 16 Jin Ping Workshop, June 9-,

12 MicroCLEAN Time dependence is more involved than just 2 or 3 exponen?ally decaying species (singlet, triplet, atomic,?) Normalized mean voltage K average trace 2-component model 3-component model Time (µs) Jin Ping Workshop, June 9-,

13 MicroCLEAN Time dependence also changes with pressure and temperature Voltage (arb. units) K, τ l = 21.5 ± 1.5 µs 27.8 K, τ l = 18.2 ± 0.4 µs 28.8 K, τ l = ± 0.05 µs Time (µs) Jin Ping Workshop, June 9-,

14 MicroCLEAN Both?me constant and rela?ve intensity are affected Time constant [µs] 1 [ns] Neon temperature (K) 2 Mixture model parameters Neon temperature (K) I 1 I 2 I 3 I 4 Results of fimng to a 4 component exponen?al model (t1,t2 correspond to the nominal triplet and singlet states) Increase in intensity of long lived component matched by a decrease in the?me constant with increasing temperature Jin Ping Workshop, June 9-,

15 MicroCLEAN Slight increase in signal with temperature Photoelectron yield (pe/kev) tot Neon temperature (K) Will need to be well understood for a large solar neutrino detector with non- uniform thermodynamics Jin Ping Workshop, June 9-,

16 MicroCLEAN Temperature/Pressure dependence remains largely unexplored Measurements on satura?on line (T and p went together) No electric field Might have something to do with bubble states Time constant (µs) τ l Bubble-mixture model, β = Neon temperature (K) Jin Ping Workshop, June 9-,

17 MicroCLEAN Response to nuclear recoils and poten?al for pulse shape discrimina?on (not nearly as good as in liquid argon) ERC 26.7 K data Statistical model (fitted parameters) 1 Statistical model (additional noise set to 0) L eff Energy 0.2 (kevr) Energy (kevr) Jin Ping Workshop, June 9-, 2014 MicroCLEAN result PicoCLEAN result Lindhard+Birks model (SRIM) Lindhard+Birks model (DM) 17

18 PMT considera/ons All studies done with Hamamatsu R MOD with the pla?num underlay to allow use at cryogenic temperatures and two extra dynode stages Jin Ping Workshop, June 9-,

19 PMT considera/ons Gain drops by factor of 0 at liquid neon temperatures V LED pulses 6.2 V LED pulses Gain Temperature (K) Jin Ping Workshop, June 9-,

20 PMT was not externally illuminated. The single photoelectron spectra PMT were considera/ons integrated and rounded off into integer multiples of the single photoelectron peak area for counting, then divided by the LED pulse length to Dark current increases at lowest temperatures obtain the rate. At room temperature, we measured a Also dark observed count rate by Hans- O\o of approximately Meyer 300 at Indiana counts per for second Hamamatsu R7725 (cps). down to 4 K 2000 t various Counts per second electron a funcdivided Temperature (K) Jin Ping Workshop, June 9-, 2014 FIG. 4: Plot of the dark count rate as a function of temper- 20

21 PMT considera/ons While single PE pulses can s?ll be iden?fied in the traces, the SPE distribu?on loses coherence At neon temperatures, we could not resolve the SPE response for one of our 2 PMTs Tried tuning first dynode voltage with limited improvement Terrible SPE dispersion Pulse area (pc) Jin Ping Workshop, June 9-, Pulse area (pc) 21