Oddities of light production in the noble elements. James Nikkel

Transcription

1 Oddities of light production in the noble elements James Nikkel 1

2 2

3 What is a scintillator? Particle with Energy Photons Stuff 3

4 What is a scintillator? We would like: Nphotons = Y Eincoming With Y as large as possible Monochromatic photons 4

5 What is a scintillator? We would like: Nphotons = Y Eincoming Monochromatic photons It would also be nice to get some particle identification information. This is typically from the timing profile of the emitted photons. 5

6 What is a scintillator? The mechanism for producing light depends on the media: Organic liquid scintillators Organic crystal scintillators Inorganic crystal scintillators Molecular gases Noble liquids etc. 6

7 Scintillation in nobles A e - ionization A+ A collisions A + 2 e - recombination A 2* A A dissociation A excitation A* A collisions 2 excited molecular states: singlet and triplet A 2* dissociation A A uv photon uv photon 7

8 Scintillation in nobles Element Liquid density g/ml Boiling point (K) Electron yield (e - /kev) Photon yield (γ/kev) Singlet decay time Triplet decay time Scintillation wavelength (nm) Radioactive 2 4 He (ns) 13 (s) 80 No Ne (ns) 15 (μs) 78 No Ar (ns) 1.5 (μs) Kr (ns) 85 (ns) Ar 1 Bq/kg 85 Kr 1 MBq/kg Xe (ns) 27 (ns) Xe <10 μbq/kg 8

9 Scintillation in nobles Element Liquid density g/ml Boiling point (K) Electron yield (e - /kev) Photon yield (γ/kev) Singlet decay time Triplet decay time Scintillation wavelength (nm) Radioactive 2 4 He (ns) 13 (s) 80 No Ne (ns) 15 (μs) 78 No Ar (ns) 1.5 (μs) Kr (ns) 85 (ns) Ar 1 Bq/kg 85 Kr 1 MBq/kg Xe (ns) 27 (ns) Xe <10 μbq/kg 9

10 Liquid neon in nanoclean ~ James Nikkel

11 Pulse tube refrigerator microclean Copper liquifier 3.1 litre argon/neon target volume 2x Hamamatsu R MOD PMTs 11 James Nikkel

12 Example of digitised PMT signals + from tagged sources 12

13 Electronic Recoils Nuclear Recoils 13

14 Electronic Recoils Nuclear Recoils 14

15 fp 15

16 We observed an unexpected temperature/pressure dependance Prompt fraction fp Temperature (K) Pressure (Bar) 16

17 We observed an unexpected temperature/pressure dependance Triplet Lifetime (µs) Temperature (K) Pressure (Bar) 17

18 Unfortunately, microclean was constrained by the phase boundary 6& 5& Neon phase diagram We could not separate out temperature from pressure effects Pressure (Bar) 4& 3& 2& 1& Liquid Gas The detector also had a limited range of operation 0& 24& 25& 26& 27& 28& 29& 30& 31& 32& 33& 34& Temperature&in&K& Temperature (K) Triple Point: K, bar 18 James Nikkel

19 Why do we care? Liquid neon has a density of 1.2 g/cm 3 The pressure increases 120 mbar per metre of depth A 5 metre tall detector (~100 tonne) will have an excess pressure of 0.6 bar at the bottom 19

20 LEELA In LEELA, the temperature and pressure can be set independently, and over a much wider range A single pmt detects the scintillation light collected from a PTFE cavity Target volume ~50ml Copper CF/Sapphire window 75mm PMT (R6091-MOD) 20 James Nikkel

21 Cut-away view Copper vessel Level sensor PTFE 75mm PMT (R6091-MOD) Sapphire window Inner volume (50 ml) coated with wavelength shifter 21

22 Gas lines Pulse tube refrigerator Source tube PMT (R5912, later replaced) Vacuum chamber 22

23 Neon phase diagram Solid Liquid Temperature and pressure range covered Gas Triple Point: K, bar 23 James Nikkel

24 Am 60 kev line Yield ~1 PE/keV Counts/Second/bin PhotoElectrons (PE) 24

25 As the goal was to map out pressure and temperature, 2 sources were used simultaneously to generate nuclear and electronic recoils: 241 Am as a gamma source AmBe as a neutron source fp Nuclear recoils Electronic recoils 25 James Nikkel

26 The discrimination can be quantified by taking slices in energy or PE Clear separation is seen between different types of interactions Counts/Second/bin Electronic recoils Nuclear recoils Prompt Fraction PE events 26 James Nikkel

27 Solid Ne Nuclear recoils Liquid Ne Electronic recoils The changes of fprompt with temperature are consistent with the microclean measurements, but over a wider range, including into solid phase microclean data 27 James Nikkel

28 There appears to be little pressure dependence on fprompt Nuclear recoils Temperature ~ 28 K Liquid Ne Electronic recoils 28 James Nikkel

29 Some dependence of light yield is observed as a function of temperature Solid Ne Yield is obtained from a 60 kev line source, however there may be some pushing of the peak due to the trigger as fprompt changes Liquid Ne 29 James Nikkel

30 Temperature ~ 28 K Liquid Ne The pressure dependence of the yield appears to be small 30 James Nikkel

31 LEELA filled with liquid argon Measured prompt fractions for electronic recoils in fp Solid Ar Liquid Ar argon as a function of temperature Triple Point: K, bar 31

32 LEELA filled with liquid argon Measured prompt fractions for electronic recoils in argon as a function of pressure fp Liquid Ar Solid Ar 32

33 LEELA filled with liquid argon Measured yield for electronic recoils in argon as a function of pressure Yield (PE/keV) Solid Ar Liquid Ar 33

34 LEELA filled with liquid argon As there appears to be an abrupt transition, both phases are present in some data sets Liquid Ar NR Solid Ar NR As argon detectors use fp to reduce backgrounds, one must be vigilant to keep parts of the detector from freezing 34 Liquid Ar ER Solid Ar ER T = 82.3 K

35 Thank you for your time I hope that was enjoyable and I welcome any questions LEELA s first light 35