Hiroyuki Sekiya Institute for Cosmic Ray Research, University of Tokyo
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Hiroyuki Sekiya June 2-7 2014, Boston, NEUTRINO2014 Development of a Rn removal system for future Xe- based neutrino detectors using resonant ionization Hiroyuki Sekiya Institute for Cosmic Ray Research, University of Tokyo Yoshihiro Iwata, Chikara Ito Japan Atomic Energy Agency Preface: Radon is one of the major background sources in low energy neutrino experiments. Accordingly it is essential to suppress radon events in future large-scale xenon detectors aiming for neutrino-less double beta decay and pp solar neutrino measurements. Although the removal of radon from air using adsorption on activated charcoal is well established, because its chemical properties are similar to those of radon this technique cannot be used with xenon; Xenon itself adsorbs to charcoal and thereby deteriorates its radon absorption efficacy. So we propose a new radon removal method. SK Xe-based neutrino detector -beyond dark matter search solar neutrino spectra in Xe SK tank 0 0.5 1.0 1.5 2.0 2.5 MeV 10 -3 10 -4 10 -5 10 -6 10 -4 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10 136 Xe T 1/2 = 2.4 x 10 21 year 0.1 1 10 MeV n e + e → n e + e counts/keV/day/kg counts/keV/day/kg 136 Xe 2nbb spectrum Y. Suzuki hep-ph/0008296 24ton 10ton fiducial Ø 2.5m pp 14 events/day 7 Be 7 events/day Future XMASS-II pp 7 Be N.B. 136 Xe can be reduced for Solar n XMASS-I 1ton 100kg fiducial Ø 80cm t 222 Rn level in XMASS-I From the 214 Bi- 214 Po chain events (dT 164ms) in 30 days commissioning data U-Chain 30days 8.2mBq/835kg (emanated from the detector itself) To observe pp n (to achieve BG~10 -6 counts/keV/day/kg), Rn must be reduced 1/100 and continuously removed. 10 -4 counts/keV/day/kg Bo-Po timing diff. gives BG of as a demonstration Kr can be resonantly ionized via 212.6nm 2g+g 3. Development of Lasers 4. Test: Kr removal from Ar Wavelength transformation in Kr gas cell 2. Resonant ionization of Rn A laser is used to promote radon atoms to an electronically excited state via resonant single- or multiple-photon absorption and these excited Rn atoms are then ionized by the introduction of another photon. Resonance-enhanced multi-photon ionization process Rn Resonant ionization scheme Selectively ionized Rn impurities can be removed with an applied electric field. Excitation cross section Assuming laser’s l shape is Gaussian, s = g 2 /g 1 ×l 2 ×A 21 / （ 8√2 ×p 3/2 ×Dn ） Dn : Laser linewidth[Hz] A 21 : Einstein coefficient[s -1 ] g 2 /g 1 : 2J+1=3 Nano second pulse laser Dn 1~10GHz s ~ 10 -13 cm 2 145.2nm = 1.368×10 -12 mJ In case of Rn l = 178.6nm or 145.2nm A 21 ~ 10 7 s -1 ( no ref., assuming Xe 5p 6 1 S 0 → 5d[1/2] o 1 ) ~10mJ/pulse laser is necessitated. 1~10L/min 1~10cm 2 x 1m 10Hz puls e 4 wave-mixing for making 178.6nm or 145.2nm • 1/355nm + 1/530nm ⇒ 1/212.6 nm 212.6 nm 262.4nm or 396.8nm 178.6 nm or 145.2 nm slit MgF 2 prism Results measured by oscilloscope How to make input wavelength 355nm: Continum ® Nd:YAG Laser • 1/794 nm x 2 ⇒ 1/396.8 nm XMASS as an example N.B. Due to the large refractive index of Kr in 145.2nm, a phase mismatch occurs. (Attenuated in Kr gas). Adding ~7% Xe (refractive index is small), the phase can be adjusted. • 1/525nm×2 ⇒ 1/262.4 nm • 178.6nm 4mJ/ pulse 7mJ/ pulse • 145.2nm ~10mJ/pulse is almost achieved. 10ppm Kr in Ar w/ 5mJ/pulse laser Conclusion: A system for removing Rn from Xe has been developed. In this study, the feasibility of this method was demonstrated by removing Kr from Ar. Since the necessary laser has already been developed, tests of Rn removal from Xe will begin soon. → oscilloscope HV 8 mm ⇔ 212.6 nm lens feedthrough 10ppm Kr in Ar oscilloscope 212.6 nm HV ~5 mJ/pulse at 212.6 nm resonant 212.6 nm HV = +1.25kV/cm non-resonant 211.6 nm HV = +1.25kV/cm resonant 212.6 nm HV = -1.25kV/cm The setup power meter pressure gauge oscilloscope lens 10ppm Kr in Ar power meter Resonant ionization of Kr and its electric “sweep” were confi → oscilloscope Positive ions! Kr + (may be + Ar + ) ionized by electrons Kr 1.5 atm Kr+Xe(6.8% ) 1.0 atm A possible system for 1/100 reduction
description
Development of a Rn removal system for future Xe -based neutrino detectors using resonant ionization. Hiroyuki Sekiya Institute for Cosmic Ray Research, University of Tokyo Yoshihiro Iwata, Chikara Ito Japan Atomic Energy Agency. - PowerPoint PPT Presentation
Transcript of Hiroyuki Sekiya Institute for Cosmic Ray Research, University of Tokyo
Hiroyuki Sekiya June 2-7 2014, Boston, NEUTRINO2014
Development of a Rn removal system for future Xe-based neutrino detectors using resonant ionization
Hiroyuki Sekiya Institute for Cosmic Ray Research, University of TokyoYoshihiro Iwata, Chikara Ito Japan Atomic Energy Agency
Preface: Radon is one of the major background sources in low energy neutrino experiments. Accordingly it is essential to suppress radon events in future large-scale xenon detectors aiming for neutrino-less double beta decay and pp solar neutrino measurements. Although the removal of radon from air using adsorption on activated charcoal is well established,because its chemical properties are similar to those of radon this technique cannot be used with xenon; Xenon itself adsorbs to charcoal and thereby deteriorates its radon absorption efficacy. So we propose a new radon removal method.
SK
1. Xe-based neutrino detector -beyond dark matter search
solar neutrino spectra in Xe
SK tank
0 0.5 1.0 1.5 2.0 2.5 MeV
10-3
10-4
10-5
10-6
10-4
10-5
10-6
10-7
10-8
10-9
10-10
136Xe T1/2= 2.4 x 1021 year
0.01 0.1 1 10 MeV
ne + e → ne + e
coun
ts/k
eV/d
ay/k
g
coun
ts/k
eV/d
ay/k
g
136Xe 2nbb spectrum
Y. Suzuki hep-ph/0008296
24ton10ton fiducialØ 2.5m
pp 14 events/day7Be 7 events/day
Future XMASS-II
pp
7Be
N.B.136Xe can be reducedfor Solar n
XMASS-I
1ton100kg fiducialØ 80cm
Current 222Rn level in XMASS-I From the 214Bi-214Po chain events (dT 164ms) in 30 days commissioning data
U-Chain 30days
8.2mBq/835kg(emanated from the detector itself)
To observe pp n (to achieve BG~10-6 counts/keV/day/kg), Rn must be reduced 1/100 and continuously removed.
10-4 counts/keV/day/kgBo-Po timing diff.
gives BG of
as a demonstration Kr can be resonantly ionized via 212.6nm 2g+g
3. Development of Lasers
4. Test: Kr removal from Ar
Wavelength transformation in Kr gas cell
2. Resonant ionization of Rn A laser is used to promote radon atoms to an electronically excited state via resonant single- or multiple-photon absorption and these excited Rn atoms are then ionized by the introduction of another photon.
Resonance-enhanced multi-photon ionization process
Rn Resonant ionization scheme
Selectively ionized Rn impurities can be removed with an applied electric field.
Excitation cross section Assuming laser’s l shape is Gaussian,
s = g2/g1×l2×A21/ （ 8√2 ×p3/2×Dn ）
Dn : Laser linewidth[Hz]
A21: Einstein coefficient[s-1] g2/g1: 2J+1=3
Nano second pulse laser Dn 1~10GHz s ~ 10-13cm2
145.2nm = 1.368×10-12mJ
In case of Rn l = 178.6nm or 145.2nm A21 ~ 107 s-1 ( no ref., assuming Xe 5p6 1S0 → 5d[1/2]o
1)
~10mJ/pulse laser is necessitated.
1~10L/min
1~10cm2 x 1m
10Hz pulse
4 wave-mixing for making 178.6nm or 145.2nm
• 1/355nm + 1/530nm 1/⇒ 212.6 nm
212.6 nm
262.4nm or 396.8nm
178.6 nm or 145.2 nm
slit
MgF2
prism
Results measured by oscilloscope
How to make input wavelength
355nm: Continum® Nd:YAG Laser • 1/794 nm x 2 1/⇒ 396.8 nm
XMASS as an example
N.B. Due to the large refractive index of Kr in 145.2nm, a phase mismatch occurs. (Attenuated in Kr gas). Adding ~7% Xe (refractive index is small), the phase can be adjusted.
• 1/525nm×2 1/⇒ 262.4 nm
• 178.6nm
4mJ/pulse 7mJ/pulse
• 145.2nm
~10mJ/pulse is almost achieved.
10ppm Kr in Ar w/ 5mJ/pulse laser
Conclusion: A system for removing Rn from Xe has been developed. In this study, the feasibility of this method was demonstrated by removing Kr from Ar. Since the necessary laser has already been developed, tests of Rn removal from Xe will begin soon.
→ oscilloscope
HV8 mm
⇔
212.6 nm
lens
feedthrough 10ppm Kr in Ar
oscilloscope
212.6 nm
HV
~5 mJ/pulse at 212.6 nm
resonant 212.6 nm HV = +1.25kV/cm non-resonant 211.6 nm HV = +1.25kV/cm resonant 212.6 nm HV = -1.25kV/cm
The setup
power meter
pressure gauge
oscilloscope
lens
10ppm Kr in Ar
power meter
Resonant ionization of Kr and its electric “sweep” were confirmed.
→ oscilloscope
Positive ions!Kr+ (may be + Ar+)
ionized by electrons
Kr 1.5 atmKr+Xe(6.8%) 1.0 atm
A possible systemfor 1/100 reduction
