SubMeV Neutrino Technology

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Sub-MeV Neutrino Technology R. S.
Raghavan Virginia Tech NOW-2006 September 10,
2006
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Lo-Nu? Low Threshold Nu Reactions30 year
Personal Theme

• Motivation
• New perspectives for Nu Flavor physics
• Lower the nu Energy larger the flavor effects
• Powerful tools for frontier new sciences
• The most interesting nu sources occur at LO
  energies
• Astro, Geo- Nu Physics
• NOT EASY!--- Need
• Radically New Ideas and/or
• Far Out New Technology
• This Science is coming into vogue and relevance
  only recently

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New Paths in LO-Nu Technology

• Four Lo Nu Reactions
• (??e ,p) 1.8 MeV
  1956 Reines
• 
  KLand
• (?e , 115In) 0.114 MeV
  1976 LENS
• (? , e) 0.020 MeV
  1992 CTF, Bxino,
• 
  Kland, Cryo?
• Recoilless Nu 0.0186 MeV 2006
  ???
• Res Cap

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Reactor Antineutrino DetectionReinesFirst
Breakthrough against LE Bgd Wall

• Source Reactor produced antineutrinos- 0-8 MeV
• 
  Major flux lt 3 MeV
• Proposition unbelievable since terrestrial
  material bgd
• formidable below 5 MeV, especially below 3
  MeV
• How to Proceed
• Major Idea Tag the neutrino reaction
  ?ep ?ne
• Serendipity Look at delayed neutron in
  concidence
• It works because neutron diffusion creates DELAY,
  thus it gives a
• coded signal that DISCRIMINATESNo tag if delay
  is too short to
• 
  
  measure
• ? Discovery of neutrino
• Still the most successful idea in Neutrino
  Physics
• Only viable way for antineutrino Science
• Reactor neutrinos, Geoneutrinos, Supernova relic
  nus

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LENS100 keV neutrino detection with tag

• Objective pp neutrinos from Sun
• 0-420 keVNo hope against bgd wallUNLESS .Nu
  Tag !
• 1976Copy the MasterCan one invent a delayed
  coincidence tag for neutrinos by imitating the
  Reines neutron tag for antinus?
• Problem Neutrinos can be detected only with
  inverse beta on nuclei heavier than proton
• Answer Choose inverse beta to
• ISOMERIC excited nuclei
• (not to the ground state as in Cl
  or Ga)
• ?
• ?e 115In ? 115Sn (t 5 µ s) 2?e-

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Indium TagIdea great but where is the Technology?

• 30 yr job !!
• Basic Detection technology-
• In liquid Sciintillator
• Background Analysis Insights
• Novel Detector Nu Reactions
• ?Scintillation Lattice Chamber
• ?Complete Low Energy Solar Nu
• Spectrum?99 of solar nu output
• What Science?
• Neutrino Luminosity of Sun
• Latest Measure Gamow Energy of pp fusion via
  ENERGY of pp nu spectrum
• ?temperature profile of energy
• production in sun
• (hep-ph/ 0609030)
• Christian GriebTalk tomorrow

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? e? ? e of lt 100 keV neutrinosTechnology,
Technology, Technology !

• Objective 7Be nus from sun (861 keV) by nu-e
  scatteringSignal extends from 0-670 keV
  Compton Edge
• ? No reaction event tag !! But
• ? Monoenergetic Nu?signature recoil electron
  profile
• ? High Rates ? 1/r2 oscillation with earths
  rotation
• ? Above all.Brute Force Tech. to suppress
  radio-bgd
• New Chemical Tech of Ultrahigh Radiopurity
  (U, Th. K)
• and methods to detect such ultrahigh
  radiopurity
• ? Proof? CTF?historic expt of 5 ton detector of
  20 keV events
• ? Borexino 15yr Research by DEDICATED Group
• now setting templates for Kamland, future
  cryoliq experiments .
• Borexino Now in High Gear operating detector
  in 2007 !
• Gioacchino Ranucci talk tomorrow

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New Perspectives with very low energy neutrinos

• Recoilless Resonant Capture Reactions
• with Tritium anti-Neutrinos
• ?Very low energy 18.6 keVcurrent limit 1800 keV
• ?Very large enhancement of reaction cross section
• ?10 orders of magnitude higher than current
  X-sec
• ? Experiments with kgrams not ktons of material
• ? Experimental baselines in cm not km
• OPENS NEW HORIZONS for NEUTRINO PHYSICS

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Neutrino Physics in bench scale baselines

• Gravitational Red Shift I linewidth in 180 cm
  fall-line
• ?First Direct test of Equivalence Principle
  for
• 
  Neutrinos
• 2. T13 flavor oscillations in 10m baseline
• ? Implications for CP violation Baryon
  Asymmetry
• 3. New problem Test of Sterile Neutrinos
• ? test LSND
  result
• LSND implies ?m2 0.5 to 1 eV2 sin2 2? 0.1 to
  0.01 .??
• Presumed conversion to sterile neutrinos
• ?for T?He Disappearance / oscillations in 5cm
  baselines ??Major Neutrino Physics Interest !

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Detecting Antineutrinos

• Low energy ?e why ?
• Detecting 40K in earth
• Short Baseline anti-neutrino oscillations
• How to lower ?e detection threshold below 1.8
  MeV?
• Basically different from ?e detection
• ?e Reaction Produces e--not e-
• ? Sets Min.Threshold 1.022 MeV
• e.g. ?ep?n e
  ? E? min 1.0220.782 1.8 MeV
• ?e3He?T e
  ? E? min 1.0220.0186 1.0406 MeV
• --No Escape
• Some but not much gain in reducing nuclear Q
  alone

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New Idea I Breakthrough in Threshold
ProblemLev Mikaelyan (1968)

• Rediscover New Idea of LM
• (Orbital electron ?e) Capture
• ?e 3He e- ( 1s orbital) ? T
• Get TWO things
• Really low threshold ? Enu min 18.6 keV !
  Voila!
• 2. All energy except E? is fixed---Resonant
  Character !
• E?
  (res) Q B(1s He)ER
• Great but, Not much use for wide band nu spectra
  from Reactors
• because neutrino density ? (dn/dE)/N is too
  small
• ? Need idea 2

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Resonant Source of AntineutrinosJ. Bahcall
(1962)

• Idea 2
• Inverse of Lev Mikaelyans reaction
• T ? 3He e- (in 1s orbit) ?e
• bound State ß-decayJohn Bahcall (1962)
• Theory 0.69 x0.8 0.54 Bß decay goes to
  ground state of He
• E?e Q B (1s)ER
• Just what is needed for resonance in LM reaction
  with extra energy to capture the 1s electron in
  the He target
• The two reactions are exact time reversed
  processes.
• Resonance means HIGH XSec
• Can go to low ?e threshold AND enhance Xsec !!
• By How much? ? IDEA 3

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RECOILLESS NEUTRINOS

• Idea 3
• Recoil energy 2xER spoils Resonance. Get rid of
  it !
• Use T and 3He embedded in solids--
• Under proper conditions -- expect Recoilless
  Transitions
• E R terms that destroy resonance energy balance
  eliminated
• Arrange experimental conditions for high spectral
  density of nuebars ?narrow linewidth G (not
  natural LW)
• Can one do this? Deeper understanding of
  process now
• New paths
  visible from technology
• Progress in
  Specific Experimental Designs

ER 0.05 eV in T
?E thermal linewidth 0.06 eV at T300K
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L. Mikaelyan-- Resonant ?e Cross section

• LM formula FOR RESONANT ?e CAPTURE
• s 4.18x10-41 go2 ?(E(?e res)/MeV) / ft1/2
  cm2
• 4.6x10-49 x ?
• go2 1.24x10-5 (1s Electron density)
• ft1/2 1132 s (weak interaction factor- T
  decay constant)
• ? no. of neutrinos/MeV (in incident
  neutrino spectrum)

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Neutrino Line Width Resonance X-section

• Thermal Motion ? E? v(kT/Mc2) 0.08eV (if
  T and He are in solids must include effect of
  Debye temperatures)
• RECOIL ENERGY! ER E?2/ 2Mc2 0.061eV
• ?(E?e res/MeV) (106/ 2?) x overlap emission
  abs
• 
  windows
• (106 / 0.16) x 0.4 ? 2.5x 106 ? Resonance
  Enhancement
• s 10-42 cm2 for 18 keV ?e
• s (?e p) for 3 MeV ?e
• ROOM FOR IDEA 3? LINE WIDTH G ltltlt thermal
  width ? ? ? s increases correspondingly
• Must eliminate ER first

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Recoilless Resonance X-section

• Recoilless Fraction f
• f exp-4/3 (ER/ Z) (Z zero point
  energy ZPE)
• for low temperatures (Tltlt T Debye Temp
  8/9 (Z/Mc2)
• Line Width G Determines resonance density, Xsec
• (not natural lw but experimental energy
  fluctuation width)? practical parameter from
  magnetic spin-spin relaxation time T2
• 3. Effective s(res) (LM formula)
• s(res) f(s)f(a) 4.6x10-49 x ?/MeV cm2
• f(s)f(a) 4.6x10-49 x 106 /
  G (eV)T
• Anticipate f(s)f(a) 0.1 T2100 µs? G
  6x10-12 eV
• s(res) 1032 cm2
• ? 10 orders of magnitude larger than s (?e p)
  

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Emitter-Target Energy Balance in Solids

• Look at energy balance of T-He reaction in solids
  
• Crucial for ultra sharp Resonance
• Perturbing Energies that affect the resonance
• Atomic (Bs already considered)
• Chemical bonding (T but not He)
• Lattice ?vibrational energy, at T? 0
• ?second order
  Doppler shift
• ? Zero Point
  Energy even at T0
• Dipolar interaction in rigid lattice of spins
• Magnetic shielding-- Site dependent chemical
  /other shifts
• Can the strict
• Energy Matching of Resonance (to 10-16 )
  Survive?

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Self Compensation of perturbing Energies in T?He
system

• Nu Resonance Involves two time reversed processes

Source Initial State Chemically bonded T
Final State ?e 3He
No recoil-No lattice phonons
emitted Target Initial State ?e 3He
Final State Chemically bonded
T No recoil-No lattice phonons
emitted Total Perturbing Energy
Tritium ET Total Perturbing Energy
Helium EH ET ? EHe in
general
Emission
E (?e res) (ET EHe) Absorption E
(?e res) (EHe-ET) E (?e res) - (ET
EHe) Energy gain in Emission is COMPENSATED
EXACTLY in absorption Resonance condition
maintained STRICTLY
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Self-Compensation Conditions

• Conditions on ET , EHe for self-compensation
• Unique energies
• Identity of ET EHe each in Source and Absorber
• Static Perturbationno relaxation
• Conceptual Framework SAFE
• What about effects in Practice?
• Sources of breakdown in energy balance
• Distribution of Es ?Inhomogeneous broadening
• Relaxation ?homogeneous broadening
• Non indentity of Es in source/absorber?Line Shift

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Basic Experimental Conditions

• Source and Absorber prepared identically
• Engineer T sites and He sites identical and
  unique
• Identical temperatures of source/absorber
• ? eliminate second order Doppler
  shift
• Spin ½ i.e. Zero Quadrupole moments of T and
  3He
• ?No electric perturbations due to random
  strain fields
• Residual Major Non-compensatable effects
• Variation of ZPE from site to site- inhomog.
  broadening
• Spin-spin magnetic relaxation homog. Broadening
• ? Final line width determined by larger of above
• two broadenings

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Tritium and He sites in metals
He
T
He?Microbubbles 1-2nm diam 4000 atoms Solid
under pressure 10 GPa at lt100K He atoms closer
than in IS sites
T?Interstitial Sites Octahedral fcc
metals Tetrahedralbcc metals
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Search for Resonance-Viable T-He Matrix

• Quest for matrix and conditions where
• IS sites dominant not bubbles
• T and He will occupy Same type of INTERSTITIAL
  Sites
• Tall Order?
• Search for metal matrix and conditions
• published data on
• EST self trapping energies? determines
  mobilities
• ? site choices for He
• ZPE to estimate recoil free fractions

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Niobium?Parameters of T and He in Nb

• Find site choice (EST self-trapping energies)
• and ZPE (for recoil free fractions)
• from theoretical study of H, D, T in Nb

Theoretical EST ZPE for T and 3He in Nb
interstitial sites (IS)
Choice for T He

• M. J. Puska R. M. Nieminen, Phys. Rev. B10
  (1983) 5382

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How to make Unique, Identical IS for He Niobium
!

• He transport in Nb T in Nb for 200 days
• Remove T and
  monitor He for 200 d

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Niobium- Unique Discovery

• Conclusions on Niobium as Matrix choice
• Calculations show that at lt200K He is ONLY in IS
  sites
• No bubbles are formed indefinitely
• The EST of Tetra and Octa sites are nearly
  degenerate
• ? He sits randomly in either site
• Available 6 Tetra and 3 Octo sites/bcc unit
  cell
• ?67 He in Tetra IS site
• ? All T in Tetra IS site
• ? Uniqueness and identical site
• requirement satisfied
• ?Nb is unique in providing these features
• ?Key Discovery

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Line widths --Homog and Inhomg

• Homog? caused by spin-spin relaxation?take T2
  data
• Inhomog? site to site variation of ZPE (no
  electric perturbations)
• ?Unknown. Guidance from successful
  observation of
• ultra sharp 67Zn ?
  resonance (?E/E 5x10-16)
• (W. Potzel
  et al, Hyp. Int. 72 (1992) 191)
• ?Observation of resonance despite ZPE and
  electric perturb.
• ? Hope that inhomg in T?He within 10 times
  that of Zn

Inhomog
Homog
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Homogeneous Broadening Dipolar Linewidth
H NMR in NbH 300Kx

Dipolar Interaction of T, 3He nuclear spins with
spins in the vicinity nuclear spins H (or D) ,
T, 93Nb and electron paramagnetism of the
lattice NMR measurement on H In NbHx
(300K) (Stoll Majors Phys Rev B 24 (1981) 2859
). Applies closely to our case since
nuclear moments of T, 3He and H are very
similar 2.9 (H), 2.8 (T), 2.1 (3He)
nm Experimental line width 13 kHz ??E
8.5x10-12 eV ??E/E 4.6 x 10-16 NMR-MASS
resolves the two NMR lines (ao ßo with
different chemical shifts) and the sidebands
introduced by MASS (magic angle sample spinning)
Homog. Broad
13 kHz
Rigid spin Splitting resolved Via magic angle
spinning
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Preliminary estimate of X-sec

• ZPE (TNb TIS) 0.071 eV
• ZPE He--Nb TIS) 0.093 eV
• f(T) f(He) 0.076
• T2 0.2x10-4 s
• G 8.6x10-12 eV
• He TIS site fraction 2/3
• ? s (res) 0.3x10-32 cm2

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Detection of Nu Resonance

• Two (Default) Methods in T-free target
• Nubar Activation Capture Rates N
• Mass Spectrometry of milked Tritium and measure
  Number N of T produced in given time by Us-MS
• ?N grows (linearly with t) signature
• Typical activation time 65 d 0.01 of 1/tau of T
• Reverse C-beta decay of signal T (a la Ray Davis)
• ? involves a reduction from N by factor 6500
  (1/tau of T)
• in situ by heat produced
• in MS T sample by counting C-betas

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Nu Resonance in PracticeTarget Questions

• He target is prepared by TT method
• This implies target has active T
• How to cope with enormouos T (1017)
• vs tiny amounts of signal T produced in
  resonance?
• ? Biggest Practical Problem to be Solved
• Best solution visible at present
• T?D exchange or T?H exchange?
• Exchange energy small 0.04 eV for H?D smaller
  for T?D, T?H
• T limit set only by dilution factor
• Multiple exchanges with D2 gas at 35 torr
  demonstrated in practiceMass spectrometry of
  exchange gas showed no T also no He (Abell
  Cowgill, Phys. Rev. B44 (1991)44)
• Must be revisited and quantified with
  ultrasensitive MS

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Preliminary Estimates of Rates

• Rec. Resonance Capture Rates for Close (5cm) and
  far (10 m) geometries
• Rates in close geometries can be high (0.1 Hz !)
• ?offers safety margins vs dilution by unknown
  
• 
  broadening effects
• Initial priority feasibility studies at close
  geometries

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Conclusions Outlook

• Conclusions
• NbT(He) major discoverysets firm conceptual
  basis for ultra high
• 
  resolution recoilless nu resonance
• Line width problems may be accommodatable
• Technical road map to experiment emerging
• To do
• Investigate and nail down T?D (H) exchange in
  Target
• Experimental determination of basic parameters
  (ZPE, site preference via n, X-ray diffraction,
  NMR in actual NbT sample prepared below 200Kno
  such data yet
• Invent Real time signal methods ???
• .

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Additional slides
34
Fast bubble growth Palladium TritideHopeless!
Calculations verify Experimental data Bubble
nucleation essentially complete in a few
days Long term He ONLY in bubbles (red
curve) not in Interstitial sites (blue curve )
35
Basic Embedding Technique Tritides and the
Tritium Trick

• How to embed T and He in solids
• Metal tritides Best approach visible
• Tritium gas reacts with metals and alloys and
  forms metal tritides (PdT, TiT, NbT...)
• ?embeds T in lattice uniformly in the bulk
• ? Tritium decays and He growsdistributed
  uniformly
• (Tritium Trick (TT))
• ?Problems
• T and He lattice Sites in TTUnique? Identical
  for T, He?
• Must Remove T from absorber to detect resonance
• ? New Issue? What effect does this have on
  identity of T and He in source and absober?

36
Resonance neutrino microspectra

• Example Gas T source and gas He target
• Doppler widths and Recoil Shifts of neutrino
  lines
• 2? is the full width due to thermal motion

?
ER
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T and He sites in Metal Tritides

• Great Deal of Data Available
• Fusion and Fuel techSandia-- prime source!
• Basic Problem of TT
• T
• Reactive-- forms chemical bond-unique sites
• Sits in tetrahedral interstitial sites (T) in bcc
  metals
• in octahedral interstitial sites (O) in fcc
  metals
• He
• Noble gasinsoluble in metals
• High mobility
• Forms pairs quickly and nucleates in microbubbles
• Non-unique, distribution of ZPE
• Unacceptably large inhomogeneous broadening

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He growth in metals-Model calculations

• Basic equations Coupled non-linear diff. eqns.

Numerical solution (at VT thanks
to Prof K. Park, Mr D. Rountree)
dc1/dt g - 2p1s1c12 2q2c2 - p1s2c1c2 -
p1sBc1cB dc2/dt p1s1c12 - p1s2c1c2 - q2c2
dcB/dt p1s2c1c2.
Parameters C1 mobile C2 pair C3
bubble P1, 2, 3 jump frequencies depending on
activation energies E1,2,3
He transport parameters in NbT at 200K M1.0
T1.0 E1 eV E2 eV E3 eV D/cm2
MNb 0.9 0.13 0.43
1.1E-26c D. F. Cowgill, Sandia National
Laboratory Report 2004-1739 (2004)
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NbT(He) vs NbD(He)--Asymmetry ?

• Is source target asymmetry an ISSUE? Diff. ZPE?

• Displacements() and measured6 activation
• energies (eV) for H, D T in Nb IS
• M. J. Puska R. M. Nieminen, Phys. Rev. B10
  (1983) 5382

T?D exchange makes little difference in Lattice
distortion Do not expect substantial line
shiftscan be compensated With external Doppler
Drive
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Real time Resonance Detection?

• Invention of real-time detection method
• of Great Interest
• Rudimentary Ideas
• Spin flip in He?T µ (He) -2.1 nm µ (T)
  2.79 nm
• ?Transient (0.2 ms) magnetic field
  generated
• ?Hyperfine coupling to T electron
• ?Can response of electron moment be
  detected by ultrasensitive SQUID magnetometers?
• Creation of T (partially) inserts electron in d
  band of metal
• ? Extra electrons (after activation for a
  time) create extra
• electronic specific heat
• ? enough electrons for detectable
  Bolometric signal?