Sub-MeV Neutrino Technology R. S. Raghavan Virginia Tech NOW-2006 September 10, 2006

1. Sub-MeV Neutrino Technology R. S. Raghavan Virginia Tech NOW-2006 September 10, 2006

2. 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

3. New Paths in LO-Nu Technology Four Lo Nu Reactions (νe ,p) 1.8 MeV 1956 Reines K’Land (νe , 115In) 0.114 MeV 1976 LENS (ν , e) 0.020 MeV 1992 CTF, B’xino, K’land, Cryo? Recoilless Nu 0.0186 MeV 2006 ??? Res Cap

4. Reactor Antineutrino Detection—ReinesFirst Breakthrough against LE Bgd Wall • Source: Reactor produced antineutrinos- 0-8 MeV Major flux < 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: ν̃e+p n+e+ Serendipity: Look at delayed neutron in concidence It works because neutron diffusion creates DELAY, thus it gives a “coded” signal that DISCRIMINATES—No 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 ……

5. LENS—100 keV neutrino detection with tag • Objective: pp neutrinos from Sun— • 0-420 keV—No hope against bgd wall—UNLESS ….Nu Tag ! • 1976—Copy the Master—Can 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)  νe + 115In  115Sn* (τ = ~5 μ s) +2γ+e-

6. Indium Tag—Idea 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 Grieb—Talk tomorrow

7. ν +e ν +e of < 100 keV neutrinosTechnology, Technology, Technology ! Objective: 7Be nus from sun (861 keV) by nu-e scattering—Signal extends from 0-670 keV “Compton” Edge •  No reaction event tag !! But… •  Monoenergetic Nusignature recoil electron profile •  High Rates  1/r2 oscillation with earth’s 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

8. New Perspectives with very low energy neutrinos • Recoilless Resonant Capture Reactions with Tritium anti-Neutrinos • Very low energy 18.6 keV—current 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

9. 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. Θ13 flavor oscillations in 10m baseline  Implications for CP violation & Baryon Asymmetry 3. New problem: Test of Sterile Neutrinos  test LSND result LSND implies Δm2 ~0.5 to 1 eV2 sin2 2θ = 0.1 to 0.01 ….?? Presumed conversion to sterile neutrinos for THe: Disappearance / oscillations in ~5cm baselinesMajor Neutrino Physics Interest !

10. Detecting Antineutrinos Low energy ν̃e – why ? • Detecting 40K in earth • Short Baseline anti-neutrino oscillations How to lower ν̃e detection threshold below 1.8 MeV? Basically different from νe detection ν̃eReactionProduces e+--not e-  Sets Min.Threshold = 1.022 MeV • e.g. ν̃e+pn+ e+  Eνmin = 1.022+0.782 = 1.8 MeV ν̃e+3HeT +e+  Eν min= 1.022+0.0186 = 1.0406 MeV --No Escape – Some but not much gain in reducing nuclear Q alone

11. New Idea I: Breakthrough in Threshold ProblemLev Mikaelyan (1968) Rediscover “New” Idea of LM (Orbital electron + ν̃e) Capture: • ν̃e +3He +e- ( 1s orbital)  T Get TWO things: • Really low threshold  Enu min = 18.6 keV ! Voila! 2. All energy except Eν is fixed---Resonant Character ! Eν(res) = Q – B(1s He)+ER Great but, Not much use for wide band nu spectra from Reactors because neutrino density ρ = (dn/dE)/N is too small  Need idea #2

12. Resonant Source of AntineutrinosJ. Bahcall (1962) Idea #2: Inverse of Lev Mikaelyan’s reaction: T  3He + e- (in 1s orbit) +ν̃e • “bound State” β-decay—John Bahcall (1962) • Theory: 0.69% x0.8 =0.54% Bβ decay goes to ground state of He • Eν̃e = 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 ν̃e threshold AND enhance Xsec !! • By How much?  IDEA # 3

13. 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 Γ (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 ΔE thermal linewidth ~0.06 eV at T=300K

14. L. Mikaelyan-- Resonant ν̃e Cross section LM formula FOR RESONANT ν̃e CAPTURE σ = 4.18x10-41 go2 ρ(E(ν̃e res)/MeV) / ft1/2 cm2 = 4.6x10-49 x ρ go2 = 1.24x10-5 (1s Electron density) ft1/2 = 1132 s (weak interaction factor- T decay constant) ρ = no. of neutrinos/MeV (in incident neutrino spectrum)

15. Neutrino Line Width & Resonance X-section Thermal Motion: Δ = Eν√(kT/Mc2) = 0.08eV;(if T and He are in solids –must include effect of Debye temperatures) RECOIL ENERGY! :ER = Eν2/ 2Mc2 = 0.061eV • ρ(Eν̃e res/MeV) = (106/ 2Δ) x overlap emission & abs • windows • (106 / 0.16) x 0.4  2.5x 106  Resonance Enhancement • σ = 10-42 cm2 for 18 keV ν̃e • = σ (ν̃e +p) for 3 MeV ν̃e • ROOM FOR IDEA # 3 LINE WIDTH Γ <<< thermal width Δ ?  σ increases correspondingly • Must eliminate ER first

16. Recoilless Resonance X-section • Recoilless Fraction f f = exp-{4/3 (ER/ Z) (Z= zero point energy ZPE) for low temperatures (T<< Θ = Debye Temp = 8/9 (Z/Mc2) • Line Width Γ –Determines resonance density, Xsec (not natural lw but experimental energy fluctuation width) practical parameter from magnetic spin-spin relaxation time T2 3. Effective σ(res) (LM formula): σ(res) = f(s)f(a) 4.6x10-49 x ρ/MeV cm2 = f(s)f(a) 4.6x10-49 x 106 / Γ (eV)T Anticipate: f(s)f(a) ~0.1; T2~100 μs Γ~ 6x10-12 eV • σ(res) ~ 1032 cm2  10 orders of magnitude larger than σ (ν̃e + p)

17. 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 (B’s already considered) • Chemical bonding (T but not He) • Lattice vibrational energy, at T≠ 0 second order Doppler shift  Zero Point Energy even at T=0 • 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?

18. T T Nu+e capture B β-decay ν̃e He He Self Compensation of perturbing Energies in THe system Nu Resonance Involves two time reversed processes Source: Initial State: Chemically bonded T Final State: ν̃e + 3He No recoil-No lattice phonons emitted Target: Initial State: ν̃e + 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 (ν̃e res) + (ET –EHe) Absorption: E (ν̃e res)+(EHe-ET) = E (ν̃e res)-(ET –EHe) Energy gain in Emission is COMPENSATED EXACTLY in absorption Resonance condition maintained STRICTLY

19. Self-Compensation Conditions Conditions on ET , EHe for self-compensation: • Unique energies • Identityof ET EHe each in Source and Absorber • StaticPerturbation—no relaxation • Conceptual Framework SAFE • What about effects in Practice? Sources of breakdown in energy balance: • Distribution of E’s Inhomogeneous broadening • Relaxation homogeneous broadening • Non indentity of E’s in source/absorberLine Shift

20. 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

21. Tritium and He sites in metals He T HeMicrobubbles: 1-2nm diam; 4000 atoms Solid under pressure ~10 GPa at <100K He atoms closer than in IS sites TInterstitial Sites Octahedral – fcc metals Tetrahedral—bcc metals

22. 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

23. 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

24. 0.035 Tritium in NbT Tritium Desorbed 200Kc1 0.03 215Kc1 220Kc1 0.025 He3/Nb (atomic fraction) 0.02 225K c1 0.015 235K c1 250K c2+c3 0.01 235K c2+c3 0.005 250K c1 0 0 50 100 150 200 250 300 350 400 time(days) 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

25. Niobium- Unique Discovery • Conclusions on Niobium as Matrix choice: • Calculations show that at <200K 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

26. 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 γ resonance (ΔE/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

27. 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 ΔE = 8.5x10-12 eV ΔE/E = 4.6 x 10-16 NMR-MASS resolves the two NMR lines (αo βo 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

28. Preliminary estimate of X-sec • ZPE (T—Nb TIS): 0.071 eV • ZPE He--Nb TIS): 0.093 eV • f(T) f(He) = 0.076 • T2 = 0.2x10-4 s • Γ = 8.6x10-12 eV • He TIS site fraction = 2/3  σ (res) = 0.3x10-32 cm2

29. 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/τau of T) • in situ by heat produced • in MS T sample by counting C-betas

30. Nu Resonance in Practice—Target 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 practice—Mass 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

31. 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

32. Conclusions & Outlook • Conclusions: • NbT(He) major discovery—sets 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 200K—no such data yet • Invent Real time signal methods ??? • ……….

33. 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 grows—distributed uniformly (Tritium Trick (TT)) Problems: • T and He lattice Sites in TT—Unique? 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 2Δ is the full width due to thermal motion Δ ER

37. T and He sites in Metal Tritides Great Deal of Data Available Fusion and Fuel tech—Sandia-- 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 gas—insoluble in metals • High mobility • Forms pairs quickly and nucleates in microbubbles • Non-unique, distribution of ZPE • Unacceptably large inhomogeneous broadening

38. 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 M=Nb 0.9 0.13 0.43 1.1E-26c D. F. Cowgill, Sandia National Laboratory Report 2004-1739 (2004)

39. 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 shifts—can be compensated With external Doppler Drive

40. 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?