POLARIZED 3 He SPIN FILTER DEVELOPMENT in the U.S. Tom Gentile, W.C. Chen, NIST Mike Snow, Indiana University Gordon Jones, Hamilton College Thad Walker, Univ. of Wisconsin thanks to Dept. of Energy, Basic Energy Sciences m F = - 1/2 m F = + 1/2 polarized metastable 3 He atom metastable 3 He atom polarized ground state 3 He atom ground state 3 He atom OPTICAL PUMPING of METASTABLE 3 He METASTABILITY EXCHANGE Excitation exchanged in collision Nuclear spins unperturbed 1s2p 3 P 0 1s2s 3 S 1 F.D. Colegrove, L.D. Schearer and G.K. Walters, Phys. Rev. A 132, 2561 (1963) 1083 nm Electric discharge excites metastable 1083 nm light pumps metastable Hyperfine mixing polarizes nucleus ++ OPTICAL PUMPING of RUBIDIUM (Rb) m s = -1/2 m s = + 1/2 ++ 5s 2 S 1/2 5p 2 P 1/2 collisional mixing SPIN-EXCHANGE FROM Rb TO 3 He Spin exchanged from Rb electron to 3 He nucleus slowly through the hyperfine interaction. Rb atom electron spin 3 He atom nuclear spin M.A. Bouchiat, T.R. Carver and C.M Varnum, Phys. Rev. Lett. 5, 373 (1960) T.E. Chupp et al, Phys. Rev. C 36, 2244 (1987) 795 nm light pumps Rb electron collisional decay 795 nm p NUCLEON STRUCTURE PHYSICS with POLARIZED 3 He n 3 He nuclear spin carried mainly by the neutron Scatter polarized electrons - obtain: Neutron magnetic and electric form factors Distribution of current and charge carried by quarks Spin structure functions - distribution of spin e-e- p polarized electron polarized 3 He high pressure cell for TJNAF polarized 3 He target Univ. of Mainz piston compressor, 1994 [E. Otten, HELION02] T.R. Gentile et al, Magn. Reson Med. 43, (2000) R.R. Rizi et al, MRM 39, (1998); D.A. Lipson et al, MRM 47, (2002) T.R. Gentile, Eur. Radiol. 9, B17 (1999). strong spin-dependence of the neutron absorption cross section polarized outgoing neutrons unpolarized incoming neutrons polarized 3 He POLARIZED 3 He NEUTRON SPIN FILTERS K.P. Coulter et al, Nucl. Instrum. Meth. A 288, 463 (1990) D. S. Hussey et al, Rev. Sci. Instrum. 76, (2005) INDIANA UNIVERSITY PISTON COMPRESSOR T.R. Gentile et al, J. Res. Natl. Inst. Stand. Technol. 106, (2001) DIFFUSE REFLECTOMETRY polarizer (supermirror) spinflipper sample spinflipper 3 He cell analyzer W.C. Chen et al, Rev. Sci. Instrum. 75, (2004) W.C. Chen et al, Physica B 335, (2003) position sensitive detector Cobalt antidot sample - results in saturating field of 1 kG non spin-flip spin-flip Results in 3 G after demagnetizing sample non spin-flip spin-flip CONTINUOUSLY OPERATING 3 He POLARIZER at THE SINGLE CRYSTAL DIFFRACTOMETER at IPNS March polarizer test G.L. Jones et al, Physica B 356, (2005) March improved polarizer, CoFe analysis, NMR-based flip G.L. Jones et al, Physica B, in press March Yb 14 MnSb 11 sample V.O. Garlea, abstract for ACNS 2006 d V.O. Garlea 1, G.L. Jones 2, B.Collett 2, W.C. Chen 3,5, T.R. Gentile 3, P.M.B. Piccoli 4, M.E. Miller 4, A.J. Schultz 4, H.Y. Yan 5, X. Tong 5, M. Snow 5, B.C. Sales 1, S.E. Nagler 1, W.T. Lee 6, C. Hoffmann 6 1 ORNL, 2 Hamilton College, 3 NCNR, 4 IPNS, 5 Indiana U, 6 SNS n + p PNC asymmetry: PARITY VIOLATION in NUCLEON-NUCLEON INTERACTIONS (meson exchange model) n p Parity operator: 3 He polarizer** for NPDGamma experiment* at LANSCE ** project headed by Univ. of Michigan, SEOP cells made at NIST one year of nearly continuous operation in 2005 T.E. Chupp et al, paper in progress * S. Page et al, J. Res. Natl. Inst. Stand. Technol. 110, (2005) PRECISION NEUTRON POLARIMETRY with POLARIZED 3 He P n = neutron polarization T n = transmission of polarized cell T 0 = transmission of unpolarized cell NEUTRON POLARIZATION determined from transmission cross section proportional to time of flight analysis ideal t = opacity = cross section * 3 He density * cell length PHYSICS ASYMMETRY proportional to P n ASTRO Relaxation time = 730 hours Yeah ! D.R. Rich et al, Appl. Phys Lett. 80, (2002) T.R. Gentile et al, J. Res. Natl. Inst. Stand. Technol. 110, (2005) SPOCK relaxation time = 70 hours Booh ! 3 He POLARIZATION for SPIN-FILTER CELLS cellvolume relax time polarization [cm 3 ] [hours] Wilma % Bullwinkle (refl) % Chekhov (refl) % Pebbles (npdg) % Rb/K hybrid cells: Syrah (TAS, SNS refl) % Zinfandel (TAS, SNS refl) % GOOD NEWS: 75% for spin filter cells approaching one liter BAD NEWS: Why only 75% ? (P Rb = 1, se -1 = hours) T.R. Gentile et al, J. Res. Natl. Inst. Stand. Technol. 110, (2005) B. Chann et al, J. Appl. Phys. 94, (2003) B. Chann et al, Phys. Rev. A 66, (2002) X vs. S/V E. Babcock et al, Phys. Rev. Lett. 96, (2006) Univ. of Wisconsin data (hot relaxation, polarization) NIST data (polarization) SEOP with POTASSIUM and Rb/K MIXTURES Motivation: spin-destruction rates lower but spin-exchange rates similar, hence higher production rate possible Issues for direct SEOP of pure K: laser availability (770 nm) smaller fine-structure splitting Hybrid SEOP*:Rb/K mixture, lean in Rb optically pump Rb obtain lower spin-destruction using same laser typical OP temp increased from 170 C to 220 C Results: factor of 2-3 gain in efficiency, agrees with with calculated estimates Polarize just under one liter to 75% in 1-2 days, using 54 W of spectrally narrowed light Five good cells exist for NCNR BT7 and SNS magnetism reflectometer Pure K: 770 nm laser based on a 40 W diode bar in use at NIST 75% polarization obtained in pure K cells improvement in efficiency, but lower than expected Studies of both methods in progress; larger gains expected for higher pressures *E. Babcock et al, Phys. Rev. Lett. 91, (2003) THE ROAD AHEAD Wide-angle polarization analysis - development at NCNR instruments and IPNS SCD Continuous optical pumping High volume polarized gas production current: 3.5 bar, 0.7 liter Rb/K cell pumped to 75% with p 6 h 4 p yields 2.4 bar-L/day (~ factor of 10 below MEOP) future: higher pressure (~ 7 bar), Rb/K or pure K (factor of ~4) simplicity, relatively small size and cost allow for multiple systems; reduced vulnerability 3 He-based polarized beam with wide-angle polarization analysis* * For low sample fields; shown for NCNR Multi-axis Crystal Spectrometer (MACS) NIST/IU postdocs: W.C. Chen, T.B. Smith, D.R. Rich, G.L. Jones, F.E. Wietfeldt NIST staff: A.K. Thompson, G.L. Greene, M.S. Dewey SURF students: G. Armstrong, J. Baker, R. Wendell, P. Gruber, D. Cuccia, A. Lee, K. Gosier NIST Materials Science and Engineering: J.A. Borchers, K.V. ODonovan, C.F. Majkrzak, R. Erwin, J. Lynn NIST glassblowing and optical shop: Jeff Anderson, Jack Fuller (the really important people) W.M. Snow et al, Indiana University G.L. Jones et al, Hamilton College T.G. Walker, E. Babcock, B. Chann, Univ. of Wisconsin Support from Dept. of Energy ACKNOWLEDGEMENTS