Presentation on theme: "Solid Oxygen based Ultra-Cold Neutron Source 9/13/07 Chen-Yu Liu, Yun Chang Shin, Chris Lavelle, Josh Long (Indiana University) Albert Young (NCSU) Andy."— Presentation transcript:
Solid Oxygen based Ultra-Cold Neutron Source 9/13/07 Chen-Yu Liu, Yun Chang Shin, Chris Lavelle, Josh Long (Indiana University) Albert Young (NCSU) Andy Saunders, Mark Makela, Chris Morris (LANL) Klaus Kirch (PSI)
Superthermal Process Cold neutrons downscatter in the solid, giving up almost all their energy, becoming UCN. UCN upscattering (the reverse process) is suppressed by cooling the moderator to low temperatures. R. Golub and J. M. Pendlebury, Phys. Lett, A53, 133 (1975)
UCN density: (Limited by loss) The figure of merit: 3 UCN loss in Superfluid 4 He
Dynamics of UCN Production -- Defeat thermal equilibrium Extract UCN out of the source before it is thermalized Spallation N source + Separation of the source and the storage by a valve
Incoherent scattering ( inc = 2.04 barn) The difference of singlet and triplet scattering Coherent contribution ( coh = 5.59 barn) –In a cold neutron flux with a continuous spectrum, more neutrons could participate in the UCN production. UCN production in Solid D2 (1,1.73,0) (1,1,0) (1,0,0) 5
UCN loss in Solid D2 Nuclear absorption by S-D 2 ~ 150 msec Nuclear absorption by Hydrogen Impurities, ~ 150 msec/0.2% of H UCN upscattering by phonons ~ 150 msec at T = 5K UCN upscattering by para-D 2 ~ 150 msec/1% of para-D 2 Solid D 2 Storage bottle
Los Alamos s-D 2 UCN Prototype Source Source has para-D 2 : 4% Bottled UCN density: 100 UCN/c.c. in a S.S. bottle 1 m away from the source. (world record) World record C. Morris et al., Phy. Rev. Lett. 89, (2002) Best vacuum: 10 4 atoms/c.c. PSI, NCSU-Pulstar, FRM, etc.. are building solid D2 based UCN source.
Solid Oxygen as a UCN Source Electronic spin S=1 in O 2 molecules. Nuclear spin = 0 in 8 O Anti-ferromagnetic ordering – -phase, T < 24K. UCN Production in S-O 2 Produce UCN through magnon excitations. –Magnetic scattering length ~ 5.4 fm. Null incoherent scattering length. Small nuclear absorption probability. P.W. Stephens and C.F. Majkrzak, Phys. Rev. B 33, 1 (1986) A very large source possible.
UCN production in Solid Oxygen Production rate –P = (30K CN in S-O 2 ) –P = (15K CN in S-O 2 ) –P = (30K CN in S-D 2 ) –Gain ~ 2 relative to S-D 2 Lifetime –375 ms in S-O 2 –40 ms in S-D 2 –Gain ~ 10 Volume gain, (l) n, n= 1-3 –l ucn = 380 cm in S-O 2 –l ucn = 8 cm in S-D 2 –Gain ~ Compared with S-D 2, Gain > 1000 is possible ! C.-Y. Liu and A.R. Young
Some Recent Results of UCN Production in Solid O 2 PSI-SINQ (2005) – CN = ( ) 10 7 /cm 2 -s-mA No superthermal temperature dependence. –Indicates unknown source of UCN loss. UCN yield is correlated with how the crystal is prepared. The UCN yield (best number) is ~ 3 times less than s-D 2. A peak in the - phase transition. (critical scattering?)
UCN Production in D 2 and CD 4 PSI, 2005 From D 2 and CD 4. Signature temperature dependence of a superthermal source.
Cold Neutron Transmission (TOF) PSI-SINQ – CN = ( ) 10 7 /cm 2 -s- mA Flight path =2.83m. Neutron Chopper. Scattering probability –I 0 (E)-I(E)/I 0 (E) Features: –Less scattering compared with D2. –Bragg edges –Additional Bragg peak in alpha phase. (indicate the presence of a magnetic structure.)
UCN Production vs. CN Transmission Material: solid O 2
Anti-Correlation of UCN production vs CN scattering UCN production was not effected by temperature or phase. Something (other than downscattering) is dominating the yield of UCN. Data from 2005 PSI run (1 week)
Probe the Magnon Mechanism using a B field An external magnetic field to perturb the magnon dispersion curve –Change the density of states. –Optimize UCN production. Definitive demonstration of the magnon mechanism. C. Uyeda at. al., J. Phys. Soc. Jpn. 54, 1107 (1985) An unique feature of oxygen! Spin flop transition around 7 Tesla.
UCN Source Cryostat at IU
Superconducting Solenoid & Solid O 2 Target Cryostat 5.5T with 90 Amp Flow He Cryostat for O2 target SC solenoid Cryostat SC Solenoid Power Supply
O 2 Gas Handling System (all VCR) Optical cell beta-gamma phase transition (slow cool-down ~0.017K/min) beta phase (slow vapor deposition) beta phase (slow cool down)
Program of O 2 UCN Source IU: Yunchang Shin (graduate student), Chris Lavelle(postdoc), Chen-Yu Liu Collaborators from LANL : Andy Saunders, Mark Makela, Chris Morris NCSU: Albert Young This summer (July – October) Lujan Center (ER2) Flight Path 12 –UCN production under B field –CN TOF transmission –UCN gravity spectrometer PHAROS: one week beam time to measure S(alpha, beta) in solid oxygen under high field. Build an university based UCN Source coupled to LENS at IUCF. –Cold neutron flux: 3.5e+9 CN/cm 2 -s (proton: 13 MeV, 2.5mA(avg), 2 cm away from the 22K moderator, hT CN =35K) –UCN density: 95 UCN/cc, UCN fluence: ~ 1e+6 UCN/s –Gamma heating: 0.003W/gram
Conclusions Magnons in the AF phase of S-O 2 offer an additional channel for inelastic neutron scattering. –UCN production rate in S-O 2 ~ (1-2) in S-D 2. –UCN lifetime in S-O 2 ~ 10 in S-D 2. –Larger source possible. (at least 10 S-D 2 ) –UCN current output from S-O 2 (at least) 100 from S-D 2 UCN Source Program –LENS provides a unique opportunity to study and develop a S-O 2 based UCN source. –FP12 to study magnon mechanism in solid oxygen. Broader impacts –A positive result would have a major impact on other UCN sources in proposal/construction PSI, TUM, NCSU Pulstar source, national UCN facility at LANSCE… –A high UCN flux will open up opportunities to perform several UCN based fundamental experiments, e.g. a UCN nnbar experiment.