Presentation on theme: "Solid Oxygen based Ultra-Cold Neutron Source"— Presentation transcript:
1Solid Oxygen based Ultra-Cold Neutron Source 9/13/07Chen-Yu Liu, Yun Chang Shin, Chris Lavelle, Josh Long(Indiana University)Albert Young (NCSU)Andy Saunders, Mark Makela, Chris Morris (LANL)Klaus Kirch (PSI)
2Superthermal ProcessR. Golub and J. M. Pendlebury, Phys. Lett, A53, 133 (1975)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.
3UCN loss in Superfluid 4He UCN density:(Limited by loss)The figure of merit:3
4Dynamics of UCN Production -- Defeat thermal equilibriumExtract UCN out of the source before it is thermalized Spallation N source +Separation of the source and the storage by a valve
5UCN production in Solid D2 Incoherent scattering (inc = 2.04 barn)The difference of singlet and triplet scatteringCoherent contribution ( coh= 5.59 barn)In a cold neutron flux with a continuous spectrum, more neutrons could participate in the UCN production.(1,1.73,0)(1,1,0)(1,0,0)5
6UCN loss in Solid D2 Storage bottle Solid D2 Nuclear absorption by S-D2 ~ 150 msecNuclear absorption by HydrogenImpurities, ~ 150 msec/0.2% of HSolid D2UCN upscattering by phonons ~ 150 msec at T = 5KUCN upscattering by para-D2 ~ 150 msec/1% of para-D2
7Los Alamos s-D2 UCN Prototype Source C. Morris et al., Phy. Rev. Lett.89, (2002)World recordSource has para-D2: 4%Bottled UCN density: 100 UCN/c.c. in a S.S. bottle 1 m away from the source. (world record)PSI, NCSU-Pulstar, FRM, etc..are building solid D2 based UCN source.Best vacuum: 104 atoms/c.c.
8Solid Oxygen as a UCN Source Electronic spin S=1 in O2 molecules.Nuclear spin = 0 in 8OAnti-ferromagnetic ordering-phase, T < 24K.UCN Production in S-O2Produce 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.
9UCN production in Solid Oxygen C.-Y. Liu and A.R. YoungUCN production in Solid OxygenProduction rateP = 2.7 10-8 0 (30K CN in S-O2)P = 3.0 10-8 0 (15K CN in S-O2)P = 1.5 10-8 0 (30K CN in S-D2)Gain ~ 2 relative to S-D2Lifetime375 ms in S-O240 ms in S-D2Gain ~ 10Volume gain, (l)n, n= 1-3lucn = 380 cm in S-O2lucn = 8 cm in S-D2Gain ~Compared with S-D2,Gain > 1000 is possible !
10Some Recent Results of UCN Production in Solid O2 PSI-SINQ (2005)CN = (4.51.0)107/cm2-s-mANo 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-D2.A peak in the - phase transition. (critical scattering?)
11UCN Production in D2 and CD4 PSI, 2005From D2 and CD4.Signature temperature dependence of a superthermal source.
12Cold Neutron Transmission (TOF) PSI-SINQCN = (4.51.0)107/cm2-s-mAFlight path =2.83m.Neutron Chopper.Scattering probabilityI0(E)-I(E)/I0(E)Features:Less scattering compared with D2.Bragg edgesAdditional Bragg peak in alpha phase. (indicate the presence of a magnetic structure.)
13UCN Production vs. CN Transmission Material: solid O2
14Anti-Correlation of UCN production vs CN scattering Data from 2005PSI run (1 week)UCN production was not effected by temperature or phase.Something (other than downscattering) is dominating the yield of UCN.
15Probe the Magnon Mechanism using a B field Spin flop transitionaround 7 Tesla.C. Uyeda at. al., J. Phys. Soc. Jpn. 54, 1107 (1985)An external magnetic field to perturb the magnon dispersion curveChange the density of states.Optimize UCN production.Definitive demonstration of the magnon mechanism.An unique feature of oxygen!
17Superconducting Solenoid & Solid O2 Target Cryostat 5.5T with 90 AmpSC solenoid CryostatSC Solenoid PowerSupplyFlow He Cryostatfor O2 target
18O2 Gas Handling System (all VCR) Optical cellbeta-gamma phasetransition(slow cool-down~0.017K/min)beta phase(slow vapor deposition)beta phase(slow cool down)O2 Gas Handling System (all VCR)
19Program of O2 UCN SourceIU: Yunchang Shin (graduate student), Chris Lavelle(postdoc), Chen-Yu LiuCollaborators from LANL : Andy Saunders, Mark Makela, Chris MorrisNCSU: Albert YoungThis summer (July – October)Lujan Center (ER2) Flight Path 12UCN production under B fieldCN TOF transmissionUCN gravity spectrometerPHAROS: one week beam time to measureS(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/cm2-s(proton: 13 MeV, 2.5mA(avg), 2 cm away from the 22K moderator, hTCN=35K)UCN density: 95 UCN/cc, UCN fluence: ~ 1e+6 UCN/sGamma heating: 0.003W/gram
20ConclusionsMagnons in the AF phase of S-O2 offer an additional channel for inelastic neutron scattering.UCN production rate in S-O2~ (1-2) in S-D2.UCN lifetime in S-O2 ~ 10 in S-D2.Larger source possible. (at least 10 S-D2)UCN current output from S-O2 (at least) 100 from S-D2UCN Source ProgramLENS provides a unique opportunity to study and develop a S-O2 based UCN source.FP12 to study magnon mechanism in solid oxygen.Broader impactsA positive result would have a major impact on other UCN sources in proposal/constructionPSI, 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.