Polarized Neutrons Hirohiko SHIMIZU Department of Physics, Nagoya University

Transcription

1 Polarized Neutrons Hirohiko SHIMIZU Department of Physics, Nagoya University

2 Introduction

3 Neutron

4 1T Ni 244neV Strong Interaction 60neV 0neV - 60neV g γ d nneutron u d W G 1m e - ν e n τ=885.7s p Weak Interaction 103neV 0neV Electromagnetic Interaction Gravitational Interaction n µ µ µ µ

5 Devices

6 Devices Magnetic Supermirror

7 Neutron Reflection Fermi pseudopotential Ni: +243neV Fermi pseudopotential 0 grazing angle

8 Multilayer Mirror (Monochromatic) Fermi pseudopotential Ni: +243neV Ti: -50neV Fermi pseudopotential 0 grazing angle

9 Supermirror Fermi pseudopotential Ni: +243neV Ti: -50neV Fermi pseudopotential 0 grazing angle

10 Magnetic Supermirror Magnetic layers Non-magnetic layers reflective transparent Fe SiGe3 Fe SiGe3 Fe SiGe3 Fermi pseudopotential 0 Fermi pseudopotential 0 Fermi pseudopotential 0 µ0h σn σn parallel anti-parallel

11 Devices Spin Filter

12 Neutron Polarizer (Spin Filter) n : nuclear number density pa : target nuclear polarization t : target thickness

13 Spin Analyzer

14 Polarized Target (solid) B=0.3T T=77K B=2.5T T=0.5K B=10T T=0.01K e p e p e p Polarization P e =tanh(µ e B/kT) P p =tanh(µ p B/kT) e p e p e p B/T [T/K]

15 Polarized Target (solid) method electron proton Brute-force DNP thermal equilibrium thermal equilibrium thermal equilibrium thermal nonequilibrium MIONP thermal nonequilibrium thermal nonequilibrium

16 e p e p microwave paramagnetic center

17 (Differential) Solid Effect narrow ESR Δωe < ωn ΔωN ESR Electron Spin Resonance ωn ωn Δωe ωn ωe ωe+ωn ω ωe-ωn ωeωe+ωn ωe NMR Nuclear Magnetic Resonance ωe-ωn ωn ωe-ωn ωe ωe+ωn ω

18 Pentacene C22H14 Chem. Phys. Lett. 165 (1990) 6 m.p.=270 C y z x H0 H0 // x H0 // y H0 // z m=+1 12% 45% 46% m=0 76% 16% 8% m=-1 12% 39% 46% 73% 12% m=+1 9GHz S1 S0 laser excitation ps intersystem crossing T0 20µs 100µs 20µs 76% 12% Ix=+1/2 DNP-ISE Ix=-1/2 m=0 m= T 0.35T

19 Naphthalene C10H8 m.p.=80 C 2 naphthalene molecules 1 pentacene molecule Pentacene < 0.01 mol% b c x b a=0.82nm b=0.6nm c=0.87nm a a=g=90 b=123 P21/a (monoclinic) The x-axis of pentacene is aligned in host crystals.

20 Experimental Result (MIONP) K.Takeda et al., J. Phys. Soc. Jpn. 73 (2004) 2313 Pp~0.7 T=105K B=0.32T Naphthalene mol% Pentacene 4 mm 4 mm (ab) 2.2 mm (c)

21 Neutron Polarizer/Analyzer Energy Regions Methods Research Fields Fast Neutron Epithermal Neutron Thermal Neutron Cold Neutron Very-Cold Neutron Ultracold Neutron Magnetic Mirror Polarized 3 He Polarized Proton Magnetic Field Heusler Crystal Nuclear Engineering Nuclear Physics Fundamental Physics Hard Matter Researches Soft Matter Researches Fundamental Physics

22 Beam Chopper

23 Neutron Beam Chopper Disk Chopper Fermi Chopper Velocity Selector Diffraction Spin-flip Chopper 2 k =2d sin

24 Neutron Accelerator/Decelerator Y.Arimoto et al., Phys. Rev. A 86 (2012)

25 Neutron Decelerator by Successive Spin Flip magnetic dipole interaction unit cell AFP-NMR (adiabatic fast passage nuclear magnetic resonance) B 1 (rf) B 1 (rf) 1T +60neV 0neV 60neV B z B 0 B max spin parallel spin flip spin antiparallel spin flip H 1 = ω γ γ = rad s -1 T -1 (29 MHz/T) ΔE = 120 B max 1 T nev inner surface = neutron guide pulsed neutron source cell L=0.12m B max =5T ΔE = 0.6 µev L total ΔE = 120 µev L=24m 200 cells sweep synchronized with neutron pulse z J = cm -2 s -1 LANSCE storage time = 50sec neutron density cm -3 LANSCE cm -3 JSNS (0.9948) 172 = reflection loss spin flip loss phase mismatch due to neutron pulse width cm -3 LANSCE cm -3 JSNS

26 Neutron Accelerator/Decelerator rebuncher M.Kitaguchi, Prog. Theor. Exp. Phys. (2017) 043D01

27 UCN Rebuncher = Neutron Accelerator Original density can be restored if faster UCNs are decelerated appropriately. Neutron Rebuncher Neutron source Rebuncher reshapes UCNs into sharp pulse. x door position high density Storage cell Rebuncher fast UCN slow UCN decelerated accelerated UCN production at converter Rebuncer decelerates the UCNs according to the velocity, synchronized with time of flight in pulsed source. M. Kitaguchi, et. al, t

28 Adiabatic Fast Passage (AFP) spin flipper Large Deceleration \NEDM\FILPA0A.AF :23: \NEDM\FILPA33A.AF :55: \NEDM\FILPA33A.AF :55: L\NEDM\FILPA0A.AF :23: Small Deceleration RF magnetic field in gradient field gives/ removes the energy with spin flip. 2µB = h! 30 MHz = 1T = 120 nev Faster neutrons arrive earlier. Large deceleration = High Freq. RF Slower neutrons arrive later. Small deceleration = Low Freq. RF Energy exchange is proportional to the RF frequency. Sweeping frequency matching to the arrival time

29 Prototype Static Magnet 0 Y. Arimoto et al. / Physics Proced (Gauss) B x Yoke SS400 () Anisotropic inter-poles make SS400+ homogeneous gradient field z (cm) y= 0.0 cm Spin flip region x= 0.0 cm y= 0.0 cm y= 1.0 cm y= 2.0 cm y= 3.0 cm Y.Arimoto, et. al.,ieee Trans. Appl. Supercond. 22, (2012). db x /dz (Gauss) Figure 8: B x (left) and db x /dz (right) as a function of z on the median plane. T 1.0 cm (square), 2.0 cm (triangle), 3.0 cm (inverse triangle), respectively. Effectiv and return yoke shape are indicated as same scale and position in z-direction on (Gauss) x= 0.0 cm y= 1.0 cm y= 2.0 cm y= 3.0 cm x= B x

30 Results RF ON / RF OFF Accelerated (opposite spin) RF ON Rebunched! TOF [sec] Blue : Exp. Data Red : Simulation Rebunching of UCNs was observed! Y. Arimoto, et., al., Phys. Rev. A 86, (2012).

31 Neutron Accelerator/Decelerator velocity concentrator M.Kitaguchi, Prog. Theor. Exp. Phys. (2017) 043D01

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