Cold & Ultra-cold Neutron Source Studies Yunchang Shin - PowerPoint PPT Presentation

Cold & Ultra-cold Neutron Source Studies Yunchang Shin Indiana University/IUCF

Outline Introduction Solid Methane S(Q, ω ) Model development Cold neutron Flux Measurement from solid methane moderators Solid Oxygen - A new, more intense UCN Source? Solid Oxygen Experiments at LANSCE

Neutron Intrinsic Spin I = 1/2 Mass m n = 939.56563 ±0.00028 MeV u d μ = -1.9130 ± 0.0000005 μ n d Mean Life τ = 885.7 ± 0.8 s Electric Dipole Moment d < 10 × 10 -26 e cm

Neutron Energy E 1eV 1meV 1 � eV 1neV 104K 103K 102K 10K 1K 0.1K 0.01K 1mK 100 � K 10 � K T � 1 � 10 � 100 � 1000 � 1 � m Epithermal Cold Ultra Cold Thermal Very Cold Room Temperature Total Reflection λ =1.8 Å , v=2200m/s λ =570 Å , v=7m/s

Physics with Slow Neutrons Fundamental Physics a. Neutron β Decay Life time b. Electric Dipole Moment (nEDM) c. Neutron Nuclear Weak Interaction (nPD Υ ) d.Cosmology, Astrophysics, Neutrino Physics Condensed Matter Physics a. Small Angle Neutron Scattering b. Neutron Interferometry , Reflectometry

Neutron Life Time

Neutron Life Time UCN Bottled UCNs N(t)=N(0) exp(-t/ τ ) τ -1 = τ -1n + τ -1loss Interaction of UCN with wall Magnetic Trapping Detector

nEDM Theoretical Prediction Electromagnetic Milliweak ILL PNPI Super-symmetry 199 Hg Comagnetometer d n <6.3 × 10 -26 e cm Standard Model ~10 -30

Neutron Source LENS Ref. G. Bauer

LENS at IUCF RF System SANS TMR Accelerator Radiography

p+Be Reaction Neutron Yield (n/mC) 13MeV 7MeV Yield~0.007~0.002 n/p

Target-Moderator- Reflector (TMR) Primary Flight Path Detector Vacuum Proton Beam Reflector Sample Moderator Collimator Air Source Collimato r Target

Solid CH 4 Moderator High proton density (~70% higher than liquid hydrogen at T < 20K) High Density of Rotational States in solid phases At LENS, T < 20K Methane Operation - No MCNP kernels in this temperature regime!

Developing a Kernel Construct a microscopic model for neutron dynamic structure factor of solid methane Total Scattering Cross Section Model ➔ S (Q, ω ) ➔ ρ ( ω ) LEAPR module of NJOY needs a frequency spectrum ρ ( ω )

CH 4 at Phase II (T<20K) 3/4 Hindered 8 Librational States T 2 T 1 , T 1 T 2 b J � 2 6 EE A 2 T 1 , T 1 A 2 � meV � 4 T 2 T 2 Energy ET 2 , T 2 E J � 1 2 Tunneling States T 1 T 1 E T a J � 0 A 1 A 1 0 A O h Molecules D 2 � d Molecules A B C 1/4 Free

Nuclear Spin exp( − E i /k B T ) Spin Distribution P i = g i � exp( − E i /k B T ) i 1 1 Ground State (I=2) Ground State (I=2) First Excited State (I=1) First Excited State (I=1) 0.8 0.8 Second Excited State (I=0) T Population Ratio Population Ratio T 0.6 0.6 0.4 0.4 A A 0.2 0.2 E 0 0 0 20 40 60 80 0 20 40 60 80 Temperature ( K ) Temperature ( K ) Free Rotation Hindered Rotation

Neutron Scattering in Solid CH 4 The Rotation of Tetrahedral Hydrogens (E n ≤ 10 meV) Inter-molecular Vibration ➔ Multi-Phone Excitation (10 ≤ E n ≤ 100 meV) Intra-molecular Vibration ➔ Harmonic Vibration (100 ≤ E n ≤ 1000 meV)

Approximations S ( Q, ω ) = S rot ( Q, ω ) ⊗ S trans ( Q, ω ) ⊗ S vib ( Q, ω ) Convolution of degrees of freedom of motion S rot ( Q, ω )exp( − γ Q 2 ) ≃ + S trans ( Q, ω )exp( − γ Q 2 ) + S vib ( Q, ω )exp( − γ Q 2 ) Treat them as uncoupled one depending on E n

σ tot (20K) 400 20K Whittermore 350 20K from Model Scattering Cross Section (b) 300 250 200 150 Rotation Phonons Vibrations 100 50 0.1 1 10 100 1000 Energy (meV)

σ tot (4K) 7K Grieger (1996) 400 4K From Model Scattering Cross Section (b) 300 200 100 0.1 1 10 100 1000 Energy (meV)

Scattering Function 0.3 0.3 10 10 S � Q, � Ω � S � Q, � Ω � 0.2 0.2 8 8 0.1 0.1 0 6 0 6 o � 1 o � 1 Q � A Q � A � � 4 4 5 5 5 5 10 10 10 10 2 2 � Ω � meV � � Ω � meV � � Ω � meV � � Ω � meV � 15 15 15 15 20 20 20K 4K ℏ ω =(0~20 meV), Q=(0~10 Å -1 )

Frequency Spectrum � ω � ω � + ∞ � � 2 kBT S ( Q, ω ) ω 2 e − = e − � v Q (0) v Q ( τ ) � e − i ωτ d τ = k B T 2 kBT 2 M p ( ω ) Q 2 2 π −∞ Q → 0 � � ω � z ( ω ) = 2 k B T � ω sinh p ( ω ) 2 k B T z( ω ) is equal to “ Generalized Frequency Spectrum” ρ ( ω ) Incoherent approximation ➔ lose coherent information

Frequency Spectrum 22K Harker & Brugger 20K Shin 60 4K Shin 40 � ( �� ) 20 0 0 5 10 15 20 �� (meV)

MCNP & Measurements (25K) 1 x 10 9 I(E) (n/sr/ � C/eV) 1 x 10 8 25K Quench 1 x 10 7 smeth22K (H&B) y-smeth20K (Shin) 1 x 10 6 0.0001 0.001 0.01 0.1 1 E (eV)

Moderator Operation O 2 doping (~1%) ➔ Boost Spin Relaxation of Rotational modes Slow Cooling (~20h) ➔ Reduce developing ``cracks” and ``holes” inside of moderator media Fully utilize the ``Neutron Scattering Cross Section” (equilibrium spin distribution is better than quenched spin distribution)

MCNP & Measurements (20K) 1 x 10 9 I(E) (n/sr/ � C/eV) 1 x 10 8 25K Quench 1 x 10 7 smeth22K (H&B) y-smeth20K (Shin) 20K O2 Doping+Slow Cooling 1 x 10 6 0.0001 0.001 0.01 0.1 1 E (eV)

MCNP & Measurements (4K) 1 x 10 9 I(E) (n/sr/ � C/eV) 1 x 10 8 4K Quench 1 x 10 7 4K O2 Doping+Slow Cooling y-smeth4K (Shin) 1 x 10 6 0.0001 0.001 0.01 0.1 1 E (eV)

New Model can do.. Model generates Scattering Kernel for Monte- Carlo Modeling between 4K < T < 20K Model can check non-spin equilibrium conditions Decompose contribution from the rotational, phonon degree of freedoms on the moderated neutron flux ➔ ``Free” vs ``Hindered” rotations

Decomposition of modes in 4K 1 x 10 10 1 x 10 9 I (E) (n/eV/ � C/sr) 1 x 10 8 4K Free Only 4K Free + Phonon 4K Hindered Only 1 x 10 7 4K Hindered + Phonon y-smeth4K 1 x 10 6 0.0001 0.001 0.01 0.1 1 E (eV)

Summary Construct New Scattering Kernel based on theory and Check its validity in MCNP modeling and measurements of Neutron Flux at LENS Optimize LENS with accurate new model Application to Very-Cold Neutron Sources

Solid Oxygen as Ultra-cold Yunchang Shin, Christopher M. Lavelle, Chen-Yu Liu Indiana University/IUCF

What is UCN ? E < 335 neV λ > 500 Å Three order of magnitude lower than cold neutron Total Reflection in material surface and large magnetic field gradient. Fundamental Physics with UCNs.

Super-thermal UCN Production Cold Neutron UCN Crystal Lattice Cold neutron loses energy in the matter by exciting collective mode and down-scattered to UCN R. Golub and J.M. Pendlebury, Phys.Lett, 53A.133 (1975)

Solid Oxygen The oxygen's small nuclear absorption cross section. σ coh σ inc σ abs Isotope c 2 D 5.59 2.04 5.2E -4 16 O 4.23 0 1.0E -4 b α phase (T<23.0K) oxygen has a long range anti-ferromagnetic ordering It sustains spin wave excitation ➔ Magnon Interaction with magnon provides down-scattering

Solid O 2 and D 2 UCN Production rate (~2) 3.0 × 10 -8 Φ 0 (12K CN in SO 2 ) 1.5 × 10 -8 Φ 0 (30K CN in Ortho-SD 2 ) ρ ucn =P ucn × τ Lifetime (~10) 375 ms in SO 2 40 ms in SD 2 due to bigger absorption Flux gain with source volume (~50) 8 cm in SD 2 (incoherent scattering length) 380 cm in SO 2 (absorption length)

UCN in Solid O 2 in PSI, Switzerland FunSpin beamline in SINQ ϕ CN =(4.5±1.0) × 10 7 (cm 2 - s-mA) with 1.2 mA proton on SINQ target PSI UCN group used this setup to study UCN production with Solid D 2 UCN Source

UCN in Solid O 2 FunSpin beam line in SINQ at PSI, Switzerland 120 � � � Liquid Gas 100 Neutron Counts (C-1) 80 60 40 20 0 20 40 60 80 100 120 Temperature (K)

UCN in Solid O 2 FunSpin beam line in SINQ at PSI, Switzerland 120 140 Temp 120 UCN count 100 100 UCN Count (N/C) Temperature(K) 80 80 60 γ 60 40 β 40 20 20 α 0 0 0 5 10 15 20 25 30 35 Time (Arb.)

UCN in Solid O 2 FunSpin beam line in SINQ at PSI, Switzerland 120 140 Temp 120 UCN count 100 100 UCN Count (N/C) Temperature(K) 80 80 60 γ 60 40 β 40 20 20 α 0 0 0 5 10 15 20 25 30 35 Time (Arb.)

UCN in Solid O 2 FunSpin beam line in SINQ at PSI, Switzerland 120 140 Temp 120 UCN count 100 100 UCN Count (N/C) Temperature(K) 80 80 60 γ 60 40 β 40 20 20 α 0 0 0 5 10 15 20 25 30 35 Time (Arb.)

UCN in Solid O 2 in PSI, Switzerland The yield of UCN is about 3 times less than in S-D 2 . UCN yields is correlated with quality of crystal How does cool down affect UCN yield? How does state of magnetic excitations affect UCN yield?

Solid O 2 at IUCF

Solid O 2 at IUCF Magnet B Field Gas Line Magnet Target Cell Window Camera

Conditions Search for First Solid Phase Transition T a. 43.6~43.8K in literature b. 44. 779~44.569K in T Cell Magnetic Field effect ( 1~2.5 Tesla ) Cooling Rate ( 1~0.1mK/hr )

T Liquid- γ (54.6K) Mar 07 Mar 16 Mar 31 Mar 29 B=0T 1T 1.5 T 2.5T

March 07, B=0T Initial T γ - β Final T γ - β (~2h) T C =44.467 K 44.213 K

March 31, B=1T Initial T γ - β Final T γ - β (~3h) 44.578 K 44.487 K