Modeling and Measurement Of Neutronic Properties of New Cryogenic - PowerPoint PPT Presentation

Modeling and Measurement Of Neutronic Properties of New Cryogenic Neutron Moderators RC No. 14161 Second Research Coordination Meeting of the Agency’s Coordinated Research Project on “ Improved production and utilization of short pulsed, cold neutrons at low-medium energy spallation neutron sources ” Kuala Lumpur, Malaysia 02 – 04 July 2009 CENTRO ATOMICO BARILOCHE - ARGENTINA

Chief Scientific Investigator: José Rolando GRANADA Scientific Investigator: Javier Roberto SANTISTEBAN Collaborators: Javier DAWIDOWSKI, Florencia CANTARGI, Aureliano TARTAGLIONE, Sergio PETRIW, Jerónimo BLOSTEIN, Luis CAPARARO Neutron Physics Group Centro Atómico Bariloche Comisión Nacional de Energía Atómica ARGENTINA CENTRO ATOMICO BARILOCHE - ARGENTINA

OUR TASK CENTRO ATOMICO BARILOCHE - ARGENTINA

DETAILED WORK PLAN FOR COMING YEAR (05/08-05/09), INCLUDING PROPOSED METHODS OR TECHNIQUES: To complete the validation of the scattering kernels developed in the last year, through comparisons of their predictions with experimental data. The hydrogeneous materials involved are: toluene, mesytilene, and mixtures of the two. MCNP calculations based on the new cross section libraries will be compared with measured spectra from those materials, at a few low temperatures. CENTRO ATOMICO BARILOCHE - ARGENTINA

DETAILED WORK PLAN FOR COMING YEAR (05/08-05/09), INCLUDING PROPOSED METHODS OR TECHNIQUES (cont.) During this second year of the project, we will tackle the problem of describing the interaction of slow-neutrons with deuterated molecular solids, typically d-methane and d-mesitylene at vey low temperatures. Those materials are of primary interest as moderators for very- and ultra-cold neutrons, on account of their very small absorption cross sections and the expected shift in the excitation energies due to isotopic effects. CENTRO ATOMICO BARILOCHE - ARGENTINA

Structure and Dynamics of the system NJOY Nuclear Data Processing System Cross Section Libraries Neutron calculations (with MCNP) CENTRO ATOMICO BARILOCHE - ARGENTINA

AROMATIC HYDROCARBONS [Nucl. Instr.Meth. B 267 , 175 (2009)] CENTRO ATOMICO BARILOCHE - ARGENTINA

MESITYLENE (C 9 H 12 ) Good radiation resistance • According to the cooling rate it • can exist in three solid phases Phase III: cooling down at 2K/min • Phases I and II: annealing process • is required Availability of low-frequency rotational • modes related to methyl groups CENTRO ATOMICO BARILOCHE - ARGENTINA

MESITYLENE 30 Phase I 25 Phase II Phase III 20 Z[E] [u.a.] 15 10 Experimental information [Natkaniec et al., Proceedings of ICANS XVI, 2003] 5 0 0.00 0.02 0.04 0.06 0.08 E [eV] CENTRO ATOMICO BARILOCHE - ARGENTINA

Natkaniec et. al studied a solution of mesitylene and toluene in a fraction 3:2 by volume It solidifies in a glassy structure irrespective of the cooling rate or thermal treatment provides a frequency spectrum with low frequency modes CENTRO ATOMICO BARILOCHE - ARGENTINA

SOLUTION MESITYLENE : TOLUENE 3:2 by volume Experimental information M esitylene:T oluene (3:2) T oluene (glassy phase) [Natkaniec et al., Proceedings of M esitylene (phase II) ICANS XVI, 2003] Z (E) [u. a.] 0.00 0.02 0.04 0.06 0.08 0.10 E [eV ] CENTRO ATOMICO BARILOCHE - ARGENTINA

MEASUREMENTS (performed at our lab using a pulsed neutron source) CENTRO ATOMICO BARILOCHE - ARGENTINA

1500 1500 1200 1200 Mesitylene Mesitylene Sección eficaz total [barns] Sección eficaz total [barns] 900 900 (293 ± 2) K (180.0 ± 0.5) K (89.45 ± 0.05) K (120.0 ± 0.5) K 600 600 (31.6 ± 0.5) K 300 300 0.001 0.01 0.1 1 10 100 0.001 0.01 0.1 1 10 100 E [eV] E [eV] 1200 800 900 Sección eficaz total [barns] Sección eficaz total [barns] 600 Toluene M:T 3:2 (120.0 ± 0.5) K 600 (120.0 ± 0.5) K (31.6 ± 0.5) K 400 (31.6 ± 0.5) K 300 200 0.001 0.01 0.1 1 10 100 0.001 0.01 0.1 1 10 100 E [eV] E [eV]

CROSS SECTION LIBRARIES: GENERATION AND VALIDATION [Nucl. Instr.Meth. B 267 , 175 (2009)] CENTRO ATOMICO BARILOCHE - ARGENTINA

TOLUENE 1000 Experimental 800 NJOY calculation Total Cross Section[barns] 600 400 T= 32 K 200 1E-3 0.01 0.1 1 10 100 E [eV] CENTRO ATOMICO BARILOCHE - ARGENTINA

MESITYLENE 1000 Total cross section (barn) 800 Experimental NJOY Calculation 600 400 T= 32 K 1E-3 0.01 0.1 1 10 E [eV] CENTRO ATOMICO BARILOCHE - ARGENTINA

1000 MIX 3:2 M:T 800 Total cross section (barn) Experimental 600 Calculation 400 T= 32 K 1E-3 0.01 0.1 1 10 1200 E [eV] 1000 Total cross section (barn) Experimental 800 Calculation 600 400 T= 120 K 1E-3 0.01 0.1 1 10 E [eV]

SPECTRA CALCULATIONS at 20 K -4 10 -4 -5 10 9x10 -5 8x10 -5 7x10 -5 6x10 -5 5x10 -5 -5 4x10 10 φ ( E)/ φ o (E) -5 3x10 -5 2x10 Methane phase I 22 K 2 4 6 8 10 -6 10 E [meV] Mesitylene phase II 20 K Mix M:T 3:2 20 K Mesitylene phase III 20 K Toluene glassy phase 20 K -7 Benzene phse I 20 K 10 0.001 0.01 0.1 1 E [eV] CENTRO ATOMICO BARILOCHE - ARGENTINA

METHANE (CH 4 ) – Phase II Simplest hydrocarbon • Gas at room temperature • Two solid crystalline phases • Best H cold neutron producer • Low radiation resistance • Phase II : T < 20.4 K [Nucl.Instr.Meth. B 266 , 164 (2008)] CENTRO ATOMICO BARILOCHE - ARGENTINA

The scattering law of a molecular system ∞ 1 i t * − ω ( ) ∑∑ { ( ) } { ( ) } S Q , ∫ dt e a a exp i Q . R 0 exp i Q . R t ω = − h lv l ´ v ´ lv l ´ v ´ 2 π l , l ´ v , v ´ − ∞ can be written as the sum of inter ( l ≠ l ´ )- and intra ( l = l ´ )- R lν (t) denotes the position of the atom v within the molecule l , molecular contributions. The intermediate scattering function is * ( ) { ( ) } { ( ) } Q , exp Q . R 0 exp Q . R t ∑∑ a a i i t χ = − + lv l ´ v ´ lv l ´ v ´ l l ´ v , v ´ ≠ * { ( ) } { ( ) } ∑∑ a a exp i Q . R 0 exp i Q . R t − lv lv ´ lv lv ´ l v , v ´ CENTRO ATOMICO BARILOCHE - ARGENTINA CENTRO ATOMICO BARILOCHE - ARGENTINA

2 2 2 intra C H H Γ ( ) [ { ( ) ( ) } ( ) ( ) Q , t b f ∑ g 4 b b f Q , t χ ≅ + + + c CC c i HH Γ Γ ) ( ) S . S 2 2 { H H Γ ( ) ( H H ) } [ ( ) ] ] 3 b b f Q , 0 1 + + − ' c i HH ( S S 1 + Convtnal. Incoher. Scatt. function 2 2 H H Γ ≅ ∑ [ { ( ) ( ) } ( ) ( ) S Q , ω 4 g b b S Q , ω + + H Γ c i Γ 2 2 2 h H H − Q 3 γ ( ) ( ) { ( ) } ( ) Γ ( ) ] b b F T j Qr e δ ω + + c i Γ 0 HH 4 CENTRO ATOMICO BARILOCHE - ARGENTINA

50 40 5K 30 S(α,β)=(k B T/ħ) S(Q,ω) 20 10 α=ħ 2 Q 2 /2Mk B T ~y 10 8 0 1 β=ħω/k B T ~x 2 6 y 3 x 4 4 CENTRO ATOMICO BARILOCHE - ARGENTINA

The distinct differential cross section of CH 4 II at several temperatures k d σ ( ) ( ) Q = ∫ d S Q ω ω , 30 H d k Ω 0 int (barn/ster/molec) 10 K 7 K 20 4 K 2.6 K 1.4 K 0.3 K 10 d σ /d Ω | 0 0 1 2 3 4 5 -1 ) Q (A CENTRO ATOMICO BARILOCHE - ARGENTINA

Differential cross sections at several temperatures relative to that at 10K 25 (a) int (barn/ster/molec) 20 15 a) 0.8K (b) d σ /d Ω {T} - d σ /d Ω {10K} b) 1.4K 10 c) 2.6K (c) d) 7K ∆ d σ /d Ω | e) 0.3K (d) 5 (e) 0 -5 0 1 2 3 4 5 -1 ) Q (A CENTRO ATOMICO BARILOCHE - ARGENTINA

Calculated components of σ T (E) for CH 4 II at 4K 400 Elast.self Total Cross Section (barn) Elast. all Inelast. Total 300 200 4K 100 1E-4 1E-3 0.01 0.1 1 E (eV) CENTRO ATOMICO BARILOCHE - ARGENTINA

Comparison of calculated σ T (E) with experimental data of Grieger et al. 800 Total Cross Section (barn) J.Chem.Phys. 109 ,3161 (1998) 0.3K 600 400 10K 200 1E-4 1E-3 0.01 E (eV) CENTRO ATOMICO BARILOCHE - ARGENTINA

Temperature dependence of σ T at low energies caused by spin correlations 600 Total Cross Section (barn) 500 0.1 meV 0.9 meV White circles: this work Closed stars.: Grieger exper. 400 1.5 meV Lines: Ozaki calculations 300 0.1 1 10 T (K) CENTRO ATOMICO BARILOCHE - ARGENTINA

1E-4 Meth 22K Meth 4K Neutron Flux (au) 1E-5 1E-6 1E-3 0.01 0.1 1 E (eV) CENTRO ATOMICO BARILOCHE - ARGENTINA

NEUTRON SCATTERING KERNEL FOR SOLID DEUTERIUM [EPL (Europhysics Letters), in press 2009] CENTRO ATOMICO BARILOCHE - ARGENTINA

D 2 Molecule Formed by bosons → Symmetric total WF ψ (1,2) ≡ φ ( R 1 , R 2 ) χ (S 1 ,S 2 ) = ψ (2,1) S i = 1 ⇒ S = S 1 + S 2 = 0, 1, 2 Ortho states : S = 0, 2 & J = 0, 2, 4,.. Even AM Para states: S = 1 & J = 1, 3, 5,.. Odd AM CENTRO ATOMICO BARILOCHE - ARGENTINA

Leaving aside for the moment the consideration of vibrational modes: out * = ∑ ( ) { ( ) } { ( ) } { ( ) } { ( ) } Q , t exp i Q . a 0 exp i Q . a t . b exp i Q . b 0 b exp i Q . b t ∑ χ − − l l ´ lv lv l ´ v ´ l ´ v ´ l l ´ v , v ´ ≠ I d ( Q ,t) u ( Q ,t) There is no correlation between atoms belonging to different molecules, and then u( Q ) = |Σ ν < b l ν exp { i Q . b ν (0) }>| 2 = 4 (b c ) 2 j 0 2 (Qd/2) ∴ χ out ( Q ,t) = 4 (b c ) 2 j 0 2 (Qd/2) . I d ( Q ,t) CENTRO ATOMICO BARILOCHE - ARGENTINA