Principles of neutron TOF cross section measurements

Principles of neutron TOF cross section measurements J. Heyse, C. Paradela, P. Schillebeeckx EC JRC IRMM Standards for Nuclear Safety, Security and Safeguards (SN3S) H.I. Kim Korea Atomic Energy Research Institute Nuclear Data Center

Neutron induced reactions Neutron + A X

Neutron induced reactions Neutron + A X A+1 X

Neutron induced reactions elastic scattering (n,n) Neutron + A X A+1 X radiative capture (n,) fission (n,f) inelastic scattering (n,n ) other reactions (n,p), (n,d), (n,α)

Neutron induced reaction cross section 1 H 3 10 Cross section is a measure for the interaction probability 0 10 3 10 6 Li 0 10 3 10 10 B Cross sections strongly depend on: 0 Total cross section / b 103 10 59 Co target nucleus incoming neutron energy 0 103 10 131 Xe 0 103 10 08 Pb Dedicated facilities required depending on energy region of interest 0 103 10 35 U 0 10 thermal energy resonance region continuum 38 U 3 10 0 10 39 Pu 3 10 0 10-3 10-10 -1 10 0 10 1 10 10 3 10 Neutron energy / ev 4 10 5 10 6 10

Production and use of nuclear data

(d n / dlne n ) / (cm - s -1 ) (d n / dlne n ) / (cm - s -1 ) Neutron energy spectrum Reactor Neutron induced fission ADS : E p = 600 MeV Spallation reactions 0.3 fast thermal 0.4 ADS-spectrum for E p = 600 MeV 0. 0.3 0. 0.1 0.1 0.0 10-10 0 10 10 4 10 6 10 8 Neutron Energy / ev 0.0 10-10 0 10 10 4 10 6 10 8 Neutron Energy / ev

(n,) / barn Neutron facilities at JRC-IRMM GELINA 10 4 10 99 Tc(n,) cross section 99 Tc + n (n,) Van de Graaff 10 0 10 - White neutron source + Time-of-flight (TOF) 10-4 10-10 0 10 10 4 10 6 Neutron Energy / ev Quasi mono-energetic neutrons through (cp,n) reactions

(n,) / barn Neutron facilities at JRC-IRMM 10 4 10 99 Tc(n,) cross section 99 Tc + n (n,) Van de Graaff 10 0 10-10 -4 10-10 0 10 10 4 10 6 Neutron Energy / ev Quasi mono-energetic neutrons through (cp,n) reactions

Quasi mono-energetic neutron beams Van de Graaff

Charged particle induced neutron reactions quasi mono-energetic neutrons produced via charged particle induced nuclear reactions n e.g. T(d,n) 4 He d a 7 MV VDG - accelerator DC (I p,d < 50 A), Pulsed beam available (1 ns) 6 beam lines fast rabbit systems (T 1/ > 1s) : activation 7 Li(p,n) 7 Be E n : 0-5.3 MeV T(p,n) 3 He E n : 0-6. MeV D(d,n) 3 He E n : 1.8-10.1 MeV T(d,n) 4 He E n : 1.1-4.1 MeV

Charged particle induced neutron reactions

(n,) / barn Neutron facilities at JRC-IRMM 99 Tc(n,) cross section 10 4 99 Tc + n (n,) 10 10 0 10-10 -4 10-10 0 10 10 4 10 6 Neutron Energy / ev

(n,) / barn Neutron facilities at JRC-IRMM GELINA 99 Tc(n,) cross section 10 4 99 Tc + n (n,) 10 10 0 10 - White neutron source + Time-of-flight (TOF) 10-4 10-10 0 10 10 4 10 6 Neutron Energy / ev

TOF - Facility GELINA GELINA

GELINA (Geel Electron LINear Accelerator) Pulsed white neutron source (10 mev < E n < 0 MeV) FLIGHT PATHS NORD Pulse frequency 50Hz 800 Hz ELECTRON LINAC Neutron energy : time of flight (TOF) Multi-user facility: 10 flight paths (10 m - 400 m) TARGET HALL FLIGHT PATHS SOUTH Measurement stations with special equipment to perform: Total cross section measurements Partial cross section measurements

GELINA : neutron production NEUTRON FLIGHT PATHS e - accelerated to E e-,max 140 MeV Bremsstrahlung in U-target (rotating & cooled with liquid Hg) (, n), (, f ) in U-target NEUTRON TARGET NEUTRON MODERATOR ELECTRON BEAMLINE EXIT Low energy neutrons by moderation (water moderator in Be-canning)

GELINA : neutron production SHIELDING for MODERATED SPECTRUM SHIELDING for FAST SPECTRUM d n /dlne n / (cm - s -1 ) 10 5 GELINA 30 m 800 Hz 10 4 10 3 Exp. Mod. Fast MCNP Mod. Fast 10 10-10 0 10 10 4 10 6 Neutron Energy / ev

Time-of-flight technique Target- moderator assembly L Detector Sample

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam Sample

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t (T s T 0 ) T s

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t (T s T 0 ) T s v L t

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t (T s T 0 ) T s v L t E mc ( 1) 1 mv

Time-of-flight technique Target- moderator assembly L Detector Sample

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam Sample T 0

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v 0 Sample T 0

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam T 0 v 1 Sample

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v 3 Sample T 0

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) T s

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) + t o T s t 0 : time-offset

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) + t o T s t 0 : time-offset determined by -flash L c (T s T 0 ) t 0

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) + t o T s v L t

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) + t o t = t m ( t t + t d ) T s v L t

Time-of-flight technique Target- moderator assembly L Detector pulsed e - - beam v Sample T 0 t m = (T s T 0 ) + t o t = t m ( t t + t d ) T s v L t E mc ( 1) 1 mv

Yield Theoretical capture yield 0.00 65 Fe 1.15 kev resonance D = R = 0 Area density : 0.0001 at / barn Y tot (1 e n tot )... 0.015 0.010 0.005 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev

Yield + Doppler 0.00 65 Fe 1.15 kev resonance Area density : 0.0001 at / barn D = R = 0 D (kt = 5 mev) Y tot (1 e n tot (E) de' S(E') (E E' ) )... 0.015 0.010 (E) D 1 de' e E' E D E' E (E') 0.005 D 4 Ek m X B T /m n 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev FWHM ln D

Yield + Doppler + Response 0.00 65 Fe 1.15 kev resonance Area density : 0.0001 at / barn D = R = 0 D (kt = 5 mev) Y tot (1 e n tot (E) de' S(E') (E E' ) )... 0.015 0.010 + R for L = 60 m Y exp R(t,E)Y (E)dE R(t,E)dE 0.005 L = 60 m E E L L t t 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev

Yield Experimental observable FWHM D with - Total resonance width R x 10-3 1.5 1.0 FWHM = Exp. Analytical (REFIT) MCNP R = D = = 43 ev 4 ev 15 ev ev - R Experimental resolution 0.5 - D Doppler broadening 0.0 34100 3400 34300 Neutron energy / ev

Time-of-flight technique: experimental resolution L v t t = (T s T 0 ) + t o ( t t +t d ) L v T 0 T s

Time-of-flight technique: experimental resolution v L t v v t t L L t = (T s T 0 ) + t o ( t t +t d ) L v T 0 T s

Time-of-flight technique: experimental resolution v L 1 E mc ( 1) mv v t L t v t L t = (T s T 0 ) + t o ( t t +t d ) E E (1 ) v v v v L v T 0 T s

Time-of-flight technique: experimental resolution v L 1 E mc ( 1) mv v t L t v t L t = (T s T 0 ) + t o ( t t +t d ) E E (1 ) v v v v L L (~1 mm) v t - Initial burst T 0 T 0 T s - Time resolution detector & electronics T s - Neutron transport in target - moderator t t - Neutron transport in detector t d

Time-of-flight technique: experimental resolution t = (T s T 0 ) + t o ( t t +t d ) t Initial burst T 0 Time resolution detector & electronics Neutron transport in target - moderator Neutron transport in detector T s t t t d

Counts Resolution: initial burst (T 0 ) Single burst : mostly normal (Gaussian) distribution GELINA : T 0 = ns (FWHM) ORELA : T 0 = 4 ns (FWHM) ntof : T 0 = 8 ns (FWHM) Double pulse structure : ISIS J-PARC 000 1500 Exp (30037) Fit ISIS Gaussian response P P 1 = 318 ns FWHM = 60 n 1000 500 0 0.8 0.9 1.0 1.1 1. 1.3 1.4 TOF / s

Resolution: detector & electronics (T s ) Mostly supposed to be normal (Gaussian) distributed Strongly depends on detector type e.g. C 6 D 6 liquid scintillator < 1 ns Li-glass scintillator < 1ns Frisch-grid ionisation chamber Ge-detector (with RTP) 10 ns 0 ns Mostly response of (T s - T 0 ) lumped in one normal distribution

R(t t,e) Resolution: Probability distribution of t t 10 0 10-1 GELINA x 10-3 x 10 - x 10-1 0.01-0.0 ev 1 - ev 1 - kev 100-15 kev Response function 10-10 -3 10-3 10-10 -1 10 0 10 1 10 Time, t t / s Flaska et al., NIM A 531, 394 (004)

Equivalent distance : L t = v t t dl P(t t,e n) P'(L t(t t ), E n) dt t t

Probability desinsity Equivalent distance : L t = v t t dl P(t t,e n) P'(L t(t t ), E n) dt t t 0.4 0.3 1-5 ev 100-500 ev 1000-000 ev 6000-8000 ev 10000-0000 ev 60000-80000 ev 0. 0.1 0.4 0.3 0. 0.1 0.0 cm 1-5 ev 0 4 6 8 10 0.0 0 5 10 15 0 5 Distance / cm

Probability desinsity TOF response function R(L t,e n ) 0.4 0.3 1-5 ev 100-500 ev 1000-000 ev 6000-8000 ev 10000-0000 ev 60000-80000 ev 0. 0.1 0.4 0.3 0. 0.1 0.0 cm 1-5 ev 0 4 6 8 10 0.0 0 5 10 15 0 5 Distance / cm

Probability desinsity Probability desinsity TOF response function R(L t,e n ) 0.4 0.3 1-5 ev 100-500 ev 1000-000 ev 6000-8000 ev 10000-0000 ev 60000-80000 ev 10 0 1-5 ev 100-500 ev 1000-000 ev 6000-8000 ev 10000-0000 ev 60000-80000 ev 10-1 0. 0.4 0.3 1-5 ev 10-0.1 0. 0.1 cm 10-3 0.0 0 4 6 8 10 0.0 0 5 10 15 0 5 Distance / cm 10-4 0 5 10 15 0 5 Distance / cm

Eq. Distance / cm Width / cm TOF response function: characteristics 10 8 6 4 Average eq. distance Target equivalent distance Moderated beam Flight path : 0 o Most probable Average 0 10-10 -1 10 0 10 1 10 10 3 10 4 10 5 0 Neutron Energy / ev 10-10 -1 10 0 10 1 10 10 3 10 4 10 5 0 18 16 14 1 10 8 6 4 Resolution function Target equivalent distance Moderated beam Flight path : 0 o FWHM.35 Neutron Energy / ev

Neutron production & transport: analytical Different components (analytical approach) Neutron production Exponential decay Neutron moderation - distribution + Storage term (Ikeda & Carpenter) Cole and Windsor function (applied at JPARC) Neutron emission : direction flight path with respect to moderator

Probability Density Neutron production & transport: analytical 10 0 Monte Carlo REFIT (adjusted to exp.) Analytical approximation 10-1 Below 0.5 ev : + storage 10 - Between 0.5 ev and 1000 ev: dominated by due to moderation 10-3 process and almost independent of E n Above 1000 kev : more complex 10-4 0.0 0.1 0. Delay distance / m Equivalent Distance / m

R(t t,e) P(t t, E) : photonuclear.0 GELINA 40 m E n = 35 kev 1.6 1. 0.8 0.4 0.0.57.58.59 (L / t m ) / (m/s)

R(t t,e) P(t t, E) : photonuclear.0 1.6 GELINA ORNL 40 m 40 m E n = 35 kev 1. 0.8 0.4 0.0.57.58.59 (L / t m ) / (m/s)

R(t t,e) P(t t, E) : photonuclear spallation reactions.0 1.6 GELINA ORNL ntof 40 m 40 m 180 m E n = 35 kev 1. 0.8 0.4 Dimensions : 80 80 60 cm 3 Pure Lead : 4 t H O moderator : 5 cm Al-window : 1.6 mm Al-container : 140 l 0.0.57.58.59 (L / t m ) / (m/s) Resolution : L GELINA : cm ORELA : cm ntof : 1 cm

R(t t,e) R(t t,e) P(t t, E) : photonuclear spallation reactions 1. 1.0 GELINA 3 m E n = 35 kev.0 1.6 GELINA ORNL ntof 40 m 40 m 180 m E n = 35 kev 0.8 0.6 0.4 1. 0.8 0. 0.4 0.0.54.56.58.60 (L / t m ) / (m/s) 0.0.57.58.59 (L / t m ) / (m/s) Resolution GELINA ORELA ntof : L : cm : cm : 1 cm

R(t t,e) R(t t,e) P(t t, E) : photonuclear spallation reactions 1. 1.0 GELINA ISIS 3 m 3 m E n = 35 kev.0 1.6 GELINA ORNL ntof 40 m 40 m 180 m E n = 35 kev 0.8 0.6 0.4 1. 0.8 0. 0.4 0.0.54.56.58.60 (L / t m ) / (m/s) 0.0.57.58.59 (L / t m ) / (m/s) Resolution GELINA ORELA ntof : L : cm : cm : 1 cm

R(t t,e) R(t t,e) P(t t, E) : photonuclear spallation reactions 1. 1.0 GELINA ISIS JPARC 3 m 3 m 3 m E n = 35 kev.0 1.6 GELINA ORNL ntof 40 m 40 m 180 m E n = 35 kev 0.8 0.6 0.4 1. 0.8 0. 0.4 0.0.54.56.58.60 (L / t m ) / (m/s) 0.0.57.58.59 (L / t m ) / (m/s) Resolution GELINA ORELA ntof : L : cm : cm : 1 cm

R(t t,e) R(t t,e) P(t t, E) : photonuclear spallation reactions 1. 1.0 GELINA ISIS JPARC 3 m 3 m 3 m E n = 35 kev.0 1.6 GELINA ORNL ntof 40 m 40 m 180 m E n = 35 kev 0.8 0.6 0.4 1. 0.8 0. 0.4 0.0.54.56.58.60 (L / t m ) / (m/s) Resolution : L ISIS (INES) : 5 cm J-PARC (MLF/ANNRI) : 13 cm Strongly depend on target/moderator configuration (coupled/decoupled) 0.0.57.58.59 (L / t m ) / (m/s) Resolution : L GELINA : cm ORELA : cm ntof : 1 cm

TOF response matrix

Neutron production & transport Photonuclear GELINA Flaska et al. NIMA 531 (004) 394 Ene et al., NIM A 618, 54 (010) ORELA Coceva et al., NIM 1, 459 (1983) RPI Overberg et al., NIM A 438, 53 (1999) Spallation source ntof Gunsing et al., NIM B 61, 95 (007) J-PARC Hasemi et al., NIM A 773 (015) 137

R(L d,e) Li-glass scintillator : response function 6 Li(n,t)a Scintillator + PMT 1.0 0.8 10 0 10-1 E n =10 ev 0.6 10-0.4 0. 10-3 0.0 0.5 1.0 1.5.0.5 MCNP 0.0 0.0 0.5 1.0 1.5.0.5 Equivalent distance, L d / cm

R(L d,e) Li-glass scintillator : response function 6 Li(n,t)a Scintillator + PMT 1.0 0.8 10 0 10-1 E n =10 ev 0.6 10-0.4 10-3 0.0 0.5 1.0 1.5.0.5 0. 0.0 MCNP Analytical (REFIT) 0.0 0.5 1.0 1.5.0.5 Equivalent distance, L d / cm

R(L d,e) R(L d,e) Li-glass scintillator : response function 1.0 E n =100 ev 1.0 E n =10 ev 10 0 10 0 0.8 10-1 0.8 10-1 0.6 10-0.6 10-0.4 10-3 0.0 0.5 1.0 1.5.0.5 0.4 10-3 0.0 0.5 1.0 1.5.0.5 0. 0.0 MCNP Analytical (REFIT) 0.0 0.5 1.0 1.5.0.5 0. 0.0 MCNP Analytical (REFIT) 0.0 0.5 1.0 1.5.0.5 Equivalent distance, L d / cm Equivalent distance, L d / cm

Time-of-flight technique v v t t L L E E (1 ) v v

Time-of-flight technique v v t t L L 1 L (vt) L E E (1 ) v v

Time-of-flight technique Components: Initial burst T 0 Time resolution detector & electronics T s Neutron transport in target - moderator t t L t (equivalent length = v t t ) Neutron transport in detector t d L d (equivalent length = v t d ) with (T 0, T s, L t, L d ) almost independent of neutron energy (velocity) v v 1 L t t (v T L L 1 L (vt) 0 ) (v Ts ) L t L d L L X E E (1 ) v v neglibible REFIT: numerical and analytical response functions + combination

E / E TOF-resolution : different components v v 1 L (v T 10-1 10-0 ) (v Ts ) L t L d L = 30 m " L " E E (1 ) v v 10-3 L = cm T = 0 10-4 T = 100 ns T = 10 ns T = 1 ns 10-5 10-6 L = cm L = cm L = 0 cm L = cm 10-7 10-10 0 10 10 4 10 6 Neutron Energy energy / kev/ ev

Doppler broadening (T,v) 1 v v V ( v V )P(V) dv v : neutron velocity V : target velocity P(V) : target velocity distribution : nuclear (microscopic) cross section : Doppler broadened (microscopic) cross section T : effective target temperature

Doppler broadened cross sections tot / b.5.0 1.5 1.0 0.5 x 10 4 38 U + n T = 0 K T = 300 K T = 1000 K (T,v) 1 v (E) de' S(E,E') (E' ) (E) D D v V ( v V )P(V) dv 1 m de' e 4 Ek X FWHM B /m E' E D T n ln D E' E (E') 0.0 6.6 6.8 65 66 67 Neutron energy / ev

Yield Theoretical capture yield 0.00 65 Fe 1.15 kev resonance D = R = 0 Area density : 0.0001 at / barn Y tot (1 e n tot )... 0.015 0.010 0.005 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev

Yield + Doppler + Response 0.00 65 Fe 1.15 kev resonance Area density : 0.0001 at / barn D = R = 0 D (kt = 5 mev) Y tot (1 e n tot (E) de' S(E') (E E' ) )... 0.015 0.010 + R for L = 60 m + R for L = 30 m Y exp R(t,E)Y (E)dE R(t,E)dE 0.005 L = 60 m L = 30 m E E L L t t 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev

Yield + Doppler + Response 0.00 65 Fe 1.15 kev resonance Area density : 0.0001 at / barn D = R = 0 D (kt = 5 mev) Y tot (1 e n tot (E) de' S(E') (E E' ) )... 0.015 0.010 + R for L = 60 m + R for L = 30 m + R for L = 1.5 m Y exp R(t,E)Y (E)dE R(t,E)dE 0.005 L = 60 m L = 30 m L = 1.5 m E E L L t t 0.000 1140 1145 1150 1155 1160 Neutron Energy / ev

Yield 197 Au(n,) at L = 1 m E E L L t t D 4 Ek m X B T /m n FWHM ln D 0.10 1 m R ~ 00 mev 0.08 0.06 0.04 ~ 10 mev D ~ 940 mev 0.0 0.00 610 60 630 640 650 Neutron Energy (ev)

Yield 197 Au(n,) at L = 1 m and 30 m E E L L t t D 4 Ek m X B T /m n FWHM ln D 0.10 1 m R ~ 00 mev 0.08 30 m R ~ 840 mev 0.06 0.04 ~ 10 mev D ~ 940 mev 0.0 0.00 610 60 630 640 650 Neutron Energy (ev)

Yield Yield 197 Au(n,) at L = 1 m and 30 m E E L L t t D 4 Ek m X B T /m n FWHM ln D 1.0 1 m R ~ 00 mev 0.10 1 m R ~ 00 mev 0.8 30 m R ~ 80 mev 0.08 30 m R ~ 840 mev 0.6 0.4 ~ 10 mev D ~ 300 mev 0.06 0.04 ~ 10 mev D ~ 940 mev 0. 0.0 0.0 58 60 6 Neutron Energy (ev) 0.00 610 60 630 640 650 Neutron Energy (ev)

Yield Experimental observable when < R or D FWHM D Ofter dominated by R or D with - Total resonance width R x 10-3 1.5 1.0 FWHM = Exp. Analytical (REFIT) MCNP R = D = = 43 ev 4 ev 15 ev ev - R Experimental resolution 0.5 - D Doppler broadening effective experimental observable is resonance area 0.0 34100 3400 34300 Neutron energy / ev