The European Commission’s science and knowledge service Joint Research Centre Neutron time-of-flight measurements and transmission measurements Peter Schillebeeckx Workshop on the Evaluation of Nuclear Reaction Data for Applications 2 – 13 October 2017 ICTP, Trieste, Italy
Neutron induced reaction cross sections GELINA Van de Graaff 238 U+n σ tot = σ n,n + σ n, γ + σ n,f + σ tot 5 10 σ n,n σ n, γ Cross section / barn σ n,f 3 10 1 10 -1 10 -3 10 -2 0 2 4 6 10 10 10 10 10 Neutron energy / eV White neutron source Mono-energetic neutrons + (cp,n) reactions Time-of-flight (TOF) 2 - 13 October, 2017, ICTP Trieste
Mono-energetic neutron beams by (cp,n) reactions quasi mono-energetic neutrons produced n n via nuclear reactions d d e.g. T(d,n) 4 He α α α α α α α α 7 Li(p,n) 7 Be E n : 0 - 5.3 MeV T(p,n) 3 He E n : 0 - 6.2 MeV D(d,n) 3 He E n : 1.8 - 10.1 MeV T(d,n) 4 He E n : 12.1 - 24.1 MeV 2 - 13 October, 2017, ICTP Trieste
Mono-energetic neutron beams by (cp,n) reactions 2 - 13 October, 2017, ICTP Trieste
Mono-energetic neutron beams by (cp,n) reactions 1.0E+09 D(d,n) 3 He, gas target, E d =0-7 MeV, 0 o Neutron yield (n/sr. µ C) 1.0E+08 7 Li(p,n) 7 Be, E p = 0-7 MeV, 0 o D(d,n) 3 He, solid target, E d =0-7 MeV, 0 o 1.0E+07 T(d,n) 4 He, E p = 1 MeV, 0 -150 o T(d,n) 4 He, Ep=0-7 MeV, 0 o T(p,n) 3 He, Ep=0-7 MeV, 0 o 1.0E+06 0 5 10 15 20 Neutron energy / MeV 2 - 13 October, 2017, ICTP Trieste
Time-of flight facility GELINA • Pulsed white neutron source (10 meV < E n < 20 MeV) • Neutron energy : time – of – flight (TOF) FLIGHT PATHS NORD • Multi-user facility: 10 flight paths (10 m – 400 m) ELECTRON LINAC • Measurement stations with special equipment: − Total cross section measurements − Reaction cross section measurements TARGET HALL FLIGHT PATHS SOUTH 7 2 - 13 October, 2017, ICTP Trieste
GELINA : neutron production NEUTRON Neutron production: FLIGHT PATHS • Bremsstrahlung in U-target • ( γ , n) and ( γ , f ) in U-target • Low energy part enhanced by moderator (water in Be-canning) GELINA 30m 800 Hz 5 10 NEUTRON ELECTRON NEUTRON Fast Moderated TARGET BEAMLINE EXIT MODERATOR MCNP MCNP Exp. Exp. -1 ) -2 s 4 10 (d ϕ /dlnE) / (cm 3 10 2 10 -2 0 2 4 6 10 10 10 10 10 Neutron energy / eV 2 - 13 October, 2017, ICTP Trieste
Characteristics of neutron source • Isotropic emission Experiment 4 10 MCNP 2 ) (at 12 m) (d φ /dE) / ( 1 / eV s cm 1 ϕ ∝ ( L ) n 2 L 2 10 • Moderated Spectrum 0 10 Maxwellian + 1/E -2 10 -3 -1 1 3 5 10 10 10 10 10 Energy / eV 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Target- moderator Detector L assembly pulsed e - - beam v Sample T 0 T s t ≈ (T s – T 0 ) L v = 1 ⇒ = 2 γ − ≅ 2 E mc ( 1 ) mv t 2 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Experiment MCNP (at 12 m) Neutron detector Evacuated tube T − T T 0 T s s 0 Event Time 1 4000 ns 2 50000 ns 3 750000 ns 4 500 ns . . . . 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Experiment MCNP (at 12 m) Neutron detector 2 10 = ε ϕ C out 1 10 Evacuated tube Counts / (1/ns) 0 10 -1 10 Event Time -2 10 5 6 7 10 10 10 1 4000 ns Time-of-flight / ns 2 50000 ns 3 750000 ns 4 500 ns . . . . 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Experiment MCNP (at 12 m) Sample Neutron detector 2 10 = T ε ϕ C in 1 10 Evacuated tube Counts / (1/ns) 0 10 -1 10 -2 10 5 6 7 10 10 10 Time-of-flight / ns 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Target- moderator Detector L assembly pulsed e - - beam v Sample T 0 T s t ≈ (T s – T 0 ) L v = 1 ⇒ = 2 γ − ≅ 2 E mc ( 1 ) mv t 2 2 - 13 October, 2017, ICTP Trieste
TOF - measurements Target- moderator Detector L assembly pulsed v 3 e - - beam v Sample t d T 0 t m = (T s – T 0 ) T s t t t = t m – ( t t + t d ) L v = t 2 - 13 October, 2017, ICTP Trieste
TOF - measurements 2 2 ∆ ∆ ∆ v t L L L = + v = 2 2 v t L t ∆ ∆ E v = + γ γ = γ − ( 1 ) 2 v E mc ( 1 ) E v ∆ ∆ E v 1 ≅ E ≅ 2 2 mv T 0 T s E v 2 t = t m – ( t t +t d ) E : eV 2 L 3 ⇒ 1 eV neutron : ≅ ≅ µ s v 13 . 8 x 10 m / s E 72 . 298 t : t L : m ⇒ γ -ray 8 ≅ : c 3 x 10 m / s ≅ µ 300 m / s 2 - 13 October, 2017, ICTP Trieste
Response of TOF-spectrometer 2 2 ∆ ∆ ∆ v t L L L = + v = 2 2 v t L t ∆ v 1 = ∆ + ∆ v 2 2 2 v t L v L T 0 T s ∆ v t = t m – ( t t +t d ) L v 2 - 13 October, 2017, ICTP Trieste
Response of TOF-spectrometer 2 2 ∆ ∆ ∆ v t L L L = + v = 2 2 v t L t • ∆ ∆ ∆ ∆ L ( ∼ ∼ 1 mm) ∼ ∼ v • ∆ ∆ ∆ ∆ t − Initial burst width ∆ T 0 T 0 T s − Time jitter detector & electronics ∆ T s t = t m – ( t t +t d ) − Neutron transport in target - moderator ∆ t t t m = (T s – T 0 ) − Neutron transport in detector ∆ t d 2 - 13 October, 2017, ICTP Trieste
Probability distribution of t t : GELINA 0 10 0.01 - 0.02 eV dL 1 - 2 eV = R ( t , E ) R ' ( L ( t ) , E ) 1 - 2 keV t t -2 x 10 dt 100 - 125 keV -3 x 10 -1 -1 x 10 10 R(t t ,E) Transformation of variables : L t = v t t -2 10 ₋ L t : equivalent distance ₋ v : neutron velocity when leaving the moderator -3 10 -3 -2 -1 0 1 2 10 10 10 10 10 10 ₋ t t : time difference between neutron Time, t t / µ s creation and moment it leaves the moderator 2 - 13 October, 2017, ICTP Trieste
Probability distribution of L t : GELINA dL 1 - 5 eV = R ( t , E ) R ' ( L ( t ) , E ) 100 - 500 eV 0.4 t t dt 1000 - 2000 eV 6000 - 8000 eV Probability desinsity 10000 - 20000 eV 0.3 60000 - 80000 eV Transformation of variables : 1 - 5 eV L t = v t t 0.4 0.2 0.3 ₋ L t : equivalent distance 0.2 2 cm 0.1 0.1 ₋ v : neutron velocity when leaving 0.0 0 2 4 6 8 10 the moderator 0.0 ₋ t t : time difference between neutron 0 5 10 15 20 25 creation and moment it leaves the Distance / cm Equivalent distance, L t / cm moderator 2 - 13 October, 2017, ICTP Trieste
Probability distribution of L t : GELINA 0 10 dL 1 - 5 eV = R ( t , E ) R ' ( L ( t ) , E ) 100 - 500 eV t t dt 1000 - 2000 eV 6000 - 8000 eV -1 Probability desinsity 10 10000 - 20000 eV 60000 - 80000 eV Between 0.5 eV and 1000 eV: χ 2 - -2 10 R’(L t ,E n ) dominated by χ 2 due to moderation process and almost -3 10 independent of E n -4 10 Below 0.5 eV : χ 2 + storage - 0 5 10 15 20 25 Distance / cm Equivalent distance, L t / cm - Above 1000 keV : more complex 2 - 13 October, 2017, ICTP Trieste
Probability distribution of L t : GELINA 0 10 Monte Carlo REFIT (adjusted to exp.) Probability Density -1 10 -2 10 -3 10 -4 10 0.0 0.1 0.2 Equivalent distance, L t / m Delay distance / m 2 - 13 October, 2017, ICTP Trieste
P(t t , E) : photonuclear E n = 35 keV 2.0 E n = 35 keV GELINA 40 m GELINA : 40 m 1.6 1.2 R(t t ,E) 0.8 0.4 0.0 2.57 2.58 2.59 (L / t m ) / (m/ µ s) ∆ L (FWHM) = 2 cm ⇒ about half of the moderator thickness ∆ L (FWHM) Resolution : GELINA : 2 cm 2 - 13 October, 2017, ICTP Trieste
P(t t , E) : photonuclear E n = 35 keV 2.0 E n = 35 keV GELINA 40 m GELINA : 40 m ORNL 40 m ORELA : 40 m 1.6 1.2 R(t t ,E) 0.8 0.4 0.0 2.57 2.58 2.59 (L / t m ) / (m/ µ s) ∆ L (FWHM) Resolution : GELINA : 2 cm ORELA : 2 cm 2 - 13 October, 2017, ICTP Trieste
P(t t , E) : photonuclear ⇔ spallation reactions E n = 35 keV 2.0 E n = 35 keV GELINA 40 m GELINA : 40 m ORNL 40 m ORELA : 40 m nTOF 180 m 1.6 nTOF : 180 m 1.2 R(t t ,E) 0.8 0.4 0.0 2.57 2.58 2.59 (L / t m ) / (m/ µ s) : 80 × 80 × 60 cm 3 Dimensions Pure Lead : 4 t ∆ L (FWHM) Resolution : H 2 O moderator : 5 cm Al-window : 1.6 mm GELINA : 2 cm Al-container : 140 l ORELA : 2 cm nTOF : 10 cm 2 - 13 October, 2017, ICTP Trieste
P(t t , E) : photonuclear ⇔ spallation reactions E n = 35 keV E n = 35 keV 1.2 2.0 E n = 35 keV E n = 35 keV GELINA 23 m GELINA 40 m GELINA : 23 m GELINA : 40 m ISIS 23 m ORNL 40 m ISIS : 23 m ORELA : 40 m 1.0 JPARC 23 m nTOF 180 m 1.6 JPARC : 23 m nTOF : 180 m 0.8 1.2 R(t t ,E) R(t t ,E) 0.6 0.8 0.4 0.4 0.2 0.0 0.0 2.54 2.56 2.58 2.60 2.57 2.58 2.59 (L / t m ) / (m/ µ s) (L / t m ) / (m/ µ s) ∆ L (FWHM) Resolution : ∆ L (FWHM) Resolution : ISIS (INES) : 5 cm GELINA : 2 cm J-PARC (MLF/ANNRI) : 13 cm ORELA : 2 cm Strongly depend on target/moderator nTOF : 10 cm configuration (coupled/decoupled) 2 - 13 October, 2017, ICTP Trieste
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