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Can we measure ( n,n ) and ( n,nx ) at high energies with n_TOF ?

Can we measure ( n,n ) and ( n,nx ) at high energies with n_TOF ?. Stephan Pomp*, Cecilia Gustavsson, Kaj Jansson, Diego Tarrio *stephan.pomp@physics.uu.se Division of applied nuclear physics (ANP) Department of physics and astronomy Uppsala University. Nuclear Reactions Research Group.

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Can we measure ( n,n ) and ( n,nx ) at high energies with n_TOF ?

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  1. Can we measure (n,n) and (n,nx) at high energies with n_TOF ? Stephan Pomp*, Cecilia Gustavsson, Kaj Jansson, Diego Tarrio *stephan.pomp@physics.uu.se Division of applied nuclear physics (ANP) Department of physics and astronomy Uppsala University

  2. Nuclear Reactions Research Group ANP: ca 50 people, Group: 16 full time, 2 adj. prof., 5 “other” “Mission statement”: • Model codes • TALYS, EMPIRE, • ... • Evaluations • TENDL, • ENDF-B/VII, • JENDL, • ... • Simulations • Serpent, • MCNP, • PHITS, • ... Nuclear physics Applications

  3. Nuclear Reactions Research Group Research activities: • Cross sections: • Elastic and inelastic neutron scattering (TSL, Uppsala) • Light-ion production with Medley (TSL, Uppsala) • - Medley will move to NFS@GANIL (Caen, France) • (light-ion production, fission cross sections and angular distributions) • Fission yields etc: • - Fission from 232Th and 238U at LLN (Belgium) • - Fission from 234U at JRC-IRMM (Geel, Belgium) • - Independent fission yields at IGISOL (Jyväskylä, Finland) • Bridge to large scale applications: • Core diagnostics for LWR (AVKOK) and GenIV-reactors (GENIUS) • Total Monte Carlo and the TENDL project (with NRG, The Netherlands)

  4. Why (n,n) and (n,nx) ? Physics: optical model, … Applications: ADS, SEE, Medical, Dosimetry, … Exp. data: some (n,n) above 30 MeV e.g. Öhrn et al., PRC77 (2008) 024605 almost nothing on (n,nx)! e.g. Sagrado Garcia et al., PRC84(2011) 044619

  5. (n,n) above 30 MeV Only few experiments with good energy resolution MSU UC Davis Los Alamos TSL Uppsala Öhrn et al., PRC77 (2008) 024605

  6. (n,nx) in EXFOR Only two measurements in 30 - 200 MeV range: and SagradoGarcia et al., PRC84 (2011) 044619 for Fe and Pb at 96 MeV

  7. The SCANDAL setup (1) SCANDAL – SCattered Nucleon Detection AssembLy The SCANDAL detector • Was placed after Medley in the TSL neutron beam line. • In use from 2000 to 2009. • Has been used to measure: • Elastic neutron scattering (n,n). • np scattering (n,p) for calibration • Inelastic neutron scattering (n,nx). • Proton content in the ANITA beam. • Unfortunately SCANDAL suffers from problems in the new background situation at TSL after the new facility was built in 2004.

  8. The SCANDAL setup (2) SCANDAL – SCattered Nucleon Detection AssembLy • Two identical arms typically cover 10-70 in lab system. • The arms can be rotated around the pivot point. • Detection of neutrons is based on: • neutron-to-proton conversion in an active CH2 scintillator. • full energy measurement of the protons in CsI crystals. • Data sets at 96 MeV: • H, D, C, O, Fe, Y, Pb (n,n) – published • C, Fe, Y, Pb (n,nx) – to be published

  9. The SCANDAL setup (3) SCANDAL – SCAtteredNucelon Detection AssembLy: • The SCANDAL setup: • Active plastic converter: CH2 • H(n,p) • C(n,p) Q-value: -12.6 MeV • Overlap from around 20°. • Opening angle criterion 10°. • Proton track measured in DCH:s • Full proton energy measured in CsI(Na) • For elastic scattering analysis, the analysis is straight forward. Always choose events with maximum energy. • For inelastic scattering it cannot be determined event-by-event if energy was lost in the target or in conversion on 12C in the converter. Lower detection limit: about 40 MeV

  10. Something similar at n_TOF? Use the available CsI(Na) – size : 8 cm x 9 cm x 22 cm (16 crystals available) Add stack of active converters + DE detectors Modular design (up to 16 individual detectors) • Goals: • Manage to run in • a white neutron beam • Achieve a low threshold • (10 MeV?) (not to scale!)

  11. Conversion by (n,p) in active converter (plastic scint) -> TOF Signal: neutral particle in (veto) charged particle “track” out Need “some” granularity in Si det. Full stop for up to about 200 MeV incoming neutrons E from Si plus CsI(Na) Response function: Simulations plus measurements at other white and/or QMN facilities (NFS, TSL, …) 8 cm x 9 cm x 22 cm

  12. Count rate estimate … • Some considerations: • Low scattering angle (that’s where the (n,n) xs is large) • Large solid angle (to get count rate) • Detectors should avoid the beam (“gamma” flash …) • Assume a distance of 5 cm from the beam axis (realistic, since the beam is 4 cm diameter with the “capture collimator”). Assume 5 cm x 15 cm as detector size. • For56Fe(n,n) we get: angle(deg) distance(cm) solidangle(msr) crosssection(mb/sr)‏ 10 1156 ~3000 15 7713 20 5822 ~70 25 4734 30 4047 ~40 35 3561 40 3178 ~8

  13. Efficiency of the (n,p) conversion Cross section H(n,p) >50 mb (several 100 mb at 20 MeV) Forward cone (20 deg opening): 1.5 sr in c.m. (about 12% of 4p) • Counts = Flux · XS · Scatteringcentres · Efficiency (≈ 12%) Conversion rate is approx 0.06 · Thickness (cm) · Efficiency • Conversion rate = Counts /Flux Typical converter thickness: 0.4 cm (or 1.2 cm for 3 layers): • Conversion rate ≈ 0.072 · Efficiency ≈ 0.01

  14. Some more “back of the envelope” Number of detected elastic scatt. events from Fe-56 at 40 MeV: • 20 neutrons·cm-2·s-1·MeV-1 • 5·10-4 s-1·g-1·mb-1 (in a 2 MeV bin). • Assume solid angle 22msr, 20 degree position, 70 mb/sr -> 1.5 mb • Conversion efficiency: 0.01 We can scale this numbers using: • 1 week of measuring time (600000 s)‏ • 225g of Fe (probably more …) (3 cm diam x4 cm long cylinder) • ‏5·10-4 s-1·g-1·mb-1 · 1.5 mb · 600 000 s · 225g · 0.01 ≈ 1000 • In total about1000 elastic events per bin and per detector @EAR1 And: Multiply by 25 (?) for EAR2…

  15. Some conclusions/questions As always: in principle we can measure (n,n) and (n,nx) at a white beam Such data are very scare in the fast energy range But is it really feasible? How about, e.g., the flash? Need to make detailed simulations of detector response to find optimal converter design We would need partners to join in and provide, e.g., Si detectors Thanks!

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