Experimental neutron capture data of 58 Ni from the CERN n TOF facility

Transcription

1 Introduction n TOF facility Data analysis Experimental neutron capture data of 58 Ni from the CERN n TOF facility Department of Physics, Faculty of Science, University of Zagreb 25. August 2014.

2 Overview Introduction n TOF facility Data analysis Overview Motivation Motivation n TOF facility Measurements and simulations Final results

3 Motivation Introduction n TOF facility Data analysis Overview Motivation fundamental research in nuclear physics astrophysical implications modeling the stellar nucleosynthesis (s-process) technological concerns 58 Ni as a constituent material in nuclear technologies C-O core He-burning shell He layer H-burning shell Radiative layer Convective H envelope 1 of 1

4 Introduction n TOF facility Data analysis Neutron production C 6 D 6 detectors Time of flight n TOF facility: neutron production Page 3 of 15 Fig. 1. Layout of the n TOF facility within the CERN accelerator complex [21]. The LINAC feeds the PS-Booster, which provides the PS with protons of 1.4 GeV/c for acceleration up to 20 GeV/c. This beam is extracted and sent to the n TOF lead spallation target in bunches of 7 12 protons. The experimental hall is located near the end of the 200 m long neutron beam line. Spallation target: Pb block (1.3 t) Proton source: PS (Proton Synchrotron) accelerator proton energy: 20 GeV pulse mode: t = n (1.2 s) 7 12 protons per pulse every proton 300 neutrons Moderation: Pb block + layer of (borated) water E n = mev GeV C. Guerrero et al., Eur. Phys. J. A 49, 27 (2013)

5 Introduction n TOF facility Data analysis Neutron production C6 D6 detectors Time of flight C6 D6 detectors R. Plag et al., Nucl. Instrum. Methods A 496, 425 (2003) Petar Z ugec

6 Introduction n TOF facility Data analysis Neutron production C 6 D 6 detectors Time of flight Time of flight technique γ p + n 0 Pb L 185 m C 6D 6 C 6D 6 E n = m n c ( ) 1 L 2 c t

7 Introduction n TOF facility Data analysis Goals and challenges Goals: to calculate the capture yield to extract the cross section Challenges: detection efficiency scattered neutrons

8 Detection efficiency E* S n E 1 (i) E 2 (j) E 3 (k) E 4 (l) E 5 (m) Efficiency for detecting a cascade C by a detector of low detection efficiency: If ε (C) i where: E (C) i ε C i ε C i then: E (C) i ε (C) i = E tot E tot = S n + E f(c)

9 Pulse height weighting technique imulation W (E) ε (K) i = αe (K) i Counts [ j E [MeV] W (E )R(j; E )de αe γ (j)] 2 = min.

10 Weighted counts For article Weighted counts 1-1 (1) 58Ni sample (2) Empty frame (3) Beam-off (4) n-background -1 1 E n 2 3 [ev] 4 5

11 GEANT4 simulation of the neutron background

12 GEANT4 simulation of the neutron background

13 γ-ray cascades (example: 28 Si) h1 5 Simulated 4 Database Counts [MeV] E γ P. Žugec et al., Nucl. Instrum. Methods A 760, 57 (2014)

14 γ-ray cascades ( 197 Au case) s - Empty - Beamoff Weighted counts - Empty - Beamoff (scaled) Counts per pulse (b) Counts per pulse (a) Experiment (Bicron) Experiment (FZK) Simulation (Bicron) Simulation (FZK) E γ [MeV] 2 3 E n [ev] Experiment (Bicron) Experiment (FZK) Simulation (Bicron) Simulation (FZK) E n [ev] Counts - Empty - Beamoff (scaled) Weighted counts per pulse (c) 3 Experiment (Bicron) Experiment (FZK) Simulation (Bicron) Simulation (FZK) 4 5 P. Žugec et al., Nucl. Instrum. Methods A 760, 57 (2014)

15 Experiment vs. simulation Yield -2 Experiment Geant4 (total) n-background Yield E n 2 3 [ev] 4 5 P. Žugec et al., Nucl. Instrum. Methods A 760, 57 (2014)

16 58 Ni capture yield Graph -1 Capture yield [ev] E n 4 5

17 Resolved resonance region (<122 kev; SAMMY) Graph Graph Graph Capture yield Capture yield Capture yield (a) n_tof SAMMY [kev] (b) [kev] (c) [kev] E n E n E n

18 Unresolved resonance region (>122 kev; SESH) Graph Capture yield n_tof n_tof* SESH [kev] E n

19 Maxwellian averaged cross sections (MACS) σ kt = 2 π 1 (kt ) 2 0 σ(e n )E n e En/kT de n

20 Maxwellian averaged cross sections (MACS) Graph 12% lower MACS at 30 kev 60% more 58 Ni in 25M stars MACS [mb] 55 n_tof 50 KADONIS v0.3 ENDF/B-VII.0 45 ENDF/B-VII kt [kev] P. Žugec et al., Phys. Rev. C 89, (2014)

21 Maxwellian averaged cross sections (MACS) Graph / MACS n_tof MACS i Beer et al. (1992) Bao et al. (2000) Guber et al. (20) Pritychenko et al. (20) KADoNiS v kt [kev] P. Žugec et al., Phys. Rev. C 89, (2014)

22 Introduction n TOF facility Data analysis Thank you for listening!