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First spectroscopy of the r-process nucleus 135 Sn

First spectroscopy of the r-process nucleus 135 Sn. Thorsten Kröll 1 / Kathrin Wimmer 2. CERN-INTC-2018-008, INTC-P-539 . Work supported by BMBF (Nr. 05P15RDCIA), LOEWE / HIC for FAIR, and the MINIBALL-, T-REX- and HIE-ISOLDE collaborations. Region of Interest.

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First spectroscopy of the r-process nucleus 135 Sn

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  1. First spectroscopy of the r-process nucleus 135Sn Thorsten Kröll1 / Kathrin Wimmer2 CERN-INTC-2018-008, INTC-P-539  Work supported by BMBF (Nr. 05P15RDCIA), LOEWE / HIC for FAIR, and the MINIBALL-, T-REX- and HIE-ISOLDE collaborations

  2. Region of Interest Nuclei around doubly-magic shell closure in 132Sn - Letter of Intent: CERN-INTC-2010-045; INTC-I-111 - Approved Proposals: IS548, IS549, IS551 ... all Coulex (beam time 2016) Higher energies from HIE-ISOLDE: first nucleon transfer 134Sn(d,p)135Sn N=82 Z=54 Xe Z=52 Te 135Sn Z=50 Sn 132Sn 7 February 2018 | INTC Meeting | Thorsten Kröll | 2

  3. 135Sn – r-process nucleus • r-process passes region around 132Sn • abundance pattern depends on both nuclear structure (m, b-T1/2, s(n), etc.) • and astrophysical conditions • ... August 2017: neutron star merger identified as (one) astrophysical site • (d,p) is surrogate reaction for (n,g) • Neutron capture rates can • change average abundances • by up to 43% • 134Sn(n,g) has no impact • (134Sb(n,g) has!!!) • ... but transfer to an • even-even nucleus • is theoretically easier • ... contributes to the • overall understanding • of (d,p) in this region R. Surman et al., Phys. Rev. C 79, 045809 (2009) 7 February 2018 | INTC Meeting | Thorsten Kröll | 3

  4. 133Sn … what has been done? ≈ 100-250 counts per peak 132Sn(d,p) @ 4.77 MeV/u - particle spectroscopy only - transferred Dℓ determined (angular distributions are quite similar) - SFs extracted K. Jones et al., Nature 465, 454 (2010) 7 February 2018 | INTC Meeting | Thorsten Kröll | 4

  5. 133Sn … what has been done? 132Sn(9Be,8Be) @ 3 MeV/u ≈ 4-2500 counts per peak J.M. Allmond et al., Phys. Rev. Lett. 112, 172701 (2014) - particle(2a)-g coincidences - gg-coincidences, g-branchings Our approach: combine the best of both light-particle and g-ray spectroscopy!!! 7 February 2018 | INTC Meeting | Thorsten Kröll | 5

  6. Set-up: MINIBALL and T-REX • MINIBALL • 24 HPGe • e ≈ 3% @ 1.3 MeV • T-REX • large solid angle • 8°- 78° and 102° - 172° • position sensitive • PID (DE-E) beam V. Bildstein et al., Eur. Phys. J A 48, 85 (2012) N. Warr et al., Eur. Phys. J A 49, 40 (2013) 7 February 2018 | INTC Meeting | Thorsten Kröll | 6

  7. 135Sn Shell model predictions Sn experimental knowledge ? 7 February 2018 | INTC Meeting | Thorsten Kröll | 7

  8. Comparison 7.5 MeV/u and 10 MeV/u 10 MeV/u • 7.5 MeV/u • mostly • larger cross section • less pronounced • angular distributions • smaller energies of • protons to be • detected 7 February 2018 | INTC Meeting | Thorsten Kröll | 8

  9. Simulation (backward direction) Simulations by Christian Berner (doct. student,TUM) 134Sn(d,p) @ 7.5 MeV/u, 1 mg/cm2 CD2 target Q0 = 45.2 keV, first 4 levels in 135Sn • Energies are well above experimental trigger threshold (≈500 keV @ 3 MeV/u • and A=80 ... we have to see at 7.5 or 10 MeV/u and A=140) • Levels are not sufficiently separated .... most likely we need g-rays!!! 7 February 2018 | INTC Meeting | Thorsten Kröll | 9

  10. Physics aims • Particle spectroscopy, particle-g(g) coincidences • èidentify excited states in 135Sn for the first time • (g-gated) particle angular distributions • èdetermine orbital angular momentum transfer • g-decay branching (and guidance by theory) • èassign (tentatively) total angular momentum • cross sections • èextract spectroscopic factors • è Comparison with shell model • Note: shell model needs interaction matrix elements AND single-particle • energies around 132Sn, i.e. 133Sn and 133Sb • ... predictive power can be evaluated only by studying nuclei beyond!! 7 February 2018 | INTC Meeting | Thorsten Kröll | 10

  11. Beam / rate estimate • MINIBALL + T-REX (maybe modified configuration in backward direction) • Beam • - molecular beam 134Sn34S+ from ISOLDE • - beam energy from HIE-ISOLDE: 7.8 MeV/u (or whatever is reachable) • - intensity on target 104/s • - highly contaminated by 134Sb (A=168 contaminations?) • Rate (1 mg/cm2 CD2 target) • - 650 protons/day (per 1 mb) • - 2-8 mb per state, 6-10 angular bins è ≈ 300 counts / bin / day • è2% statistical error • - g-gated: factor 10-30 less è ≈ 150 counts / bin / week • è10% statistical error • - particle-integrated g-rate per state è ≈ 350 / mb / week • è the excitation energy can be determined even for very low cross sections We request 24 shifts (8 days) of beam time 7 February 2018 | INTC Meeting | Thorsten Kröll | 11

  12. Simulation (forward direction) DE ERest Because of high energies many p and d punch through both DE and E detectors E=DE+ERest 7 February 2018 | INTC Meeting | Thorsten Kröll | 12

  13. Simulation 134Sb(d,p) @ 7.5 MeV/u Q0 = 1516.5 keV 134Sn(d,p) @ 7.5 MeV/u Q0 = 45.2 keV • States at high excitation energy in 135Sb* partially overlap with states • at low excitation energy in 135Sn • States at higher excitation energy are likely to emit g-rays in coincidence • (which are, of course, not detected with 100% efficiency)! • * For simplicity, the same excitation energies as in Sn have been assumed 7 February 2018 | INTC Meeting | Thorsten Kröll | 13

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