Timereversal and inverse reactions A little bit of
Time-reversal and inverse reactions • A little bit of history of n_TOF • Neutron capture & Coulomb dissociation: the case study of 14 C(n, �� )15 C • Other reaction channels: 7 Be(n, p)7 Li and 7 Li(p, n)7 Be 3 rd n_TOF Winter School, Zermatt, 15 -19 January 2018 alberto. mengoni@enea. it
The first n_TOF workshop 21 -22 September 1988
Neutron capture in light nuclei
Neutron capture in light nuclei
apture in light nuclei
apture in light nuclei
apture in light nuclei
apture in light nuclei
apture in light nuclei
A little bit of n_TOF history
Excavation of the n_TOF tunnel
The first n_TOF target-moderator assembly neutrons
inhomogeneities in the big bang The standard big-bang model assumes a homogeneous distribution of baryons (nucleons). If, during the nucleosynthesis some In-homogeneities were present, sizable amounts of heavy elements can be produced Source: T Rauscher et al. , Ap. J 429 (1994) 499. alberto. mengoni@cern. ch
Runaway from SBBN • 7 Li(n, )8 Li(a, n)11 B(n, )12 B(b-)12 C(n, )13 C(n, )14 C(n, )15 C … alberto. mengoni@cern. ch
Runaway from SBBN • 7 Li(n, )8 Li(a, n)11 B(n, )12 B(b-)12 C(n, )13 C(n, )14 C(n, )15 C … • 7 Li(n, )8 Li(n, )9 Li(b-)9 Be(n, )10 Be(n, )11 Be(b-)11 B(n, )12 B(b-)12 C(n, ) … alberto. mengoni@cern. ch
14 C(n, )15 C
i. BBM full network Source: T Rauscher et al. , Ap. J 429 (1994) 499. alberto. mengoni@cern. ch
Neutron capture cross section Direct methods Indirect methods (ANC, TH, Surrogate, etc. ) Direct measurements • (n, ) • Transfer reactions with stable beams Inverse measurements • ( , n) • Coulomb dissociation • Transfer reactions with radioactive beams
14 C(n, )15 C: Activation measurements • neutron production via 7 Li(p, n)7 Be reaction at Ep = 1912 ke. V. • induced activity measured after irradiation with HPGe detectors. - product nucleus must be radioactive ü high sensitivity small sample masses or small cross sections ü natural samples possible, isotopic enrichment not required ü Direct Capture component included Courtesy of F Kӓeppeler
14 C(n, )15 C: Activation measurements reactions detected via 5. 298 Me. V line in 15 C total mass = 600 mg or 2. 3 1022 atoms enrichment in 14 C: canning: Ni decay (t 1/2=2. 45 s) copper neutron flux via 197 Au(n, g)198 Au neutron source: 7 Li(p, n)7 Be proton beam lithium Au neutron cone 14 C Sounrce: F. Käppeler, Cologne, March 8 -12, 2004
Activation measurements induced gold activity yields strong and almost backgroundfree line at 412 ke. V
Activation measurements induced activity: Na = φtot · Nt · σt(n, ) · fa Aa = Na l a line strength in g-spectrum: Cγ = A · Kγ · εγ · Iγ · [1 − exp(−λtm)] · exp(−λtw) Aa Na · σt(n, ) · fa = AAu NAu · σAu · f. Au Courtesy of F Kӓeppeler
14 C(n, )15 C measured by activation Eg=5. 298 Me. V
14 C(n, )15 C measured by activation R Raifarth et al.
14 C(n, )15 C measured by activation R Raifarth et al. PRC 77 (2008) 015804
14 C(n, )15 C direct and inverse approaches
Time-reversal and detailed balance
Time-reversal and detailed balance where
Time-reversal and detailed balance In particular,
Capture & Dissociation The time-reversal invariance for nuclear reactions allows to use detailed balance
Time-reversal at work
14 C(n, )15 C and 15 C Coul_diss
Coulomb dissociation
Coulomb dissociation
Experimental setup RIPS @ RIKEN 100 Me. V/u 18 O beam on Be produced a secondary beam of 15 C of 68 Me. V/u on Pb NEUT n n Pb Target 14 C HOD DC DALI 15 C 68 Me. V/nucleon BOMAG Source: T Nakamura et al. (2008)
RIKEN experiment T Nakamura (private communication, 2004)
14 C(n, )15 C: direct and inverse approaches Activation measurement R Reifarth et al. , PRC 77 (2008) 015804: DRC & Coul_diss (RIKEN data):
Conclusion Coulomb breakup is a useful tool to extract the corresponding radiative capture cross section, showed by a rare case in which both reactions, the (n, γ) and the time-reversal (γ, n) could be measured.
Theory: DRC, R-matrix and HF • Direct Radiative Capture (DRC) • Isolated Compound States: R-matrix theory • Hauser-Feshbach theory average over many compound states:
Direct Radiative Capture See , for example: A Mengoni, T Otsuka and M Ishihara, Phys. . Rev C 52 (1995) R 2334.
Direct Radiative Capture
Direct Radiative Capture A Mengoni, T Otsuka and M Ishihara, Phys. . Rev C 52 (1995) R 2334.
Charged particle channels Part 2 >>
- Slides: 43