1. |
- Alikhani, B., et al.
(författare)
-
Compton polarimetry with a 36-fold segmented HPGe-detector of the AGATA-type
- 2012
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 675, s. 144-154
-
Tidskriftsartikel (refereegranskat)abstract
- The calibration of a highly-segmented AGATA-type HPGe-detector as a gamma-ray Compton polarimeter and a method for (quasi-)continuous angle Compton polarimetry are presented. The high granularity, combined with the large detection efficiency of the AGATA-type HPGe-crystals, offers a significant advantage for polarization measurements of gamma-radiation. A polarization-directional correlation experiment with gamma-rays from a Co-60 source with an activity of about 680 kBq was used to determine the polarization sensitivity of a single AGATA-type HPGe-crystal at 1173 and 1332 key and to demonstrate the method. The polarization measurement was based on segment information. In our set-up a polarization sensitivity of 19% at 1332 keV has been achieved.
|
|
2. |
- Caesar, C., et al.
(författare)
-
Beyond the neutron drip line: The unbound oxygen isotopes O-25 and O-26
- 2013
-
Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993 .- 0556-2813. ; 88:3
-
Tidskriftsartikel (refereegranskat)abstract
- The very neutron-rich oxygen isotopes O-25 and O-26 are investigated experimentally and theoretically. The unbound states are populated in an experiment performed at the R3B-LAND setup at GSI via proton-knockout reactions from F-26 and F-27 at relativistic energies around 442 and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into O-24 plus one or two neutrons, the O-25 ground-state energy and width are determined, and upper limits for the O-26 ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in O-26 at around 4 MeV. The experimental findings are compared to theoretical shell-model calculations based on chiral two- and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added.
|
|
3. |
- Heine, M., et al.
(författare)
-
Determination of the neutron-capture rate of C-17 for r-process nucleosynthesis
- 2017
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 95:1, s. Article no 014613 -
-
Tidskriftsartikel (refereegranskat)abstract
- With the (RB)-B-3-LAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of C-18 at a projectile energy around 425A MeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of C-17 into the ground state of C-18. Those data have been used to constrain theoretical calculations for transitions populating excited states in C-18. This allowed to derive the astrophysical cross section sigma(n gamma)*. accounting for the thermal population of C-17 target states in astrophysical scenarios. The experimentally verified capture rate is significantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures T-9
|
|
4. |
- Vandebrouck, M., et al.
(författare)
-
Effective proton-neutron interaction near the drip line from unbound states in F-25,F-26
- 2017
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 96:5
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The F-26 nucleus, composed of a deeply bound pi 0d(5/2) proton and an unbound v0d(3/2) neutron on top of an O-24 core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J(pi) = 1(1)(+) - 4(1)(+) multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The J(pi) = 1(1)(+), 2(1)(+), 4(1)(+) bound states have been determined, and only a clear identification of the J(pi) = 3(1)(+) is missing. Purpose: We wish to complete the study of the J(pi) = 1(1)(+) - 4(1)(+) multiplet in F-26, by studying the energy and width of the J(pi) = 3(1)(+) unbound state. The method was first validated by the study of unbound states in F-25, for which resonances were already observed in a previous experiment. Method: Radioactive beams of Ne-26 and Ne-27, produced at about 440AMeV by the fragment separator at the GSI facility were used to populate unbound states in F-25 and F-26 via one-proton knockout reactions on a CH2 target, located at the object focal point of the (RB)-B-3/LAND setup. The detection of emitted. rays and neutrons, added to the reconstruction of the momentum vector of the A - 1 nuclei, allowed the determination of the energy of three unbound states in F-25 and two in F-26. Results: Based on its width and decay properties, the first unbound state in F-25, at the relative energy of 49(9) keV, is proposed to be a J(pi) = 1/ 2(-) arising from a p1/2 proton- hole state. In F-26, the first resonance at 323(33) keV is proposed to be the J(pi) = 3(1)(+) member of the J(pi) = 1(1)(+) - 4(1)(+) multiplet. Energies of observed states in F-25,F-26 have been compared to calculations using the independent-particle shell model, a phenomenological shell model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton- neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need for implementing the role of the continuum in theoretical descriptions or to a wrong determination of the atomic mass of F-26.
|
|