69 research outputs found
Experimental investigation of ground-state properties of <sup>7</sup>H with transfer reactions
The properties of nuclei with extreme neutronâtoâproton ratios, far from those naturally occurring on Earth, are key to understand nuclear forces and how nucleons hold together to form nuclei. 7H, with six neutrons and a single proton, is the nuclear system with the most unbalanced neutronâtoâproton ratio known so far. However, its sheer existence and properties are still a challenge for experimental efforts and theoretical models. Here we report experimental evidences on the formation of 7H as a resonance, detected with independent observables, and the first measurement of the structure of its ground state. The resonance is found at âŒ0.7 MeV above the 3H+4n mass, with a narrow width of âŒ0.2 MeV and a 1/2+ spin and parity. These data are consistent with a 7H as a 3H core surrounded by an extended four-neutron halo, with a unique four-neutron decay and a relatively long half-life thanks to neutron pairing; a prime example of new phenomena occurring in what would be the most pure-neutron nuclear matter we can access in the laboratory.</p
Study of fission using multi-nucleon transfer reactions
Multi-nucleon transfer channels of the reactions of 18O+232Th, 18O+238U, 18O+248Cm were used to measure fission-fragment mass distribution for various nuclides and their excitation energy dependence. Predominantly asymmetric fission is observed at low excitation energies for all the studied cases, with an increase of the symmetric fission towards high excitation energies. Experimental data are compared with predictions of the fluctuation-dissipation model, where effects of multi-chance fission (neutron evaporation prior to fission) was introduced. It was shown that a reliable understanding of the observed fission fragment mass distributions can be obtained only invoking multi-chance fissions
Coulomb dissociation of P 27 at 500 MeV/u
The proton-capture reaction Si26(p,Îł)P27 was studied via Coulomb dissociation (CD) of P27 at an incident energy of about 500 MeV/u. The three lowest-lying resonances in P27 have been populated and their resonance strengths have been measured. In addition, a nonresonant direct-capture component was clearly identified and its astrophysical S factor measured. The experimental results are compared to Monte Carlo simulations of the CD process using a semiclassical model. Our thermonuclear reaction rates show good agreement with the rates from a recent compilation. With respect to the nuclear structure of P27 we have found evidence for a negative-parity intruder state at 2.88-MeV excitation energy
New experimental approaches to investigate the fission dynamics
Abstract. The first ever achieved full identification of both fission fragments, in atomic and mass number, made it possible to define new observables sensitive to the fission dynamics along the fission path up to the scission point. Moreover, proton-induced fission of 208 Pb at high energies offers optimal conditions for the investigation of dissipative, and transient effects, because of the high-excitation energy of the fissioning nuclei, its low angular momentum, and limited shape distortion by the reaction. In this work we show that the charge distribution of the final fission fragments can constrain the ground-to-saddle dynamics while the mass distribution is sensitive to the dynamics until the scission point
Coulomb breakup of 17 Ne from the view point of nuclear astrophysics
6 pags., 5 figs. -- XII International Symposium on Nuclei in the Cosmos, August 5-12, 2012, Cairns, AustraliaBy the Coulomb breakup of 17Ne, the time-reversed reaction 15O(2p, Îł) 17Ne has been studied.
This reaction might play an important role in the rp process, as a break-out reaction of the hot
CNO cycle. The secondary 17Ne ion beam with an energy of 500 MeV/nucleon has been dissociated in a Pb target. The reaction products have been detected with the LAND-R3B experimental
setup at GSI. The preliminary differential and integral Coulomb dissociation cross section ÏCoul
has been determined, which then will be converted into a photo-absorption cross section Ïphoto,
and a two-proton radiative capture cross section Ïcap. Additionally, information about the structure of the 17Ne, a potential two-proton halo nucleus, will be received. The analysis is in progress.This project was supported by the German Federal Ministry for Education and Research
(BMBF), EU(EURONS), EMMI-GSI, and HIC for FAI
Cross-shell states in C: a test for p-sd interactions
The low-lying structure of C has been investigated via the
neutron-removal C reaction. Along with bound neutron sd-shell
hole states, unbound p-shell hole states have been firmly confirmed. The
excitation energies and the deduced spectroscopic factors of the cross-shell
states are an important measure of the neutron
configurations in C. Our results show a very good agreement with
shell-model calculations using the SFO-tls interaction for C. However, a
modification of the - and - monopole terms was applied in order
to reproduce the isotone O. In addition, the excitation energies
and spectroscopic factors have been compared to the first calculations of
C with the self-consistent Green's function method
employing the NNLO interaction. The results show the sensitivity to the
size of the shell gap and highlight the need of going beyond the current
truncation scheme in the theory
Re-examining the transition into the N=20 island of inversion: structure of 30Mg
Intermediate energy single-neutron removal from Mg has been employed
to investigate the transition into the N=20 island of inversion. Levels up to
5~MeV excitation energy in Mg were populated and spin-parity assignments
were inferred from the corresponding longitudinal momentum distributions and
-ray decay scheme. Comparison with eikonal-model calculations also
permitted spectroscopic factors to be deduced. Surprisingly, the 0
level in Mg was found to have a strength much weaker than expected in
the conventional picture of a predominantly intruder configuration
having a large overlap with the deformed Mg ground state. In addition,
negative parity levels were identified for the first time in Mg, one of
which is located at low excitation energy. The results are discussed in the
light of shell-model calculations employing two newly developed approaches with
markedly different descriptions of the structure of Mg. It is concluded
that the cross-shell effects in the region of the island of inversion at Z=12
are considerably more complex than previously thought and that
configurations play a major role in the structure of Mg.Comment: Physics Letters B, Volume 779, 10 April 2018, Pages 124-12
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