The first direct experimental evidence of a multiparticle-hole ground state configuration of the neutron-rich Mg-33 isotope has been obtained via intermediate energy (400 A MeV) Coulomb dissociation ...measurement. The major part similar to(70 +/- 13)% of the cross section is observed to populate the excited states of Mg-32 after the Coulomb breakup of Mg-33. The shapes of the differential Coulomb dissociation cross sections in coincidence with different core excited states favor that the valence neutron occupies both the s(1/2) and p(3/2) orbitals. These experimental findings suggest a significant reduction and merging of sd-pf shell gaps at N similar to 20 and 28. The ground state configuration of Mg-33 is predominantly a combination of Mg-32(3.0,3.5MeV; 2(-), 1(-)) circle times nu(s1/2), Mg-32(2.5MeV; 2(+)) circle times nu(p3/2), and Mg-32(0; 0(+)) circle times nu(p3/2). The experimentally obtained quantitative spectroscopic information for the valence neutron occupation of the s and p orbitals, coupled with different core states, is in agreement with Monte Carlo shell model (MCSM) calculation using 3 MeV as the shell gap at N = 20.
Fission Fragments from 1 A GeV $^{238}$U ions impinging a hydrogen target were studied using the fragment separator FRS from GSI for magnetic selection including ray-tracing, and $\Delta$E-ToF ...techniques. From the kinematics of the fragments, binary fission can be assigned as production process up to very heavy fragments. Fission fragments were identified as far as $^{184}$Re for the first time. Cross sections are measured and found in the range of 500 $\mu$b to 5 $\mu$b. Isobaric cross sections decrease smoothly with increasing mass. Beyond tungsten, fission fragments are hidden in the more abundant spallation evaporation residues. Fission cross sections of 283 isotopes of Gd to Re in the mass range 147 to 184 were obtained. All fragments result from fission of excited parent nuclei and after emission of secondary neutrons
Background: Models describing nuclear fragmentation and fragmentation fission deliver important input forplanning nuclear physics experiments and future radioactive ion beam facilities. These models ...are usuallybenchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions withexotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a needfor models to describe also these reactions.Purpose: We want to extend the presently available data on fragmentation reactions towards the light exoticregion on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentationespecially for unstable isotopes.Method: We have measured projectile fragments from 10,12−18C and 10−15B isotopes colliding with a carbontarget. These measurements were all performed within one experiment, which gives rise to a very consistent dataset. We compare our data to model calculations.Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic 10,12−18Cand 10−15B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that theEPAX code is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that theaverage excitation energy per abraded nucleon needs to be decreased from 27MeV to 8.1 MeV.With that decreaseABRABLA07 describes the data surprisingly well.Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data hasallowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Moststriking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless,this parameter, which has been related to final-state interactions, requires further study.
The radionuclide Fe-60 has been of great interest to the nuclear astrophysics community for over a decade. An initial discrepancy between the observed and modeled Galactic Fe-60/Al-26 ratio motivated ...numerous studies focused on the nucleosynthesis of these two isotopes, though the cross section of the primary astrophysical production reaction, Fe-59(n,gamma)Fe-60, has remained purely theoretical. The present work offers a first experimental constraint on the Fe-59(n,gamma)Fe-60 cross section at astrophysical energies, obtained indirectly via Coulomb dissociation, and demonstrates that the theoretical reaction rates used in present stellar models are not highly erroneous.
Transient effects in highly-excited fissioning systems Ayyad, Y; Benlliure, J; Rodríguez-Sánchez, J L ...
Journal of physics. Conference series,
01/2014, Letnik:
569, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
In this work we report the proton- and deuteron-induced fission of 208Pb at 500A MeV in inverse kinematics. We obtained two observables that allow us to investigate dynamical effects in the fission ...process: partial fission cross sections and the width of the fission fragment charge distribution as a function of the atomic number of the fissioning system. Results are compared to nuclear reaction model calculations in order to describe the evolution of the system from ground to saddle.
The measurements of neutron capture cross sections of neutron-rich nuclei are challenging but essential for understanding nucleosynthesis and stellar evolution processes in the explosive burning ...scenario. In the quest of -process abundances, according to the neutrino-driven-wind model, light neutron-rich unstable nuclei may play a significant role as seed nuclei that influence the abundance pattern. Hence, experimental data for neutron capture cross sections of neutron-rich nuclei are needed. Coulomb dissociation of radioactive ion beams at intermediate energy is a powerful indirect method for inferring capture cross section. As a test case for validation of the indirect method, the neutron capture cross section (, ) for was inferred from the Coulomb dissociation of at intermediate energy ( MeV). A comparison between different theoretical approaches and experimental results for the reaction is discussed. We report for the first time experimental reaction cross sections of , , , and . The reaction cross sections were inferred indirectly through Coulomb dissociation of , , and at incident projectile energies around 400-430 MeV using the FRS-LAND setup at GSI, Darmstadt. The neutron capture cross sections were obtained from the photoabsorption cross sections with the aid of the detailed balance theorem. The reaction rates for the neutron-rich Na, Mg, Al nuclei at typical -process temperatures were obtained from the measured () capture cross sections. The measured neutron capture reaction rates of the neutron-rich nuclei, , , and are significantly lower than those predicted by the Hauser-Feshbach decay model. A similar trend was observed earlier for and but in the case of the trend is opposite. The situation is more complicated when the ground state has a multi-particle-hole configuration. For , the measured cross section is about higher than the Hauser-Feshbach prediction.
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