230 research outputs found
Isotopic distribution of fission fragments in collisions between 238U beam and 9Be and 12C targets at 24 MeV/u
Inverse kinematics coupled to a high-resolution spectrometer is used to
investigate the isotopic yields of fission fragments produced in reactions
between a 238U beam at 24 MeV/u and 9Be and 12C targets. Mass, atomic number
and isotopic distributions are reported for the two reactions. These
informations give access to the neutron excess and the isotopic distribution
widths, which together with the atomic-number and mass distributions are used
to investigate the fusion-fission dynamics.Comment: Submitted to PR
Identification of new transitions and mass assignments of levels in Pr
The previously reported levels assigned to 151,152,153Pr have recently been
called into question regarding their mass assignment. The above questioned
level assignments are clarified by measuring g-transitions tagged with A and Z
in an in-beam experiment in addition to the measurements from 252Cf spontaneous
fission (SF) and establish new spectroscopic information from to
in the Pr isotopic chain. The isotopic chain 143-153Pr has been studied from
the spontaneous fission of 252Cf by using Gammasphere and also from the
measurement of the prompt g-rays in coincidence with isotopically-identified
fission fragments using VAMOS++ and EXOGAM at GANIL. The latter were produced
using 238U beams on a 9Be target at energies around the Coulomb barrier. The
g-g-g-g data from 252Cf (SF) and those from the GANIL in-beam A- and Z-gated
spectra were combined to unambiguously assign the various transitions and
levels in 151,152,153Pr and other isotopes. New transitions and bands in
145,147,148,149,150Pr were identified by using g-g-g and g-g-g-g coincidences
and A and Z gated g-g spectra. The transitions and levels previously assigned
to 151,153Pr have been confirmed by the (A,Z) gated spectra. The transitions
previously assigned to 152Pr are now assigned to 151Pr on the basis of the
(A,Z) gated spectra. Two new bands with 20 new transitions in 152Pr and one new
band with 7 new transitions in 153Pr are identified from the g-g-g-g
coincidence spectra and the (A,Z) gated spectrum. In addition, new g-rays are
also reported in 143-146Pr. New levels of 145,147-153Pr have been established,
reliable mass assignments of the levels in 151,152,153Pr have been reported and
new transitions have been identified in 143-146Pr showing the new avenues that
are opened by combining the two experimental approaches.Comment: Accepted in Phys. Rev.
Experimental investigation of ground-state properties of <sup>7</sup>H with transfer reactions
The properties of nuclei with extreme neutron–to–proton 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 neutron–to–proton 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 ∼0.7 MeV above the 3H+4n mass, with a narrow width of ∼0.2 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
Spatio-temporal permanence and plasticity of foraging trails in young and mature leaf-cutting ant colonies (Atta spp.)
The distribution and formation of foraging trails have largely been neglected as factors explaining harvesting
patterns of leaf-cutting ants.We applied fractal analysis, circular, and conventional statistics to published and newly
recorded trailmaps of seven Atta colonies focusing on three aspects: permanence, spatio-temporal plasticity and colony
life stage. In the long term, trail patterns of young and mature Atta colonies revealed that foraging activities were
focused on distinct, static sectors that made up only parts of their potentially available foraging range. Within these
foraging sectors, trails were typically ephemeral and highly variable in space and time. These ephemeral trails were
concentrated around permanent trunk trails in mature and around nest entrances in young colonies. Besides these
similarities, the comparison of trail systems between the two life stages indicated that young colonies exploited fewer
leaf sources, used smaller and less-complex systems of foraging trails, preferred different life forms as host plants, and
switched hosts more often compared with mature colonies. Based on these analyses, we propose a general hypothesis
which describes the foraging pattern in Atta as a result of initial foraging experiences, spatio-temporal distribution of
suitable host plants, energetic constraints, and other factors such as seasonality and interspecific predatio
Fission Dynamics: The Quest of a Temperature Dependent Nuclear Viscosity
oai:ojs2.jnp.chitkara.edu.in:article/2This paper presents a journey within some open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable frame-work since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the dependence of viscosity on the temperature may change with the fissility of the composite system; iii) the opportunity to measure also observables in the evaporation residues channel translates into a larger set of effective constraints for the models
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
- …