175 research outputs found
A new analysis method to determine beta-decay half-lives in experiments with complex background
This paper reports the first application of a new technique to measure the
beta-decay half -lives of exotic nuclei in complex background conditions. Since
standard tools were not adapted to extract the relevant information, a new
analysis method was developed. The time distribution of background events is
established by recording time correlations in backward time. The beta half
lives of the nuclides and the detection efficiency of the set-up are determined
simultaneously from a least-squares fit of the ratio of the time-correlation
spectra recorded in forward and in backward time, using numerical functions.
The necessary numerical functions are calculated in a Monte-Carlo code using
the known operation parameters of the experiment and different values for the
two free parameters, half-life and detection efficiency, as input parameters.Comment: 21 pages, 9 figure
Coincidence measurement of residues and light particles in the reaction 56Fe+p at 1 GeV per nucleon with SPALADIN
The spallation of Fe in collisions with hydrogen at 1 A GeV has been
studied in inverse kinematics with the large-aperture setup SPALADIN at GSI.
Coincidences of residues with low-center-of-mass kinetic energy light particles
and fragments have been measured allowing the decomposition of the total
reaction cross-section into the different possible de-excitation channels.
Detailed information on the evolution of these de-excitation channels with
excitation energy has also been obtained. The comparison of the data with
predictions of several de-excitation models coupled to the INCL4 intra-nuclear
cascade model shows that only GEMINI can reasonably account for the bulk of
collected results, indicating that in a light system with no compression and
little angular momentum, multifragmentation might not be necessary to explain
the data.Comment: 4 pages, 5 figures, revised version accepted in Phys. Rev. Let
Extending the north-east limit of the chart of nuclides
The existence of nuclei with exotic combinations of protons and neutrons
provides fundamental information on the forces acting between nucleons. The
maximum number of neutrons a given number of protons can bind, neutron drip
line1, is only known for the lightest chemical elements, up to oxygen. For
heavier elements, the larger its atomic number, the farther from this limit is
the most neutron-rich known isotope. The properties of heavy neutron-rich
nuclei also have a direct impact on understanding the observed abundances of
chemical elements heavier than iron in our Universe. Above half of the
abundances of these elements are thought to be produced in rapid-neutron
capture reactions, r-process, taking place in violent stellar scenarios2 where
heavy neutron-rich nuclei, far beyond the ones known up today, are produced.
Here we present a major step forward in the production of heavy neutron-rich
nuclei: the discovery of 73 new neutron-rich isotopes of chemical elements
between tantalum (Z=72) and actinium (Z=89). This result proves that
cold-fragmentation reactions3 at relativistic energies are governed by large
fluctuations in isospin and energy dissipation making possible the massive
production of heavy neutron-rich nuclei, paving then the way for the full
understanding of the origin of the heavier elements in our Universe. It is
expected that further studies providing ground and structural properties of the
nuclei presented here will reveal further details on the nuclear shell
evolution along Z=82 and N=126, but also on the understanding of the stellar
nucleosyntheis r-process around the waiting point at A~190 defining the speed
of the matter flow towards heavier fissioning nuclei
β-delayed γ-proton decay in 56Zn: analysis of the charged-particle spectrum
A study of the beta decay of the proton-rich T-z = 2 nucleus Zn-56 has been reported in a recent publication. A rare and exotic decay mode, beta-delayed gamma-proton decay, has been observed there for the first time in the fp shell. Here, we expand on some of the details of the data analysis, focussing on the charged particle spectrum
Discovery and Cross-Section Measurement of Neutron-Rich Isotopes in the Element Range from Neodymium to Platinum at the FRS
With a new detector setup and the high-resolution performance of the fragment
separator FRS at GSI we discovered 57 new isotopes in the atomic number range
of 60: \nuc{159-161}{Nb}, \nuc{160-163}{Pm}, \nuc{163-166}Sm,
\nuc{167-168}{Eu}, \nuc{167-171}{Gd}, \nuc{169-171}{Tb}, \nuc{171-174}{Dy},
\nuc{173-176}{Ho}, \nuc{176-178}{Er}, \nuc{178-181}{Tm}, \nuc{183-185}{Yb},
\nuc{187-188}{Lu}, \nuc{191}{Hf}, \nuc{193-194}{Ta}, \nuc{196-197}{W},
\nuc{199-200}{Re}, \nuc{201-203}{Os}, \nuc{204-205}{Ir} and \nuc{206-209}{Pt}.
The new isotopes have been unambiguously identified in reactions with a
U beam impinging on a Be target at 1 GeV/u. The isotopic production
cross-section for the new isotopes have been measured and compared with
predictions of different model calculations. In general, the ABRABLA and COFRA
models agree better than a factor of two with the new data, whereas the
semiempirical EPAX model deviates much more. Projectile fragmentation is the
dominant reaction creating the new isotopes, whereas fission contributes
significantly only up to about the element holmium.Comment: 9 pages, 4 figure
The High-Acceptance Dielectron Spectrometer HADES
HADES is a versatile magnetic spectrometer aimed at studying dielectron
production in pion, proton and heavy-ion induced collisions. Its main features
include a ring imaging gas Cherenkov detector for electron-hadron
discrimination, a tracking system consisting of a set of 6 superconducting
coils producing a toroidal field and drift chambers and a multiplicity and
electron trigger array for additional electron-hadron discrimination and event
characterization. A two-stage trigger system enhances events containing
electrons. The physics program is focused on the investigation of hadron
properties in nuclei and in the hot and dense hadronic matter. The detector
system is characterized by an 85% azimuthal coverage over a polar angle
interval from 18 to 85 degree, a single electron efficiency of 50% and a vector
meson mass resolution of 2.5%. Identification of pions, kaons and protons is
achieved combining time-of-flight and energy loss measurements over a large
momentum range. This paper describes the main features and the performance of
the detector system
Beta-delayed neutron spectroscopy of In
The decay properties of In were studied in detail at the ISOLDE Decay
Station (IDS). The implementation of the Resonance Ionization Laser Ion Source
(RILIS) allowed separate measurements of its ground state (In)
and isomer (In). With the use of -delayed neutron and
spectroscopy, the decay strengths above the neutron separation energy
were quantified in this neutron-rich nucleus for the first time. The allowed
Gamow-Teller transition was located at 5.92 MeV in the
In decay with a logft = 4.7(1). In addition, several neutron-unbound
states were populated at lower excitation energies by the First-Forbidden
decays of In. We assigned spins and parities to those
neutron-unbound states based on the -decay selection rules, the logft
values, and systematics
Evolution of deformation in neutron-rich Ba isotopes up to A=150
The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N = 90. To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z = 56 isotopic chain accessible at present, Ba-148,Ba-150, has been studied via beta decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive-and negative-parity low-spin excited states of 150Ba and presents an extension of the beta-decay scheme of Cs-148. Employing the fast timing technique, half-lives for the 2(1)(+) level in both nuclei have been determined, resulting in T-1/2 = 1.51(1) ns for Ba-148 and T-1/2 = 3.4(2) ns for Ba-150. The systematics of low-spin states, together with the experimental determination of the B(E2 : 2(+) -> 0(+)) transition probabilities, indicate an increasing collectivity in Ba148-150, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.Peer reviewe
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