62 research outputs found
Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40
The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied
using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb
excitation reactions. The deduced E2 strengths illustrate the enhanced
collectivity of the neutron-rich Fe isotopes up to N=40. The results are
interpreted by the generalized concept of valence proton symmetry which
describes the evolution of nuclear structure around N=40 as governed by the
number of valence protons with respect to Z~30. The deformation suggested by
the experimental data is reproduced by state-of-the-art shell calculations with
a new effective interaction developed for the fpgd valence space.Comment: 4 pages, 2 figure
Shape and structure of N=Z 64Ge; Electromagnetic transition rates from the application of the Recoil Distance Method to knock-out reaction
Transition rate measurements are reported for the first and the second 2+
states in N=Z 64Ge. The experimental results are in excellent agreement with
large-scale Shell Model calculations applying the recently developed GXPF1A
interactions. Theoretical analysis suggests that 64Ge is a collective
gamma-soft anharmonic vibrator. The measurement was done using the Recoil
Distance Method (RDM) and a unique combination of state-of-the-art instruments
at the National Superconducting Cyclotron Laboratory (NSCL). States of interest
were populated via an intermediate-energy single-neutron knock-out reaction.
RDM studies of knock-out and fragmentation reaction products hold the promise
of reaching far from stability and providing lifetime information for excited
states in a wide range of nuclei
Lifetime measurements in Co and Co
Lifetimes of the and states in Co and the
state in Co were measured using the recoil distance Doppler
shift and the differential decay curve methods. The nuclei were populated by
multi-nucleon transfer reactions in inverse kinematics. Gamma rays were
measured with the EXOGAM Ge array and the recoiling fragments were fully
identified using the large-acceptance VAMOS spectrometer. The E2 transition
probabilities from the and states to the ground
state could be extracted in Co as well as an upper limit for the
(E2) value in Co. The experimental
results were compared to large-scale shell-model calculations in the and
model spaces, allowing to draw conclusions on the single-particle
or collective nature of the various states.Comment: 8 pages, 8 figures, 1 table, accepted for publication in Physical
Review
Lifetime measurements of excited states in neutron-rich nuclei around 48 Ca
The lifetimes of the first excited states of the N = 30 isotones 50Ca and 51Sc and the Z = 18 isotopes 44â46Ar isotopes have been determined using a novel technique that combines the Recoil Distance Doppler Shift method with the CLARA-PRISMA spectrometers in multinucleon transfer reactions. The results allow determinination of the effective charges above 48Ca and test the strength of the N = 28 magic number when moving away from the stability line.Gadea Raga, AndrĂ©s, [email protected] ; Algora, Alejandro, [email protected] ; Rubio Barroso, Berta, [email protected]
Search for one-phonon mixed-symmetry states in the radioactive nucleus ÂčâŽâ°Nd
Low-spin excited states of ÂčâŽâ°Nd have been studied via the ÂčâŽâ°Ce(ÂłHe,3n)ÂčâŽâ°Nd reaction. The results from the data analysis show that one of the candidates for the one-phonon mixed symmetry state of ÂčâŽâ°Nd, namely the 2âșâ state at 2140 keV with an effective lifetime of 220(90) fs, decay with a fast M1 transition to the 2âșâ state. Therefore consequently this state can be treated as, at least a fragment of the one-phonon MSS of ÂčâŽâ°Nd. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A â 140 region based on the data on absolute M1 transition rates
Search for one-phonon mixed-symmetry states in the radioactive nucleus Nd-140
Low-spin excited states of Nd-140 have been studied via the Ce-140(He-3,3n)Nd-140 reaction. The data show that one of the candidates for the one-phonon mixed-symmetry state (MSS) of Nd-140, namely, the 2(3)(+) state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 2(1)(+) state. Thus, this state can be considered, at least, as a fragment of the one-phonon MSS of Nd-140. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A approximate to 140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon MSS of Nd-140 is fragmented
Lifetime measurement in
The lifetime of the 17/2+ yrast state in 195Po has been measured using the recoil distance Doppler-shift technique to be = 43(11) ps. The lifetime was extracted from the singles -ray spectra obtained by using the recoil-decay tagging method. The present work provides more information of the coupling schemes, shapes and configuration mixing in neutron-deficient odd-mass Po nuclei
Collectivity of Po-196 at low spin
Absolute electromagnetic transition probabilities in Po-196 have been measured using the recoil distance Doppler-shift technique. The lifetimes of the three lowest yrast states in Po-196 were extracted from singles gamma-ray spectra by using the recoil-decay tagging method. In addition, configuration mixing calculations of angular momentum projected mean-field states have been carried out for Po-196. The present study sheds light on the onset of collectivity and mixing of competing structures in neutron-deficient Po nuclei
Collectivity of Exotic Heavy Fe Isotopes
The properties of exotic neutron-rich nuclei between the proton shell closures Z = 20 and Z = 28 are of particular interest for the understanding of the shell structure for large neutron excess. Effects related to the energy gap between the neutron fp and 1g9/2 shells lead to a strong variation of collectivity for nuclei around N = 40. Whereas (68)Ni was found to have doubly magic properties, this was not observed in neighbouring nuclei. Recent shell model calculations for the neutron rich iron isotopes clearly reveal the difficulty to describe nuclei in this mass region and resulted in large deviations of the predicted collectivity depending on the valence space. However, no experimental data on the transition strength existed for the very exotic nucleus (66)Fe at N = 40. Here we present the newest results on absolute transition strengths of the lowest excited states in (62,64,66)Fe measured model independently using the recoil distance Doppler-shift (RDDS) method. The experiments were performed at NSCL at Michigan State University with the Cologne/NSCL plunger device using Coulomb excitation in inverse kinematics at energies of 80 MeV/u. Our results yield a much higher collectivity for (64,66)Fe than expected and allow tests of new calculations
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