arXiv subjects

F. Delaunay

Publications and source records attributed to F. Delaunay.

46 records · Page 3Linked to original sources

arXiv2013

Tracking rare-isotope beams with microchannel plates

A system of two microchannel-plate detectors has been successfully implemented for tracking projectile-fragmentation beams. The detectors provide interaction positions, angles, and arrival times of ions at the reaction target. The current design is an adaptation of an assembly used for low-energy beams ($\sim$1.4 MeV/nucleon). In order to improve resolution in tracking high-energy heavy-ion beams, the magnetic field strength between the secondary-electron accelerating foil and the microchannel plate had to be increased substantially. Results from an experiment using a 37-MeV/nucleon ${}^{56}$Ni beam show that the tracking system can achieve sub-nanosecond timing resolution and a position resolution of $\sim$1 mm for beam intensities up to $5\times10^{5}$ pps.

physics.ins-det↗

arXiv2012

Comment on "First Observation of Ground State Dineutron Decay: 16Be"

A recent measurement [Spyrou et al., PRL 108, 102501 (2012)] of the in-flight decay of 16Be into 14Be+n+n has been interpreted as the first case of dineutron emission. Here we point out that the inclusion of the n-n interaction neglected in the description of the direct three-body decay can generate strong enhancements at low n-n relative energy and angle, as observed, without any need to invoke dineutron decay.

nucl-ex↗

arXiv2012

The N = 16 spherical shell closure in 24O

The unbound excited states of the neutron drip-line isotope 24O have been investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed from the momenta of 23O and the neutron. The spin-parity of the first excited state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from the angular distribution of the cross section. Higher lying states were also observed. The quadrupole transition parameter beta2 of the 2+ state was deduced, for the first time, to be 0.15 +/- 0.04. The relatively high excitation energy and small beta2 value are indicative of the N = 16 shell closure in 24O.

nucl-ex↗

arXiv2010

Emergence of the N=16 shell gap in 21O

The spectroscopy of 21O has been investigated using a radioactive 20O beam and the (d,p) reaction in inverse kinematics. The ground and first excited states have been determined to be Jpi=5/2+ and Jpi=1/2+ respectively. Two neutron unbound states were observed at excitation energies of 4.76 +- 0.10 and 6.16 +- 0.11. The spectroscopic factor deduced for the lower of these interpreted as a 3/2+ level, reveals a rather pure 0d3/2 single-particle configuration. The large energy difference between the 3/2+ and 1/2+ states is indicative of the emergence of the N=16 magic number. For the higher lying resonance, which has a character consistent with a spin-parity assignment of 3/2+ or 7/2-, a 71% branching ratio to the first 2+ state in 20O has been observed. The results are compared with new shell model calculations.

nucl-ex↗

arXiv2007

Fragmentation cross-sections and binding energies of neutron-rich nuclei

An exponential dependence of the fragmentation cross-section on the average binding energy is observed and reproduced with a statistical model. The observed functional dependence is robust and allows the extraction of binding energies from measured cross-sections. From the systematics of 75,77,78,79Cu isotope cross-sections have been extracted. They are 636.94 +/- 0.40 MeV, 647.1 +/- 0.4 MeV, 651.6 +/- 0.4 MeV and 657.8 +/- 0.5 MeV, respectively. Specifically, the uncertainty of the binding energy of 75Cu is reduced from 980 keV (listed value in the 2003 mass table of Audi and Wapstra) to 400 keV. The predicted cross-sections of two near drip-line nuclei, 39Na and 40Mg, from the fragmentation of 48Ca are discussed.

nucl-ex↗

arXiv2007

On the measurement of B(E2, 0+ -> 2+) using intermediate-energy Coulomb excitation

Coulomb excitation is a standard method used to extract quadrupole excitation strengths of even-even nuclei. In typical analyses the reaction is assumed to be one-step, Coulomb only, and is treated within a semi-classical model. In this work, fully-quantal coupled-channel calculations are performed for three test cases in order to determine the importance of multi-step effects, nuclear contributions, feeding from other states and corrections to the semi-classical approximation. We study the excitation of 30S, 58Ni and 78Kr on 197Au at ~ 50 AMeV. We find that nuclear effects may contribute more than 10% and that feeding contributions can be larger than 15%. These corrections do not alter significantly the published B(E2) values, however an additional theoretical error of up to 13% should be added to the experimental uncertainty if the semi-classical model is used. This theoretical error is reduced to less than 7% when performing a quantal coupled-channel analysis.

nucl-th↗

arXiv2007

Projectile Fragmentation of $^{86}$Kr at 64 MeV/nucleon

We measured fragmentation cross sections produced using the primary beam of $^{86}$Kr at 64 MeV/nucleon on $^9$Be and $^{181}$Ta targets. The cross sections were obtained by integrating the momentum distributions of isotopes with 25<Z<36 measured using the RIPS fragment separator at RIKEN. The cross-section ratios obtained with the $^{181}$Ta and $^{9}$Be targets depend on the fragment masses, contrary to the simple geometrical models. We compared the extracted cross sections to EPAX; an empirical parameterization of fragmentation cross sections. Predictions from current EPAX parameterization severely overestimate the production cross sections of very neutron-rich isotopes. Attempts to obtain another set of EPAX parameters specific to the reaction studied here, to extrapolate the neutron-rich nuclei more accurately have not been very successful, suggesting that accurate predictions of production cross sections of nuclei far from the valley of stability require information of nuclear properties which are not present in EPAX.

nucl-ex↗

arXiv2007

Extrapolation of neutron-rich isotope cross-sections from projectile fragmentation

Using the measured fragmentation cross sections produced from the 48Ca and 64Ni beams at 140 MeV per nucleon on 9Be and 181Ta targets, we find that the cross sections of unmeasured neutron rich nuclei can be extrapolated using a systematic trend involving the average binding energy. The extrapolated cross-sections will be very useful in planning experiments with neutron rich isotopes produced from projectile fragmentation. The proposed method is general and could be applied to other fragmentation systems including those used in other radioactive ion beam facilities.

nucl-ex↗

arXiv2006

Reduced neutron spectroscopic factors when using potential geometries constrained by Hartree-Fock calculations

We carry out a systematic analysis of angular distribution measurements for selected ground-state to ground-state (d,p) and (p,d) neutron transfer reactions, including the calcium isotopes. We propose a consistent three-body model reaction methodology in which we constrain the transferred-neutron bound state and nucleon-target optical potential geometries using modern Hartree-Fock calculations. Our deduced neutron spectroscopic factors are found to be suppressed by ~30% relative to independent-particle shell-model values, from 40Ca through 49Ca. The other nuclei studied, ranging from B to Ti, show similar average suppressions with respect to large-basis shell-model expectations. Our results are consistent with deduced spectroscopic strengths for neutrons and protons from intermediate energy nucleon knockout reactions, and for protons from (e,e'p) reactions, on well-bound nuclei. PACS: 24.50.+g, 24.10.Eq, 25.40.-h, 25.45.-z

nucl-ex↗

arXiv2005

Coupling and higher-order effects in the 12C(d,p)13C and 13C(p,d)12C reactions

Coupled channels calculations are performed for the 12C(d,p)13C and 13C(p,d)12C reactions between 7 and 60 MeV to study the effect of inelastic couplings in transfer reactions. The effect of treating transfer beyond Born approximation is also addressed. The coupling to the 12C 2+ state is found to change the peak cross-section by up to 15 %. Effects beyond Born approximation lead to a significant renormalization of the cross-sections, between 5 and 10 % for deuteron energies above 10 MeV, and larger than 10 % for lower energies. We also performed calculations including the remnant term in the transfer operator, which has a small impact on the 12C(d,p)13C(g.s.) and 13C(p,d)12C(g.s.) reactions. Above 30 MeV deuteron energy, the effect of the remnant term is larger than 10 % for the 12C(d,p)13C(3.09 MeV) reaction and is found to increase with decreasing neutron separation energy for the 3.09 MeV state of 13C. This is of importance for transfer reactions with weakly bound nuclei.

nucl-th↗