New pathway to bypass the 15O waiting point

We propose the sequential reaction process $^{15}$O($p$,$\gamma)(\beta^{+}$)$^{16}$O as a new pathway to bypass of the $^{15}$O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 10$^{10}$ times higher than the $^{15}$O($p$,$\beta^{+}$)$^{16}$O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound $^{16}$F low lying states, obtained using the H($^{15}$O,p)$^{15}$O reaction. The large $(p,\gamma)(\beta^{+})$ cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte

Probing Nuclear forces beyond the drip-line using the mirror nuclei 16^{16}N and 16^{16}F

Radioactive beams of $^{14}$O and $^{15}$O were used to populate the resonant states 1/2$^+$, 5/2$^+$ and $0^-,1^-,2^-$ in the unbound $^{15}$F and $^{16}$F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in $^{16}$F can be viewed as a core of $^{14}$O plus a proton in the 2s$_{1/2}$ or 1d$_{5/2}$ shell and a neutron in 1p$_{1/2}$. Experimental energies were used to derive the strength of the 2s$_{1/2}$-1p$_{1/2}$ and 1d$_{5/2}$-1p$_{1/2}$ proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus $^{16}$N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an $\ell=0$ proton configuration.Comment: 6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review

Fast-timing lifetime measurements of excited states in Cu-67

The half-lives of the 9/2(+), 13/2(+), and 15/2(+) yrast states in the neutron-rich Cu-67 nucleus were determined by using the in-beam fast-timing technique. The experimentally deduced E3 transition strength for the decay of the 9/2(+) level to the 3/2(-) ground state indicates that the wave function of this level might contain a collective component arising from the coupling of the odd proton p(3/2) with the 3(-) state in Ni-66. Theoretical interpretations of the 9/2(+) state are presented within the particle-vibration weak-coupling scheme involving the unpaired proton and the 3(-) state from Ni-66 and within shell-model calculations with a Ni-56 core using the jj44b residual interaction. The shell model also accounts reasonably well for the other measured electromagnetic transition probabilities

An above-barrier narrow resonance in F-15

Intense and purified radioactive beam of post-accelerated O-14 was used to study the low-lying states in the unbound F-15 nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E-R = 4.757(6)(10) MeV with a width of Gamma = 36(5)(14) keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a C-12 core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the 2s(1/2) shell. (C) 2016 The Authors. Published by Elsevier B.V

An above-barrier narrow resonance in ¹⁵F

Intense and purified radioactive beam of post-accelerated $^{14}$O was used to study the low-lying states in the unbound $^{15}$F nucleus. Exploiting resonant elastic scattering in inverse kinematics with a thick target, the second excited state, a resonance at E$\_R$=4.757(6)(10)~MeV with a width of $\Gamma$=36(5)(14)~keV was measured for the first time with high precision. The structure of this narrow above-barrier state in a nucleus located two neutrons beyond the proton drip line was investigated using the Gamow Shell Model in the coupled channel representation with a $^{12}$C core and three valence protons. It is found that it is an almost pure wave function of two quasi-bound protons in the $2s\_{1/2}$ shell.Comment: 8 pages, 2 figures, 1 table, Submitted to Phys. Lett.

Potential of the Bucharest 3 MV Tandetron™ for IBA studies of deer antler mineralization

Combined PIXE and PIGE analysis was applied at the new Bucharest Tandetron to investigate biomineralization in two calcified tissues, deer antlers and femur bone. By annual loss and fast re-growth, antlers are a valuable model for bone as a dynamical system. Samples characterized by optical microscopy and histology were analyzed for P, Ca, F, Na, Mg, S, Cl, K, Zn, Sr by 3 MeV proton simultaneous PIXE and PIGE, using a hydroxyapatite standard and other reference materials. Good correlation between methods was found for P, and the concentrations were related to biological data. Antlers showed lower mineralization than femur, with the lowest values in the third antler beam. A power function of mineralization vs. >mineral age> of antlers was found. Thus combined PIXE and PIGE of antlers may bring highly relevant insights in biomineralization research.Peer Reviewe

Study of the structural modifications induced by He implantation in cubic zirconia

International audienceThis article deals with the study of the structural modifications induced in yttria-stabilized zirconia implanted with low-energy (30 keV) He ions. For this purpose, three complementary analysis techniques, namely RBS/C, XRD and TEM, were used. After implantation at 5 x 10(16) cm(-2) (similar to 4 at% to similar to 1.7 dpa), it is found that the disorder level is weak, and the damage likely consists in small interstitial-type defects and helium-vacancy clusters. These defects induce a tensile strain gradient in the direction normal to the implanted crystal surface. This weak damage indicates a strong mechanical resistance of the zirconia matrix against He implantation. (c) 2010 Elsevier B.V. All rights reserved

Thermal behaviour of helium-implanted spinel single crystals

The study of the microstructural modifications induced in spinet implanted with (4)He(+) at 4.7 at.% and subsequently annealed at 1075 K is addressed in this paper. The combination of three analysis techniques Rutherford backscattering spectrometry in channeling geometry (RBS/C), X-ray diffraction and transmission electron microscopy was used in order to gain information about the damage depth distribution, the nature of radiation defects, and the occurrence of microstructural modifications. In as-implanted crystals the disorder level is weak, and the damage principally consists of small helium-vacancy clusters. These defects induce a tensile strain in the direction normal to the implanted crystal surface. After annealing, a surprising increase of the disorder level is measured by RBS/C. This increased backscattering yield is due to the formation of a particular type of He-vacancy clusters, namely He platelets, which also induce a relaxation of the strain. (C) 2010 Elsevier B.V. All rights reserved