arXiv subjects

J. C. Thomas

Publications and source records attributed to J. C. Thomas.

At least 37 records · Page 2Linked to original sources

arXiv2020

First investigation of the response of solar cells to heavy ions above 1 AMeV

Solar cells have been used since several decades for the detection of fission fragments at about 1 AMeV. The advantages of solar cells regarding their cost (few euros) and radiation damage resistance make them an interesting candidate for heavy ion detection and an appealing alternative to silicon detectors. A first exploratory measurement of the response of solar cells to heavy ions at energies above 1 AMeV has been performed at the GANIL facility, Caen, France. Such measurements were performed with 84Kr and 129Xe beams ranging from 7 to 13 AMeV. The energy and time response of several types of solar cells were studied. The best performance was observed for cells of 10x10 mm2, with an energy and time resolution of σ(E)/E=1.4% and 3.6 ns (FWHM), respectively. Irradiations at rates from a few hundred to 106 particles per second were also performed to investigate the behavior of the cells with increasing intensity.

physics.ins-det↗

arXiv2019

The MORA project

The MORA (Matter's Origin from the RadioActivity of trapped and oriented ions) project aims at measuring with unprecedented precision the D correlation in the nuclear beta decay of trapped and oriented ions. The D correlation offers the possibility to search for new CP-violating interactions, complementary to searches done at the LHC and with Electric Dipole Moments. Technically, MORA uses an innovative in-trap orientation method which combines the high trapping efficiency of a transparent Paul trap with laser orientation techniques. The trapping, detection, and laser setups are under development, for first tests at the Accelerator laboratory, JYFL, in the coming years.

physics.ins-det↗

arXiv2019

New exotic beams from the SPIRAL 1 upgrade

Since 2001, the SPIRAL 1 facility has been one of the pioneering facilities in ISOL techniques for reaccelerating radioactive ion beams: the fragmentation of the heavy ion beams of GANIL on graphite targets and subsequent ionization in the Nanogan ECR ion source has permitted to deliver beams of gaseous elements (He, N, O, F, Ne, Ar, Kr) to numerous experiments. Thanks to the CIME cyclotron, energies up to 20 AMeV could be obtained. In 2014, the facility was stopped to undertake a major upgrade, with the aim to extend the production capabilities of SPIRAL 1 to a number of new elements. This upgrade, which is presently under commissioning, consists in the integration of an ECR booster in the SPIRAL 1 beam line to charge breed the beam of different 1+ sources. A FEBIAD source (the so-called VADIS from ISOLDE) was chosen to be the future workhorse for producing many metallic ion beams. The charge breeder is an upgraded version of the Phoenix booster which was previously tested in ISOLDE. The performances of the aforementioned ingredients of the upgrade (targets, 1+ source and charge breeder) have been and are still being optimized in the frame of different European projects (EMILIE, ENSAR and ENSAR2). The upgraded SPIRAL 1 facility will provide soon its first new beams for physics and further beam development are undertaken to prepare for the next AGATA campaign. The results obtained during the on-line commissioning period permit to evaluate intensities for new beams from the upgraded facility.

physics.acc-ph↗

arXiv2017

High Precision Measurement of the $^{19}$Ne Half-life using real-time digital acquisition

The half-life of $^{19}$Ne has been measured using a real-time digital multiparametric acquisition system providing an accurate time-stamp and relevant information on the detectors signals for each decay event. An exhaustive offline analysis of the data gave unique access to experimental effects potentially biasing the measurement. After establishing the influence factors impacting the measurement such as after-pulses, pile-up, gain and base line fluctuations, their effects were accurately estimated and the event selection optimized. The resulting half-life, $17.2569\pm0.0019_{(stat)}\pm0.0009_{(syst)}$~s, is the most precise up to now for $^{19}$Ne. It is found in agreement with two recent precise measurements and not consistent with the most recent one [L.J. Broussard {\it et al.}, Phys. Rev. Lett. {\bf112}, 212301 (2014)] by 3.0 standard deviations. The full potential of the technique for nuclei with half-lives of a few seconds is discussed.

nucl-ex↗

arXiv2017

Study of fusion-fission in inverse kinematics with a fragment separator

The systematic study of fission fragment yields under different initial conditions provides a valuable experimental benchmark for fission models that aim to understand this complex decay channel and to predict reaction product yields. Inverse kinematics coupled to the use of a high-resolution spectrometer is shown to be a powerful tool to identify and measure the inclusive isotopic yields of fission fragments. In-flight fusion fission was used to produce secondary beams of neutron-rich isotopes in the collision of a 238U beam at 24 MeV/u with 9Be and 12C targets at GANIL using the LISE3 fragment-separator. Unique A,Z,q identification of fission products was attained with the dE-TKE-Brho-ToF measurement technique. Mass, and atomic number distributions are reported for the two reactions that show the importance of different reaction mechanisms for these two targets.

nucl-ex↗

arXiv2016

Observation of the 2$^+$ isomer in $^{52}$Co

We report the first observation of the 2$^+$ isomer in $^{52}$Co, produced in the $β$ decay of the 0$^+$, $^{52}$Ni ground state. We have observed three $γ$-rays at 849, 1910, and 5185 keV characterizing the $β$ de-excitation of the isomer. We have measured a half-life of 102(6) ms for the isomeric state. The Fermi and Gamow-Teller transition strengths for the $β$ decay of $^{52m}$Co to $^{52}$Fe have been determined. We also add new information on the $β$ decay of the 6$^+$, $^{52}$Co ground state, for which we have measured a half-life of 112(3) ms.

nucl-ex↗

arXiv2016

High-precision quadrupole moment reveals significant intruder component in 33Al20 ground state

The electric quadrupole moment of the 33Al20 ground state, located at the border of the island of inversion, was obtained using continuous-beam beta-detected nuclear quadrupole resonance (beta-NQR). From the measured quadrupole coupling constant Q = 2.31(4) MHz in an alpha-Al2O3 crystal, a precise value for the electric quadrupole moment is extracted: Qs= 141(3) mb. A comparison with large-scale shell model calculations shows that 33Al has at least 50% intruder configurations in the ground state wave function, favoring the excitation of two neutrons across the N = 20 shell gap. 33Al therefore clearly marks the gradual transition north of the deformed Na and Mg nuclei towards the normal Z>14 isotopes.

nucl-ex↗

arXiv2016

Beta decay of the exotic $T_z$ = -2 nuclei $^{48}$Fe, $^{52}$Ni and $^{56}$Zn

The results of a study of the beta decays of three proton-rich nuclei with $T_z=\text{-}2$, namely $^{48}$Fe, $^{52}$Ni and $^{56}$Zn, produced in an experiment carried out at GANIL, are reported. In all three cases we have extracted the half-lives and the total $β$-delayed proton emission branching ratios. We have measured the individual $β$-delayed protons and $β$-delayed $γ$ rays and the branching ratios of the corresponding levels. Decay schemes have been determined for the three nuclei, and new energy levels are identified in the daughter nuclei. Competition between $β$-delayed protons and $γ$ rays is observed in the de-excitation of the $T=2$ Isobaric Analogue States in all three cases. Absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. In addition, we discuss in detail the data analysis taking as a test case $^{56}$Zn, where the exotic $β$-delayed $γ$-proton decay has been observed.

nucl-ex↗

arXiv2016

An above-barrier narrow resonance in $^{15}$F

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 $Γ$=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.

nucl-ex↗

arXiv2016

Competition of $β$-delayed protons and $β$-delayed $γ$ rays in $^{56}$Zn and the exotic $β$-delayed $γ$-proton decay

Remarkable results have been published recently on the $β$ decay of $^{56}$Zn. In particular, the rare and exotic $β$-delayed $γ$-proton emission has been detected for the first time in the $fp$ shell. Here we focus the discussion on this exotic decay mode and on the observed competition between $β$-delayed protons and $β$-delayed $γ$ rays from the Isobaric Analogue State.

nucl-ex↗

arXiv2015

Precision measurements with LPCTrap at GANIL

The experimental achievements and the results obtained so far with the LPCTrap device installed at GANIL are presented. The apparatus is dedicated to the study of the weak interaction at low energy by means of precise measurements of the BETA-NU angular correlation parameter in nuclear BETA decays. So far, the data collected with three isotopes have enabled to determine, for the first time, the charge state distributions of the recoiling ions, induced by shakeoff process. The analysis is presently refined to deduce the correlation parameters, with the potential of improving both the constraint deduced at low energy on exotic tensor currents (6He1+) and the precision on the V u d element of the quark-mixing matrix (35Ar1+ and 19Ne1+) deduced from the mirror transitions dataset.

nucl-ex↗

arXiv2015

Spectroscopy of $^{28}$Na: shell evolution toward the drip line

Excited states in $^{28}$Na have been studied using the $β$-decay of implanted $^{28}$Ne ions at GANIL/LISE as well as the in-beam $γ$-ray spectroscopy at the NSCL/S800 facility. New states of positive (J$^π$=3,4$^+$) and negative (J$^π$=1-5$^-$) parity are proposed. The former arise from the coupling between 0d$\_{5/2}$ protons and a 0d$\_{3/2}$ neutron, while the latter are due to couplings with 1p$\_{3/2}$ or 0f$\_{7/2}$ neutrons. While the relative energies between the J$^π$=1-4$^+$ states are well reproduced with the USDA interaction in the N=17 isotones, a progressive shift in the ground state binding energy (by about 500 keV) is observed between $^{26}$F and $^{30}$Al. This points to a possible change in the proton-neutron 0d$\_{5/2}$-0d$\_{3/2}$ effective interaction when moving from stability to the drip line. The presence of J$^π$=1-4$^-$ negative parity states around 1.5 MeV as well as of a candidate for a J$^π$=5$^-$ state around 2.5 MeV give further support to the collapse of the N=20 gap and to the inversion between the 0f$\_{7/2}$ and 1p$\_{3/2}$ levels below Z=12. These features are discussed in the framework of Shell Model and EDF calculations, leading to predicted negative parity states in the low energy spectra of the $^{26}$F and $^{25}$O nuclei.

nucl-ex↗

arXiv2015

Heavy ion irradiation of crystalline water ice

Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisation was previously monitored mainly in the keV to hundreds of keV ion energies. We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays, and explore the water-ice sputtering yield. We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The ice infrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of the initial crystalline state into a compact amorphous phase). The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures. At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combined with previous measurements, is quadratic over three decades of electronic stopping power. The final state of cosmic ray irradiation for porous amorphous and crystalline ice, as monitored by infrared spectroscopy, is the same, but with a large difference in cross-section, hence in time scale in an astrophysical context. The cosmic ray water-ice sputtering rates compete with the UV photodesorption yields reported in the literature. The prevalence of direct cosmic ray sputtering over cosmic-ray induced photons photodesorption may be particularly true for ices strongly bonded to the ice mantles surfaces, such as hydrogen-bonded ice structures or more generally the so-called polar ices.

astro-ph.GA↗

arXiv2015

Competition between $β$-delayed proton and $β$-delayed $γ$ decay of the exotic $T_z$ = -2 nucleus $^{56}$Zn and fragmentation of the IAS

A very exotic decay mode at the proton drip-line, $β$-delayed $γ$-proton decay, has been observed in the $β$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $γ$-proton sequences have been observed following the $β$ decay. The fragmentation of the IAS in $^{56}$Cu has also been observed for the first time. The results were reported in a recent publication. At the time of publication the authors were puzzled by the competition between proton and $γ$ decays from the main component of the IAS. Here we outline a possible explanation based on the nuclear structure properties of the three nuclei involved, namely $^{56}$Zn, $^{56}$Cu and $^{55}$Ni, close to the doubly magic nucleus $^{56}$Ni. From the fragmentation of the Fermi strength and the excitation energy of the two populated 0$^{+}$ states we could deduce the off-diagonal matrix element of the charge-dependent part of the Hamiltonian responsible for the mixing. These results are compared with the decay of $^{55}$Cu with one proton less than $^{56}$Zn. For completeness we summarise the results already published.

nucl-ex↗

arXiv2015

$β$-delayed $γ$-proton decay in $^{56}$Zn: analysis of the charged-particle spectrum

A study of the $β$ decay of the proton-rich $T_{z}$ = -2 nucleus $^{56}$Zn has been reported in a recent publication. A rare and exotic decay mode, $β$-delayed $γ$-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.

nucl-ex↗

arXiv2015

Nuclear structure studies of $^{24}$F

The structure of the $^{24}$F nucleus has been studied at GANIL using the $β$ decay of $^{24}$O and the in-beam $γ$-ray spectroscopy from the fragmentation of projectile nuclei. Combining these complementary experimental techniques, the level scheme of $^{24}$F has been constructed up to 3.6 Mev by means of particle-$γ$ and particle-$γγ$ coincidence relations. Experimental results are compared to shell-model calculations using the standard USDA and USDB interactions as well as ab-initio valence-space Hamiltonians calculated from the in-medium similarity renormalization group based on chiral two- and three-nucleon forces. Both methods reproduce the measured level spacings well, and this close agreement allows unidentified spins and parities to be consistently assigned.

nucl-ex↗

arXiv2014

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

nucl-ex↗

arXiv2014

Observation of the $β$-delayed $γ$-proton decay of $^{56}$Zn and its impact on the Gamow Teller strength evaluation

We report the observation of a very exotic decay mode at the proton drip-line, the $β$-delayed $γ$-proton decay, clearly seen in the $β$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $γ$-proton sequences have been observed after the $β$ decay. Here this decay mode, already observed in the $sd$-shell, is seen for the first time in the $fp$-shell. Both $γ$ and proton decays have been taken into account in the estimation of the Fermi (F) and Gamow Teller (GT) strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

nucl-ex↗