The NECTAR (Nuclear rEaCTions At storage Rings) experiment at the ESR heavy-ion storage ring at GSI/FAIR Darmstadt is dedicated to surrogate reaction studies of neutron-induced reactions on heavy nuclei in inverse kinematics. In this work, we report on the implementation and performance of a newly developed fission-fragment detection system integrated into the NECTAR experimental setup. The upgraded detector configuration enables, for the first time in a surrogate experiment, the simultaneous detection ofgamma-decay residues, multi-neutron-emission residues, and fission fragments. The full setup was used for the first time in an experiment where a stored beam of bare 238U92+ ions at 17.24 MeV/u interacted with a gas-jet deuterium target, populating excited 238U and 239U nuclei via the 238U(d,d') and 238U(d,p) reactions. We describe the geometry of the used fission fragment detectors, design constraints, and simulation-based efficiency determination. The target-like particle identification and beam-like residue spectra demonstrating the performance of the complete setup are also shown.

Neutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the ^{208}Pb(p,p^{'}) reaction as a surrogate for neutron capture on ^{207}Pb. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of ^{208}Pb. We have used this probability to select different descriptions of the γ-ray strength function and nuclear level density, and provide reliable results for the neutron-induced radiative capture cross section of ^{207}Pb at energies for which no experimental data exist.

The probabilities for gamma-ray and particle emission as a function of the excitation energy of a decaying nucleus are valuable observables for constraining the ingredients of the models that describe the deexcitation of nuclei near the particle emission threshold. These models are essential in nuclear astrophysics and applications. In this paper, we have for the first time simultaneously measured the gamma-ray and neutron emission probabilities of 208Pb. The measurement was performed in inverse kinematics at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, where a 208Pb beam interacted through the 208Pb(p, p') reaction with a hydrogen gas jet target. Instead of detecting the gamma rays and neutrons emitted by 208Pb, we detected the heavy beamlike residues produced after gamma and neutron emission. These heavy residues were fully separated by a dipole magnet of the ESR and were detected with outstanding efficiencies. The comparison of the measured probabilities with model calculations has allowed us to test and select different descriptions of the gamma-ray strength function and the nuclear level density available in the literature.

Determining the cross sections of neutron-induced reactions on short-lived nuclei is imperative to rate calculations in stellar nucleosynthesis and applications of nuclear physics. It is also an immense experimental challenge due to the radioactivity of the targets involved. Our goal is to circumvent this obstacle by using surrogate reactions in inverse kinematics at the heavy-ion storage rings of GSI/FAIR. We present here preliminary results from the first proof of principle experiment, where a beam of 208 Pb impinged on a H 2 gas jet target in the Experimental Storage Ring (ESR).

This contribution presents a precise measurement of the excitation energy of the lowest (0 + , T=2) state in 32 S. Combined with the mass excesses of the 32 S ground state and of the four other members of the (A=32,T=2) quintet of analogue states, it allows to test the validity of the Isobaric Multiplet Mass Equation to the third order in T z , which renders it highly sensitive to the mechanisms inducing isospin mixing in the involved sd-shell nuclei. The (0 + , T=2) isobaric analogue state in 32 S was resonantly populated in the 31 P(p, γ) reaction at ~3.3 MeV incident energy. The measurement procedure, involving high-purity germanium detectors, is described and the preliminary result obtained with a digital data acquisition system is presented.

We report on the conception and first tests of the General Purpose Ion Buncher (GPIB), the radio-frequency beam-cooler and buncher that will supply the DESIR (Decay, Excitation and Storage of Radioactive Ions) experimental hall to be constructed to complement the SPIRAL1 and SPIRAL2 facilities in GANIL. Its goals are both to reduce the emittance and if necessary to bunch the radioactive ion beam from the GANIL production facilities to adapt it to the needs of the different experimental setups in the DESIR hall. The mechanical design is similar to the existing ISCOOL quadrupole at ISOLDE but the new radio-frequency system enables a much stronger radial confinement. The GPIB is developed at LP2i Bordeaux(1) in parallel with the PIPERADE double Penning trap and a beamline has been constructed there to characterize both. The cooling of a 30 keV beam to an emittance of 3 pi mm mrad and a transmission above 80% in continuous mode is demonstrated for currents up to a few nA. Some first results concerning the bunching mode are also shown though this mode is still under development.

The article describes the commissioning and technical development of the Weak Interaction Studies with 32Ar Decay (WISArD) experiment, installed at the radioactive ion-beam facility ISOLDE/CERN. The experiment aims to extend the present limits on scalar and tensor currents in the weak interaction and hence search for physics beyond the Standard Model. The evaluation of these limits relies on measuring the proton energy in beta-delayed proton emission, sensitive to both the beta-neutrino angular correlation coefficient aβν and the Fierz interference term b. The method tries to improve previous studies by considering the positron-proton coincidences when determining the kinematic shift in the energy of the emitted protons. Using this coincidence technique, the aβν and b coefficients will be measured at the per mil level. Simulations were employed to optimize the ion beam transport efficiency and validate proof-of-principle results obtained in November 2018 (Nov2018). Upgrades are ongoing, and we are looking into improvements to the overall performance of the setup.

The observation of a weak proton-emission branch in the decay of the 3174-keV 53mCo isomeric state marked the discovery of proton radioactivity in atomic nuclei in 1970. Here we show, based on the partial half-lives and the decay energies of the possible proton-emission branches, that the exceptionally high angular momentum barriers, [Formula: see text] and [Formula: see text], play a key role in hindering the proton radioactivity from 53mCo, making them very challenging to observe and calculate. Indeed, experiments had to wait decades for significant advances in accelerator facilities and multi-faceted state-of-the-art decay stations to gain full access to all observables. Combining data taken with the TASISpec decay station at the Accelerator Laboratory of the University of Jyväskylä, Finland, and the ACTAR TPC device on LISE3 at GANIL, France, we measured their branching ratios as bp1 = 1.3(1)% and bp2 = 0.025(4)%. These results were compared to cutting-edge shell-model and barrier penetration calculations. This description reproduces the order of magnitude of the branching ratios and partial half-lives, despite their very small spectroscopic factors.

In this work we present the preliminary results of analysing the 46 Mn β + decay channel as a way to study the 45 V( p , γ ) 46 Cr reaction. 46 Mn was selected among other species in the cocktail beam delivered by the LISE fragment separator at GANIL (Caen, France) in order to study its beta decay and the excited states of its daughter nucleus 46 Cr. As part of the validation process we present the 46 Mn half-life, the proton and gamma emission peaks related to the 46 Mn decay and compare them with the results from previous works.

The very proton-rich 71 Kr isotope was produced through the in-flight fragmentation of 78 Kr on a beryllium target at RIKEN – Nishina Center in order to study its β-decay properties. A stack of double-sided silicon strip detectors, called WAS3ABi, was used as the decay station, where the detection of ion implants, β-decays and β-delayed protons took place. Beta-delayed γ-rays were measured using a system of 84 HPGe detectors, called EURICA, surrounding the decay station. The main goal of the present study was the precise measurement of the half-life of 71 Kr, as in the literature there is an almost 10 σ difference between the most precise independent results. Implant–β time correlations, implant–proton time correlations and implant–β–γ time correlations were all used to derive the half-life value, followed by a thorough investigation of systematic uncertainties for each method. As these values were found to be consistent, the weighted average t 1 / 2 = 94.40 +19 ms is reported as a new half-life value in this work. Furthermore a total of 26 previously unreported γ following the β-decay of 71 Kr were also identified in the analysis.

Characterizing a (high resolution) magnetic separator may not be easy as it is difficult to find a stable ion source providing species with close enough masses to separate. As these instruments perform a momentum separation (Bρ=p/q), their mass and energy resolution are strictly the same. One can use this property to characterize the mass resolution of a spectrometer through its energy resolution. Hence, multiple identical beams with close energies can be used to test a magnetic spectrometer in almost real conditions. The method we present allows to populate an ion beam with multiple close and well-defined energies. It consists in using an arbitrary pulse generator to temporally change the acceleration potential of the ion source, and create a custom energy distribution, where the length in time of the pulse is the production ratio of the contaminant and the amplitude its relative energy (i.e. its mass).

Neutron-induced reaction cross sections of unstable nuclei are essential for understanding the synthesis of heavy elements in stars. However, their measurement is very difficult due to the radioactivity of the targets involved. We propose to circumvent this problem by using for the first time the surrogate reaction method in inverse kinematics at heavy-ion storage rings. In this contribution, we describe the developments we have done to perform surrogate-reaction studies at the storage rings of GSI/FAIR. In particular, we present the first results of the proof of principle experiment, which we conducted recently at the Experimental Storage Ring (ESR).

DESIR is, together with S3-LEB, the low-energy part of the SPIRAL2 ISOL facility at GANIL. The High-Resolution mass Separator (HRS) included in DESIR is a 180 degrees symmetric online separator with two 90 degrees magnetic dipole sections arranged with electrostatic quadrupoles, sextupoles and a 48-pole electrostatic multipole on the mid plane. The HRS is now completely mounted at LP2i Bordeaux and under commissioning for the next years before its transfer to the entrance of the DESIR facility. Optical aberrations, mainly introduced by the dipoles, must be corrected up to the highest possible order to guarantee an optimal resolution of the separator. They are measured with a pepperpot-type emittance-meter, analyzed then corrected with the multipole. Up to now, 2nd order (hexapolar) and part of 3rd order (octupolar) aberrations are under control and an optimal FWHM separation has been achieved for two identical beams with a relative energy difference of dE/E(& EQUIV; dM/M) = 1/23400.In this paper, we present the effects of optical aberrations on the beam and its emittance figure, as well as the effect of the associated corrections with the multipole. Finally, we will show the latest resolution measurements and associated methodology.

The β-decay of the even-even nucleus 70Kr with Z=N+2, has been investigated at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center using the BigRIPS fragment separator, the ZeroDegree Spectrometer, the WAS3ABI implantation station and the EURICA HPGe cluster array. Fifteen γ-rays associated with the β-decay of 70Kr into 70Br have been identified for the first time, defining ten populated states below Eexc=3300 keV. The half-life of 70Kr was derived with increased precision and found to be t1/2=45.19±0.14 ms. The β-delayed proton emission probability has also been determined as εp=0.545(23)%. An increase in the β-strength to the yrast 1+ state in comparison with the heaviest Z=N+2 system studied so far (62Ge decay) is observed that may indicate increased np correlations in the T=0 channel. The β-decay strength deduced from the results is interpreted in terms of the proton-neutron quasiparticle random-phase approximation (pnQRPA) and also with a schematic model that includes isoscalar and isovector pairing in addition to quadrupole deformation. The application of this last model indicates an approximate realization of pseudo-SU(4) symmetry in this system.

Proton radioactivity was discovered exactly 50 years ago. First, this nuclear decay mode sets the limit of existence on the nuclear landscape on the neutron-deficient side. Second, it comprises fundamental aspects of both quantum tunnelling as well as the coupling of (quasi)bound quantum states with the continuum in mesoscopic systems such as the atomic nucleus. Theoretical approaches can start either from bound-state nuclear shell-model theory or from resonance scattering. Thus, proton-radioactivity guides merging these types of theoretical approaches, which is of broader relevance for any few-body quantum system. Here, we report experimental measurements of proton-emission branches from an isomeric state in 54m Ni, which were visualized in four dimensions in a newly developed detector. We show that these decays, which carry an unusually high angular momentum, ℓ = 5 and ℓ = 7, respectively, can be approximated theoretically with a potential model for the proton barrier penetration and a shell-model calculation for the overlap of the initial and final wave functions.

Proton-emission branches of the 10+ isomer in the Tz=−1 nucleus 54Ni have been imaged with the active target and time projection chamber (ACTAR TPC) in an experiment conducted at the Grand Accélérateur National d'Ions Lourds (GANIL). The completed decay scheme allows derivation of the reduced transition strengths, B(E2;10+→8+) and B(E4;10+→6+), for the two competing γ-ray transitions. By means of a comparison with their well-known ‘mirror transitions’ in Tz=+1 54Fe, and aided by a variety of shell-model calculations in the fp model space, effective charges for E4 transitions near N=Z 56Ni can be deduced: επ≈1.40 and εν≈0.30. Mirror-energy differences are explored with various shell-model interactions and isospin-symmetry breaking terms.

Many nuclear reactions used to create radioactive isotopes for nuclear research produce, in addition to the isotope of interest, many contaminants, which are often produced in much larger amounts than the isotope of interest. Many installations using the ISOL approach are therefore equipped with high-resolution mass separators to remove at least isotopes with a different mass number. In the present paper, we present the results of the commissioning of the DESIR HRS presently under development at LP2I Bordeaux (formerly CENBG). Optical aberrations are corrected up to 3rd order and a mass resolution of M/ΔM of 25000 is reached with a transmission of about 70 beam at 25 keV.

An experiment was conducted at the GANIL/LISE3 facility to produce the 10+ isomer of 54Ni and measure its proton radioactivity decay branches. The proton detection was achieved with the ACTAR TPC device that enabled the separation of the small signal of the emitted proton from the large signal of the implanted ion, while the decay half-life is of the order of 150 ns. From the measured data, the emitted proton track length and the decay time of the ion can be extracted simultaneously. The full proton radioactivity pattern could be established, with two emission branches and their relative branching ratio. Data processing and analysis that allowed to identify and separate the ion and the proton signals in order to reconstruct the particles trajectories and decay time are detailed. The evaluation of the detection efficiency for the proton radioactivity branches based on a full simulation is described.

In an experiment performed at the SPIRAL1 facility of GANIL, the $$\beta $$ decay of $$^{32}$$ Ar has been studied by means of the “Silicon Cube” device associated with germanium clover detectors from the EXOGAM array. Beta-delayed protons and $$\gamma $$ rays have been observed and allowed the determination of all relevant decay branches. The Gamow–Teller strength distribution is compared to shell-model calculations and excellent agreement is found. The Fermi strength is inline with expectations. A quasi-complete decay scheme of $$^{32}$$ Ar is established.