Future Radioactive Beam Research Articles

Nuclear physics with TriSol at Notre Dame’s Nuclear Science Laboratory

The detailed study of radioactive nuclei has resulted in opportunities for addressing many open questions in low-energy nuclear physics. For over three decades, the TwinSol separator at the University of Notre Dame has produced high-quality in-flight radioactive beams at low-energy for light isotopes that have been used in experiments aimed at nuclear structure, astrophysics, and fundamental symmetries studies. We have recently upgraded the TwinSol separator by adding additional elements: a dipole magnet, and a third solenoid. This new TriSol separator will improve the quality and purity of future radioactive beams. This improvement will enable the use of heavier beams and address beam contamination that has hindered past experiments. The current status of TriSol and its science program will be presented along with the role the TriSol program plays in the current landscape of nuclear physics user facilities. The TriSol program includes plans for studies of 11C(p, p)11C reaction for investigating the nature of the first stars, 14O(α, p)17F and its influence on reaction networks in X-ray bursts, the measurement of fusion reactions on Ne isotopes important for pycnonuclear reactions, precision half-life measurements for fundamental symmetries studies, and the use of TriSol as a magnetic spectrometer.

Nuclear structure dependence of fusion hindrance in heavy element synthesis

The production of the heaviest elements in fusion-evaporation reactions is substantially limited by very low cross sections, as fusion cross sections (including fusion-fission) are greatly reduced by the competing quasifission mechanism. Using the Australian National University Heavy Ion Accelerator Facility and CUBE detector array, fission fragments from the $^{48}\mathrm{Ti}+^{204,208}\mathrm{Pb}$ and $^{50}\mathrm{Ti}+^{206,208}\mathrm{Pb}$ reactions have been measured, with the aim to investigate how the competition between quasifission and fusion-fission evolves with small changes in entrance-channel properties associated mainly with the nuclear structure. Analysis of mass-distribution widths of strongly mass-angle-correlated fission fragments within the framework of the compound-nucleus fission theory demonstrates significant differences in quasifission (and therefore fusion) probabilities among the four reactions. The impact of nuclear structure on fusion highlights the importance of future radioactive beams.

Isotopic production cross sections of residual nuclei in the spallation reactionXe136(200AMeV)+p

The residual nuclei produced in the spallation reaction of Xe-136 nuclei at 200A MeV on protons have been studied by measuring the isotopic distributions for the elements from cadmium (Z = 48) to cesium (Z = 55) by using the fragment separator (FRS) spectrometer at GSI and the inverse kinematics technique. This is one of the few measurements performed at such a low projectile energy, close to the validity limit for intranuclear cascade models such as INCL or ISABEL. The experimental results have been compared to these intranuclear cascade codes coupled to the evaporation code ABLA. Both code combinations reproduce qualitatively the measured isotopic distributions; however, both underestimate the production of residues with mass numbers between 126 and 134. The measured cross sections are of interest for the planning of future radioactive beam or neutron source facilities.

The Prototype Active-Target Time-Projection Chamber used with TwinSol radioactive-ion beams

The study of low-energy reactions with radioactive-ion beams has been greatly enhanced by the recent use of active-target detectors, which have high efficiency and low thresholds to detect low-energy charged-particle decays. Both of these features have been used in experiments with the Prototype Active-Target Time-Projection Chamber to study α-cluster structure in unstable nuclei and 3-body charged-particle decays after implantation. Predicted α-cluster structures in 14C were probed using resonant α scattering and the nature of the 3-α breakup of the 02+ Hoyle state in 12C after the beta decay of 12N and 12B was studied. These experiments used in-flight radioactive-ion beams that were produced using the dual superconducting solenoid magnets TwinSol at the University of Notre Dame. Preliminary results from these experiments as well as the development of future radioactive beams to be used in conjunction with the PAT-TPC are presented.

Impact of individual nuclear masses onr-process abundances

We have performed for the first time a comprehensive study of the sensitivity of $r$-process nucleosynthesis to individual nuclear masses across the chart of nuclides. Using the latest version (2012) of the Finite-Range Droplet Model, we consider mass variations of $\pm0.5$ MeV and propagate each mass change to all affected quantities, including $Q$-values, reaction rates, and branching ratios. We find such mass variations can result in up to an order of magnitude local change in the final abundance pattern produced in an $r$-process simulation. We identify key nuclei whose masses have a substantial impact on abundance predictions for hot, cold, and neutron star merger $r$-process scenarios and could be measured at future radioactive beam facilities.

Large gamma-ray detector arrays and electromagnetic separators

The use of large gamma-ray detector arrays with electromagnetic separators is a powerful combination. Various types of gamma-ray detectors have been used; some provide high detector efficiency such as scintillation detector array, others use Ge detectors for good energy resolution, and recently developed Ge energy tracking arrays gives both high peak-to-background ratio and position resolution. Similarly, different types of separators were used to optimize the performance under different experimental requirements and conditions. For example, gas-filled separators were used in heavy element studies for their large efficiency and beam rejection factor. Vacuum separators with good isotope resolution were used in transfer and fragmentation reactions for the study of nuclei far from stability. This paper presents results from recent experiments using gamma-ray detector arrays in combination with electromagnetic separators, and discusses the physics opportunities provided by these instruments. In particular, we review the performance of the instruments currently in use, and discuss the requirements of instruments for future radioactive beam accelerator facilities.

The Orsay Universal Plunger System

A new plunger device for Recoil-Distance Doppler Shift and Time-Differential Recoil-In-Vacuum measurements has been developed at the CSNSM in collaboration with the IPN Orsay. It is conceived to be easily adapted to different experimental setups and facilities, in particular to the future radioactive beam facility Spiral2. An electronic feedback system keeping the distance between target and stopper foils constant, imperative for precision measurements of short lifetimes, was also developed.The plunger device was commissioned with an experiment performed at the IPN Orsay Tandem accelerator laboratory using the Orgam germanium detector array. Excited states in 76Kr were populated using the reaction 45Sc(35Cl,2p2n)76Kr. The lifetime τ of the 41+ state was determined to 4.3(6)ps, in accordance with previous measurement, confirming the functionality of the new plunger device. The commissioning experiment showed in particular that the electronic feed back system works as foreseen.

Determining and calculating spectroscopic factors from stable nuclei to the drip lines

A survey of our present understanding of absolute spectroscopic factors near stable closed-shell nuclei is given based on our current interpretation of the (e, e′p) reaction. Uncertainties associated with the imprecise knowledge of the degree of nonlocality of the optical potential of the knocked out proton are identified. Theoretical expectations for the dependence of spectroscopic factors on the nucleon asymmetry are outlined. Conflicting results obtained from various reactions concerning the asymmetry dependence of spectroscopic factors are surveyed. The possibility of obtaining reliable absolute spectroscopic factors with reactions initiated by hadrons is discussed with special emphasis on present and future radioactive beam experiments. The combined and integrated analysis of such reactions using a Green's function framework in the form of an extended dispersive optical model may provide a useful approach to resolve this theoretical open problem.

Charge state breeders: On-line results

The transformation of radioactive ions from 1+ to n+ in the low-energy stage of a post-accelerator – also called charge breeding, has become a mature technique. Several machines using the method are in operation or under construction. This paper will present and evaluate on-line and off-line results from two different breeder types, the EBIS and the ECRIS-based systems. Notable on-line results, in terms of versatility, efficiency and beam purity among other things, have been achieved with the trap-EBIS charge breeding system for REX-ISOLDE, a post-accelerator operational since 2001. These will be compared with breeding results of stable and radioactive beams obtained with ECRIS at a number of facilities using or developing ECRIS breeders. Finally an outlook will be given of the predicted evolution of the charge breeders and how they can meet the requirements of future radioactive beam facilities.

The heavy-ion magnetic spectrometer PRISMA

PRISMA is a tracking magnetic spectrometer for heavy ions [1], designed for the A = 100 − 200, E = 5 − 10 MeV · A heavy-ion beams of the XTU Tandem-ALPI-PIAVE accelerator complex, and for possible use with future radioactive beams [2]. Its most interesting features are its large solid angle of 80 msr and momentum acceptance ± 10%, mass resolution 1/300 via TOF, energy resolution up to 0.1% and rotation around the target in a large angular range (−20° to +130°). These performances will be made possible by software reconstruction of the ion tracks using the position, time and energy signals from the entrance and focal plane detectors.

Production of heavy neutron-rich nuclei “south" of lead

The production of heavy neutron-rich nuclei is investigated using cold-fragmentation reactions. More than 25 new heavy neutron-rich nuclei were produced in the fragmentation of 208Pb projectiles at 1 A GeV impinging a beryllium target. The precise measurement of their production cross sections enables to benchmark the predictive power of different model calculations and make reliable predictions of the production rates expected in future radioactive beam facilities.

A solenoidal spectrometer for reactions in inverse kinematics

A new type of spectrometer for the study of reactions in inverse kinematics is proposed, in which the target and detector are placed inside a uniform magnetic field. This device has significant advantages over more conventional approaches to measurements of key reactions, and should prove useful in the study of short-lived nuclei. The technique is directly applicable to existing research programs at present accelerators with secondary beams, and the technique is likely to be important at future radioactive beam facilities.

RNB Facilities in Europe - Present and Future

A brief overview is given of present and future radioactive nuclear beam (RNB) facilities in Europe. Recent developments and extensions of RNB schemes and their uses are mentioned. The two major facilities planned for Europe employing, respectively, the in-flight and ISOL schemes are briefly presented.

GRETA: the gamma-ray energy-tracking array. Status of the development and physics opportunities

A gamma-ray energy-tracking array (GRETA) consisting of a 4π array of highly segmented Ge detectors is a new concept for the detection of gamma radiation. In such an array, all of the individual interactions of each gamma-ray are identified by their energies and positions, the three-dimensional positions being determined by pulse-shape analysis of the signals from the segmented Ge detectors. Then, using tracking algorithms based on the properties of photoabsorption, Compton scattering and pair production, the gamma-ray scattering sequences can be reconstructed, even if many gamma-rays hit the array at the same time. Such a detector will have new and much improved capabilities compared to the current generation of gamma-ray spectrometers and will be vital to fully exploit the most exotic beams from future radioactive beam facilities. One implementation of the tracking array concept, called GRETA, is currently under development in the US. In this presentation the progress of the GRETA project will be reviewed and future plans and prospects will be discussed.

Ab initio calculations of light nuclei

results from such a nucleon-based model will pro-vide a baseline against which to gauge effects of quarkand other degrees of freedom. This approach will alsoallow the accurate calculation of nuclear matrix ele-ments needed for some tests of the standard model, andof nuclei and processes not presently accessible in thelaboratory. This can be useful for astrophysical studiesand for comparisons to future radioactive beam experi-ments. To achieve this goal, we must both determine theHamiltonians to be used and devise reliable methods formany-body calculations using them. Presently, we haveto rely on phenomenological models for the nuclear in-teraction, because a quantitative understanding of thenuclear force based on quantum chromodynamics is stillfar in the future.In order to make statements about the correctness ofa given phenomenological Hamiltonian, one must beable to make calculations whose results reflect the prop-erties of the Hamiltonian and are not obscured by ap-proximations. Because the Hamiltonian is still unknown,the correctness of the calculations cannot be determinedfrom comparison with experiment. For this reason it isessential to have a number of different

Present and future RNB facilities in Europe

This contribution starts with a short summary of how the experimental knowledge about exotic nuclei has developed over the years. It then gives an overview of the present and future radioactive beam facilities in Europe. The organization of the work towards the next generation RNB facilities in Europe is presented at the end.