Neutron-rich Radioactive Beams Research Articles

Properties and synthesis of the superheavy nucleus Fl114298

The one-nucleon separation energy ${S}_{n}$, two-nucleon separation energy ${S}_{2n}$, one-proton separation energy ${S}_{p}$, two-proton separation energy ${S}_{2p}, \ensuremath{\alpha}$-decay energy ${Q}_{\ensuremath{\alpha}}, \ensuremath{\alpha}$-decay half-life and spontaneous fission half-life of $Z=114$ isotopes and $N=184$ isotones are calculated by the finite-range droplet model (FRDM2012). It is found that $N=184$ is a neutron magic number, and $Z=114$ is a proton magic number. The properties of $Z=114$ isotopes and $N=184$ isotones provide a vital signal that $_{114}^{298}\mathrm{Fl}$ may be a spherical double-magic nucleus and also the center of the stability island of superheavy nuclei. Based on this, we began to investigate the optimal conditions for the synthesis of superheavy nucleus $_{114}^{298}\mathrm{Fl}$ within the dinuclear system model. To produce such neutron-rich compound nucleus, we consider using the extremely neutron-rich radioactive beams to bombard actinide targets. The evaporation residue cross section of superheavy nuclei synthesized by radioactive beam is analyzed in detail. Finally, we suggest that for the synthesis of $_{114}^{298}\mathrm{Fl}$, the radioactive beam-induced fusion reaction $^{64}\mathrm{Ti}+^{238}\mathrm{U}$ in the $4n$ evaporation channel with an excitation energy of 43 MeV is optimal.

Systematic Study of Neutron-Rich Rare Isotope Production in Peripheral Heavy-Ion Collisions at Beam Energies 15–25 MeV/nucleon

The production cross sections of projectile-like fragments from collisions of 86Kr projectiles with 64,58Ni and 124,112Sn targets at 15 and 25 MeV/nucleon are studied systematically with emphasis on the neutron-rich isotopes. Our recent experimental data are compared with calculations for the above collisions employing a hybrid approach. The dynamical stage of the projectile-target interaction was described with either the phenomenological deep-inelastic transfer (DIT) model or with the the microscopic constrained molecular dynamics model (CoMD). Subsequently, for the de-excitation of the projectile-like fragments, the statistical multifragmentation model (SMM) or the binary-decay code GEMINI were employed. An overall good agreement with the experimental results was obtained. We point out that our current understanding of the reaction mechanism at beam energies below the Fermi energy suggests that such nuclear reactions, involving peripheral nucleon exchange, can be exploited as a novel route to access extremely neutron-rich rare isotopes toward the r-process path and the hard-to-reach neutron drip-line. For this purpose, we believe that the use of re-accelerated neutron-rich radioactive beams may offer unique and exciting opportunities toward unexplored regions of the nuclear landscape.

Theoretical study on production of unknown neutron-deficient Fl280–283 and neutron-rich Fl290–292 isotopes by fusion reactions

We attempt to calculate the production cross sections of unknown $^{280--283}\mathrm{Fl}$ and $^{290--292}\mathrm{Fl}$ isotopes by using hot fusion reaction mechanism within the dinuclear system model. The production of unknown neutron-deficient Fl isotopes ($^{280--283}\mathrm{Fl}$) is studied in the reactions $^{44}\mathrm{Ca}+^{242}\mathrm{Pu}$ and $^{36}\mathrm{S}+^{249}\mathrm{Cf}$ with the maximum evaporation residue cross sections values 0.91 pb, 6.17 pb, 36.16 pb, and 2.02 pb, respectively. The use of neutron-rich radioactive beams $^{44}\mathrm{Ar}$ and $^{46}\mathrm{Ar}$ may help us produce new neutron-rich Fl isotopes via fusion reaction mechanism only if an extremely high beam intensity were to be achieved in the future. The maximum production cross sections of unknown neutron-rich isotopes ($^{290--292}\mathrm{Fl}$) in the reactions $^{46}\mathrm{Ar}+^{248}\mathrm{Cm}$ and $^{46}\mathrm{Ar}+^{250}\mathrm{Cm}$ are predicted to be 4.06 pb, 8.55 pb, and 3.35 pb, respectively. At present, reaction with radioactive ion beams is not a promising method to produce neutron-rich superheavy nuclei and other reaction mechanisms such as transfer reaction need to be developed.

Production of heavy neutron-rich nuclei with radioactive beams in multinucleon transfer reactions

The production mechanism of heavy neutron-rich nuclei is investigated by using the multinucleon transfer reactions of $$^{136,148}{\hbox {Xe}}+^{208}$$ Pb and $$^{238}{\hbox {U}}+^{208}$$ Pb in the framework of a dinuclear system model. The evaporation residual cross sections of target-like fragments are studied with the reaction system $$^{148}{\hbox {Xe}}+^{208}$$ Pb at near barrier energies. The results show that the final isotopic production cross sections in the neutron-deficient side are very sensitive to incident energy while it is not sensitive in the neutron-rich side. Comparing the isotopic production cross sections for the reactions of $$^{208}$$ Pb bombarded with stable and radioactive projectiles, we find that neutron-rich radioactive beams can significantly increase the production cross sections of heavy neutron-rich nuclei.

Operational experience with the Argonne National Laboratory Californium Rare Ion Breeder Upgrade facility and electron cyclotron resonance charge breeder

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory Argonne Tandem Linac Accelerator System (ATLAS) facility provides low-energy and accelerated neutron-rich radioactive beams to address key nuclear physics and astrophysics questions. A 350 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The ECR charge breeder has achieved stable beam charge breeding efficiencies of 10.1% for (23)Na(7+), 17.9% for (39)K(10+), 15.6% for (84)Kr(17+), and 12.4% for (133)Cs(27+). For the radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The typical breeding times are 10 ms/charge state, but the source can be tuned such that this value increases to 100 ms/charge state with the best breeding efficiency corresponding to the longest breeding times-the variation of efficiencies with breeding time will be discussed. Efforts have been made to characterize and reduce the background contaminants present in the ion beam through judicious choice of q/m combinations. Methods of background reduction are being investigated based upon plasma chamber cleaning and vacuum practices.

Using resonant nuclear reaction ²⁷Al(p,γ)²⁸Si to calibrate beam energy for pelletron accelerator 5SDH-2 at Hanoi university of science

Although electron accelerators are equipments which accelerate electron, in fact they are intense sources of bremsstrahlung photon and neutron beams. Therefore the study on spectroscopy of bremsstrahlung is of great importance. This work presents the results obtained by the authors about the energy distribution of bremsstrahlung spectra, the method for determination of bremsstrahlung photon flux as well as the possibilities for producing neutron and neutron rich radioactive ions beams for fundamental research and practical applications.

Reaction dynamics of Pt*isotopes formed using stable and radioactive Sn beams

The decay of various isotopes of Pt${}^{*}$ formed using stable and neutron-rich radioactive beams of Sn is studied by using the dynamical cluster-decay model (DCM). The entrance channel effect in ${}^{190}$Pt${}^{*}$ compound nuclei is investigated using different targets and projectiles. For both entrance channels, i.e., ${}^{132}$Sn+${}^{58}$Ni and ${}^{126}$Sn+${}^{64}$Ni, the fragmentation potential and preformation probability of decaying fragments are almost identical at comparable center-of-mass energies (${E}_{\mathrm{c}.\mathrm{m}.}$), enabling us to conclude that decay of ${}^{190}$Pt${}^{*}$ is independent of its formation effects. In order to check for the persistence of entrance channel independence in the decay of Pt${}^{*}$ compound nuclei, various versions of nuclear proximity potentials and different values of level density parameter are employed in the calculations, and the results are sustained. It is also observed that, with inclusion of deformation effects up to quadrupole (${\ensuremath{\beta}}_{2}$) within the optimum orientation approach, the structure of potential energy surfaces changes significantly. Besides this, the fission mass distribution of Pt${}^{*}$ isotopes is investigated and consequently the barrier modification is estimated to account for the phenomena of fusion hindrance. The ${}^{132}$Sn+${}^{58}$Ni reaction is also studied using four proximity potentials, i.e., Prox 1977, Prox 1988, mod-Prox 1988, and Denisov 2002 within the framework of the $\ensuremath{\ell}$-summed extended-Wong model for addressing the fusion hindrance phenomena. We find that Prox 77 and Prox 88 fit the total fusion cross-section data only at above-barrier energies, whereas Denisov 2002 underestimates the data at all energies due to being least sensitive towards asymmetry and isospin. So a stronger nuclear interaction potential mod-Prox 1988 that accounts for isospin effect and asymmetry of the colliding nuclei is employed, which fits the data with smooth variation of ${\ensuremath{\ell}}_{\mathrm{max}}$(${E}_{\mathrm{c}.\mathrm{m}.}$). Our calculations indicate that the isospin and asymmetry of colliding nuclei also play an important role in the fusion dynamics, particularly in the below-barrier region.

Unexpected results in neutron-rich radioactive beams induced fusion

The fission-fragment beams at HRIBF provide a unique opportunity for studying the mechanisms of fusion involving nuclei with large neutron excess. To explore the role of transfer couplings, fusion excitation functions have been measured using neutron-rich radioactive 132Sn beams incident on 40Ca and 58Ni targets. The sub-barrier fusion enhancement for 132 Sn+40Ca is larger than that for 132Sn+58Ni although the neutron transfer Q-values are similar for the two reactions. The fusion excitation function for 46Ti+124Sn has been measured in an attempt to resolve the differences observed in 132Sn+40Ca and 132Sn+58Ni.

Recent Results of Fusion Induced by Neutron-rich Radioactive Beams Studied at HRIBF

Recent Results of Fusion Induced by Neutron-rich Radioactive Beams Studied at HRIBF

Charge breeding results and future prospects with electron cyclotron resonance ion source and electron beam ion source (invited)

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory ATLAS facility will provide low-energy and reaccelerated neutron-rich radioactive beams for the nuclear physics program. A 70 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The final CARIBU configuration will utilize a 1 Ci (252)Cf source to produce radioactive beams with intensities up to 10(6) ions∕s for use in the ATLAS facility. The ECR charge breeder has been tested with stable beam injection and has achieved charge breeding efficiencies of 3.6% for (23)Na(8+), 15.6% for (84)Kr(17+), and 13.7% for (85)Rb(19+) with typical breeding times of 10 ms∕charge state. For the first radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The project has been commissioned with a radioactive beam of (143)Ba(27+) accelerated to 6.1 MeV∕u. In order to take advantage of its lower residual contamination, an EBIS charge breeder will replace the ECR charge breeder in the next two years. The advantages and disadvantages of the two techniques are compared taking into account the requirements of the next generation radioactive beam facilities.

The SPES project: a second generation ISOL facility

SPES is an INFN project to develop a Radioactive Ion Beam facility as an intermediate step toward EURISOL, the next generation European ISOL facility. The facility will be installed at the Laboratori Nazionali di Legnaro where the superconductive linac ALPI will reaccelerate the exotic beams at energies larger than 10 AMeV. Neutron-rich radioactive beams will be produced by proton-induced Uranium fission at an expected in-target fission rate of 1013 fissions per second. As proton driver, a 70 MeV cyclotron with a total current of 0.750 mA shared on two exit ports will be installed. The key feature of SPES is to provide high intensity and high-quality beams of neutron-rich nuclei to perform forefront research in nuclear physics as well as to develop and interdisciplinary research center based on the cyclotron proton beam. Neutron production at a rate of 1014 n/s is expected using the proton beam on thick target. The status of the project and the layout of the neutron facility will be presented. Two facilities can be operated at the same time, with a capability of 5000 h per year each. The ISOL facility will use 0.2 mA to reach the goal of 10 13 fissions per second and more than 0.5 mA will be available for applied physics applications, mainly neutron beam and medical isotopes production.

Studies of near-barrier fusion induced by neutron-rich nuclei at HRIBF

Fusion induced by neutron-rich radioactive beams is a topic of current interest. The f ndings will be useful for using radioactive beams to produce superheavy elements. Results from recent measurements performed with neutron-rich radioactive Sn and Te beams are presented. Coupled-channels calculations were carried out to study the observed sub-barrier fusion enhancement. The fusion probability in Sn on Ni was probed by comparing the evaporation residue cross sections at high excitation energies.

Highlights of heavy ion fusion induced by neutron-rich radioactive nuclei near the Coulomb barrier

The use of neutron-rich radioactive isotope beams for synthesizing heavy elements is a subject of continuing interest. Current experiments utilize low intensity beams to study reaction mechanisms for fusion induced by neutron-rich radioactive nuclei. Enhanced fusion cross sections were observed near and below the Coulomb barrier. A lowering of the barrier height was observed for heavy mass compound systems. Future experiments will benefit from improving detectors and increasing beam intensities.

Elastic and quasielastic barrier distributions for light neutron-rich nuclei: The role of neutron stripping channels

Recent interest in the elastic and quasielastic barrier distributions of systems involving weakly bound light projectiles has concentrated on the influence of coupling to breakup. We show that, for light neutron-rich radioactive beams, single-neutron stripping also has an important effect on the calculated barrier distribution. We also show that the recent suggestion that for such systems the quasielastic barrier distribution will not be exactly equivalent to the true fusion barrier distribution seems to hold true, although in the particular case investigated here the discrepancy in the barrier peak position, $0.25$ MeV, is considerably smaller than that found experimentally for the $^{6}\mathrm{Li}+^{144}\mathrm{Sm}$ system, $1.5$ MeV, where breakup is considered to be most important.

Projectile fragmentation of radioactive beams ofNi68,Cu69, andZn72

The fragment production cross sections of secondary neutron-rich beams of $^{68}\mathrm{Ni}$, $^{69}\mathrm{Cu}$, and $^{72}\mathrm{Zn}$ isotopes at energies of about $95A$ MeV have been measured. We compare the measured cross sections to EPAX, an empirical parametrization of fragmentation cross sections. A reasonable agreement of the experimental data and EPAX predictions suggests that an EPAX parametrization used for stable beams seems to be valid for unstable neutron-rich ion beams. EPAX tends to overestimate the yields of neutron-rich isotopes. This problem is amplified when neutron-rich radioactive beams are employed, leading to overly optimistic estimates of the production of neutron-rich isotopes.

The SPES project: An ISOL facility for exotic beams

SPES (Selective Production of Exotic Species) is an INFN project to develop a Radioactive Ion Beam (RIB) facility as an intermediate step toward EURISOL. The SPES project is part of the INFN Road Map for the Nuclear Physics development in Italy and is supported by the whole Italian Nuclear Physics community and mainly by LNL and LNS the INFN National Laboratories of Nuclear Physics in Legnaro and Catania. The Laboratori Nazionali di Legnaro (LNL) was chosen as the site for the facility construction due to the presence of the PIAVE-ALPI accelerator complex, which will be used as re-accelerator for the RIBs. The SPES project is based on the ISOL method with an UCx Direct Target and makes use of a proton driver of at least 40 MeV energy and 200 microA current. Neutron-rich radioactive beams will be produced by Uranium fission at an expected fission rate in the target in the order of 1013 fissions per second. The key feature of SPES is to provide high intensity and high-quality beams of neutron rich nuclei to perform forefront research in nuclear structure, reaction dynamics and interdisciplinary fields like medical, biological and material sciences. The exotic isotopes will be re-accelerated by the ALPI superconducting linac at energies up to 10AMeV for masses in the region of A=130 amu with an expected rate on target of 109 pps.

Synthesis of superheavy nuclei: A search for new production reactions

Nuclear reactions leading to the formation of new superheavy (SH) elements and isotopes are discussed in the paper. ``Cold'' and ``hot'' synthesis, fusion of fission fragments, transfer reactions, and reactions with radioactive ion beams are analyzed along with their abilities and limitations. If the possibility of increasing the beam intensity and the detection efficiency (by a total of one order of magnitude) is found, then several isotopes of new elements with $Z=120\text{\ensuremath{-}}124$ could be synthesized in fusion reactions of titanium, chromium, and iron beams with actinide targets. The use of light- and medium-mass neutron-rich radioactive beams may help us fill the gap between the SH nuclei produced in the hot fusion reactions and the mainland. In these reactions, we may really approach the ``island of stability.'' Such a possibility is also provided by the multinucleon transfer processes in low-energy damped collisions of heavy actinide nuclei. The production of SH elements in fusion reactions with accelerated fission fragments looks less encouraging.

Influence of light nuclei on neutrino-driven supernova outflows

We study the composition of the outer layers of a protoneutron star and show that light nuclei are present in substantial amounts. The composition is dominated by nucleons, deuterons, tritons and alpha particles; $^{3}\mathrm{He}$ is present in smaller amounts. This composition can be studied in laboratory experiments with new neutron-rich radioactive beams that can reproduce similar densities and temperatures. After including the corresponding neutrino interactions, we demonstrate that light nuclei have a small impact on the average energy of the emitted electron neutrinos, but are significant for the average energy of antineutrinos. During the early post-explosion phase, the average energy of electron antineutrinos is slightly increased, while at later times during the protoneutron star cooling it is reduced by about 1 MeV. The consequences of these changes for nucleosynthesis in neutrino-driven supernova outflows are discussed.

Fusion of neutron-rich oxygen isotopes in the crust of accreting neutron stars

Fusion reactions in the crust of an accreting neutron star are an important source of heat, and the depth at which these reactions occur is important for determining the temperature profile of the star. Fusion reactions depend strongly on the nuclear charge $Z$. Nuclei with $Z\ensuremath{\leqslant}6$ can fuse at low densities in a liquid ocean. However, nuclei with $Z=8$ or 10 may not burn until higher densities where the crust is solid and electron capture has made the nuclei neutron rich. We calculate the $S$ factor for fusion reactions of neutron rich nuclei including $^{24}\mathrm{O}+^{24}\mathrm{O}$ and $^{28}\mathrm{Ne}+^{28}\mathrm{Ne}$. We use a simple barrier penetration model. The $S$ factor could be further enhanced by dynamical effects involving the neutron rich skin. This possible enhancement in $S$ should be studied in the laboratory with neutron rich radioactive beams. We model the structure of the crust with molecular dynamics simulations. We find that the crust of accreting neutron stars may contain micro-crystals or regions of phase separation. Nevertheless, the screening factors that we determine for the enhancement of the rate of thermonuclear reactions are insensitive to these features. Finally, we calculate the rate of thermonuclear $^{24}\mathrm{O}+^{24}\mathrm{O}$ fusion and find that $^{24}\mathrm{O}$ should burn at densities near ${10}^{11}$ g/cm${}^{3}$. The energy released from this and similar reactions may be important for the temperature profile of the star.

Radioactivity distribution in the MAFF beamline

The Munich Accelerator for Fission Fragments (MAFF) facility planned at the research reactor FRM-II in Munich is dedicated to produce, cool and accelerate high-intensity neutron-rich radioactive beams. The radioactive beam of fission fragments results from bombarding a uranium target by the thermal neutrons emerging from the reactor. Part of the nuclides is released from the target/ion source unit in a non-ionized state. This contribution is concerned with simulating the distribution of the non-ionized radioactivity along the MAFF beamline. The calculations are performed with the help of the computer program MOVAK3D. The calculated fraction of non-ionized radioactivity at the border of the experimental area is at the level of about 10 −7, relative to the activity produced in the target.