Search

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $\gamma$-ray data. For known, intense $\gamma$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised.

CITATION: Liu, C. et al. 2019. New candidate chiral nucleus in the A≈80 mass region: 82 35Br47. Physical Review C, 100(5). doi:10.1103/PhysRevC.100.054309

CITATION: Li, C. G. et al. 2019. “Stapler” mechanism for a dipole band in 79Se. Physical Review C, 100(4). doi:10.1103/PhysRevC.100.044318

CITATION: Ndayishimye, J. 2019. Competition of rotation around the intermediate and long axes in 193Tl. Physical Review C, 100(1):014313, doi:10.1103/PhysRevC.100.014313.

CITATION: Kaya, B. D. C. K., et al. 2018. Comparison of double-folding effective interactions within the cluster model. Physical Review C, 98(4):044308, doi:10.1103/PhysRevC.98.044308.

CITATION: Liu, L., et al. 2018. Evolution from quasivibrational to quasirotational structure in 155Tm and yrast 27/2− to 25/2− energy anomaly in the A ≈ 150 mass region. Physical Review C, 97(4):044306, doi:10.1103/PhysRevC.97.044306.

CITATION: Niu, C. Y., et al. 2018. Spectroscopic study of the possibly triaxial transitional nucleus 75Ge. Physical Review C, 97(3):034322, doi:10.1103/PhysRevC.97.034322.

Experiments in physics, Astro-particle physics and cosmology that require careful shielding against cosmic rays include dark matter searches, studies of radioactive decays, and neutrino detection experiments. The need for such shielding has motivated the construction of laboratory caverns in mines and adjacent to tunnels under mountains. There are currently about a dozen such laboratories, in existence or under construction, all in the Northern Hemisphere. A motivation has been made for the establishment of a Southern Hemisphere facility. In this paper a feasibility study of measurements of radon in air (using electret ion chambers and alpha spectroscopy), background gamma ray measurements (inside/outside) the tunnel using scintillator (inorganic) detectors, cosmic ray measurements using organic scintillators and radiometric analyses of representative rock samples for the establishment of such a facility in the South Africa is presented.

High-spin states in $^{155}\mathrm{Yb}$ have been studied via the $^{144}\mathrm{Sm}(^{16}\mathrm{O},5n)^{155}\mathrm{Yb}$ reaction at a beam energy of 118 MeV. One negative-parity and one positive-parity cascade built on the $\ensuremath{\nu}{f}_{7/2}$ and $\ensuremath{\nu}{i}_{13/2}$ states, respectively, are established for the first time. The structures observed in $^{155}\mathrm{Yb}$ are compared with those in the neighboring $N=85$ isotones and with semiempirical shell-model (SESM) calculations. According to adiabatic and configuration-fixed constrained triaxial covariant density functional theory (CDFT) calculations, a coexistence of prolate and oblate shapes is predicted to exist in $^{155}\mathrm{Yb}$.

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen $(Z=7)$, are measured in PHOBOS. These fragments are observed in Au+Au $(\sqrt{{s}_{{}_{NN}}}=19.6\phantom{\rule{0.16em}{0ex}}\mathrm{GeV})$ and Cu+Cu (22.4 GeV) collisions at high pseudorapidity $(\ensuremath{\eta})$. The dominant multiply-charged fragment is the tightly bound helium $(\ensuremath{\alpha})$, with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $\ensuremath{\alpha}$ fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for $\ensuremath{\alpha}$ and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

A selection of experimental results from the PHOBOS Collaboration relevant for probing high-energy nuclear collisions with high transverse momentum particles is presented. The inclusive yields of charged particles and comparisons between nuclear and elementary collisions already reveal a large amount of parton energy loss in the hot and dense medium created in heavy ion collisions. Remarkable scaling and factorization features are observed, unifying the data taken at various collision energies, centralities and nuclear sizes. To further analyze the nature of the energy loss, a measurement of pseudorapidity (Δη) and azimuthal angle (Δφ) correlations between high transverse momentum charged hadrons (pT>2.5 GeV/c) and all associated charged particles is presented at both short-range (small Δη) and long-range (large Δη) over a continuous detector acceptance covering −4

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive- and negative-parity bands have been identified in ^{78}Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei.

The spectroscopy of $^{76}\mathrm{Se}$ has been studied using the $^{70}\mathrm{Zn}(^{12}\mathrm{C}, \ensuremath{\alpha}2{\mathrm{n})}^{76}\mathrm{Se}$ fusion evaporation reaction. The yrast band of $^{76}\mathrm{Se}$ has been extended to substantially higher spin, allowing observation of the second band crossing. The much-delayed ${g}_{9/2}$ proton-pair alignment is discussed in terms of the cranked shell model and most likely is caused by a shape transition from prolate to oblate along the yrast line occurring in $^{76}\mathrm{Se}$. Based on the systematic investigation of the band crossings associated with the ${g}_{9/2}$ quasiparticle alignments and their relationships with the shape evolutions in the even-$A$ Se and Kr isotopes, a comprehensive picture of shape evolution along with spin and isospin in these nuclei is obtained.

The PHOBOS collaboration has studied the pseudorapidity and transverse momentum distributions of charged particles produced in heavy ion collisions. Results from Au+Au collisions at various center-of-mass energies and over a broad range of centrality are presented here. The data are compared to Cu+Cu, p+p and d+Au collisions at corresponding energies and centralities. The data are found to exhibit simple scaling properties such as the observed factorization of collision energy and geometry dependences. The presented data help us distinguish between models of particle production in relativistic heavy ion collisions.

Based on the relativistic plane-wave impulse approximation for quasielastic ({rvec p},{rvec p}{sup {prime}}) and ({rvec p},{rvec n}) polarization observables, we provide quantitative estimates of nuclear medium modifications of the NN interaction. We employ a {sup 40}Ca target for proton energies ranging from 135 to 300 MeV at a momentum transfer of 1.97 fm{sup {minus}1}. Compared to former calculations, we have generated new meson-exchange parameters for the relativistic NN amplitudes between 80 and 200 MeV. Finally, the results are compared to the limited available data. {copyright} {ital 1998} {ital The American Physical Society}

CITATION: Ndayishimye, J. et al. 2017. Chiral Bands in 193TI. Acta Physica Polonica B, 48(3):343-346, doi:10.5506/APhysPolB.48.343.

Excited states of ${}^{116}$Sb were investigated using in-beam $\ensuremath{\gamma}$-ray spectroscopy techniques with the ${}^{114}$Cd(${}^{7}$Li, $5n$) reaction. About 25 new states and 35 new transitions were added into the level scheme of ${}^{116}$Sb. The previously known two rotational bands based on the $\ensuremath{\pi}{g}_{9/2}^{}{}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ and $\ensuremath{\pi}{g}_{9/2}^{}{}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\nu}{d}_{5/2}$ configurations have been extended up to (16)${}^{\ensuremath{-}}$ and (13)${}^{+}$ states, respectively. A new $\ensuremath{\Delta}I=1$ band was identified, and interpreted in terms of the triaxial particle rotor model calculations.

The solutions of the N-dimensional Klein-Gordon and Dirac wave equations with equal scalar and vector Rosen-Morse potentials are studied. The energy equations and the radial wave functions are derived using the Nikiforov-Uvarov method. The low-dimensional (N = 3 s-wave limits and the variation of the bound-state energies with the dimension and the angular momentum are discussed.

We generate a hybrid potential by combining the best features of a microscopic and a phenomenological core-cluster potential and use it to analyze the spectra, $B(E2)$ transition rates, and the exotic decays of heavy even-even nuclei.

Excited states of $^{80}$Br have been investigated via the $^{76}$Ge($^{11}$B, $\alpha$3n) and $^{76}$Ge($^{7}$Li, 3n) reactions and a new $\Delta I$ = 1 band has been identified which resides $\sim$ 400 keV above the yrast band. Based on the experimental results and their comparison with the triaxial particle rotor model calculated ones, a chiral character of the two bands within the $\pi g_{9/2}\otimes \nu g_{9/2}$ configuration is proposed, which provides the first evidence for chirality in the $A\sim80$ region., Comment: 15 pages, 6 figures, accepted for publication in Physics Letters B

Cluster-core potentials derived microscopically or phenomenologically each have some desirable features. We combine these features in an analysis of the properties of $^{212}\mathrm{Po}$ treated as an $\ensuremath{\alpha}$-$^{208}\mathrm{Pb}$ system.

In the collisions of ultrarelativistic heavy ions the energy of the nuclei is released in a small volume leading to the creation of a hot and dense nuclear matter. The study of the particles produced from it gives the information on the conditions in the early stage of the collision and the evolution of the system. The PHOBOS experiment provides unique data on the particle production in the almost full phase space and down to very small transverse momenta. This overview shortly presents the most important features of the nucleus-nucleus collisions observed by the PHOBOS experiment, but concentrates on the most recent studies. The extensive analyses of charged particles production are based on the multiplicity measurements in a very wide pseudorapidity range and reveal strong short and long range correlations. The correlations with a high p T trigger particle extends at least 4 units in pseudorapidity, while two-particle correlations suggest production of particles in large and wide clusters. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Measuring alpha particles from a neutron induced break‐up reaction with a mass spectrometer can be an excellent tool for detecting neutrons in a high neutron flux environment. Break‐up reactions of 6Li and 12C can be used in the detection of slow and fast neutrons, respectively. A high neutron flux detection system that integrates the neutron energy sensitive material and helium mass spectrometer has been developed. The description of the detector configuration is given and it is soon to be tested at iThemba LABS, South Africa.

The centrality dependence of the midrapidity charged-particle multiplicity density (|η| < 1) is presented for Au + Au and Cu + Cu collisions at RHIC over a broad range of collision energies. The multiplicity measured in the Cu + Cu system is found to be similar to that measured in the Au + Au system, for an equivalent Npart, with the observed factorization in energy and centrality still persistent in the smaller Cu + Cu system. The extent of the similarities observed for bulk particle production is tested by a comparative analysis of the inclusive transverse momentum distributions for Au + Au and Cu + Cu collisions near midrapidity. It is found that, within the uncertainties of the data, the ratio of yields between the various energies for both Au + Au and Cu + Cu systems are similar and constant with centrality, both in the bulk yields and as a function of pT ,u p to at least 4 GeV/c. The effects of multiple nucleon collisions that strongly increase with centrality and energy appear to only play a minor role in bulk and intermediate transverse momentum particle production.

Antiparticle to particle ratios for identified protons, kaons, and pions at {radical}(s{sub NN})=62.4 and 200 GeV in Cu+Cu collisions are presented as a function of centrality for the midrapidity region of 0.2 / ratio at {approx_equal}0.51 GeV/c, we observe an average value of 0.50{+-}0.003{sub (stat)}{+-}0.04{sub (syst)} and 0.77{+-}0.008{sub (stat)}{+-}0.05{sub (syst)} for the 10% most central collisions of 62.4 and 200 GeV Cu+Cu, respectively. The values for all three particle species measured at {radical}(s{sub NN})=200 GeV are in agreement within systematic uncertainties with that seen in both heavier and lighter systems measured at the same RHIC energy. This indicates that system size does not appear to play a strong role in determining the midrapidity chemical freeze-out properties affecting the antiparticle to particle ratios of the three most abundant particle species produced in these collisions.

We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, \sqrtsnn = 22.4, 62.4 and 200 GeV, over a wide range of pseudorapidity, using the PHOBOS detector. Making a global comparison of Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same Npart/2A value rather than the same Npart value. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies., Submitted to Physical Review Letters

We present results on two-particle angular correlations in proton-proton collisions at center-of-mass energies of 200 and 410 GeV. The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in $\ensuremath{\Delta}\ensuremath{\eta}$ and $\ensuremath{\Delta}\ensuremath{\phi}$ is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.

We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at {radical}(s{sub NN})=62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25

The PHOBOS collaboration has carried out a systematic study of charged particle multiplicities in Cu+Cu and Au+Au collisions at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory. A unique feature of the PHOBOS detector is its ability to measure charged particles over a very wide angular range from 0.5 to 179.5 deg. corresponding to |eta, Proceedings of "Lake Louise Winter Institute 2006", Lake Louise, Alberta, Canada, February 17-23, 2006, World Scientific 5 pages, 3 figures

Within the framework of the relativistic distorted wave impulse approximation (DWIA), we investigate the sensitivity of complete sets of polarization transfer observables for exclusive proton knockout from the 3s$_{1/2}$, 2d$_{3/2}$ and 2d$_{5/2}$ states in $^{208}$Pb, at an incident laboratory kinetic energy of 202 MeV, and for coincident coplanar scattering angles ($28.0^{\circ}$, $-54.6^{\circ}$), to different distorting optical potentials, finite-range (FR) versus zero-range (ZR) approximations to the DWIA, as well as medium-modified meson-nucleon coupling constants and meson masses. Results are also compared to the nonrelativistic DWIA predictions based on the Schr\"{o}dinger equation., Comment: Submitted for publication to Physicical Review C, 23 pages, 7 figures

We investigate the cluster emission of Ne isotopes from the nuclei and . Experiments are unable to distinguish between the isotopes and , but by establishing a method of determining the cluster, with associated preformation probability, and using a binary cluster formalism, we deduce that the most likely emitted cluster is .

The ?-decay preformation probabilities of superheavy nuclei are determined within the binary cluster model by using an interaction generated from a combination of a microscopic and a phenomenological interactions. The calculated ?-decay half-lives are compared with the experimental data by also taking into consideration, the predicted angular momentum transfer in the decay process.

A relativistic plane wave model is presented for the calculation of complete sets of (p,2p) spin transfer observables. We examine the sensitivity of these observables to different kinematic prescriptions, nuclear medium modifications of the nucleon mass, as well as different forms of the πNN vertex.

Double differential cross sections for inclusive (p, p’) reactions have been measured at the National Accelerator Centre, Faure, South Africa for a range of targets with mass numbers between 12 and 197, and for incident energies from 80 to 200 MeV. Extensive comparisons have been made with multistep direct calculations based on the Feshbach, Kerman and Koonin theory. Good general agreement has been found using a short-range Yukawa two-body interaction, and some systematic discrepancies at the lowest and highest excitation energies have also been investigated. In the most recent experiments analyzing powers have been measured in addition to the cross-sections.

Very little is known about clustering in heavy nuclei and in particular the interaction between the correlated cluster nucleons and remaining core nucleons. Currently the phenomenological Saxon-Woods plus cubic Saxon-Woods core-cluster potential successfully predicts the alpha decay half-life and energy band spectra of a number of heavy nuclei. This model, however, lacks a microscopic understanding of clustering phenomenon in these heavy nuclear systems. A fully relativistic microscopic formalism is presented, which generates the core-cluster potential by means of the McNeil, Ray and Wallace based double folding procedure. The core and cluster baryon densities are calculated by using a relativistic mean field approach. The Lorentz covariant IA1 representation of the nucleon-nucleon interaction is folded with the core and cluster densities. Theoretical predictions of the ground-state decay half-life and positive parity energy band of 212Po are obtained with the relativistic mean field formalism and which are compared to the results from the phenomenological Saxon-Woods plus cubic Saxon-Wood core-cluster potential and microscopic M3Y interaction.

An exotic cluster model of 238U is extended to allow nonzero E1 transitions to proceed between states of the negative and positive parity bands and the formalism required for the calculation of B(E1) and B(E2) values within the model is presented. Comparison of theoretical values with experimental data is made for the ratios B(E1;Ji → Ji + 1)/B(E1;Ji → Ji − 1) and B(E1;Ji → Ji − 1)/B(E2;Ji → Ji − 2)—in both cases from negative parity initial states. Good agreement is obtained with the data of Ward et al (1996 Nucl. Phys. A 600 88) and it is concluded that any rotational model should provide an adequate account of their data.

Over the past two years there has been discussion among South African physicists about the possibility of establishing a deep underground physics laboratory to study, amongst others, double beta decay, geoneutrinos, reactor neutrinos and dark matter. As a step towards a full proposal for such a laboratory a number of smaller programmes are currently being performed to investigate feasibility of the Huguenot Tunnel in the Du Toitskloof Mountains near Paarl (Western Cape, South Africa) as a possible sight for the South African Underground Laboratory facility. The programme includes measurements of radon in air (using electret ion chambers and alpha spectroscopy), background gammaray measurements (inside / outside) the tunnel using scintillator (inorganic) detectors, cosmic ray measurements using organic scintillators and radiometric analyses of representative rock samples.