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Two recent studies of the evolution of the isoscalar giant monopole resonance (ISGMR) within the calcium isotope chain report conflicting results. One study suggests that the monopole resonance energy, and thus the incompressibility of the nucleus $K_{A}$ increase with mass, which implies that $K_{\tau}$, the asymmetry term in the nuclear incompressibility, has a positive value. The other study reports a weak decreasing trend of the energy moments, resulting in a generally accepted negative value for $K_{\tau}$. An independent measurement of the central region of the ISGMR in the Ca isotope chain is provided to gain a better understanding of the origin of possible systematic trends. Inelastically scattered $\alpha$ particles from a range of calcium targets ($\mathrm{^{40,42,44,48}Ca}$), observed at small scattering angles including 0$^\circ$, were momentum analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. Monopole strengths spanning an excitation-energy range between 9.5 and 25.5 MeV were obtained using the difference-of-spectra (DoS) technique. The structure of the $E0$ strength distributions of $^{40,42,44}$Ca agrees well with the results from the previous measurement that supports a weak decreasing trend of the energy moments, while no two datasets agree in the case of $^{48}$Ca. Despite the variation in the structural character of $E0$ strength distribution from different studies, we find for all datasets that the moment ratios, calculated from the ISGMR strength in the excitation-energy range that defines the main resonance region, display at best only a weak systematic sensitivity to a mass increase. Different trends observed in the nuclear incompressibility are caused by contributions to the $E0$ strength outside of the main resonance region, and in particular for high excitation energies., Comment: 11 pages, 11 figures, submitted to Physical Review C

Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Determining the ^{12}C+^{12}C fusion cross section at relevant energies by extrapolation of direct measurements is challenging due to resonances at and below the Coulomb barrier. A study of the ^{24}Mg(α,α^{'})^{24}Mg reaction has identified several 0^{+} states in ^{24}Mg, close to the ^{12}C+^{12}C threshold, which predominantly decay to ^{20}Ne(ground state)+α. These states were not observed in ^{20}Ne(α,α_{0})^{20}Ne resonance scattering suggesting that they may have a dominant ^{12}C+^{12}C cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states may play a decisive role in ^{12}C+^{12}C fusion in analogy to the Hoyle state in helium burning. We present estimates of updated ^{12}C+^{12}C fusion reaction rates.

Background: Nuclei in the $sd$ shell demonstrate a remarkable interplay of cluster and mean-field phenomena. The $N=Z$ nuclei, such as $^{24}\mathrm{Mg}$ and $^{28}\mathrm{Si}$, have been the focus of the theoretical study of both phenomena in the past. A variety of different cluster structures in these nuclei are predicted, characterized by isoscalar dipole and monopole transitions. For example, low-energy isoscalar vortical dipole states were predicted in $^{24}\mathrm{Mg}$. The cluster and vortical mean-field phenomena can be probed by excitation of isoscalar monopole and dipole states in scattering of isoscalar particles such as deuterons or $\ensuremath{\alpha}$ particles.Purpose: We investigate, both experimentally and theoretically, the isoscalar dipole $IS1$ and monopole $IS0$ strengths in three essentially different light nuclei with different properties: stiff prolate $^{24}\mathrm{Mg}$, soft prolate $^{26}\mathrm{Mg}$, and soft oblate $^{28}\mathrm{Si}$. We analyze possible manifestations of clustering and vorticity in these nuclei.Methods: Inelastically scattered $\ensuremath{\alpha}$ particles were momentum analyzed in the K600 magnetic spectrometer at iThemba LABS, Cape Town, South Africa. The scattered particles were detected in two multiwire drift chambers and two plastic scintillators placed at the focal plane of the K600. In the theoretical discussion, the Skyrme quasiparticle random-phase approximation (QRPA) and antisymmetrized molecular dynamics $+$ generator coordinate method ($\mathrm{AMD}+\mathrm{GCM}$) were used.Results: A number of isoscalar monopole and dipole transitions were observed in the nuclei studied. Using this information, suggested structural assignments have been made for the various excited states. $IS1$ and $IS0$ strengths obtained within QRPA and $\mathrm{AMD}+\mathrm{GCM}$ are compared with the experimental data. The QRPA calculations lead us to conclude that (i) the mean-field vorticity appears mainly in dipole states with $K=1$, (ii) the dipole (monopole) states should have strong deformation-induced octupole (quadrupole) admixtures, and (iii) near the $\ensuremath{\alpha}$-particle threshold there should exist a collective state with $K=0$ for prolate nuclei and $K=1$ for oblate nuclei, with an impressive octupole strength. The results of the $\mathrm{AMD}+\mathrm{GCM}$ calculations suggest that some observed states may have a mixed (mean-field $+$ cluster) character or correspond to particular cluster configurations.Conclusion: A tentative correspondence between observed states and theoretical states from QRPA and $\mathrm{AMD}+\mathrm{GCM}$ was established. The QRPA and $\mathrm{AMD}+\mathrm{GCM}$ analysis shows that low-energy isoscalar dipole states combine cluster and mean-field properties. The QRPA calculations show that the low-energy vorticity is well localized in $^{24}\mathrm{Mg}$, fragmented in $^{26}\mathrm{Mg}$, and absent in $^{28}\mathrm{Si}$.

Background: Inelastic proton scattering at energies of a few hundred MeV and very-forward angles including $0^\circ$ has been established as a tool to study electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Purpose: Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the IsoVector Giant Dipole Resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at iThemba LABS in Cape Town, South Africa. The scattering products were momentum-analysed by the K600 magnetic spectrometer positioned at $\theta_{\mathrm{Lab}}=0^\circ$. Using dispersion-matching techniques, energy resolutions of $\Delta E \approx 40 - 50$ keV were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photo-absorption cross sections using the equivalent virtual-photon method. Results: Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Comparisons with the Quasiparticle-Phonon Model (QPM) and Skyrme Separable Random Phase Approximation (SSRPA) predictions provide insight into the role of different giant resonance damping mechanisms. Conclusions: Fine structure is observed even for the most deformed nuclei studied. Fragmentation of the one particle-one hole ($1p1h$) strength seems to be the main source of fine structure in both spherical and deformed nuclei. Some impact of the spreading due to coupling of the two particle-two hole ($2p2h$) states to the $1p1h$ doorway states is seen in the spherical/transitional nuclei, where calculations beyond the $1p1h$ level are available.

In this contribution, we describe the method used to produce deuterated polyethylene (C2D4) targets. The modification of method based on polyethylene dissolution in hot xylene resulted with stable thin C2D4 targets.

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: Mukwevho, N. J., et al. 2018. Second T = 3/2 state in 9B and the isobaric multiplet mass equation. Physical Review C, 98(5):051302, doi:10.1103/PhysRevC.98.051302.

A new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam.

A method for making oxygen targets in a form of lithium carbonate compound is described. Targets were prepared for nuclear physics experiments which required oxygen with a mass greater than 60 %. Both natural and isotopic enriched targets of O-18 with thicknesses of less than 1 mg/cm(2) were produced and characterised by elastic recoil detection analysis and elastic backscattering techniques. The results obtained showed that enriched foils had limited isotopic exchange when exposed to air and good stability with time compared to foils with natural oxygen.

Self-supporting beryllium (9Be) targets were produced by mechanical rolling method in which a double pack technique was implemented. Targets were used for the investigation of the low-lying excitation energy region in 9B through the 9Be(3He,t)9B reaction at the K600 spectrometer, at iThemba LABS facility. Beryllium is a semi-metal in nature and this makes it hard to deform by rolling or vacuum evaporate as a self-supporting target. Therefore heat treatment was needed to avoid brittleness and breakage of the material during rolling process. A description is given on how beryllium targets were manufactured.Self-supporting beryllium (9Be) targets were produced by mechanical rolling method in which a double pack technique was implemented. Targets were used for the investigation of the low-lying excitation energy region in 9B through the 9Be(3He,t)9B reaction at the K600 spectrometer, at iThemba LABS facility. Beryllium is a semi-metal in nature and this makes it hard to deform by rolling or vacuum evaporate as a self-supporting target. Therefore heat treatment was needed to avoid brittleness and breakage of the material during rolling process. A description is given on how beryllium targets were manufactured.

A number of nuclear physics experiments at iThemba LABS require target foils that consist of specific isotopes of elements which are reactive in air. Not only is it important to prepare these targets in a suitable environment to prevent oxidation, but consideration should also be given to the long term storage and handling facilities of such targets. The target vacuum storage facility at iThemba LABS, as well as additional hardware necessary to transport and install the target foils in the experimental chamber, will be discussed.

Background: The $^{22}\mathrm{Ne}$($\ensuremath{\alpha},n$)$^{25}\mathrm{Mg}$ reaction is one of the neutron sources for the $s$ process in massive stars. The properties of levels in $^{26}\mathrm{Mg}$ above the $\ensuremath{\alpha}$-particle threshold control the strengths of the $^{22}\mathrm{Ne}$($\ensuremath{\alpha},n$)$^{25}\mathrm{Mg}$ and $^{22}\mathrm{Ne}$($\ensuremath{\alpha},\ensuremath{\gamma}$)$^{26}\mathrm{Mg}$ reactions. The strengths of these reactions as functions of temperature are one of the major uncertainties in the $s$ process.Purpose: Information on the existence, spin, and parity of levels in $^{26}\mathrm{Mg}$ can assist in constraining the strengths of the $^{22}\mathrm{Ne}$($\ensuremath{\alpha},\ensuremath{\gamma}$)$^{26}\mathrm{Mg}$ and $^{22}\mathrm{Ne}$($\ensuremath{\alpha},n$)$^{25}\mathrm{Mg}$ reactions, and therefore in constraining $s$-process abundances.Methods: Inelastically scattered $\ensuremath{\alpha}$ particles from a $^{26}\mathrm{Mg}$ target were momentum-analyzed in the K600 magnetic spectrometer at iThemba LABS, South Africa. The differential cross sections of states were deduced from the focal-plane trajectory of the scattered $\ensuremath{\alpha}$ particles. Based on the differential cross sections, spin and parity assignments to states are made.Results: A newly assigned ${0}^{+}$ state was observed in addition to a number of other states, some of which can be associated with states observed in other experiments. Some of the deduced ${J}^{\ensuremath{\pi}}$ values of the states observed in the present study show discrepancies with those assigned in a similar experiment performed at RCNP Osaka. The reassignments and additions of the various states can strongly affect the reaction rate at low temperatures.Conclusion: The number, location, and assignment of levels in $^{26}\mathrm{Mg}$ that may contribute to the $^{22}\mathrm{Ne}+\ensuremath{\alpha}$ reactions are not clear. Future experimental investigations of $^{26}\mathrm{Mg}$ must have an extremely good energy resolution to separate the contributions from different levels. Coincidence experiments of $^{26}\mathrm{Mg}$ provide a possible route for future investigations.

A series of frozen xenon targets of thicknesses ranging between 1 and 15 mg/cm2 were characterised by elastic backscattering technique using a 3 MeV proton beam. Xenon was kept solid on a gold substrate having a thickness of 1 g/cm2 which was mounted on a cold copper finger. The temperature of targets during the experiment was maintained at 55 K by a compact solid nitrogen sublimation system under pressure of 10−5 mbar. Targets were used in series of experiments for populating samarium and gadolinium isotopes in the 136Xe (18O, Xn) and 136Xe (22Ne, Xn) nuclear reactions.

Background: Aspects of the nuclear structure of light α-conjugate nuclei have long been associated with nuclear clustering based on α particles and heavier α-conjugate systems such as C12 and O16. Such structures are associated with strong deformation corresponding to superdeformed or even hyperdeformed bands. Superdeformed bands have been identified in Ca40 and neighboring nuclei and find good description within shell model, mean-field, and α-cluster models. The utility of the α-cluster description may be probed further by extending such studies to more challenging cases comprising lighter α-conjugate nuclei such as Mg24, Si28, and S32. Purpose: The purpose of this study is to look for the number and energy of isoscalar 0+ states in Si28. These states are the potential bandheads for superdeformed bands in Si28 corresponding to the exotic structures of Si28. Of particular interest is locating the 0+ bandhead of the previously identified superdeformed band in Si28. Methods: α-particle inelastic scattering from a Sinat target at very forward angles including 0 has been performed at the iThemba Laboratory for Accelerator-Based Sciences in South Africa. Scattered particles corresponding to the excitation energy region of 6 to 14 MeV were momentum-analysed in the K600 magnetic spectrometer and detected at the focal plane using two multiwire drift chambers and two plastic scintillators. Results: Several 0+ states have been identified above 9 MeV in Si28. A newly identified 9.71 MeV 0+ state is a strong candidate for the bandhead of the previously discussed superdeformed band. The multichannel dynamical symmetry of the semimicroscopic algebraic model predicts the spectrum of the excited 0+ states. The theoretical prediction is in good agreement with the experimental finding, supporting the assignment of the 9.71-MeV state as the bandhead of a superdeformed band. Conclusion: Excited isoscalar 0+ states in Si28 have been identified. The number of states observed in the present experiment shows good agreement with the prediction of the multichannel dynamical symmetry.

The low-spin structure of the nearly spherical nucleus 146Gd was studied using the 144Sm(4He, 2n) fusion-evaporation reaction. High-statistics $\gamma - \gamma$ coincidence measurements were performed at iThemba LABS with 7× 109 $ \gamma$ - $ \gamma$ coincidence events recorded. Gated $ \gamma$ -ray energy spectra show evidence for the $ 6^{+}_{2} \rightarrow 3^{-}_{1} \rightarrow 0^{+}_{1}$ cascade of E3 transitions in agreement with recent findings by Caballero and co-workers, but with a smaller branching ratio of $ I_{\gamma} = 4.7(10)$ for the $6^{+}_{2} \rightarrow 3^{-}_{1}$ 1905.1 keV $ \gamma$ ray. Although these findings may support octupole vibrations in spherical nuclei, sophisticated beyond mean-field calculations including angular-momentum projection are required to interpret in an appropriate way the available data due to the failure of the rotational model assumptions in this nucleus.

A complete kinematics measurement was performed using the 6 Li (3 He ,t) charge exchange reaction to populate 6 Be at Elab = 50 MeV . Decay mode of the ground and first excited states were studied through the analysis of the energy and angular distributions of the break-up particles in the 6 Be center of mass frame. Two-body decay is observed above the first excited state but not firmly assigned to a 6 Be resonant state. Experimental challenges regarding the identification of true 6 Be events in the excitation energy region 5 < Ex < 20 MeV are discussed.

A semi-thick target has been used to measure the stopping power for recoils, produced in heavy ion induced reactions, by γ-ray lineshape analysis. The target thickness has been chosen such that the recoils are partially slowed down in the target and subsequently escape into vacuum. For transitions deexciting long-lived states the Doppler lineshape then depends only on the stopping power. Stopping-power parameters have been determined for Pm, Sm and Nd nuclei in Cd. The results for the electronic stopping power agree within uncertainties with the predictions of the Lindhard, Scharff and Schiott theory. The nuclear stopping power can be well described in the framework of the Ziegler, Biersack and Littmark parameterization using the software package Stopping and Range of Ions in Matter (SRIM)2006.

We report on the thickness and homogeneity characterization of thin metallic targets of Zr-96 by means of alpha absorption spectrometry, Particle Induced X-ray Emission (PIXE) and X-ray absorption. The target thicknesses determined by means of the above mentioned methods are critically compared. The thicknesses were determined before and after irradiation with a 70 MeV beam of 14N ions.

A brief survey of results of studies of nuclear chirality in the mass 80 and 190 region at iThemba LABS is given, before looking at the case of 106 Ag in detail. Here, the crossing of a pair of candidate chiral bands is re-interpreted as the crossing of a prolate band by an aligned four-quasiparticle band.

The nature of the chiral candidate bands in $^{106}\mathrm{Ag}$, one of only two known examples of candidates which actually cross, is investigated experimentally and theoretically. Lifetimes have been determined for these bands in $^{106}\mathrm{Ag}$ using the Doppler-shift attenuation method with the $\ensuremath{\gamma}$-detector array AFRODITE. The level scheme of $^{106}\mathrm{Ag}$ has been extended, and three negative-parity bands have been observed to high spins. Configurations were assigned to the negative-parity bands based on a quasiparticle alignment analysis and on configuration-fixed constrained relativistic mean field calculations. The excitation energies, $B(M1)$ and $B(E2)$ values, as well as $B(M1)/B(E2)$ ratios have been compared with results of particle-rotor model calculations. From the investigations, it is concluded that the three close-lying negative-parity bands are a two-quasiparticle high-$K$ band and a pair of four-quasiparticle bands. The proposal that the two lowest-lying bands are chiral partners has not been confirmed.

This paper describes methods used in the manufacturing of chemically reactive targets such as calcium (natCa), lithium-6 (6Li) and molybdenum–97 (97Mo) for nuclear physics experiments at the iThemba LABS cyclotron facility (Faure, South Africa). Due to the chemical properties of these materials a suitable and controlled environment was established in order to minimize oxygen contamination of targets. Calcium was prepared by means of vacuum evaporation while lithium was cold rolled to a desired thickness. In the case of molybdenum, the metallic powder was melted under vacuum using an e-gun followed by cold rolling of the metal bead to a desired thickness. In addition, latest developments toward the establishment of a dedicated nuclear physics target laboratory are discussed.

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

When a left-handed and a right-handed nuclear system form in angular momentum space, a pair of nearly degenerate rotational bands is observed. To identify chiral symmetry most important is to establish near-degeneracy not only in excitation energies of the partner bands, but also in their intra-band and inter-band B(M1) and B(E2) transition probabilities. This needs dedicated lifetime measurements. Such measurements were performed for four bands of 194Tl. Two of these have very close near-degeneracy and form a prime candidate for best chiral pair. The lifetime measurements confirm the excellent near-degeneracy in this chiral pair.

Most important for the identification of chiral symmetry in atomic nuclei is to establish a pair of bands that are near-degenerate in energy, but also in B(M1) and B(E2) transition probabilities. Dedicated lifetime measurements were performed for four bands of 194Tl, including the pair of four-quasiparticle chiral bands with close near-degeneracy, considered as a prime candidate for best chiral symmetry pair. The lifetime measurements confirm the excellent near-degeneracy in this pair and indicate that a third band may be involved in the chiral symmetry scenario.