Search

Improvements in Radio-Isotope IDentification (RIID) algorithms have seen a resurgence in interest with the increased accessibility of machine learning models. Convolutional Neural Network (CNN)-based models have been developed to identify arbitrary mixtures of unstable nuclides from gamma spectra. In service of this, methods for the simulation and pre-processing of training data were also developed. The implementation of 1D multi-class, multi-label CNNs demonstrated good generalisation to real spectra with poor statistics and significant gain shifts. It is also shown that even basic CNN architectures prove reliable for RIID under the challenging conditions of heavy shielding and close source geometries, and may be extended to generalised solutions for pragmatic RIID.

The present contribution explores the symmetries of the deformed harmonic oscillator for both prolate and oblate deformations. It demonstrates the emergence of clustering from the degeneracies of the deformed harmonic oscillator and the appearance of the cluster structures in the associated densities. The universality of molecular structures is presented, demonstrating that molecular-like exchange of protons and neutrons is encoded into the mean-field. The nature of oblate-like structures is also explored.

We investigate an implication of the most recent observation of a second Jπ=2+ state in 12C, which was measured using the 12C(γ,α)8Be(g.s.) reaction. In addition to the dissociation of 12C to an α-particle and 8Be in its ground state, a small fraction of events (2%) were identified as direct decays and decays to excited states in 8Be. This allowed a limit on the direct 3α partial decay width to be determined as Γ3α

The first investigation of the single-particle structure of the bound states of 17C, via the d(16C, p) transfer reaction, has been undertaken. The measured angular distributions confirm the spin-parity assignments of 1/2+ and 5/2+ for the excited states located at 217 and 335 keV, respectively. The spectroscopic factors deduced for these states exhibit a marked single-particle character, in agreement with shell model and particle-core model calculations, and combined with their near degeneracy in energy provide clear evidence for the absence of the N = 14 sub-shell closure. The very small spectroscopic factor found for the 3/2+ ground state is consistent with theoretical predictions and indicates that the {\nu}1d3/2 strength is carried by unbound states. With a dominant l = 0 valence neutron configuration and a very low separation energy, the 1/2+ excited state is a one-neutron halo candidate., Comment: 7 pages, 5 figures, Accepted for publication in Physics Letters B

The relationship between the deformed harmonic oscillator and the formation of molecular cluster structures, whereby valence neutrons are exchanged between cluster cores, is examined. It is found that there is a strong connection between the properties of the valence orbitals associated with deformed structures in the deformed harmonic oscillator and the molecular orbitals created by linear combinations of single-centre orbitals around nuclear clusters. The conclusion is that in addition to the appearance of clustering in the deformed harmonic oscillator that every prolate deformed cluster structure should have molecular orbitals built on that structure. This is demonstrated through a series of examples that range from 13C to 57Ni.

Two novel approaches to improving the signal-to-background ratio (SBR) for silicon resistive charge-division strip detectors (RSDs), when performing low energy charged-particle spectroscopy, are presented. Firstly, the normally-unutilized rear contact of the detector was used to veto events where the charge collected by this rear face did not match the sum of the charges collected by the strips on the front. Secondly, leading edge discriminator time walk was used to determine complementary information about the hit position along a strip. Using this alongside the position extracted from the charge division allowed clearer identification of true events over background, leading to an improved SBR. These methods were tested by measuring radiation from a triple-α source and then the 12C(4He,α)ααα breakup reaction at 40 MeV beam energy. The first method was found to improve the SBR by a factor of 4.0(2). The second method gave a SBR improve- ment of factor of 3.7(4). When both methods are applied together, a total improvement by a factor of 5.7(3) was measured.

In this paper, a measurement of the atomic mass and mass excess of Re 75 190 are presented. This isotope and Ir 77 192 were produced at the Maier-Leibnitz Laboratory (MLL) in Munich in the 192Os(d, α)190Re and 194Pt(d, α)192Ir reactions. The Q3D magnetic spectrograph was used to measure the momenta of the α-particle ejectiles in order to reconstruct states in both 190Re and 192Ir. A mass calibration was performed using known energy levels in 192Ir. These measurements were used to obtain a new value of the mass excess of 190Re, −35583 ± 5 keV. The previously known literature value is −35640 ± 70 keV.

A novel technique has been developed, making use of the continuous wavelet transform to identify α-clustered states from resonant scattering measurements in regions of high nuclear state density. This technique expedites the investigation of α-clustering in medium mass and heavy nuclei, where the role that α-clustering plays in the structure of the nucleus is poorly understood. Here we report the application of this technique to measurements of the 4He(40,44,48Ca,α) resonant reactions, leading to an assessment of the α-cluster structure of 44,48,52Ti. Alpha-clustering was identified in 44Ti and 52Ti, but was observed to break down in 48Ti. The implications of these results are discussed.

International audience; Background: Near-threshold α-clustered states in light nuclei have been postulated to have a structure consisting of a diffuse gas of α particles which condense into the 0s orbital. Experimental evidence for such a dramatic phase change in the structure of the nucleus has not yet been observed. Purpose: To understand the role of α condensation in light nuclei experimentally. Method: To examine signatures of this α condensation, a compound nucleus reaction using 160-, 280-, and 400-MeV O16 beams impinging on a carbon target was used to investigate the C12(O16,7α) reaction. This permits a search for near-threshold states in the α-conjugate nuclei up to Mg24. Results: Events up to an α-particle multiplicity of seven were measured and the results were compared to both an extended Hauser-Feshbach calculation and the Fermi breakup model. The measured multiplicity distribution exceeded that predicted from a sequential decay mechanism and had a better agreement with the multiparticle Fermi breakup model. Examination of how these 7α final states could be reconstructed to form Be8 and C12(02+) showed a quantitative difference in which decay modes were dominant compared to the Fermi breakup model. No new states were observed in O16, Ne20, and Mg24 due to the effect of the N-α penetrability suppressing the total α-particle dissociation decay mode. Conclusion: The reaction mechanism for a high-energy compound nucleus reaction can only be described by a hybrid of sequential decay and multiparticle breakup. Highly α-clustered states were seen which did not originate from simple binary reaction processes. Direct investigations of near-threshold states in N-α systems are inherently impeded by the Coulomb barrier prohibiting the observation of states in the N-α decay channel. No evidence of a highly clustered 15.1-MeV state in O16 was observed from [Si★28,C12(02+)]O16(06+) when reconstructing the Hoyle state from three α particles. Therefore, no experimental signatures for α condensation were observed.

We present the first results of the experiment: “Examining the helium cluster decays of the \(^{12}\)Be excited states by triton transfer to the \(^9\)Li beam” (spokespersons: N. Soic, M. Freer), done at TRIUMF, Vancouver, CA, with the main goal of providing precise experimental data on the internal structure of the \(^{12}\)Be excited states.

7 pags., 5 figs., 1 app., The space and time configurations of the dissociation of He into He+n+n, on C and Pb targets, have been explored simultaneously for the first time. The final-state interactions in the n-n and He-n channels are successfully described within a model that considers independent emission of neutrons from a Gaussian volume with a given lifetime. The dissociation on C target exhibits a dominant sequential decay through the ground state of He, consistent with neutrons being emitted from a Gaussian volume of fm with a n-n delay in the sequential channel of 1400 400 fm/c, in agreement with the lifetime of He. The lower-statistics data on Pb target correspond mainly to direct breakup, and are well described using the n-n volume measured, without any n -n delay. The validity of the phenomenological model used is discussed., The support provided by the technical staff of LPC and the LISE crew is gratefully acknowledged, as are the efforts of the GANIL cyclotron operation team for providing the primary beam. We also wish to express our appreciation for the vital contributions made by our late colleague and friend Jean-Marc Gautier to all the CHARISSA+DEMON experiments undertaken by our collaboration.

Gamma-Beams at the HIgS facility in the USA and anticipated at the ELI-NP facility, now constructed in Romania, present unique new opportunities to advance research in nuclear astrophysics; not the least of which is resolving open questions in oxygen formation during stellar helium burning via a precise measurement of the 12C(a,g) reaction. Time projection chamber (TPC) detectors operating with low pressure gas (as an active target) are ideally suited for such studies. We review the progress of the current research program and plans for the future at the HI{\gamma}S facility with the optical readout TPC (O-TPC) and the development of an electronic readout TPC for the ELI-NP facility (ELITPC)., Comment: Contribution Symposium on Radiation Measurements and Applications (SORMA XVII), June 11 - June 14 , 2018, University of Michigan, Ann Arbor

The neutron-unbound isotope Be-13 has been studied in several experiments using different reactions, different projectile energies, and different experimental setups. There is, however, no real consensus in the interpretation of the data, in particular concerning the structure of the low-lying excited states. Gathering new experimental information, which may reveal the Be-13 structure, is a challenge, particularly in light of its bridging role between Be-12, where the N = 8 neutron shell breaks down, and the Borromean halo nucleus Be-14. The purpose of the present study is to investigate the role of bound excited states in the reaction product Be-12 after proton knockout from B-14, by measuring coincidences between Be-12, neutrons, and gamma rays originating from de-excitation of states fed by neutron decay of Be-13. The Be-13 isotopes were produced in proton knockout from a 400 MeV/nucleon B-14 beam impinging on a CH2 target. The Be-12-n relative-energy spectrum d sigma/dE(fn) was obtained from coincidences between Be-12(g.s.) and a neutron, and also as threefold coincidences by adding gamma rays, from the de-excitation of excited states in Be-12. Neutron decay from the first 5/2(+) state in Be-13 to the 2(+) state in Be-12 at 2.11 MeV is confirmed. An energy independence of the proton-knockout mechanism is found from a comparison with data taken with a 35 MeV/nucleon B-14 beam. A low-lying p-wave resonance in Be-13(1/2(-)) is confirmed by comparing proton- and neutron-knockout data from B-14 and Be-14.

Intermediate energy single-neutron removal from $^{31}$Mg has been employed to investigate the transition into the N=20 island of inversion. Levels up to 5~MeV excitation energy in $^{30}$Mg were populated and spin-parity assignments were inferred from the corresponding longitudinal momentum distributions and $\gamma$-ray decay scheme. Comparison with eikonal-model calculations also permitted spectroscopic factors to be deduced. Surprisingly, the 0$^{+}_{2}$ level in $^{30}$Mg was found to have a strength much weaker than expected in the conventional picture of a predominantly $2p - 2h$ intruder configuration having a large overlap with the deformed $^{31}$Mg ground state. In addition, negative parity levels were identified for the first time in $^{30}$Mg, one of which is located at low excitation energy. The results are discussed in the light of shell-model calculations employing two newly developed approaches with markedly different descriptions of the structure of $^{30}$Mg. It is concluded that the cross-shell effects in the region of the island of inversion at Z=12 are considerably more complex than previously thought and that $np - nh$ configurations play a major role in the structure of $^{30}$Mg., Comment: Physics Letters B, Volume 779, 10 April 2018, Pages 124-129

The structure of the Hoyle state, a near-threshold 0+ state of extreme astrophysical significance in 12C has long been investigated. An experiment was performed to measure the branching ratio for the decay of this state directly into 3 α-particles. Such a branching ratio is expected to be a good observable for whether the resonance can be described as a dilute gas of α- particles known as an α-condensate. This experiment gave the best upper limits to date for this direct decay via the improvement of the traditionally used DDΦ model to isotropic decay to the available phase space. The new DDP2 model includes three-body penetrabilities and gives a limit of < 0.026% (95% C.L.), a factor of 5 improvement over the previous experimentally obtained limit.

Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The F-26 nucleus, composed of a deeply bound pi 0d(5/2) proton and an unbound v0d(3/2) neutron on top of an O-24 core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J(pi) = 1(1)(+) - 4(1)(+) multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The J(pi) = 1(1)(+), 2(1)(+), 4(1)(+) bound states have been determined, and only a clear identification of the J(pi) = 3(1)(+) is missing. Purpose: We wish to complete the study of the J(pi) = 1(1)(+) - 4(1)(+) multiplet in F-26, by studying the energy and width of the J(pi) = 3(1)(+) unbound state. The method was first validated by the study of unbound states in F-25, for which resonances were already observed in a previous experiment. Method: Radioactive beams of Ne-26 and Ne-27, produced at about 440AMeV by the fragment separator at the GSI facility were used to populate unbound states in F-25 and F-26 via one-proton knockout reactions on a CH2 target, located at the object focal point of the (RB)-B-3/LAND setup. The detection of emitted. rays and neutrons, added to the reconstruction of the momentum vector of the A - 1 nuclei, allowed the determination of the energy of three unbound states in F-25 and two in F-26. Results: Based on its width and decay properties, the first unbound state in F-25, at the relative energy of 49(9) keV, is proposed to be a J(pi) = 1/ 2(-) arising from a p1/2 proton- hole state. In F-26, the first resonance at 323(33) keV is proposed to be the J(pi) = 3(1)(+) member of the J(pi) = 1(1)(+) - 4(1)(+) multiplet. Energies of observed states in F-25,F-26 have been compared to calculations using the independent-particle shell model, a phenomenological shell model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton- neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need for implementing the role of the continuum in theoretical descriptions or to a wrong determination of the atomic mass of F-26.

International audience; The N=20 island of inversion is an excellent playground for testing shell model calculations. The Mg chain is a region of shell evolution still far from being well understood. In this paper we present preliminary results of a single-neutron knockout experiment from 31Mg performed at GANIL to study the structure of 31Mg and of the core 30Mg. The level scheme and longitudinal momentum distributions were mesured and spectroscopic factors were deduced. Negative parity states arise at low energy and the spectroscopic factor for the isomeric in 30Mg was determined to be smaller than foreseen in the standard picture. The preliminary experimental results are compared to state-of the art shell model calculations revealing opposed interpretations.

A prominent candidate for a Hoyle-analogue state in 16O is the 0+ 6 state, previously observed at Ex = 15.097(5) MeV. This state is identified by several theoretical cluster calculations to be a good candidate for the 4-α cluster state, analogous to the Hoyle state in 12C. Whilst much theoretical work has been performed to reconcile a calculated α-cluster state with this resonance, the experimental information on this state remained very scarce. To investigate this state, the 16O(α, α') reaction was studied at θlab = 0° at an incident energy of Elab = 200 MeV using the K600 magnetic spectrometer at iThemba LABS. For the first time, the decay channels of the Ex = 15.097(5) MeV state were isolated using a large acceptance silicon-strip detector array at backward angles. The lineshapes of the states were analysed within a phenomenological R-matrix framework. Results indicate the presence of a resonance at Ex ≈ 15 MeV which does not exhibit a Jπ = 0+ nature.

The $^{16}\mathrm{O}(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}})$ reaction was studied at ${\ensuremath{\theta}}_{\mathrm{lab}}={0}^{\ensuremath{\circ}}$ at an incident energy of ${E}_{\mathrm{lab}}=200$ MeV using the K600 magnetic spectrometer at iThemba LABS. Proton decay and $\ensuremath{\alpha}$ decay from the natural parity states were observed in a large-acceptance silicon strip detector array at backward angles. The coincident charged-particle measurements were used to characterize the decay channels of the ${0}_{6}^{+}$ state in $^{16}\mathrm{O}$ located at ${E}_{x}=15.097(5)$ MeV. This state is identified by several theoretical cluster calculations to be a good candidate for the $4\text{\ensuremath{-}}\ensuremath{\alpha}$ cluster state. The results of this work suggest the presence of a previously unidentified resonance at ${E}_{x}\ensuremath{\approx}15$ MeV that does not exhibit a ${0}^{+}$ character. This unresolved resonance may have contaminated previous observations of the ${0}_{6}^{+}$ state.

Scattering of 8He from 4He has been performed through the coincident detection of the scattered particles using a silicon array within a helium-4 gas volume with a 8He beam. This permitted the reconstruction of the interaction probability as a function of position within the gas and hence the excitation function to be calculated together with the angular distribution of the products. These measurements also enabled the reconstruction of the two-neutron transfer to 6He + 6He. The measurements provide the first characterisation of the scattering of the α+4n, 8He, halo nucleus from 4He and the 2n-transfer to populate the symmetric final state. The results indicate the presence of a L=4 component at excitation energies of 14–15 MeV, consistent with a broad (∼1 MeV) Jπ=4+ resonance. These measurements would agree with generalized two-centre cluster model (GTCM) calculations indicating a cluster, or molecular, structure predicted at this energy. ispartof: Physics Letters B vol:775 pages:58-62 status: published

The nucleus 12C has a rather significant role in modern nuclear physics, but whose influence can be traced to the work of Hoyle in the 1950s, when it was concluded that there should be a state close to 7.68 MeV responsible for the synthesis of carbon in stellar nucleosynthesis. Although a state at 7.65 MeV was subsequently discovered, its properties have remained something of a mystery until rather recently. This paper explores our current understanding of the structure of 12C, in particular the nature of the Hoyle state.

The 7.65 MeV, J π = 0 + , second excited state in 12C is known as the Hoyle-state after Fred Hoyle. In the 1950s Hoyle proposed the existence of the state in order to account for the stellar abundance of carbon. Aside from its key role in the synthesis of the elements it is believed to possess a rather unusual structure, where the dominant degrees of freedom are those of α -particle clusters rather than nucleons. An understanding of the properties of the Hoyle state, for example its radius and excitations, has been the focus of a major experimental activity. Similarly, unravelling precisely why a cluster state should arise at precisely the right energy to promote synthesis of carbon has been a central theoretical challenge. To a significant extent, the Hoyle-state has become a cornerstone for state-of-the-art nuclear theory. This review examines the present status of both theory and experiment and indicates directions for future developments to resolve some of the remaining open questions.

The excitation function of Mg28 above the α-decay threshold has been measured for the first time using the resonant scattering of α particles with the technique of a thick target in inverse kinematics. Thirteen new states are reported between Ex=15.5 and Ex=20.5 MeV, and suggestions for spin-parity assignments are given for two of these. Calculations of the branching ratio to α decay for these states as well as comparison of the measured cross sections to calculations suggest that α+Neg.s.24 clustering is not dominant in this energy regime.

The $^{13}\mathrm{C}(^{4}\mathrm{He},4\ensuremath{\alpha})n$ breakup reaction has been studied at beam energies of 27.0, 27.5, and 28.0 MeV. A comparison with previous measurements of the $^{12}\mathrm{C}(^{4}\mathrm{He},^{8}\mathrm{Be})^{8}\mathrm{Be}$ excitation function and $^{12}\mathrm{C}(^{16}\mathrm{O},4\ensuremath{\alpha})^{12}\mathrm{C}$ breakup channel suggests the $^{8}\mathrm{Be}_{\mathrm{gs}}+\phantom{\rule{0.16em}{0ex}}^{8}\mathrm{Be}_{\mathrm{gs}}$ decay of $^{16}\mathrm{O}$ is observed from a possible ${2}^{+}$ state at $17.3\ifmmode\pm\else\textpm\fi{}0.2$ MeV, a ${4}^{+}$ state at $18.0\ifmmode\pm\else\textpm\fi{}0.2$ MeV, a ${2}^{+}$ or ${4}^{+}$ state at $19.4\ifmmode\pm\else\textpm\fi{}0.2$ MeV, and a ${4}^{+}$ or ${6}^{+}$ state at $21.0\ifmmode\pm\else\textpm\fi{}0.2$ MeV. The ${2}^{+}$ or ${4}^{+}$ assignment for the ($19.4\ifmmode\pm\else\textpm\fi{}0.2$)-MeV state appears to be supported by the relative cross sections expected for resonant and sequential breakup reactions.

The breakup reaction $^{9}\mathrm{Be}(^{4}\mathrm{He},3\ensuremath{\alpha})\mathit{n}$ was measured using an array of four double-sided silicon strip detectors at beam energies of 22 and 26 MeV. Excited states in $^{9}\mathrm{Be}$ up to 8 MeV were populated and reconstructed through measurements of the charged reaction products. Evidence is given for a state in $^{9}\mathrm{Be}$ at $3.{82}_{\text{-0.09}}^{\text{+0.08}}$ MeV with $\mathrm{\ensuremath{\Gamma}}={1240}_{\text{-90}}^{\text{+270}}$ keV. This is consistent with two recent measurements of a state with similar properties in the mirror nucleus $^{9}\mathrm{B}$. An analysis of the reduced widths ($^{8}\mathrm{Be}_{\mathrm{g}.\mathrm{s}.}$ channel) of this state along with the proposed mirror state has led to a firm limit of $J\ensuremath{\le}7/2$ and a tentative assignment of ${J}^{\ensuremath{\pi}}=1/{2}^{\ensuremath{-}}$ or $3/{2}^{\ensuremath{-}}$.

International audience; Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ and $^{20}\mathrm{N}(\mathrm{n},\gamma)^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T

International audience; An experiment was performed to investigate α-condensate states via high α-particle multiplicity breakup. The nucleus of interest was (28)Si therefore to measure multiplicity 7 particle breakup events, a highly granular detector with a high solid angle coverage was required. For this purpose, the CHIMERA and FARCOS detectors at INFN LNS were employed. Particle identification was achieved through ΔE-E energy loss. The α-particle multiplicity was measured at three beam energies to investigate different excitation regimes in (28)Si. At a beam energy where the energy is sufficient to provide the 7 α-particles with enough energy to be identified using the ΔE-E method, multiplicity 7 events can be seen. Given these high multiplicity events, the particles can be reconstructed to investigate the breakup of α-condensate states. Analysing the decay paths of these states can elucidate whether the state of interest corresponds to a non-cluster, clustered or condensed state.

A number of experiments are underway to search for a rare form of radioactivity, neutrinoless double beta decay, as a measurement of the half-life would enable the neutrino mass to be determined. The COBRA collaboration [1] , [2] (Zuber, 2001; Dawson, 2009) employs CdZnTe detectors in such a search. This paper describes techniques using pulse shape analysis for identifying two-centre events in a coplanar grid CdZnTe detector. This enables Compton scatter events to be identified and so suppressing the background present within the COBRA detectors.

The structure of the nucleus C 12 is discussed, in particular the spectrum of states above the α-decay threshold. A search for the 2+ excitation of the Hoyle-state is reported. The structural link between halo-like states and molecular states is explored in the case of Be 11 .

The experimental evidence for dilute α-particle states in 12 C and 16 O is discussed. The question of the location of the 2+ excitation of the 7.65 MeV 12 C state remains unresolved. It is proposed that the 17.1 and 17.5 MeV 2+ excited states in 16 O may correspond to the excitation of the α-particle 4α gas state.

The B(E1;1/2{sup +}{yields} 1/2{sup -}) strength for {sup 11}Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for {sup 11}Be+{sup 208}Pb at 38.6 MeV/nucleon is reported. The B(E1) strength of 0.105(12) e{sup 2}fm{sup 2} derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, in contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e{sup 2}fm{sup 2}. This value is in good agreement with the value deduced independently from the lifetime of the 1/2{sup -} state in {sup 11}Be, and has a comparable precision.

The COBRA neutrinoless double beta-decay experiment is currently based in the Gran Sasso underground laboratory. It employs CdZnTe (CZT) detectors which provide both source and detector. Key to these measurements is the reduction of backgrounds to a level at which the system becomes sensitive to half-lives which would potentially allow a determination of the neutrino mass. Here, we evaluate how a pixellated detector with a pixel size approaching 200 μ m would provide a method for enhancing both the experimental signal and suppressing backgrounds present inside the detector volume. It is found that it could be possible to reduce backgrounds from natural activities by up to three orders of magnitude and that neutrinoless double beta-decays can be distinguished from single β -particles with an efficiency of 70 % .

The breakup reaction 9Be(4He, 3α)n was measured using an array of four double-sided silicon strip detectors at beam energies of 22 and 26 MeV. Excited states in 9Be up to 12 MeV were populated and reconstructed through the measurement of the charged reaction products. It is proposed that limits on the spins and parities of the states can be derived from the way that they decay. Various breakup paths for excited states in 9Be have been explored including the 8Be(g.s.) + n, 8Be(2+) + n and 5He(g.s.) + 4He channels. By imposing the condition that the breakup proceeded via the 8Be ground state, clean excitation spectra for 9Be were reconstructed. The remaining two breakup channels were found to possess strongly-overlapping kinematic signatures and more sophisticated methods (referenced) are required to completely disentangle these other possibilities. Emphasis is placed on the development of the experimental analysis and the usefulness of Monte-Carlo simulations for this purpose.

The excited states of the $^{20}\mathrm{Ne}$ nucleus from the ground state to ${E}_{x}$ = 25 MeV were investigated with the $^{22}\mathrm{Ne}$($p,t$)$^{20}\mathrm{Ne}$ reaction at a beam energy of ${E}_{p}$ = 60 MeV using the QDD magnetic spectrometer at iThemba LABS. Narrow, low-spin ${J}^{\ensuremath{\pi}}={0}^{+},{1}^{\ensuremath{-}}$, and ${2}^{+}$ states have been observed for the first time at high-excitation energies in $^{20}\mathrm{Ne}$, namely at ${E}_{x}$ = 17.67, 18.84, 20.59, 21.16, 21.80, and 22.5 MeV. Shell-model and coupled reaction channel calculations were performed to determine the nature of the newly observed states. Candidates for $T$ = 2 states are proposed at 3.86(5), 4.43(5) MeV and 5.07(5) MeV above the lowest ${0}^{+},T$ = 2 state at ${E}_{x}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}16.73$ MeV. Two of these $T$ = 2 candidates appear to result from core excitations in the $0p$ shell. The state at ${E}_{x}$ = 22.5 MeV, which could not be interpreted by the shell-model calculations, is a tentative candidate for the 5-$\ensuremath{\alpha}$ cluster state.

An experiment has been carried out using the $^{9}\mathrm{Be}(^{3}\mathrm{He},\phantom{\rule{0.16em}{0ex}}t)^{9}\mathrm{B}^{*}$ reaction at a beam energy of 33 MeV. A large acceptance silicon-strip array was used to detect the $^{9}\mathrm{B}^{*}$ break-up in coincidence with the triton ejectiles in the high-resolution Munich-Q3D spectrograph. The excitation energy regime $l3$ MeV has been explored and the spectrum resulting from proton decaying states, isolated and characterized. Additional resonance strength is observed at 1.86 MeV $\ifmmode\pm\else\textpm\fi{}70$ keV(stat) $\ifmmode\pm\else\textpm\fi{}35$ keV(syst), in agreement with two other recent measurements at higher energies and different angles. The consequences for the ``missing'' ${\textonehalf{}}^{+}$ first excited state are discussed. Additionally, the branching ratios for the 2.36 MeV ${5/2}^{\ensuremath{-}}$ state have been measured as ${\ensuremath{\Gamma}}_{\ensuremath{\alpha}0}/\ensuremath{\Gamma}=0.98\ifmmode\pm\else\textpm\fi{}0.12$ and ${\ensuremath{\Gamma}}_{p0}/\ensuremath{\Gamma}=0.016\ifmmode\pm\else\textpm\fi{}0.008$, in close agreement with earlier work.

An examination of the role of the cluster in nuclear reactions is made in the longstanding case of 12 C +12 C cluster resonances in 24 Mg . A description of both resonant scattering and breakup measurements can be found in terms of shape isomeric cluster structures.

The $^{12}$C($^{18}$O, $^{14}$C + $^{8}$Be)$^{8}$Be reaction was studied at a beam energy of 140 MeV. Two multi-element charged-particle telescopes were used to detect the decay of $^{22}$Ne states into $^{14}$C + $^{8}$Be. The reconstructed excitation energy spectrum indicates that two states at 24.14(20) and 26.89(20) MeV decay by $^{8}Be emission. These states may be linked to a $^{14}$C + 2$\alpha$ cluster structure in $^{22}$Ne.

The 14C + α breakup of 18O has been studied at energies of Ebeam = 136 MeV and 148.5 MeV, using a 200 µg cm−2 thick Be target. Several states belonging to the proposed octupole deformed band, previously associated with the 8.04 MeV, 1− and 8.22 MeV, 2+ states, have been populated through inelastic excitation. A candidate for the 7− member was not found, providing evidence that the negative parity component of the band terminates at the 5− member. This is shown to be consistent with the Nilsson description of the systematics in the 16O, 18O and 20Ne nuclei. In addition, several states at Ex > 13 MeV in 18O have been measured to α-decay for the first time. The α-transfer reactions 9Be(18O, 12C 10Be)5He, 9Be(18O, 13C 9Be)5He and 9Be(18O, 18O 4He)5He were also measured; however, little or no evidence for the population of states in 22Ne was found.

Measurements of the 14C(13C, 13C[9Be+α]) and 14C(13C, 14C[10Be+α]) break-up reactions have been made at beam energies of 77.8, 112.25 and 119.25 MeV. The studies were performed with two charged particle telescopes which measured the energy, mass, charge and emission angle of each detected particle. These data provide evidence for α-decaying states at 13.2(1), (13.6(2)), 14.2(1), 15.0(1) and 16.0(1) MeV in 13C and 14.9(1), 15.9(1), 16.5(1), 18.5(3), (19.1(2)), (19.9(2)) and 21.3(4) MeV in 14C. The 13C angular distributions were analysed and give an indication of the parity of the various states populated. These data are interpreted from the perspective of the α-cluster structure of 13,14C, and indicate the preferential population of oblate type cluster states.

A number of high-lying excited states in 14C, above the α-decay threshold, are believed to exhibit molecular-like configurations of three α-particles and two valence neutrons. The nature of these states can be determined by the measurement of their spins, parities and partial decay widths. An experiment using the 12C(16O,14O)14C reaction was performed recently at the ISL facility at the Hahn-Meitner-Institut, Berlin. The 14O ejectile was detected using a Q3D spectrometer at small forward angles. The recoil's decay products were detected in co-incidence using two double-sided silicon strip detectors at backward angles. This technique allows the possibility of a full kinematic reconstruction of the reaction, as well as enhanced background suppression. Analysis of the data is currently underway and the latest results are shown here.

Studies of the 12C(12C,8Be+8Be)8Be and 12C(12C,8Be+12C(0+2))α reactions, using a large array of strip detectors, have provided evidence for states in 16O and 20Ne which decay to α-cluster states in 8Be and 12C. The spins of the resonances have been determined which allows the energy-spin systematics to be characterized.

NESTER; The first physics results measured using the TIARA array are reported. The reaction $^{24}$Ne(d,p)$^{25}$Ne has been studied in inverse kinematics with a radioactive beam of $^(24)$Ne provided by SPIRAL at GANIL. TIARA is very compact with a high geometrical coverage for charged particles, and is designed specifically for the study of transfer reactions in inverse kinematics, with radioactive beams. From the (d,p) differential cross sections, the ground state of $^{25}$Ne is assigned to have $J^\pi$ = $1/2^+$ and the lowest states with $J^\pi$ = $5/2^+$ and $3/2^+$ are tentatively identified at excitation energies of 1.70 and 2.05 (±0.05) MeV, respectively. Coincident gamma-ray data proved essential to resolve these two excited states. Strongly populated levels observed at 3.30 and 4.05 (±0.05) MeV are candidates for negative parity states. Further analysis of the differential cross sections is in progress, with the aim of improving the identification of the higher lying states and determining absolute spectroscopic factors.

Understanding the processes which create and destroy 22Na is important for diagnosing classical nova outbursts. Conventional 22Na(p,γ) studies are complicated by the need to employ radioactive targets. In contrast, we have formed the particle-unbound states of interest through the heavy-ion fusion reaction, 12C(12C,n)23Mg and used the Gamma-sphere array to investigate their radiative decay branches. Detailed spectroscopy was possible and the 22Na(p,γ) reaction rate has been re-evaluated. Hydrodynamical calculations incorporating the revised rate indicate a reduction in the yield of 22Na by a factor of four from previous estimates implying a reduction by a factor of two for the maximum detectability distance for 22Na γ rays from novae.

A study of the 7 Li( 9 Be, 4 He 9 Be) 3 H reaction at E beam =70 MeV has been performed using resonant particle spectroscopy techniques and provides a measurement of α -decaying states in 13 C. Excited states are observed at 12.0, 13.4, 14.1, 14.6, 15.2, 16.8, 17.9, 18.7, 21.3 and 23.9 MeV. This study provides the first measurement of the three highest energy states. Angular distribution measurements have been performed and have been employed to indicate the transferred angular momentum for the populated states. These data are compared with recent speculations of the presence of chain-like structures in 13 C.

Some recent studies of clustering in carbon and beryllium isotopes using break-up reaction studies are reported. Studies of the 7Li(9Be,9Be+α) and 7Li(9Be,10Be+α) reactions provide an insight into clustering in three-centre systems. Similarly, neutron knockout reactions involving the 4n removal channel with a 12Be projectile may provide an insight into the nature of molecular states in two-centre systems.