Search

A near-threshold proton resonance in ^{11}B at E_{ex}=11.44±0.04 MeV is observed via the reaction ^{10}Be(d,n)^{11}Be→^{10}Be+p in inverse kinematics, measured with a beam of the radioactive isotope ^{10}Be. The resonance energy at E_{res}=211(40) keV is consistent with a proton signal observed by Ayyad et al. in the β-delayed proton decay of ^{11}Be. By comparison to a distorted wave Born approximation calculation, a 0.27(6) spectroscopic factor is extracted and a tentative (ℓ=0) character is assigned for this resonance. The significant cross section in the proton-transfer (d,n) reaction, as well as the observation of its proton-decay signal, point to the threshold-resonance character of this state. The position of this state, its structure, and strong coupling to the s-wave continuum represent an ideal case to study quantum near-threshold many-body dynamics of unstable states. The presence of this state is an important step toward understanding the excessively large beta-delayed proton-decay branch of ^{11}Be.

The design and performance of a new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, are described. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminium Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7-54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with minimal $\gamma$-ray attenuation. GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal are sustainable. Fundamental characteristics of GAGG:Ce are measured and presented, including light- and heavy-ion particle identification (PID) capability, pulse-height defects, radiation hardness, and emission spectra. The CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors ($\approx4\%$ efficiency at 1 MeV) configured into four rings (eight HPGe crystal rings) using a non-Archimedean geometry that suppresses back-to-back coincident 511-keV gamma rays. The entire array is instrumented with 100- and 500-MHz (14 bit) waveform digitizers which enable triggerless operation, pulse-shape discrimination, fast timing, and pileup correction. Finally, two examples of experimental data taken during the commissioning of the CLARION2-TRINITY system are given: a PID spectrum from $^{16}$O + $^{18}$O fusion-evaporation, and PID and Doppler-corrected $\gamma$-ray spectra from $^{48}$Ti + $^{12}$C Coulomb excitation., Comment: 14 pages, 21 figures

Background: The Li 6 ( p , γ ) Be 7 cross section influences a variety of astrophysical scenarios, including big-bang and stellar nucleosynthesis. In recent years, conflicting results of direct measurements have been published, reporting contradictory low-energy trends. Purpose: To shed light on the contradiction between the existing data sets, the reaction was studied using the asymptotic normalization coefficient (ANC) technique which was up-to-now never used for this reaction. Methods: To derive the ANC, the Li 6 ( He 3 , d ) Be 7 transfer reaction, studied at the Department of Physics and Astronomy of the University of Catania and at the John. D. Fox Superconducting Accelerator Laboratory at Florida State University, was re-analyzed, focusing on the proton transfer mechanism [the α transfer process is discussed by Kiss et al. [Phys. Lett. B 807, 135606 (2020)]. The energy of the He 3 beam impinging on a Li 6 target was E lab = 3 MeV and E lab = 5 MeV. The yield of the emitted deuterons was measured with high precision by using silicon Δ E - E telescopes. Results: From the DWBA analysis of the angular distributions of the emitted deuterons populating the ground ( E * = 0.0 MeV; 3 2 − ) and the first excited ( E * = 0.429 MeV ; 1 2 − ) states of Be 7 , the ANCs for the Li 6 + p → Be 7 system were deduced. Furthermore, the recently measured Li 6 ( p , γ ) Be 7 reaction cross sections [Piatti , Phys. Rev. C 102, 052802 (2020)] were also analyzed within this theoretical framework. Excellent agreement was found between ANC values derived indirectly and those determined from the direct data, which strengthens the conclusion of the present work. The astrophysical S factor—at energies characterizing the Sun—for the Li 6 ( p , γ ) Be 7 reaction was calculated using the weighted mean of the experimentally derived ANC values. Conclusions: The result of the present comprehensive study supports the extrapolation of Piatti [Phys. Rev. C 102, 052802 (2020)], Dong [J. Phys. G Nucl. Partic. 44, 045201 (2017)], and Gnech and Marcucci [Nucl. Phys. A 987, 1 (2019)], and thus disfavors the conclusions drawn by He [Phys. Lett. B 725, 287 (2013)] and Xu [Nucl. Phys. A 918, 61 (2013)].

A measurement of the $^{50}\mathrm{Ti}(d,p)^{51}\mathrm{Ti}$ reaction at 16 MeV was performed using the Super Enge Split-Pole Spectrograph to measure the magnitude of the $N=32$ subshell gap in Ti. Seven states were observed that had not been observed in previous $(d,p)$ measurements, and the $L$ transfer values for six previously measured states were either changed or measured for the first time. The results were used to determine single neutron energies for the ${p}_{3/2}$, ${p}_{1/2}$, and ${f}_{5/2}$ orbitals. The resulting single neutron energies in $^{51}\mathrm{Ti}$ confirm the existence of the $N=32$ gap in Ti. These single neutron energies and those from previous measurements in $^{49}\mathrm{Ca}$, $^{53}\mathrm{Cr}$, and $^{55}\mathrm{Fe}$ are compared to values from a covariant density functional theory calculation.

The total fusion cross section for the $^{17}\mathrm{F}+^{12}\mathrm{C}$ system at incident energies near the top of the Coulomb barrier was studied using the newly developed Encore active-target detector at Florida State University. The $^{17}\mathrm{F}$ nucleus exhibits interesting nuclear structure properties in that although it has a low threshold against $^{17}\mathrm{F}\ensuremath{\rightarrow}^{16}\mathrm{O}+p$ breakup $({S}_{p}=600\phantom{\rule{0.28em}{0ex}}\mathrm{keV})$, the valence proton is in the $1{d}_{5/2}$ shell in the ground state so that the nuclear matter radius is predicted to be similar to that of the $^{16}\mathrm{O}$ core. By contrast, the low-lying $1/{2}^{+}$ first excited state (bounded by 105 keV) with the valence proton in the $2{\phantom{\rule{4pt}{0ex}}s}_{1/2}$ shell is considered to be a proton halo. In this paper possible influences of both the weak binding and the halo nature of the excited state on the total fusion cross section were investigated. The new data reported here complement existing measurements for the total fusion of $^{17}\mathrm{F}$ with heavy $(^{208}\mathrm{Pb})$ and medium mass ($^{58}\mathrm{Ni}$) targets by extending the range of systems studied to one where Coulomb effects should be minimal. Total fusion cross sections for the stable counterpart systems $^{16}\mathrm{O}+^{12}\mathrm{C}$ and $^{19}\mathrm{F}+^{12}\mathrm{C}$ were also measured to enable a systematic comparison. No significant influence of either the weak binding or the halo nature of the $^{17}\mathrm{F}\phantom{\rule{0.28em}{0ex}}1/{2}^{+}$ first excited state on the above barrier total fusion excitation function was observed when compared with the stable counterpart systems.

Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance.Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target.Method: The excitation function for $p+^{8}\mathrm{Li}$ resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating $T=3/2$ isobaric analog states (IAS) in $^{9}\mathrm{Be}$.Results: A good fit of the $^{8}\mathrm{Li}(p,p)^{8}\mathrm{Li}$ resonance elastic scattering excitation function was obtained using previously tentatively known $5/{2}^{\ensuremath{-}}\phantom{\rule{4pt}{0ex}}T=3/2$ state at 18.65 MeV in $^{9}\mathrm{Be}$ and a new broad $T=3/2\phantom{\rule{4pt}{0ex}}s$-wave state---the $5/{2}^{+}$ at 18.5 MeV. These results fit the expected isomirror properties for the $T=3/2\phantom{\rule{4pt}{0ex}}A=9$ isoquartet.Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited $T=3/2$ states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.

The detection of the neutrinos produced in the p − p chain and in the CNO cycle can be used to test the Standard Solar Model. The 3He( α , γ )7Be reaction is the first reaction of the 2nd and 3rd branch of the p − p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the 7Be and 8B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the 3He( α , γ )7Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reaction were measured with high precision at E H 3 e = 3.0 MeV and E H 3 e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for 3He( α , γ )7Be reaction was found to be 0.534 ± 0.025 keVb.

A high-count-rate ionization chamber design with position-sensitivity has been developed and deployed at several accelerator facilities. Counting rates of ≥ 500 kHz with good Z -separation (up to 5% energy resolution) for particle identification have been demonstrated in a series of commissioning experiments. A position-sensitive capability, with a resolution of 3 mm, has been implemented for the first time to record position information and suppress pileup. The design and performance of the detectors are described.

The resoneut detector setup is described, which was developed for resonance spectroscopy using (d,n) reactions with radioactive beams in inverse kinematics and at energies around the Coulomb barrier. The goal of experiments with this setup is to determine the spectrum and proton-transfer strengths of the low-lying resonances, which have an impact on astrophysical reaction rates. The setup is optimized for l = 0 proton transfers in inverse kinematics, for which most neutrons are emitted at backward angles with energies in the 80–300 keV range. The detector system is comprised of 9 p-terphenyl scintillators as neutron detectors, two annular silicon-strip detectors for light charged particles, one position-resolving gas ionization chamber for heavy ion detection, and a barrel of NaI-detectors for the detection of γ -rays. The detector commissioning and performance characteristics are described with an emphasis on the neutron-detector components.

The Silicon Array for Branching Ratio Experiments (SABRE) has been developed for use to study reactions of interest to nuclear structure and astrophysics . The array has been incorporated into the Super Enge Split-Pole Spectrograph (SE-SPS) experimental setup at Florida State University’s John D. Fox accelerator laboratory to detect charged-particle decays in coincidence with reaction products detected by the SE-SPS focal plane detector. Its construction and electronics processing are discussed, as well as the commissioning data used to validate its performance.

An active target detector array, ANASEN, has been developed for nuclear reaction studies with rare isotope beams at low energies. It aims at measurements of the excitation functions for proton and α - particle elastic and inelastic scattering and direct measurements of ( α , p) reactions with exotic nuclei in inverse kinematics. ANASEN is composed of three types of charged particle detectors. The length of the active area is 340 mm and the total covered area is 1300 cm 2 (almost 3 π steradian solid angle coverage) providing high efficiency for experiments with low intensity radioactive beams. A mix of 78 conventional electronics channels (for Proportional Counter and CsI-detectors) and 480 dedicated high-density ASICs electronics channels for the silicon detector are used for readout.

Measuring the fusion excitation function for an isotopic chain of projectile nuclei provides a stringent test of a microscopic description of fusion. We report the first measurement of the fusion excitation function at near-barrier energies for the 19 O + 12 C system. The measured excitation function is compared with the fusion excitation function of 18 O + 12 C. A significant enhancement in the fusion probability of 19 O ions with a 12 C target as compared to 18 O ions is observed. The experimental cross-sections observed at near-barrier energies are compared with a state-of-the-art microscopic model.

The cross sections of nuclear reactions between the radioisotope $^{7}\mathrm{Be}$ and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in big-bang nucleosynthesis, were measured at center-of-mass energies between 0.2 and 1.5 MeV. The measured cross sections are dominated by the $(d,\ensuremath{\alpha})$ reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of $\ensuremath{\omega}\ensuremath{\gamma}=1.7(5)\text{ }\text{ }\mathrm{keV}$ was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial $^{7}\mathrm{Li}$, but not sufficiently to solve the primordial lithium problem.

The cross sections of nuclear reactions between the radioisotope ^{7}Be and deuterium, a possible mechanism of reducing the production of mass-7 nuclides in big-bang nucleosynthesis, were measured at center-of-mass energies between 0.2 and 1.5 MeV. The measured cross sections are dominated by the (d,α) reaction channel, towards which prior experiments were mostly insensitive. A new resonance at 0.36(5) MeV with a strength of ωγ=1.7(5) keV was observed inside the relevant Gamow window. Calculations of nucleosynthesis outcomes based on the experimental cross section show that the resonance reduces the predicted abundance of primordial ^{7}Li, but not sufficiently to solve the primordial lithium problem.

In nuclear facilities utilizing plutonium, polymeric materials are subjected to long-term, close-contact, and continuous α radiation exposure, which can lead to compounding material degradation and eventual failure. Herein we model the attenuation of α particles by linear-low-density polyethylene (LLDPE), polyvinyl alcohol (PVA) thin films, and C60 using Monte Carlo N-Particle Extended (MCNPX) software. The degradation of these materials was investigated experimentally by irradiating them with a beam of α particles of 5.8 MeV energy at a tandem Van de Graaff accelerator delivering a dose rate of 2.95 × 106 rad s−1 over a 7.1 mm2 sample area. Our development of a method to test α particle-induced material degradation using a tandem accelerator is significant as degradation from naturally occurring α sources (i.e. Pu, Am) occurs too slowly for these sources to be used in practical experiments. Our results show that PVA nanocomposites containing 5 wt% C60 were found to withstand about 7 times the α dose of undoped PVA films before a puncture in the film was detected. When these films were adhered to a LLDPE sheet the dual layer polymer was capable of withstanding about 13 times the dose of LLDPE and nearly twice the dose of the doped PVA thin film alone. Doping polymers with C60 is an attractive way to generate more durable, radiation tolerant materials without increasing the thickness of the material which would lead to greater waste for disposal. Thus, the results herein help to resolve a prevalent technical challenge faced in nuclear facilities that utilize polymeric materials for nuclear processing and disposal.

A beam containing a substantial component of both the J^{π}=5^{+}, T_{1/2}=162 ns isomeric state of ^{18}F and its 1^{+}, 109.77-min ground state is utilized to study members of the ground-state rotational band in ^{19}F through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2^{+} band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.

A beam containing a substantial component of both the $J^{\pi}=5^+$, $T_{1/2}=162$ ns isomeric state of $^{18}$F and its $1^+$, 109.77-min ground state has been utilized to study members of the ground-state rotational band in $^{19}$F through the neutron transfer reaction $(d$,$p)$ in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2$^+$ band-terminating state. The agreement between shell-model calculations, using an interaction constructed within the $sd$ shell, and our experimental results reinforces the idea of a single-particle/collective duality in the descriptions of the structure of atomic nuclei.

Background: The $^{17}\mathrm{F}(p,\ensuremath{\gamma})^{18}\mathrm{Ne}$ reaction is part of the astrophysical ``hot CNO'' cycles that are important in astrophysical environments like novas. Its thermal reaction rate is low owing to the relatively high energy of the resonances and therefore is dominated by direct, nonresonant capture in stellar environments at temperatures below 0.4 GK.Purpose: An experimental method is established to extract the proton strength to bound and unbound states in experiments with radioactive ion beams and to determine the parameters of direct and resonant capture in the $^{17}\mathrm{F}(p,\ensuremath{\gamma})^{18}\mathrm{Ne}$ reaction.Method: The $^{17}\mathrm{F}(d,n)^{18}\mathrm{Ne}$ reaction is measured in inverse kinematics using a beam of the short-lived isotope $^{17}\mathrm{F}$ and a compact setup of neutron, proton, $\ensuremath{\gamma}$-ray, and heavy-ion detectors called resoneut.Results: The spectroscopic factors for the lowest $l=0$ proton resonances at ${\mathrm{E}}_{\mathrm{c}.\mathrm{m}.}=0.60$ and 1.17 MeV are determined, yielding results consistent within $1.4\ensuremath{\sigma}$ of previous proton elastic-scattering measurements. The asymptotic normalization coefficients of the bound ${2}_{1}^{+}$ and ${2}_{2}^{+}$ states in $^{18}\mathrm{Ne}$ are determined and the resulting direct-capture reaction rates are extracted.Conclusions: The direct-capture component of the $^{17}\mathrm{F}(p,\ensuremath{\gamma})^{18}\mathrm{Ne}$ reaction is determined for the first time from experimental data on $^{18}\mathrm{Ne}$.

Previous experiments observed a 4^{+} state in the N=28 nucleus ^{44}S and suggested that this state may exhibit a hindered E2-decay rate, inconsistent with being a member of the collective ground state band. We populate this state via two-proton knockout from a beam of exotic ^{46}Ar projectiles and measure its lifetime using the recoil distance method with the GRETINA γ-ray spectrometer. The result, 76(14)_{stat}(20)_{syst} ps, implies a hindered transition of B(E2;4^{+}→2_{1}^{+})=0.61(19) single-particle or Weisskopf units strength and supports the interpretation of the 4^{+} state as a K=4 isomer, the first example of a high-K isomer in a nucleus of such low mass.

Reactions on certain proton-rich, radioactive nuclei have been shown to have a significant influence on X-ray bursts. We provide an overview of two recent measurements of important X-ray burst reactions using in-flight radioactive ion beams from the RESOLUT facility at the J. D. Fox Superconducting Accelerator Laboratory at Florida State University. The 17 F(d,n) 18 Ne reaction was measured, and Asymptotic Normalization Coefficients were extracted for bound states in 18 Ne that determine the direct-capture cross section dominating the 17 F(p, γ ) 18 Ne reaction rate for T≲ 0.45 GK. Unbound resonant states were also studied, and the single-particle strength for the 4.523-MeV (3 + ) state was found to be consistent with previous results. The 19 Ne(d,n) 20 Na proton transfer reaction was used to study resonances in the 19 Ne(p, γ ) 20 Na reaction. The most important 2.65-MeV state in 20 Na was observed to decay by proton emission to both the ground and first-excited states in 19 Ne, providing strong evidence for a 3 + spin assignment and indicating that proton capture on the thermally-populated first-excited state in 19 Ne is an important contributor to the 19 Ne(p, γ ) 20 Na reaction rate.

Measurement of the fusion excitation function for 18 O + 12 C and 19 O + 12 C is described. The fusion cross-section is extracted through the direct measurement of evaporation residues resulting from the fusion process. At near barrier energies, the single additional neutron present in 19 O results in an enhancement in the fusion cross-section by a factor of over three as compared to 18 O.

International audience; Note from publisher: This article contains the abstract only.

The $^{19}\mathrm{Ne}(p,\ensuremath{\gamma})^{20}\mathrm{Na}$ reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the $^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma})^{19}\mathrm{Ne}$ reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in $^{20}\mathrm{Na}$ in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction $^{19}\mathrm{Ne}(d,n)^{20}\mathrm{Na}$ is measured with a beam of the radioactive isotope $^{19}\mathrm{Ne}$ at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the $^{19}\mathrm{Ne}$ ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned ${3}^{+}$, ${1}^{+}$, and (${0}^{+}$), respectively. In addition, we identify two resonances with the first excited state in $^{19}\mathrm{Ne}$, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in $^{19}\mathrm{Ne}(p,\ensuremath{\gamma})^{20}\mathrm{Na}$, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.

Evaporated amniotic fluid (AF) targets have been bombarded with a 13 MeV 6Li3+ beam. Forward angle data have served to identify the 1H(6Li,1H)6Li reaction as an alternative for hydrogen characterization of such organic samples. Detected 6Li ions elastically scattered from C, N, O, Na and Cl can also be used to determine the concentrations of these elements in AF. The analyzed AF samples have been diluted with distilled water. The effect of sample dilution on the improvement of spectrum energy resolution has been observed, confirming previous reports. The hydrogen concentration determined in the studied AF targets is shown to vary linearly with sample dilution. Two detector arrangements have been used to find out which detection scheme is the most convenient. The combination of a counter telescope and a single detector, set up at the same polar angle on the opposite side of the beam, seems to be the best choice to have a reliable particle identification and an adequate energy resolution simultaneously.

The ^{19}Ne(p,γ)^{20}Na reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the ^{15}O(α,γ)^{19}Ne reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in ^{20}Na in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction ^{19}Ne(d,n)^{20}Na is measured with a beam of the radioactive isotope ^{19}Ne at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the ^{19}Ne ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned 3^{+}, 1^{+}, and (0^{+}), respectively. In addition, we identify two resonances with the first excited state in ^{19}Ne, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in ^{19}Ne(p,γ)^{20}Na, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle.

A study of high spin states in the odd-neutron isotones 239 Pu and 237 U is reported. Striking differences were found in the high-spin properties of rotational bands built on the 1 /2 + [631] ground states in these two nuclei. These differences mirror those observed in the even–even Pu and U immediate neighbors and appear to be related to the strength of octupole correlations.

Deep-inelastic reactions between a beam of 1360 MeV 208Pb ions and a thick 238U target have been used to populate the neutron-rich nucleus 211Pb. The observation of its γ decay has allowed identification of excited states up to the highest spin which can be formed from the three valence neutrons, including identification of three high-spin isomers. Level energies and transition strengths are compared to shell-model calculations with empirical interactions and predictions are made for the expected behaviour of more neutron-rich lead isotopes. The evidence for a possible increase in the neutron effective charge moving away from the N = 126 shell gap is evaluated.

Particle gamma-ray angular correlation measurements have been used to study the spin alignment and magnetic-substate population parameters for the 2 + 1 (4.443 MeV) state in 12 C, populated in the 12 C ( 12 C , 12 C [0 + 2 ]) 12 C (2 + 1 ) inelastic scattering reaction in the vicinity of a prominent, narrow peak in the scattering excitation function. The data show a strong alignment of the spin with the orbital angular momentum, and suggest that the cross section peak corresponds to a spin 14 + resonance at E c.m. =28.0 MeV. This energy is close to that where a strong peak is also observed in the 0 + 1 +0 + 2 excitation function. A comparison between the data for these two channels lends some support to recent theoretical calculations of resonance behavior for angular-momentum-mismatched channels in 12 C + 12 C inelastic scattering.

Dipole and electric quadrupole excitations in 204,206,207,208 Pb have been measured up to 6.75 MeV in resonant photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC using two Euroball-Cluster detector modules. In 208 Pb, 14 excited states have been populated; in 206 Pb, the decays of 41 states have been detected. Information about 45 heretofore unknown excited states in 204 Pb could be measured as well as eleven known levels in 207 Pb. The extracted dipole strength distributions are discussed within phenomenological (“pygmy resonance”) and microscopic models (quasiparticle-phonon model). A strong fragmentation and a small shift of the detected E1 strength towards higher energies is observed with the opening of the neutron shell closure.

Among the many production and destruction nuclear reactions that bear on the net 44 Ti yield in the supernova environment, recently highlighted by γ-ray astronomy observations, the α capture on 40 Ca stands out in the α-rich freezeout phase conjectured by astrophysical models. We activate a He-gas target with a 40 Ca beam and implant recoiling 44 Ti nuclei (∼10 6 ) in a Cu catcher. The 44 Ti atoms chemicallyextracted with a nat Ti carrier are counted by accelerator mass spectrometry (AMS). The measurement of the 44 Ti/Ti ratio, together with the amount of Ti carrier added, determine the number of 44 Ti nuclei produced in the activation, independent of chemical yield or transmission efficiency. The resonance strength (7.4±2.5 eV) at E cm ∼1.1 MeV/n determined for two close-by levels of 44 Ti is in excellent agreement with previous prompt-γ measurements. We plan to extend our experiments to the lower energy range.

Entry distributions in angular momentum and excitation energy have been measured for several very proton-rich isotopes of Pt and Au. This is the first systematic study of the energy-spin phase space for nuclei near and beyond the proton drip line. Comparisons are made between the distributions associated with proton-unbound Au nuclei and more stable Pt isobars. In 173 Au the first evidence is seen for the limits of excitation energy and angular momentum which a nucleus beyond the proton drip line can sustain.

The level structure of 5422Ti32 has been explored for the first time by combining β-decay measurements from fragmentation products with prompt γ-ray spectroscopy following deep inelastic reactions. The latter technique was also instrumental in tracing 52Ti30 to higher spin. The data provide new tests of effective interactions for full pf-shell calculations in neutron-rich nuclei above 48Ca. The data indicate the presence of a significant subshell gap at N=32 and comparisons between theory and experiment suggest an additional shell closure at N=34 in Ca and Ti isotopes.

An automatic gain-matching method has been developed for the energy calibrations of the 32 segments of a large-volume germanium detector. The method calibrates the small-volume segments relative to the central contact, which collects the charge from the total germanium crystal volume and can be efficiently calibrated with known sources. The method presented here can employ photons of arbitrary energy. With the use of in-beam γ-rays for segment calibrations it presents an efficient way to perform continuous energy calibrations in experiments.

The decay properties of low-lying collective states in 132Ba were studied by means of γ spectroscopy following the β-decay of the 2− ground state (T1/2=4.8 h) and a 6− isomer (T1/2=24.3 min) of 132La. The lanthanum nuclei were produced at the Cologne fn tandem accelerator using the reaction 122Sn(14N, 4n)132La. The γγ coincidences and singles spectra were measured with the osiris -cube spectrometer. Beside ground and quasi-gamma band many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins to the excited states, and to determine the multipolarities of the depopulating the γ transitions. We also confirmed the expected dominant E2 character of transitions in the quasi-gamma band and from the quasi-gamma to the ground band but with a certain deviation: the decay 6+2→6+1 shows an unexpected large M1 fraction. Also the decays of the third, fourth and fifth 2+ states are dominated by M1 radiation. A level at 1660 keV could be identified as the 0+3 state in 132Ba. The experimental data are compared with calculations using the proton–neutron interacting boson model (IBM-2). Good agreement is reached in the vicinity of the O(6) limit.

Background: Measurement of the energy dependence of the fusion cross section at sub-barrier energies provides an important test for theoretical models of fusion.Purpose: The aim of the study is to extend the measurement of fusion cross sections in the sub-barrier domain for the $^{18}\mathrm{O}+^{12}\mathrm{C}$ system, and to use the new experimental data to confront microscopic calculations of fusion.Method: Evaporation residues produced in fusion of $^{18}\mathrm{O}$ ions with $^{12}\mathrm{C}$ target nuclei were detected with good geometric efficiency and identified by measuring their energy and time-of-flight. Theoretical calculations with a density-constrained time-dependent Hartree-Fock (DC-TDHF) theory include for the first time the effect of pairing on the fusion cross section.Results: Comparison of the measured fusion excitation function with the predictions of the DC-TDHF calculations reveal that the experimental data exhibit a smaller decrease in cross section with decreasing energy than is theoretically predicted.Conclusion: The larger cross sections observed at the lowest energies measured indicate a larger tunneling probability for the fusion process. This larger probability can be associated with a smaller, narrower fusion barrier than presently included in the theoretical calculations.

The nonyrast states of 124 Xe have been investigated with the 123 Te ( 3 He , 2 n ) reaction by means of in-beam γ -spectroscopy using a setup of 6 Compton-suppressed high-purity-germanium (HPGe) detectors. More than 65 new transitions, establishing 34 new levels, were observed. γγ -angular correlations were analyzed to assign spins and parities to the low-lying states, and to determine the multipolarities of the γ -transitions. In addition, the γ -excitation-function method was used for spin assignments. With these methods 10 (18) spin and parity assignments were made (some of them tentative) and 7 multipole mixing ratios could be determined. The excitation energies and B (E2) ratios of low-lying states are compared with predictions of the sd-IBM-1, giving rise to the identification of a 0 + state with O(6) quantum number σ=N−2 . Quadrupole shape invariants for the ground state and effective deformation parameters are calculated, showing an admixture of U(5) symmetry to the ground-state wave function.

High-spin properties of the nucleus 169Hf have been studied through the fusion evaporation reaction 96Zr(76Ge,3n)169Hf at a beam energy of 310 MeV. The known rotational bands have been extended considerably and 6 new bands have been established, four of which form coupled bands with pronounced M1 connections. Quasiparticle assignments are suggested for the new band structures, and it appears that coupling to vibrational degrees of freedom plays a role. Both coupled bands involve the excitation of quasiprotons. In the region of highest spin, a large alignment gain is interpreted in terms of a mixed crossing where an h 9/2 and an h 11/2 quasiproton provide the two signatures of the aligning configuration.

Excited states in the proton-unbound 173,175,177 Au nuclei were identified for the first time. Level structures associated with three different shapes were observed in 175 Au. While the yrast lines of 175 Au and 177 Au consist of a prolate band built upon the intruder 1/2 + [660] ( i 13/2 ) proton orbital, no sign of collectivity was observed in the lighter 173 Au isotope. Implications for the deformation associated with these structures are discussed with a focus on shape co-existence in the vicinity of the proton-drip line.

Three superdeformed (SD) bands have been found in 168Hf. Lifetime measurements revealed a large quadrupole moment, Q t ∼11.4 e b , for the strongest band (TSD1). Theoretical calculations using the Ultimate Cranker code predict high-spin SD minima (ϵ2∼0.43) with stable triaxial deformations of γ∼+20° and γ∼−15°. The measured Qt value suggests that band TSD1 corresponds, most likely, to a deformation with a positive γ value. This constitutes the first evidence for triaxial superdeformation in an even proton system.

The non-yrast states of 123 Xe have been investigated with the reaction 123 Te( 3 He, 3n) by means of in-beam γ -spectroscopy using a setup of 6 Compton-suppressed high-purity-germanium (HPGe) detectors. More than 130 new transitions establishing over 35 new levels were observed. γγ angular correlations were analyzed to assign spins and parities to the low-lying states, and to determine the multipole mixing ratios of the γ -transitions. With this method 9 spin and parity assignments were made and 19 multipole mixing ratios could be determined. Excitation energies of negative-parity states and the branching ratios of their decays are compared with predictions of the Rigid Triaxial Rotor plus Particle model (RTRP).

The domain of nuclei situated far from the line of b stability has always been an arena of numerous experimental pursuits and a testing ground for new theoretical models. With radioactive beams on the horizon, the physics of nuclei with an excess of neutrons or protons has become one of the focal points of nuclear physics. These nuclei define the very limits of nuclear existence and will be susceptible to phenomena associated with low binding energy, such as halos, skins, or mixing between bound and continuum states. The proton separation energy decreases with decreasing neutron number. Proton-rich nuclei, which have a negative proton separation energy and are, thus, situated beyond the proton drip-line, can spontaneously emit protons. The proton decay rate is governed by the energy and orbital angular momentum of the emitted proton. It also depends on the wave function of the proton-decaying state, which is determined by the shape of the nuclear potential and by residual interactions between valence nucleons. Most of the known proton emitters have decay rates consistent with the assumption of a spherical potential. The recent experimental