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General Fusion is building the Fusion Demonstration Plant to demonstrate a magnetized target fusion scheme in which a deuterium plasma is heated from 200 eV to 10 keV by piston-driven compression of a liquid-lithium liner. The multilayer coaxial time-of-flight (MCTOF) neutron emission spectrometer is designed to measure the ion temperature near peak compression at which time the neutron yield will approach $10^{18}$ neutrons/s. The neutron energy distribution is expected to be Gaussian since the machine uses no neutral beam or radiofrequency heating. In this case, analysis shows that as few as 500 coincidence events should be sufficient to accurately measure the ion temperature. This enables a fast time resolution of 10 $\mu s$, which is required to track the rapid change in temperature approaching peak compression. We overcome the challenges of neutron pileup and event ambiguity with a compact design having two layers of segmented scintillators. The error in the ion temperature measurement is computed as a function of the neutron spectrometer's geometric parameters and used to optimize the design for the case of reaching 10 keV at peak compression., Comment: The following article has been accepted by Review of Scientific Instruments. After it is published, it will be found at https://aip.scitation.org/toc/rsi/HTPD2022/1. High Temperature Plasma Diagnostics 2022 conference. 5 pages, 9 figures

An array of 128 CsI(Tl) charged particle detectors providing nearly 4 π coverage has been developed at Simon Fraser University (SFU) and commissioned at TRIUMF, Canada’s particle accelerator center. The new CsI ball array replaces a previous 24-detector array and offers improved charged particle detection efficiency and discrimination between reaction channels due to its increased angular coverage. A technical overview of the CsI ball array, as well as commissioning data including measurements of the charged particle detection efficiency, is presented.

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency γ -ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF’s Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) γ -ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

The level structure of $^{25}\mathrm{Na}$ and $^{22}\mathrm{Ne}$ in the high excitation energy/high spin regime was studied using $\ensuremath{\gamma}$-ray spectroscopy and Doppler shift lifetime measurements following $^{12}\mathrm{C}(^{18}\mathrm{O},\ensuremath{\alpha}p)^{25}\mathrm{Na}$ and $^{12}\mathrm{C}(^{18}\mathrm{O},2\ensuremath{\alpha})^{22}\mathrm{Ne}$ reactions. Multiple new levels and transitions were identified in both nuclides based on $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence data. In $^{25}\mathrm{Na}$, evidence was found for higher-spin negative-parity states up to ${I}^{\ensuremath{\pi}}=13/{2}^{\ensuremath{-}}$ resulting from neutron excitation into the $pf$ shell, in good agreement with shell model calculations using the SDPF-MU and FSU interactions. Candidates for the yrast ${7}^{+}$ and ${8}^{+}$ levels in $^{22}\mathrm{Ne}$, consistent with calculations using the USDB interaction, were also identified.

The TIGRESS Integrated Plunger device (TIP) has been developed for recoil distance method (RDM) lifetime measurements using the TIGRESS array of HPGe γ -ray detectors at TRIUMF’s ISAC-II facility. A commissioning experiment was conducted utilizing a 250 MeV 84Kr beam at ≈ 2 × 1 0 8 particles per second. The 84Kr beam was Coulomb excited to the 2 1 + state on a movable 27Al target. A thin Cu foil fixed downstream from the target was used as a degrader. Excited nuclei emerged from the target and decayed by γ -ray emission at a distance determined by their velocity and the lifetime of the 2 1 + state. The ratio of decays which occur between the target and degrader to those occurring after traversing the degrader changes as a function of the target–degrader separation distance. Gamma-ray spectra at 13 target–degrader separation distances were measured and compared to simulated lineshapes to extract the lifetime. The result of τ = 5 . 541 ± 0 . 013 (stat.) ± 0 . 063 (sys.) ps is shorter than the literature value of 5 . 84 ± 0 . 18 ps with a reduction in uncertainty by a factor of approximately two. The TIP plunger device, experimental technique, analysis tools, and result are discussed.

In 1937, Hermann Jahn and Edward Teller published their research describing a mechanism of symmetry breaking in nonlinear polyatomic molecules resulting in a lifting of orbital degeneracy of an electronic state (Proc. R. Soc. London, Ser. A 1937, 161, 220), yielding insight into molecular structure. The impact of symmetry breaking on the energy and structure of quantum states is not unique to molecules and may be applied to nuclei, involving degenerate nucleon states as opposed to electronic states. Reinhard and Otten showed that the nuclear Jahn–Teller effect provides a mechanism applicable to describe the commonly observed collective quadrupole surface motion (Nucl. Phys. A 1984, 420, 173). To take into account single-particle effects, it is important to properly model the valence nucleons, especially those occupying large angular momenta orbitals near the Fermi level. In this work, a model has been developed in which two valence nucleons of the same kind are coupled to an axially symmetric quadrupole deformed rotor of the D2 symmetry and interact through the nuclear delta force. To test this model, the band of the lowest-energy state at a given spin for 126Ce is reproduced. The resultant wavefunctions are then used to calculate the g factor, reduced electric quadrupole transition probability, and spectroscopic quadrupole moment all as a function of spin. This method lays the groundwork to explore higher order symmetries following the multipole expansion.

Despite the many studies that have shown minimal health risks to individuals living outside of Japan following the Fukushima Nuclear Accident, there are persisting concerns regarding the consumption of Pacific seafood that may be contaminated with radioactive species from Fukushima. To address these concerns, the activity concentrations of anthropogenic 134Cs and 137Cs, as well as naturally occurring 40K, were measured in Pacific salmon collected from Kilby Provincial Park, British Columbia (BC), in 2013 and from the Quesnel River, BC, in 2014 using low-background gamma-ray spectroscopy. In addition, soil samples and a single roof-debris sample were collected and analysed to provide a record of Fukushima-derived contamination in BC. Cesium-134 was not detected in the salmon samples. Cesium-137 was not detected in any of the sockeye or chum samples, although it was detected in all of the Chinook samples. The weighted average (±1σ) 137Cs activity concentration in the Chinook salmon collected in 2013 and 2014 was 0.23 (3) and 0.20 (3) Bq/kg fresh weight, respectively. A conservative annual dose estimate for an adult who consumes the average Canadian quantity of seafood per year, contaminated with radiocesium at the maximum concentrations measured in this campaign, was calculated to be 0.054 μSv per year. Cesium-134 was detected in all but two of the soil samples. A weak positive correlation was observed between presence of 134Cs and of 7Be suggesting that the 134Cs arrived via atmospheric deposition. Cesium-137 was present in every soil sample, although the total radiocesium activity concentrations measured were significantly less than action levels set by Health Canada.

To investigate potential radioisotope contamination from the Fukushima nuclear accident, measurements of 10 sockeye salmon ( Oncorhynchus nerka ) collected on June 21 and June 31, 2014 in the Alberni Inlet on the west coast of Vancouver Island, British Columbia, Canada were performed using low-background gamma-ray spectroscopy. Activity concentrations of the anthropogenic radioisotopes 134 Cs and 137 Cs as well as the naturally occurring radioisotope 40 K were measured. Detection of 137 Cs occurred in half of the sockeye with activity concentrations ranging from 0.23 to 1.43 Bq/kg dry weight. The 134 Cs isotope was detected in a single sockeye salmon with activity concentrations (± σ ) measured in the two subsamples of 0.31(8) and 0.37(10) Bq/kg dry weight. The dose contribution from each of the measured radionuclides was calculated. In the sockeye salmon with the greatest radiocesium concentrations, the dose contribution from anthropogenic radiocesium ( 134 Cs+ 137 Cs) was found to be 450 times less than the dose from naturally occurring radionuclides in the same sample. In conclusion, the total radiocesium activity concentration in every sample is at least 500 times lower than Health Canada's action levels for radioactively contaminated food following a nuclear emergency. Assuming all seafood has as much radiocesium as the most contaminated sample measured, the added annual dose from radiocesium to an adult individual with an average Canadian level of seafood consumption would be 0.046 μSv per year.

A method is presented for the determination of gamma-ray energies and transition rates in nuclei populated using the fusion-evaporation reaction mechanism and measured using the Doppler-shift attenuation method (DSAM). This method is applied to data collected for the stable benchmark nucleus 22Ne during a commissioning experiment at TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics, employing a 12C(18O,2α)22Ne fusion-evaporation reaction. Gamma-ray energies were determined using offline reconstruction to correct for the Doppler shift. Mean lifetimes of the corresponding transitions were then measured via a comparison to Monte-Carlo lineshape simulations developed using the GEANT4 framework. Best fit lifetimes obtained using χ2 analysis were in general agreement with the existing literature, validating the analysis method used.

Gamma-ray spectroscopy and lifetime measurements using the Doppler shift attenuation method (DSAM) were performed on the nucleus $^{28}\mathrm{Mg}$ near the $N=20$ ``island of inversion,'' which was populated using a $^{12}\mathrm{C}(^{18}\mathrm{O},2\mathrm{p})^{28}\mathrm{Mg}$ fusion-evaporation reaction to investigate the impact of shell evolution on its high-lying structure. Three new levels were identified at 7203(3), 7747(2), and 7929.3(12) keV along with several new gamma rays. A newly extracted $B(E2;{4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ of 42(7) ${e}^{2}{\mathrm{fm}}^{4}$ indicates reduced collectivity in the yrast band at high spin, consistent with ab initio symmetry adapted no-core shell model (SA-NCSM) calculations. At high excitation energy, evidence for the population of intruder orbitals was obtained through identification of negative parity levels $[{I}^{\ensuremath{\pi}}={(0,4)}^{\ensuremath{-}}$, ${(4,5)}^{\ensuremath{-}}]$. Calculations using the SDPF-MU interaction indicate that these levels arise from single neutron excitation to the $pf$ shell and provides evidence for the lowering of these intruder orbitals approaching the island of inversion.

The Tz=−32 nucleus 21Mg has been studied by Coulomb excitation on 196Pt and 110Pd targets. A 205.6(1)-keV γ-ray transition resulting from the Coulomb excitation of the 52+ ground state to the first excited 12+ state in 21Mg was observed for the first time. Coulomb excitation cross-section measurements with both targets and a measurement of the half-life of the 12+ state yield an adopted value of B(E2;52+→12+)=13.3(4) W.u. A new excited state at 1672(1) keV with tentative 92+ assignment was also identified in 21Mg. This work demonstrates a large difference in the B(E2;52+→12+) value between T=32, A=21 mirror nuclei. The difference is investigated in the shell-model framework employing both isospin conserving and breaking USD interactions and using modern ab initio nuclear structure calculations, which have recently become applicable in the sd shell. (Less)

Materials possessing a defect-fluorite pyrochlore structure can have a range of useful properties that are sought after, which include their radiation tolerance, nuclear waste immobilization, and phase stability at elevated temperatures. In this study, we demonstrate for the first time the synthesis and a detailed analysis of defect-fluorite pyrochlore sodium niobate (NaNbO3) nanoparticles. This analysis included an investigation into their stability to elevated temperatures and neutron irradiation. A surfactant-assisted solvothermal method is used to prepare nanoparticles of NaNbO3. This solution-phase approach results in the formation of crystalline nanoparticles of a defect-fluorite pyrochlore NaNbO3 at relatively low temperatures. The products had an average diameter of ∼74 ± 11 nm. The nanoparticles adopted a defect-fluorite pyrochlore phase and matched the cubic Fm3[combining macron]m space group. This pyrochlore form of NaNbO3 was found to be stable up to 500 °C. The nanoparticles transformed into the orthorhombic and rhombohedral perovskite phases of NaNbO3 along with the introduction of a pseudo-hexagonal Nb2O5 at higher temperatures. These defect-fluorite pyrochlore nanoparticles of NaNbO3 also exhibited a resistance to radiation induced amorphization. The dimensions, phase, and crystallinity of the defect-fluorite pyrochlore nanoparticles after exposure to a flux of neutrons were comparable to those of the as-synthesized product. The thermal stability and radiation tolerance of these pyrochlore nanoparticles could be useful in the design of thermally resilient materials, high temperature catalysts, and durable materials for the handling and storage of radioactive waste.

New rotational bands built on the ν(h_{11/2}) configuration have been identified in ^{105}Pd. Two bands built on this configuration show the characteristics of transverse wobbling: the ΔI=1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the A∼100 mass region.

The 117mSn isotope was produced via fast, 14.1MeV neutron activation of natural tin and studied with a background shielded HPGe detector. To enable time-resolved γ-ray spectroscopy to precisely measure the half-life of 117mSn, a commercial DAQ was replaced with a CAMAC-based analogue DAQ. The deadtime response of the applied DAQ was verified for the measurement. The half-life of 117mSn was measured to be 13.91±0.03 days and the I(158.6keV)/I(156.0keV) γ-ray ratio was measured to be 43.6±1.5.

Solid experimental evidence for triaxial nuclear shape is difficult to obtain and is quite rare. Such evidence can be provided by the phenomena of chiral rotation and wobbling motion, as these can occur only in triaxially deformed nuclei. Although nuclear chirality is well documented in different mass regions, experimental evidence for multiple chiral bands as well as for wobbling motion has been reported so far only in a few nuclei. Pd and Rh nuclei in the A ≈ 100 mass region have been recently studied, and transverse wobbling motion as well as multiple chiral band structures were identified for the first time in this region. These observations provide experimental evidence for the predicted triaxial shape in this mass region, and new data which enable a better understanding of the studied phenomena.

An error was discovered in the extraction of the singles intensities in the original article. The corrections are reported in this erratum.

Background: The evolution of nuclear magic numbers at extremes of isospin is a topic at the forefront of contemporary nuclear physics. $N=50$ is a prime example, with increasing experimental data coming to light on potentially doubly magic $^{100}\mathrm{Sn}$ and $^{78}\mathrm{Ni}$ at the proton-rich and proton-deficient extremes, respectively; however, experimental discrepancies exist in the data for less exotic systems.Purpose: In $^{86}\mathrm{Kr}$ the $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value---a key indicator of shell evolution---has been experimentally determined by two different methodologies, with the results deviating by $3\ensuremath{\sigma}$. Here, we report on a new high-precision measurement of this value, as well as the first measured lifetimes and hence transition strengths for the ${2}_{2}^{+}$ and ${3}_{(2)}^{\ensuremath{-}}$ states in the nucleus.Methods: The Doppler-shift attenuation method was implemented using the TRIUMF-ISAC $\ensuremath{\gamma}$-ray escape-suppressed spectrometer (TIGRESS) $\ensuremath{\gamma}$-ray spectrometer and the TIGRESS integrated plunger device. High-statistics Monte Carlo simulations were utilized to extract lifetimes in accordance with state-of-the-art methodologies.Results: Lifetimes of $\ensuremath{\tau}({2}_{1}^{+})=336\ifmmode\pm\else\textpm\fi{}4\text{(stat.)}\ifmmode\pm\else\textpm\fi{}20\text{(sys.)}$ fs, $\ensuremath{\tau}({2}_{2}^{+})=263\ifmmode\pm\else\textpm\fi{}9\text{(stat.)}\ifmmode\pm\else\textpm\fi{}19\text{(sys.)}$ fs, and $\ensuremath{\tau}({3}_{(2)}^{\ensuremath{-}})=73\ifmmode\pm\else\textpm\fi{}6\text{(stat.)}\ifmmode\pm\else\textpm\fi{}32\text{(sys.)}$ fs were extracted. This yields a transition strength for the first-excited state of $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})=259\ifmmode\pm\else\textpm\fi{}3\text{(stat.)}\ifmmode\pm\else\textpm\fi{}16\text{(sys.)}$ ${e}^{2}$ ${\mathrm{fm}}^{4}$.Conclusions: The measured lifetime disagrees with the previous Doppler-shift attenuation method measurement by more than $3\ensuremath{\sigma}$, while agreeing well with a previous value extracted from Coulomb excitation. The newly extracted $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})$ value indicates a more significant reduction in the $N=50$ isotones approaching $Z=40$.

Three- and two-level mixing models are proposed to understand the doubling of states at the same spin and parity in triaxially-deformed atomic nuclei with odd numbers of protons and neutrons. The Particle-Rotor Model for such nuclei is solved using the newly proposed basis which couples angular momenta of two valence nucleons and the rotating triaxial mean-field into left-handed $|\mathcal{L}\rangle$, right-handed $|\mathcal{R}\rangle$, and planar $|\mathcal{P}\rangle$ configurations. The presence and the impact of the planar component is investigated as a function of the total spin for mass A$\approx$130 nuclei with the valence h$_{11/2}$ proton particle, valence h$_{11/2}$ neutron hole and the maximum difference between principle axes allowed by the quadrupole deformation of the mean field. It is concluded that at each spin value the higher-energy member of a doublet of states is built on the anti-symmetric combination of $|\mathcal{L}\rangle$ and $|\mathcal{R}\rangle$ and is free of the $|\mathcal{P}\rangle$ component, indicating that it is of pure chiral geometry. For the lower-energy member of the doublet, the contribution of the $|\mathcal{P}\rangle$ component to the eigenfunction first decreases and then increases as a function of the total spin. This trend as well as the energy splitting between the doublet states are both determined by the Hamiltonian matrix elements between the planar ($|\mathcal{P}\rangle$) and non-planar ($|\mathcal{L}\rangle$ and $|\mathcal{R}\rangle$) subspaces of the full Hilbert space., 12 pages, 5 figures, accepted as a Rapid Communication in Physical Review C

A method is proposed for establishing the absolute efficiency calibration of a HPGe detector including the confidence interval in the energy range of 79.6–3451.2 keV. The calibrations were accomplished with the 133 Ba, 60 Co, 56 Co and 152 Eu point-like radioactive sources with only the 60 Co source being activity calibrated to an accuracy of 2% at the 90% confidence level. All data sets measured from activity calibrated and uncalibrated sources were fit simultaneously using the linearized least squares method. The proposed fit function accounts for scaling of the data taken with activity uncalibrated sources to the data taken with the high accuracy activity calibrated source. The confidence interval for the fit was found analytically using the covariance matrix. Accuracy of the fit was below 3.5% at the 90% confidence level in the 79.6–3451.2 keV energy range.

The $g$ factor of the 56 ns half-life isomeric state in $^{128}\mathrm{Cs}$ has been measured using the time-differential perturbed angular distribution method. This state is the bandhead of the positive-parity chiral rotational band, which emerges when an unpaired proton, an unpaired neutron hole, and an even-even core are coupled such that their angular momentum vectors are aplanar (chiral configuration). $g$-factor measurements can give important information on the relative orientation of the three angular momentum vectors. The measured $g$ factor $g=+0.59(1)$ shows that there is an important contribution of the core rotation in the total angular momentum of the isomeric state. Moreover, a quantitative theoretical analysis supports the conclusion that the three angular momentum vectors lie almost in one plane, which suggests that the chiral configuration in $^{128}\mathrm{Cs}$ demonstrated in previous works by characteristic patterns of electromagnetic transitions appears only above some value of the total nuclear spin.

Electromagnetic transition rate measurements play an important role in characterizing the evolution of nuclear structure with increasing proton-neutron asymmetry. At TRIUMF, the TIGRESS Integrated Plunger device and its suite of ancillary detector systems have been implemented for charged-particle tagging and light-ion identification in coincidence with gamma-ray spectroscopy for Doppler-shift lifetime studies and low-energy Coulomb excitation measurements. Digital pulse-shape analysis of signals from these ancillary detectors for particle identification improves the signal-to-noise ratio of gamma-ray energy spectra. Here, we illustrate the reaction-channel selectivity achieved by utilizing digital rise-time discrimination of waveforms from alpha particles and carbon ions detected with silicon PIN diodes, thereby enhancing gamma-ray line-shape signatures for precision lifetime studies.

The 116Sn nucleus was studied via the $\beta^{-}$ decay of 116In utilizing the $8\pi$ spectrometer and its auxiliary detectors at TRIUMF-ISAC. The resulting K-shell conversion coefficients, K/L ratios, and multipole mixing ratios are presented. The $2_{3}^{+} \rightarrow 2_{1}^{+} 931$ keV and $ 2_{2}^{+} \rightarrow 2_{1}^{+} 819$ keV transition mixing ratios were re-measured and found to be $ \delta = +1.8_{-0.5}^{+0.7}$ and $ -1.83(8)$ , respectively. Newly measured mixing ratios for transitions among the low-lying $ I^{\pi} = 4^{+}$ states in 116Sn, when combined with $\gamma$ -ray intensity data, suggest that the 2529 keV $4_{2}^{+}$ state possesses a neutron broken-pair admixture in addition to its dominant proton 2p-2h component.

A new $\beta^{+}$ /EC branch of $0.11\pm 0.02$ % from the $(7)^{+}$ isomer of 124Cs was identified in a measurement of the decay of 124Cs using the $8\pi$ spectrometer at TRIUMF. Combinations of $\gamma$ - $\gamma$ , $\gamma$ - $e^{-}$ , and $e^{-}$ - $e^{-}$ coincidence data were used to further investigate the isomeric decay. Six new transitions were observed and their branching ratios were measured.

At TRIUMF, the TIGRESS Integrated Plunger device and its suite of ancillary detector systems have been implemented for charged-particle tagging and light-ion identification in coincidence with $\ensuremath{\gamma}$-ray spectroscopy for Doppler-shift lifetime studies and low-energy Coulomb excitation measurements. As a test of the device, the lifetime of the first ${2}^{+}$ excited state in $^{36}\mathrm{Ar}$ was measured from the $\ensuremath{\gamma}$-ray line shape of the ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{g}.\mathrm{s}.}^{+}$ transition using the Doppler-shift attenuation technique following Coulomb excitation. The line-shape signatures, vital for precision lifetime measurements, were significantly improved by enhanced reaction-channel selectivity using a complementary approach of kinematic gating and digital rise-time discrimination of recoiling charged particles in a silicon PIN diode array. The lifetime was determined by comparisons between the data and simulated line shapes generated using our TIGRESS Coulomb excitation code as an input to the Lindhard method, which was then extended and included as a class in geant4. The model-independent lifetime result of $490\ifmmode\pm\else\textpm\fi{}50$ fs corresponds to a reduced quadrupole transition strength of $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{g}.\mathrm{s}.}^{+})=56\ifmmode\pm\else\textpm\fi{}6\phantom{\rule{0.28em}{0ex}}{\mathrm{e}}^{2}{\mathrm{fm}}^{4}$ and agrees well with previous intermediate energy Coulomb excitation measurements, thereby resolving reported discrepancies in the ${2}_{1}^{+}$ level lifetime in this self-conjugate nucleus.

The 116Sn nucleus contains a collective rotational band originating from proton $\pi$ 2p-2h excitations across the proton $Z=50$ shell gap. Even though this nucleus has been extensively investigated in the past, there was still missing information on the low-energy interband transitions connecting the intruder and normal structures. The low-lying structure of 116Sn was investigated through a high-statistics study of the $\beta^{-}$ decay of 116m1In with the $8\pi$ spectrometer and its ancillary detectors at TRIUMF. These measurements are critical in order to properly characterize the $\pi$ 2p-2h rotational band. Weak $\gamma$ -decay branches are observed utilizing $\gamma$ - $\gamma$ coincidence spectroscopy methods, leading to the first direct observation of the 85 keV $2_{2}^{+}\rightarrow 0_{3}^{+}$ $\gamma$ ray with a transition strength of $B(E2) = 99.7(84)$ W.u. The analysis of these results strongly suggests that the 2027 keV $0_{3}^{+}$ state should replace the previously assigned 1757 keV $0_{2}^{+}$ state as the band-head of the $\pi$ 2p-2h rotational band.

The TIGRESS Integrated Plunger device is a new experimental tool for nuclear structure investigations via gamma-ray spectroscopy with post-accelerated beams from the ISAC-II facility at TRIUMF. Several ancillary detection systems integral to the device׳s capabilities for charged-particle tagging and light-ion identification following a variety of nuclear reaction mechanisms have been constructed and characterized. In particular, a silicon PIN diode wall, an annular silicon segmented detector, and a CsI(Tl) scintillator wall have together enabled particle-gamma correlations for reaction channel selectivity and precision kinematic reconstruction in recent measurements. We highlight the construction, characteristics, and implementation of the device׳s ancillary detectors as they enable a rich set of electromagnetic transition rate measurements via Doppler-shift lifetime techniques and low-energy Coulomb excitation.

The electromagnetic dipole strength in Be 11 between the bound states has been measured using low-energy projectile Coulomb excitation at bombarding energies of 1.73 and 2.09 MeV/nucleon on a Pt 196 target. An electric dipole transition probability B ( E 1 ; 1 / 2 − → 1 / 2 + ) = 0.102 ( 2 ) e 2 fm 2 was determined using the semi-classical code Gosia, and a value of 0.098 ( 4 ) e 2 fm 2 was determined using the Extended Continuum Discretized Coupled Channels method with the quantum mechanical code FRESCO. These extracted B ( E 1 ) values are consistent with the average value determined by a model-dependent analysis of intermediate energy Coulomb excitation measurements and are approximately 14 % lower than that determined by a lifetime measurement. The much-improved precisions of 2% and 4% in the measured B ( E 1 ) values between the bound states deduced using Gosia and the Extended Continuum Discretized Coupled Channels method, respectively, compared to the previous accuracy of ∼ 10 % will help in our understanding of and better improve the realistic inter-nucleon interactions.

For targets requiring thick backing foils, the straight-forward and usual method is to deposit the target material directly on the backing by thermal evaporation. In some instances the reverse is more desirable, adding a backing to an already existing target foil, for example. A recent study involving measurement of the lifetime of the first 2+ excited state in 36Ar by the Doppler shift attenuation method required 0.5 mg/cm2 natural carbon targets on thick (18 mg/cm2) gold and lead backings. Problems of delamination had arisen after beam irradiation using thick gold backings for these experiments. Carbon target foils were then prepared by mechanical rolling in direct contact with a thick lead backing using an intermediate layer of indium to assure good adhesion of the layers. Details of the method will be discussed.

The Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new experimental facility for radioactive decay studies at the TRIUMF-ISAC laboratory. The performance of the 16 high-purity germanium (HPGe) clover detectors that will make up the GRIFFIN spectrometer is reported. The energy resolution, efficiency, timing resolution, crosstalk and preamplifier properties of each crystal were measured using a combination of analog and digital data acquisition techniques. The absolute efficiency and add-back factors are determined for the energy range of 80–3450 keV. The detectors show excellent performance with an average over all 64 crystals of a FWHM energy resolution of 1.89(6) keV and relative efficiency with respect to a 3 in . × 3 in . NaI detector of 41(1)% at 1.3 MeV.

High precision measurements of the $ft$ values for superallowed Fermi $\beta$ transitions between $J^\pi~=~0^+$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the Conserved-Vector-Current hypothesis, enable the most precise determination of the up-down ($V_{ud}$) element of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix, and allow one to set stringent limits on the existence of scalar currents in the weak interaction. An extensive program of superallowed branching-ratio and half-life measurements at TRIUMF's Isotope Separator and Accelerator (ISAC) facility has covered the full range of superallowed emitters, from the lightest case, $^{10}$C, to the heaviest case for which precision data are currently available, $^{74}$Rb. These experiments have been performed using a 4$\pi$ continuous-flow gas proportional $\beta$ counter, the 8$\pi$ $\gamma$-ray spectrometer, and, most recently, the new high-efficiency GRIFFIN $\gamma$-ray spectrometer. In this paper, recent highlights from the superallowed Fermi $\beta$ decay program at TRIUMF will be summarized, including high-precision half-life measurements for all three of the lightest superallowed emitters, $^{10}$C, $^{14}$O, and $^{18}$Ne, with the greatest sensitivity to a potential weak scalar current contribution, as well as high-precision branching-ratio measurements for the heavy superallowed emitters $^{62}$Ga and $^{74}$Rb.

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First predictions for a specific case of the particle-hole-core coupling model which takes advantage of symmetries of a triaxial rotor with γ = 90° are reviewed. Results of the model calculations point towards existence of stable chiral geometry in specific configurations involving high-j orbitals. Next, experimental information on doublet bands built on unique parity, πh11/2νh11/2 intruder states in odd-odd 134 Pr is discussed; in particular observed disagreements between electromagnetic transitions within the doublet structures which is pointed out as inconsistent with the simplest models. Finally, the unique experimental infrastructure developed at the Tri-University Meson Facility (TRIUMF) Canada's National Laboratory for Particle and Nuclear Physics is presented including a range of isotopes in the mass 130 region that are accessible as beams and which can possibly yield significant new information in investigations of nuclear chirality.

Multi-layer thin targets are vital in low-energy nuclear physics experiments employing the use of accelerated beams. In this paper, we describe the fabrication of encapsulated calcium targets produced by evaporation on gold and lead backings for radioactive beam experiments at TRIUMF’s ISAC-II facility.

A 624-channel Digital Data Acquisition System capable of instrumenting the Segmented Germanium Array at National Superconducting Cyclotron Laboratory has been implemented using Pixie-16 Digital Gamma Finder modules by XIA LLC. The system opens an opportunity for determination of the first interaction position of a γ ray in a SeGA detector from implementation of γ ‐ ray tracking. This will translate into a significantly improved determination of angle of emission, and in consequence much better Doppler corrections for experiments with fast beams. For stopped-beam experiments the system provides means for zero dead time measurements of rare decays, which occur on time scales of microseconds.

A detailed, universal simulation tool for the Recoil Distance Method lifetime measurements at the National Superconducting Cyclotron Laboratory (NSCL) is presented. The measurements are made with the Koln-NSCL plunger-SeGA setup and utilize fast, secondary beams of exotic nuclei provided by the Coupled Cyclotron Facility and the A1900 fragment separator. The simulation tool, built upon GEANT4 and Root toolkits, incorporates all relevant aspects of a plunger experiment. The tool is applied in two ways. First, to aid in the design of new experiments by facilitating the choice of optimal experimental conditions. Second, to aid in off-line analysis of the experimental data and in particular to deduce the lifetime by comparison of experimental and simulated peak shapes in the γ -ray energy spectra. All the important features of the simulation tool are described, followed by examples of the application of the tool in the cases of real experiments completed or proposed at NSCL.

The first 2+ states in 134Ce and 136Nd and the second 2+ state in 136Nd were populated by Coulomb excitation at relativistic energies, and γ-rays were measured using the RISING setup at GSI. For 134Ce an indication of the excitation to the second 2+ state was observed. This experiment performed for the first time Coulomb excitation to second 2+ states with rare isotope beams at relativistic energies. For 136Nd the B ( E 2 ; 2 1 + → 0 + ) , B ( E 2 ; 2 2 + → 0 + ) , and B ( E 2 ; 2 2 + → 2 1 + ) values relative to the previously known B ( E 2 ; 2 1 + → 0 + ) value for 134Ce are determined as 81(10), 11(3) and 180(92) W.u., respectively. The results are discussed in the framework of geometrical models that indicate pronounced γ-softness in these nuclei.

We describe a high efficiency detector for measuring electron-positron pair transitions in nuclei. The device was built to be insensitive to gamma rays and to accommodate high overall event rates. The design was optimized for total pair kinetic energies up to about 7 MeV., Accepted for publication by Nucl. Inst. & Meth. in Phys. Res. A (NIM A)

Shape coexistence between the strongly deformed ground state and the weakly deformed ${0}_{2}^{+}$ state in $^{98}\mathrm{Sr}$ has been a major topic of interest due to the energy difference of 215 keV, which is the smallest in all even-even nuclei. The electric monopole transition strength ${\ensuremath{\rho}}^{2}(E0)$ is an important quantity that can relate the deformation difference and the shape mixing between the two ${0}^{+}$ states, which are admixtures of the vibrational (S) and the rotational (D) states in a simple mixing model. In a $\ensuremath{\beta}$-decay spectroscopy experiment, the experimental ${\ensuremath{\rho}}^{2}(E0)$ was measured. A value of 0.053(5) is consistent with the previous measurement and was combined with known electric quadrupole transition strengths $B(E2)$ in calculations of a two-state mixing model. Based on a systematic study on neighboring Kr, Zr, and Mo isotopes, the mixing of the ${0}^{+}$ and ${2}^{+}$ states in $^{98}\mathrm{Sr}$ was determined to be 8.6% and 1.3%, respectively, corresponding to deformation parameters ${\ensuremath{\beta}}_{\text{D}}=0.38(1)$ and ${\ensuremath{\beta}}_{\text{S}}=\ensuremath{-}0.23(2)$. These parameters reproduce experimental transition strengths well except for the ${4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+}$ transition, which suggests a smaller D-band deformation for $J\ensuremath{\ge}4$.

The 113Ru and 113Rh nuclei, produced in the spontaneous fission of 248Cm and in proton-induced fission of 238U , were studied by means of prompt gamma spectroscopy using the EUROGAM 2 array of Anti-Compton spectrometers and the IGISOL mass separator, respectively. For the 0.5s isomer, found in 113Ru in our recent study we propose the 7/2-[523] configuration. The present data indicate spin and parity 1/2+ for the ground state in 113Ru . This and some new data on the excited levels in 113Rh allows reinterpretation and a better understanding of the β- {} decay scheme of 113Ru . The properties of 113Ru were studied in the frame of the Core-Quasiparticle Coupling model, which has well reproduced the experimental data.

Quadrupole deformation parameters, | β 2 , ( p , p ′ ) | , have been deduced for 36,38,40Si from measured inelastic proton-scattering cross sections. Due to the strong Z = 14 subshell gap, low-lying quadrupole collectivity in these nuclei is attributed to the excitation of valence neutrons. Enhanced collectivity at N = 26 indicates a reduced N = 28 shell gap at large neutron excess in this chain of isotopes. Data are compared to large-scale shell-model calculations and prior Coulomb excitation measurements on 36,38Si.

The nuclear structure of $^{124}\mathrm{Xe}$ has been investigated via measurements of the ${\ensuremath{\beta}}^{+}$/EC decay of $^{124}\mathrm{Cs}$ with the $8\ensuremath{\pi}\ensuremath{\gamma}$-ray spectrometer at the TRIUMF-ISAC facility. The data collected have enabled branching ratio measurements of weak, low-energy transitions from highly excited states, and the ${2}^{+}\ensuremath{\rightarrow}{0}^{+}$ in-band transitions have been observed. Combining these results with those from a previous Coulomb excitation study, $B(E2;{2}_{3}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})=78(13)$ W.u. and $B(E2;{2}_{4}^{+}\ensuremath{\rightarrow}{0}_{3}^{+})=53(12)$ W.u. were determined. The ${0}_{3}^{+}$ state, in particular, is interpreted as the main fragment of the proton-pairing vibrational band identified in a previous $^{122}\mathrm{Te}$($^{3}\mathrm{He},n$)$^{124}\mathrm{Xe}$ measurement, and has quadrupole collectivity equal to, within uncertainty, that of the ground-state band.

Three strongly coupled sequences have been established in Te-110,Te-112 up to high spins. They are interpreted in terms of deformed structures built on proton 1-particle-1-hole excitations that reach termination at I similar to 40h. This is the first observation of smooth terminating dipole structures in this mass region. Lifetime measurements have allowed the extraction of experimental B(M 1; 1 -> I - 1) and B(E2; I -> I - 2) reduced transition rates for one of the dipole bands in Te-110. The results support the deformed interpretation. (c) 2006 Elsevier B.V. All rights reserved.

Current work explores the impact of gamma-softness on partner bands built on the h11/2h11/2 proton-particle-neutron-hole configurations in triaxial odd-odd nuclei. The results of calculations conducted using a core-particle-hole coupling are presented. The model Hamiltonian includes the collective core, the single-particle valence nucleons, and separable quadrupole-quadrupole interactions. The Kerman-Klein method was applied to find eigenstates, which provided a convenient way for exploring core effects. Calculations were made for triaxial cores with various gamma-softness using the General Collective Model keeping the expectation value for the triaxiality parameter fixed at =30 deg. The degeneracy in the proton-neutron h11/2h11/2 bands results from the calculations for the gamma-rigid core but is lifted for the gamma-unstable core., Comment: 6 pages, 5 figures, Proceedings of the 21st Winter Workshop on Nuclear Dynamics, Breckenridge, Colorado, February 5-12, 2005