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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.

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

Chirality in atomic nuclei is a direct consequence of the existence of triaxial nuclear shapes. This phenomenon is known to exist in the A ~ 130 region. We have now observed several pair of bands built upon the negative parity configuration, πg−19/2 ⊗ νh11/2, in Rh and Tc isotopes in the A ~ 104 region which can be understood in terms of the phenomenon of chiral symmetry breaking. Results of the search for chiral bands in 106Ag are presented in the current paper.

Experimental properties of nearly degenerate ΔI = 1 doublet bands, which are built on the same single-particle configuration, are tested against three criteria for spontaneous formation of chirality in nuclei via the coupling of three mutually perpendicular angular momenta. Four representative nuclei, 134 Pr, 130 Cs, 104 Rh and 105 Rh are discussed. The doublet bands in these nuclei exhibit chiral characteristics except for 134 Pr, which shows a significant difference in electromagnetic properties between the two candidate chiral structures.

Two low lying positive-parity bands in 130Cs have been examined for chiral signatures. Small energy differences between the two bands, which have been previously observed, have been confirmed and the bands, as well as the number of transitions within and between the bands, extended. The intraband B(M1)/B(E2) ratios and B(M1)intraband/B(M1)interband ratios and the energy staggering parameter, S(I), have been deduced for these partner bands. The results are found to be consistent with a chiral interpretation for the two structures. Core–quasiparticle coupling model calculations have been performed to study 130Cs assuming a triaxial core. The experimental level energies and electromagnetic properties of the bands, resulting from the configuration, are reasonably well reproduced by the model, providing further evidence in support of the chiral interpretation of the two structures.

Excited states in 100Tc have been studied using the 96Zr( 7Li, 3n) reaction at a beam energy of 27 MeV. In the present work, evidence has been found for a second ΔI = 1 band decaying via several stretched dipole transitions to the previously known ΔI = 1 negative-parity band. Comparison of these data with those in neighbouring nuclei and also against recently reported criteria for chiral bands in nuclei, suggests that the two structures can be interpreted as chiral partners. Core quasi-particle coupling model calculations show reasonable agreement with the data and generally support the chiral interpretation of the states.

A novel background subtraction method for Doppler-shift attenuation and angular correlation measurements with large multi-detector HpGe arrays is presented. The formalism is designed for recently developed data base storage techniques with the event format resembling the original raw data structure. The background spectrum is constructed based on parameters extracted from one-dimensional spectra; the method, therefore, is complementary to currently applied methods which are designed for multi-dimensional, symmetrized histograms.

High-spin states in the doubly odd N = 77 nucleus 132Cs have been studied. Gamma-ray linear polarization and angular correlation measurements have been performed to determine the spin and parity of the states. A rotational sequence of enhanced dipole transitions was established. This band can be described within the framework of the the tilted axis cranking (TAC) model as a band based on a weakly deformed structure in which the total angular momentum vector does not coincide with any of the principal axes of the triaxial nucleus but still is in the plane defined by the short and long axes. The theoretical description of the previously proposed chiral bands in 132Cs was extended in the framework of the core–particle coupling model (CPCM) confirming that the total angular momentum for the πh11/2 ⊗ νh11/2 configuration is well outside any planes defined by the principal axes of the nucleus and revealing the important role of the residual proton–neutron interaction between the valence particles.

The ground state two-proton decay lifetime of Mg19, populated by the one-neutron knockout of an intermediate-energy Mg20 radioactive beam, was measured utilizing a new experimental technique. A thin silicon detector positioned at varying distances (0.0–1.0 mm) downstream of the reaction target measured the energy loss of Mg19 and the two-proton decay product Ne17. The lifetime was deduced from fits to the measured energy-loss line shapes and depended upon the contribution of prompt reaction processes to the yield of Ne17. For relative Ne17 prompt contributions from 82% to 92%, the extracted lifetimes ranged from 1.75+0.43−0.42 to 6.4+2.4−2.7 ps. The results are consistent with the previously reported Mg19 lifetime measurement and serve as both an important complementary study and a validation of this new technique, which can provide lifetime information for short-lived states beyond the proton drip line.

The high-spin structure of the nucleus ${}^{104}$Pd was studied through the ${}^{96}$Zr(${}^{13}$C,5$n$) reaction at incident energies of 51 and 58 MeV, using the Euroball IV $\ensuremath{\gamma}$-ray spectrometer in conjunction with the DIAMANT charged-particle array. Several new medium- and high-spin bands were revealed. The already known positive-parity yrast and the negative-parity cascades were extended up to ${E}_{x}\ensuremath{\sim}13$, $\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}11$, and $\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}9$ MeV with ${I}^{\ensuremath{\pi}}=({26}^{+}$), ${I}^{\ensuremath{\pi}}=({23}^{\ensuremath{-}}$), and (20${}^{\ensuremath{-}}$), respectively. The deduced band structures were compared with Woods-Saxon total Routhian surface (TRS) calculations. In addition, non-yrast low-lying positive-parity bands were identified, which were assigned to soft $\ensuremath{\gamma}$-vibrational excitations.

The ``island of the inversion'' isotope $^{31}\mathrm{Mg}$ was investigated using an intermediate energy proton knockout reaction from $^{32}\mathrm{Al}$ at 90 MeV/nucleon at the National Superconducting Cyclotron Laboratory. A negligible cross section to the ground state supports an intruder-dominant configuration in $^{31}\mathrm{Mg}$. The partial cross sections to excited final states preferentially populate configurations in the $^{31}\mathrm{Mg}$ residues which have no neutron excitations across the $N=20$ shell closure. There is strong evidence that the reaction populates the $3/{2}^{+}$ and $5/{2}^{+}$ states which correspond with the neutron-hole states predicted by the shell model with the model space truncated above the $\mathit{sd}$-shell.

Absolute transition probabilities for the first 2{sup +} states in {sup 110,114}Pd were measured using the recoil distance Doppler shift technique following projectile Coulomb excitation at intermediate beam energy. This technique was applied for the first time to projectiles produced in a primary fragmentation reaction, which get Coulomb excited in a secondary reaction. The {sup 110}Pd data was used to check the novel experimental technique as well as the data analysis procedure, which is based on the examination of {gamma}-ray line shapes. Whereas the measured B(E2) value for {sup 110}Pd agrees very well with the literature, the value obtained for {sup 114}Pd differs considerably. The new experimental data are compared to calculations in the framework of the Interacting Boson Model. The data are also used to test the novel concept of valence proton symmetry, which allows for extrapolation of nuclear properties to very neutron-rich nuclei.

Lifetimes of chiral candidate structures in {sup 103,104}Rh were measured using the recoil distance Doppler-shift method. The Gammasphere detector array was used in conjunction with the Cologne plunger device. Excited states of {sup 103,104}Rh were populated by the {sup 11}B({sup 96}Zr,4n){sup 103}Rh and {sup 11}B({sup 96}Zr,3n){sup 104}Rh fusion-evaporation reactions in inverse kinematics. Three and five lifetimes of levels belonging to the proposed chiral doublet bands are measured in {sup 103}Rh and {sup 104}Rh, respectively. The previously observed even-odd spin dependence of the B(M1)/B(E2) values is caused by the variation in the B(E2) values, whereas the B(M1) values decrease as a function of spin.

The high-spin structure of the $^{105}\mathrm{Ag}$ nucleus has been studied by using the $^{100}\mathrm{Mo}$($^{10}\mathrm{B}$, $5n)$$^{105}\mathrm{Ag}$ reaction to search for chiral doublet bands based on the three-quasiparticle $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}({h}_{11/2}){}^{2}$ configuration. The level scheme of $^{105}\mathrm{Ag}$ has been extended. New bands were found and the placement of the yrast $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}({h}_{11/2}){}^{2}$ band was corrected. No side band to the yrast $\ensuremath{\pi}{g}_{9/2}\ensuremath{\nu}({h}_{11/2}){}^{2}$ band could be found in the present experiment. This observation indicates that the \ensuremath{\gamma}-soft shape in the $^{106}\mathrm{Ag}$ changed to a more \ensuremath{\gamma}-rigid axially symmetric shape in the yrast $^{105}\mathrm{Ag}$ configuration. However, a new pair of bands was observed to show the expected properties of a chiral doublet structure.

The Gammasphere spectrometer, in conjunction with the Microball charged-particle array, was used to investigate high-spin states in Te-112 via Ni-58(Ni-58, 4p gamma) reactions at 240 and 250 MeV. Several smooth terminating bands were established, and lifetime measurements were performed for the strongest one using the Doppler-shift attenuation method. Results obtained in the spin range 18-32h yield a transition quadrupole moment of 4.0 +/- 0.5eb, which corresponds to a quadrupole deformation epsilon(2)=0.26 +/- 0.03; this value is significantly larger than the ground-state deformation of tellurium isotopes. It was also possible to extract a transition quadrupole moment for the yrast band in Xe-114, produced via the 58Ni (58Ni, 2p gamma) reaction. A value of 3.0 +/- 0.5eb was found in the spin range 16-24h, which corresponds to a quadrupole deformation epsilon(2)=0.19 +/- 0.03. Cranked Nilsson-Strutinsky calculations are used to interpret the results. (Less)

In applications with segmented high purity Ge detectors or other detector arrays with tens or hundreds of channels, where the high development cost and limited flexibility of application specific integrated circuits outweigh their benefits of low power and small size, the readout electronics typically consist of multi-channel data acquisition modules in a common chassis for power, clock and trigger distribution, and data readout. As arrays become larger and reach several hundred channels, the readout electronics have to be divided over several chassis, but still must maintain precise synchronization of clocks and trigger signals across all channels. This division becomes necessary not only because of limits given by the instrumentation standards on module size and chassis slot numbers, but also because data readout times increase when more modules share the same data bus and because power requirements approach the limits of readily available power supplies. In this paper, we present a method for distributing clocks and triggers between 4 PXI chassis containing DGF Pixie-16 modules with up to 226 acquisition channels per chassis in a data acquisition system intended to instrument the over 600 channels of the SeGA detector array at the National Superconducting Cyclotron Laboratory. Our solution is designed to achieve synchronous acquisition of detector waveforms from all channels with a jitter of less then 1 ns, and can be extended to a larger number of chassis if desired., Comment: CAARI 2006

The {alpha} decay of the neutron-deficient nuclide {sup 105}Te was observed. The {sup 50}Cr({sup 58}Ni,3n) reaction was used to produce {sup 105}Te nuclei. The {sup 105}Te residues were selected with the Argonne Fragment Mass Analyzer and implanted into a double-sided Si strip detector where their subsequent {alpha} decay was detected. An {alpha}-decay Q value of Q{sub {alpha}}=4900(50) keV and a half life of T{sub 1/2}=0.70(-0.17+0.25){mu}s were measured for {sup 105}Te and a reduced {alpha}-decay width of W{sub {alpha}}=3.3(-1.7+2.1) was deduced. The decay properties of {sup 105}Te are compared with those of heavier Te isotopes and theoretical predictions.

The nucleus $^{160}\mathrm{Er}$, with the structural parameter ${R}_{4/2}=E({4}_{1}^{+})/E({2}_{1}^{+})=3.10$, falls on the transition path between the critical point of the vibrator-rotor shape phase transition and the rigid rotor limit, thus serving as a critical test of the CBS rotor model, which describes this transition region. Medium-spin states of $^{160}\mathrm{Er}$ have been populated via the reaction $^{159}\mathrm{Tb}$($^{6}\mathrm{Li}$,5n) and new levels have been identified and interpreted as the even-spin members of the \ensuremath{\gamma} band and members of the \ensuremath{\beta} vibrational band. Level energies and branching ratios are compared to the CBS rotor model predictions.

A novel method for picosecond lifetime measurements of excited gamma-ray emitting nuclear states has been developed for fast beams from fragmentation reactions. A test measurement was carried out with a beam of 124Xe at an energy of ~55 MeV/u. The beam ions were Coulomb excited to the first 2+ state on a movable target. Excited nuclei emerged from the target and decayed in flight after a distance related to the lifetime. A stationary degrader positioned downstream with respect to the target was used to further reduce the velocity of the excited nuclei. As a consequence, the gamma-ray decays from the 2+ excited state that occurred before or after traversing the degrader were measured at a different Doppler shift. The gamma-ray spectra were analyzed from the forward ring of the Segmented Germanium Array; this ring positioned at 37 deg. simultaneously provides the largest sensitivity to changes in velocity and the best energy resolution. The ratio of intensities in the peaks at different Doppler shifts gives information about the lifetime if the velocity is measured. The results and range of the application of the method are discussed., Comment: 24 pages, 10 figures

Parity is a key observable in nuclear spectroscopy. Linear polarization measurements of $\gamma$-rays are a probe to access the parities of energy levels. Utilizing the segmentation of detectors in the Segmented Germanium Array (SeGA) at the NSCL and analyzing the positions of interaction therein allows the detectors to be used as Compton polarimeters. Unlike other segmented detectors, SeGA detectors are irradiated from the side to utilize the transversal segmentation for better Doppler corrections. Sensitivity in such an orientation has previously been untested. A linear polarization sensitivity $Q \approx 0.14$ has been measured in the 350-keV energy range for SeGA detectors using $\alpha$-$\gamma$ correlations from a \nuc{249}{Cf} source., Comment: 7 pages, 9 figures

We have measured the lifetime of the T=0,J{sup {pi}}=3{sub 1}{sup +} state of {sup 58}Cu at 444 keV. The excited states in {sup 58}Cu were populated with the {sup 58}Ni(p,n{gamma}) reaction at the SUNY at Stony Brook TANDEM-LINAC facility. A lifetime {tau} = 0.468 {+-} 0.085 ns was found with the delayed {gamma}-radiofrequency coincidence method with respect to the pulsed LINAC beam. It corresponds to an isoscalar E2 transition strength of 7.6 {+-} 1.4 W.u. to the T=0,J{sup {pi}}=1{sub 1}{sup +} ground state. The result agrees with the interpretation of the 3{sub 1}{sup +} state as a collective quadrupole excitation of the 1{sub 1}{sup +} ground state of {sup 58}Cu.

High-spin states in the nucleus $^{102}\mathrm{Ru}$ have been investigated via the $^{96}\mathrm{Zr}$($^{13}\mathrm{C}$,\ensuremath{\alpha}3n) reaction at beam energies of 51 and 58 MeV, using the euroball IV \ensuremath{\gamma}-ray spectrometer and the diamant charged particle array. Several new high-spin bands have been established. The ground-state band has been extended up to ${E}_{x}~12$ MeV with ${I}^{\ensuremath{\pi}}=({26}^{+}$); the previously published negative-parity bands have been extended up to ${E}_{x}~11$ and \ensuremath{\sim} 9 MeV with ${I}^{\ensuremath{\pi}}=({23}^{\ensuremath{-}}$) and $({20}^{\ensuremath{-}})$, respectively. The deduced high-spin structure has been compared with Woods-Saxon total Routhian surface calculations and, on the basis of the measured Routhians, aligned angular momenta, and $B(M1)/B(E2)$ ratios, $\ensuremath{\nu}{h}_{11/2}({g}_{7/2},{d}_{5/2}$) configurations are suggested for the negative-parity structures.

Excited states of the nucleus $^{102}\mathrm{Ru}$ have been studied using the $^{96}\mathrm{Zr}$($^{10}\mathrm{B}$,$p3n$) reaction at a beam energy of $42\phantom{\rule{0.3em}{0ex}}\text{MeV}$. The emitted \ensuremath{\gamma} rays were detected with the Gammasphere spectrometer. The known positive-parity structure built on the second ${2}^{+}$ state was extended up to the ${10}^{+}$ and ${11}^{+}$ states. This structure has been interpreted as a quasi-\ensuremath{\gamma} band. Its energy staggering as a function of spin has been analyzed in order to derive information on the type of triaxiality present in $^{102}\mathrm{Ru}$, a nucleus that serves as one of the cores for chiral structures in the mass $A\ensuremath{\approx}100$ region.

High-spin states in the doubly odd $N=77$ nucleus ${}^{132}\mathrm{Cs}$ have been studied. The known positive-parity structures have been extended. $\ensuremath{\gamma}$-ray linear-polarization and angular-correlation measurements have been performed to establish the spin and parity assignment of these structures. A new chiral partner of the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ band has been proposed. Three-dimensional tilted axis cranking model calculations have been performed and compared with the experimental results.

Chiral partner candidate bands have been found in $^{103}\mathrm{Rh}$. As a result of this observation, a special quartet of neighboring chiral candidate nuclei can be investigated for the first time. With this quartet identified, a comparison between the behavior of the nearly degenerate doublet bands belonging to the same core but to different valence quasiparticle configurations, as well as belonging to different cores but to the same valence quasiparticle configuration, becomes possible. The comparison shows that the energy separation of these doublet band structures depends mainly on the core properties and to a lesser extent on the valence quasiparticle coupling. This observation sets up new criteria for the explanations of the band doublings, restricting the possible scenarios and providing new information on the characteristics of the underlying mechanism; it is in qualitative agreement with the chiral scenario.

High-spin states in 105 Rh were populated by the 96 Zr( 13 C, p3n) reaction at beam energies of 51 and 58 MeV, and studied using the EUROBALL IV γ -ray spectrometer and the DIAMANT charged particle array. A pair of nearly degenerate Δ I = 1 three-quasiparticle bands with the same spins and parity have been observed. Comparison of the experimental results with tilted axis cranking calculations confirms the chiral character of the two bands, while arguments based on the excitation of particles within the π g 9 / 2 ν ( h 11 / 2 ) 2 configuration of the yrast band and comparison with the previously observed γ band exclude the other possible interpretations. This is the first experimental evidence for three-quasiparticle chiral structure in the A ∼ 100 region, and the first simultaneous observation of a γ band and chiral partner bands in one nucleus.

International audience; 136 P. Joshi et al. / Physics Letters B 595 (2004) 135–142AbstractThe nucleus 106Rh was populated using the reaction 96Zr(13C, p2n) at a beam energy of 51 MeV. γ -ray transitions wereidentified using the EUROBALL-IV γ -ray spectrometer and the DIAMANT charged particle array. The yrast band, which isbased upon a πg−19/2 ⊗ νh11/2 configuration, has been extended to I π = (22−). A new I = 1 band has been identified whichresides ∼ 300 keV above the yrast band. Core–quasiparticle coupling model calculations show reasonably good agreement withthe data. The properties of the two pairs of strongly coupled bands are consistent with a chiral interpretation for these states. 2004 Elsevier B.V