Search

The fusion cross section of 60 Ni + 100 Mo has been measured down to microbarn level, looking for hindrance at low energy, in a system with positive Q-values for neutron transfer. The measured cross sections look similar to those of the nearby 64 Ni + 100 Mo, but no conclusive statement can be made at this stage, as to the onset of hindrance in this system.

The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of ($\ensuremath{\alpha}$,$p$) reactions via high-lying resonances in $sd$-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the ($\ensuremath{\alpha}$,$p$) reaction to natural parity states. We measured the ${}^{28}$Si($p$,$t$)${}^{26}$Si reaction with a high-resolution spectrometer to identify resonance levels in ${}^{26}$Si above the $\ensuremath{\alpha}$-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the ${}^{22}$Mg($\ensuremath{\alpha}$,$p$)${}^{25}$Al reaction and to test the validity of the statistical assumption.

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{mu}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {approx}30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z=104, which describes nuclei with Z=92-103 very well.

The structure of 15 C, with an s1/2 neutron weakly bound to a closed-neutron shell nucleus 14 C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction 15 C + 232 Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring 14 C + 232 Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for 15 C, while the cross sections for 14 C match the trends measured for 12,13 C.

The structure of 15C, with an s1/2 neutron weakly bound to a closed-neutron shell nucleus 14C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction 15C + 232Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring 14C + 232Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for 15C, while the cross sections for 14C match the trends measured for 12,13C., 4 pages, 2 figures, Phys. Rev. Lett. (accepted)

Four previously known rotational bands in 76Rb have been extended to moderate spins using the Gammasphere and Microball gamma ray and charged particle detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g9/2 particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape co-existing structures at medium spins., Comment: Accepted for publication in Physics Letters B

An increased demand for low-level radioactive targets has created the need for a laboratory dedicated to the production of these foils. A description is given of the radioactive targets produced as well as source development work being performed at the Physics Division target facility of Argonne National Laboratory (ANL). Highlights include equipment used and the techniques employed. In addition, some examples of recent source preparation are given as well as work currently in progress.

We have searched for the effect of a neutrino of mass 17 keV/[ital c][sup 2] in the beta decay of [sup 35]S with an appartus incorporating a high-resolution solid-state detector and a superconducting solenoid. The experimental mixing probability, sin[sup 2][theta]=[minus]0.0004[plus minus]0.0008(stat) [plus minus]0.0008(syst), is consistent with zero, in disagreement with several previous experiments. Our sensitivity to neutrino mass is verified by measurements with a mixed source of [sup 35]S and [sup 14]C, which artificially produces a distortion in the beta spectrum similar to that expected from the massive neutrino.

Two of the four known rotational bands in {sup 75}Rb were studied via the {sup 40}Ca({sup 40}Ca,{alpha}p){sup 75}Rb reaction at a beam energy of 165 MeV. Transitions were observed up to the maximum spin I{sub max} of the assigned configuration in one case and one-transition short of I{sub max} in the other. Lifetimes were determined using the residual Doppler shift attenuation method. The deduced transition quadrupole moments show a small decrease with increasing spin, but remain large at the highest spins. The results obtained are in good agreement with cranked Nilsson-Strutinsky calculations, which indicate that these rotational bands do not terminate, but remain collective at I{sub max}.

A 98% pure Am-242m ( K = 5(-), t(1/2) = 141 years) isomeric target was Coulomb excited with a 170.5-MeV Ar-40 beam. The selectivity of Coulomb excitation, coupled with the sensitivity of Gammasphere plus CHICO, was sufficient to identify 46 new states up to spin 18h in at least four rotational bands; 11 of these new states lie in the isomer band, 13 in a previously unknown yrast K-pi = 6(-) rotational band, and 13 in a band tentatively identified as the predicted yrast K-pi = 5(+) band. The rotational bands based on the K-pi = 5- isomer and the 6(-) bandhead were populated by Coulomb excitation with unexpectedly equal cross sections. The gamma-ray yields are reproduced by Coulomb excitation calculations using a two-particle plus rotor model (PRM), implying nearly complete Delta K = 1 mixing of the two almost-degenerate rotational bands, but recovering the Alaga rule for the unperturbed states. The degeneracy of the 5(-) and 6(-) bands allows for precise determination of the mixing interaction strength V, which approaches the strong-mixing limit; this agrees with the 50% attenuation of the Coriolis matrix element assumed in the model calculations. The fractional admixture of the I-K(pi) = 6(6)(-) state in the nominal 6(5)(-) isomer band state is measured within the PRM as 45.6(-1.1)(+0.3)%. The E2 and M1 strengths coupling the 5(-) and 6(-) bands are enhanced significantly by the mixing, while E1 and E2 couplings to other low-K bands are not measurably enhanced. The yields of the 5(+) band are reproduced by an E3 strength of approximate to 15 W.u., competitive with the interband E2 strength. Alignments of the identified two-particle Nilsson states in Am-242 are compared with the single-particle alignments in Am-241. (Less)

Rotational bands have been identified up to high spins ($\ensuremath{\approx}$$28\ensuremath{\hbar}$) in the odd-$A$ nuclei $^{247,249}\mathrm{Cm}$ and $^{249}\mathrm{Cf}$ through inelastic excitation and transfer reactions around the $Z=100$ region where stability results from shell effects. The [620]1/2 Nilsson configuration in $^{249}\mathrm{Cm}$ is the highest-lying neutron orbital, from above the $N=164$ spherical subshell gap, for which high-spin rotational behavior has been established. The data allow for an unambiguous experimental assignment of configurations to the observed bands, unusual for odd-$A$ nuclei near $Z=100$. The high-spin properties are described in terms of Woods-Saxon cranking calculations.

The medium-spin structure of the nuclei {sup 93}Rb and {sup 95}Rb is studied following the neutron-induced fission of {sup 235}U at the PF1B neutron guide, using the FIFI spectrometer, and at the Lohengrin mass spectrometer of the Institut Laue-Langevin Grenoble. These nuclei, plus {sup 91}Rb, are also studied following the spontaneous fission of {sup 248}Cm and {sup 252}Cf sources, using the EUROGAM-II and Gammasphere detector arrays, respectively. A high-spin isomeric state, with a half-life of 111(11) ns, is found in {sup 93}Rb at an excitation energy of 4422.4 keV, which most likely corresponds to the fully aligned [{pi}(g{sub 9/2}) x {nu}(g{sub 7/2}h{sub 11/2})]{sub 27/2}{sup -} configuration. An analogous configuration is proposed for the 5297.9-keV level observed in {sup 91}Rb. A new E3 decay branch of the 1133.9-keV isomer in {sup 91}Rb is found, for which the rather low transition rate of B(E3)=3.8(10) W.u. is determined. The energy of the isomeric state of {sup 95}Rb is now proposed to be at 810.6 keV, with a spin of (9/2{sup +}), and its half-life determined to be T{sub 1/2}=94(7) ns. A cascade of prompt transitions is observed on top of the 810.6-keV isomer in {sup 95}Rb. The near-yrast structures of {sup 91}Rb, {supmore » 93}Rb, and {sup 95}Rb are compared to the results of shell-model calculations, which support the proposed 27/2{sup -} interpretation of states in {sup 91}Rb and {sup 93}Rb. An analogous 27/2{sup -} state is expected to occur in {sup 95}Rb, as a long-lived isomer at 3.24 MeV. No such isomeric decay could be observed in a measurement using the Lohengrin spectrometer, which shows that, if it exists, its population, following the fission of {sup 235}U, is at least four times lower than that of the analogous 27/2{sup -} isomer in {sup 97}Y.« less

A measurement of the $\ensuremath{\beta}$-delayed $\ensuremath{\alpha}$ decay of $^{16}\mathrm{N}$ using a set of twin ionization chambers is described. Sources were made by implantation, using a $^{16}\mathrm{N}$ beam produced via the In-Flight Technique. The energies and emission angles of the $^{12}\mathrm{C}$ and $\ensuremath{\alpha}$ particles were measured in coincidence and very clean $\ensuremath{\alpha}$ spectra, down to energies of $450$ keV, were obtained. The structure of the spectra from this experiment is in good agreement with results from previous measurements. An analysis of our data with the same input parameters as used in earlier studies gives ${S}_{E1}(300)=86\ifmmode\pm\else\textpm\fi{}22$ keVb for the $E1$ component of the $S$-factor. This value is in excellent agreement with results obtained from various direct and indirect measurements. In addition, the influence of new measurements including the phase shift data from Tischhauser et al. on the value of ${S}_{E1}(300)$ is discussed.

Fusion evaporation cross sections for the {sup 27}Al+{sup 45}Sc (Q=9.63 MeV) system are measured down to about 300 nb. Deviations from standard coupled-channels calculations were observed in this system at the lowest energies. The steep fall-off of the fusion cross sections can be reproduced by calculations using a shallow potential model, which was originally developed to explain the hindrance behavior of heavy-ion fusion in medium-mass systems with negative Q values. Comparisons of the hindrance behavior between the present experiment and other systems, for example, {sup 28}Si+{sup 30}Si (Q=14.3 MeV) and {sup 36}S+{sup 48}Ca (Q=7.55 MeV) are presented.

Two neutron-rich N=93 isotones, {sup 155}Sm and {sup 153}Nd, have been studied by delayed gamma-ray and conversion-electron spectroscopy at the Lohengrin mass spectrometer. A half-life of 2.9(5) mus has been measured for the nu5/2{sup +}[642] state at 16.5 keV in {sup 155}Sm. The decay of a 1.17(7)-mus isomer in {sup 153}Nd, at 191.7 keV, has been remeasured and its spin has been reassigned as (5/2){sup +}. This state contains a strong component of the nu5/2{sup +}[642] Nilsson orbital. In addition, a new 1.00(8)-mus isomeric state at 538.6 keV, with a probable nu11/2{sup -}[505] Nilsson configuration, has been observed in {sup 155}Sm. Triple gamma-ray coincidence data from the spontaneous fission of a {sup 252}Cf source placed inside the Gammasphere array were used to extend the collective band on top of the (5/2{sup +}) isomeric state of {sup 153}Nd, and a new band with the same bandhead spin has been observed in {sup 151}Ce. The observation of this new band and an additional new transition in the ground-state band has led us to change the ground-state spin of {sup 151}Ce to (3/2{sup -}). Calculations using the quasiparticle-rotor model successfully reproduce the majority of the features of the gamma decays of these nuclei,more » including branching ratios and isomeric half-lives. Because this model uses a reflection-symmetric core, we conclude that the polarizing effect of the odd particle is responsible for the dipole moment present in the nu5/2{sup +}[642] states of the three nuclei studied and the nu11/2{sup -}[505] level of {sup 155}Sm.« less

The role ${j}_{15/2}$ neutron orbitals play in the transuranic region of actinides has been studied by exploring $\ensuremath{\gamma}$-ray transitions between yrast states in $^{235}\mathrm{Np}$, populated utilizing the nucleon-transfer reaction $^{237}\mathrm{Np}$($^{116}\mathrm{Sn}$,$^{118}\mathrm{Sn}$). Two rotational sequences, presumably the two signatures of the ground-state band, have been delineated to high spin for the first time, with the $\ensuremath{\alpha}=+1/2$ and $\ensuremath{\alpha}=\ensuremath{-}1/2$ signature partners reaching $49/{2}^{+}\ensuremath{\hbar}$ (tentatively $53/{2}^{+}\ensuremath{\hbar}$) and $47/{2}^{+}\ensuremath{\hbar}$ (tentatively $51/{2}^{+}\ensuremath{\hbar}$), respectively. Definite isotopic assignments for these in-band transitions were established through $\ensuremath{\gamma}$-ray cross correlations between $^{235}\mathrm{Np}$ and $^{118}\mathrm{Sn}$ and events where at least three $\ensuremath{\gamma}$ rays corresponding to neptunium-like particles were detected. These transitions reveal clear upbends in the aligned angular momentum and kinematic moment of inertia plots; such a phenomenon could indicate a strong interaction between an aligned $\ensuremath{\nu}{j}_{15/2}$ configuration crossing the ground-state band in $^{235}\mathrm{Np}$, which is based on a $\ensuremath{\pi}{i}_{13/2}$ orbital. However, the lack of any signature splitting over the observed frequency range of the $^{235}\mathrm{Np}$ rotational sequences cannot remove the possibility of a $\ensuremath{\pi}{h}_{9/2}$ assignment for the observed band. The role of the $\ensuremath{\nu}{j}_{15/2}$ and $\ensuremath{\pi}{i}_{13/2}$ alignment mechanisms in the deformed U-Pu region is discussed in light of the current spectroscopic data and in the context of the cranked-shell model.

We have studied the neutron-transfer reactions {sup 11,12}B(d,p){sup 12,13}B in inverse kinematics to obtain information about the neutron-capture reactions {sup 11,12}B(n,{gamma}). These capture reactions are suggested to play a role in seeding r-process nucleosynthesis through the production of light, neutron-rich nuclei. The neutron spectroscopic factors of the states in {sup 12,13}B were deduced and the branching ratio of the neutron-unbound state at E{sub X}=3.389 MeV in {sup 12}B was obtained to provide the ratio of partial widths, {Gamma}{sub n}/{Gamma}{sub {gamma}}. The reaction rates for {sup 11,12}B(n,{gamma}) are estimated for direct captures and resonant captures and compared with previous compilations. The astrophysical implications, especially for neutrino-driven wind models in core-collapse supernovae, are discussed in the r-process network framework using our updated reaction rates.

The lifetime of the $7s6d$ ${^{1}D}_{2}$ state of atomic radium is determined to be $385(45)\text{ }\ensuremath{\mu}\text{s}$ using cold $^{226}\text{R}\text{a}$ atoms prepared in a magneto-optical trap. The ${^{1}D}_{2}$ state is populated from the decay of the ${^{1}P}_{1}$ state which is excited by a pulse of 483 nm light. The decay of the ${^{1}D}_{2}$ state is observed by detecting delayed fluorescence at 714 nm from the last step in the decay sequence ${^{1}P}_{1}\text{\ensuremath{-}}{^{1}D}_{2}\text{\ensuremath{-}}{^{3}P}_{1}\text{\ensuremath{-}}{^{1}S}_{0}$. The measured lifetime is compared to a number of theoretical calculations. An improved value of the $7s7p$ ${^{1}P}_{1}$ level of $20\text{ }715.598(6)\text{ }{\text{cm}}^{\ensuremath{-}1}$ is obtained.

In order to test {\it ab-initio} calculations of light nuclei, we have remeasured lifetimes in $^{10}$Be using the Doppler Shift Attenuation Method (DSAM) following the $^{7}$Li($^7$Li,$\alpha$)$^{10}$Be reaction at 8 and 10 MeV. The new experiments significantly reduce systematic uncertainties in the DSAM technique. The J$^{\pi}$ = $2^+_1$ state at 3.37 MeV has $\tau$ = 205${\pm}$(5)$_{stat}\pm$(7)$_{sys}$ fs corresponding to a $B$($E2\downarrow$) of 9.2(3) $e^2$fm$^4$ in broad agreement with many calculations. The J$^{\pi}$ = $2^+_2$ state at 5.96 MeV was found to have a $B$($E2\downarrow$) of 0.11(2) $e^2$fm$^4$ and provides a more discriminating test of nuclear models. New Green's Function Monte Carlo (GFMC) calculations for these states and transitions with a number of Hamiltonians are also reported and compared to experiment., Comment: 4 Pages

Measurements of ($^{3}\mathrm{He}$,$d$) reactions can provide information on the proton widths of states that play a role in astrophysically important ($p,\ensuremath{\gamma}$) reactions. We report on the first study of the ($^{3}\mathrm{He}$,$d$) reaction in inverse kinematics with a $^{56}\mathrm{Ni}$$ ({T}_{1/2}=6.1 \mathrm{d})$ ion beam. The $Q$-value resolution of $~$ keV achieved in this experiment was sufficient to separate the transitions populating the ground state and the $1/{2}^{\ensuremath{-}}\text{\ensuremath{-}}5/{2}^{\ensuremath{-}}$ doublet at ${E}_{x}~1.1$ MeV in $^{57}\mathrm{Cu}$. Prospects for similar ($^{3}\mathrm{He}$,$d$) experiments with improved energy resolution are also discussed.

The total cross sections for the $^{120}\mathrm{Te}(p,\ensuremath{\gamma})^{121}\mathrm{I}$ and $^{120}\mathrm{Te}(p,n)^{120}\mathrm{I}$ reactions have been measured by the activation method in the effective center-of-mass energies 2.47 MeV$ \ensuremath{\leqslant} {E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{eff}} \ensuremath{\leqslant} 7.93$ MeV and $6.44 \mathrm{MeV} \ensuremath{\leqslant} {E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{eff}} \ensuremath{\leqslant} 7.93 \mathrm{MeV},$ respectively. The targets were prepared by evaporation of $99.4%$ isotopically enriched $^{120}\mathrm{Te}$ on aluminum and carbon backing foils, and bombarded with proton beams provided by the FN tandem accelerator at the University of Notre Dame. The cross sections and $S$ factors were deduced from the observed $\ensuremath{\gamma}$ ray activity, which was detected off-line by two Clover HPGe detectors mounted in close geometry. The results are presented and compared with the predictions of statistical model calculations using the codes NON-SMOKER and TALYS.

International audience; Due to recent advances in detection techniques, excited states in several trans-fermium nuclei were studied in many laboratories worldwide, shedding light on the evolution of nuclear structure between stable nuclei and the predicted island of stability centered around spherical magic numbers. In particular, studies of K-isomers around the Z=100 and N=152 deformed shell closures extended information on the energies of Nilsson orbitals at the Fermi surface. Some of these orbitals originate from spherical states, which are relevant to the magic gaps in super-heavy nuclei. The single-particle energies can be used to test various theoretical predictions and aid in extrapolations towards heavier systems. So far, the Woods-Saxon potential reproduces the data best, while self-consistent approaches miss some of the observed features, indicating a need to modify the underlying effective nucleon-nucleon interactions.

The decay of a new $3.2\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{s}$, $({4}^{\ensuremath{-}})$ isomeric state at 1298.0 keV has been observed using $\ensuremath{\gamma}$-ray spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin. By comparison with theoretical calculations this state was assigned a $\ensuremath{\nu}5/2[642]\ensuremath{\bigotimes}\ensuremath{\nu}3/2[521]$ dominant configuration. Prompt $\ensuremath{\gamma}$-ray data from a spontaneous fission experiment have also been analyzed allowing the observation of a collective band on top of this isomeric state, the identification of a new band on top of the previously reported (${5}^{\ensuremath{-}}$) isomer of $^{156}\mathrm{Nd}$ and the extension of collective bands on top of (${5}^{\ensuremath{-}}$) isomers of the neighboring $^{156,158}\mathrm{Sm}$ nuclei. Quasiparticle rotor model calculations reported in this work correctly predict the energies and decay patterns of these bands. A new (${5}^{\ensuremath{-}}$) isomer in $^{160}\mathrm{Sm}$ has also been observed. The calculations predict $\ensuremath{\nu}5/2[642]\ensuremath{\bigotimes}\ensuremath{\nu}5/2[523]$ dominant configurations for all these (${5}^{\ensuremath{-}}$) isomers.

The isotope {sup 257}Rf was produced in the fusion-evaporation reaction {sup 208}Pb({sup 50}Ti,n){sup 257}Rf. Reaction products were separated and identified by mass. Delayed spectroscopy of {sup 257}Rf and its decay products was performed. A partial decay scheme with configuration assignments is proposed based on {alpha} hindrance factors. The excitation energy of the 1/2{sup +}[620] configuration in {sup 253}No is proposed. The energy of this 1/2{sup +} state in a series of N=151 isotones increases with nuclear charge, reflecting an increase in the N=152 gap. This gap is deduced to grow substantially from 850 to 1400 keV between Z=94 and 102. An isomeric state in {sup 257}Rf, with a half-life of 160{sub -31}{sup +42} {mu}s, was discovered by detecting internal conversion electrons followed by {alpha} decay. It is interpreted as a three-quasiparticle high-K isomer. A second group of internal conversion electrons, with a half-life of 4.1{sub -1.3}{sup +2.4} s, followed by {alpha} decay, was also observed. These events might originate from the decay of excited states in {sup 257}Lr, populated by electron-capture decay of {sup 257}Rf. Fission of {sup 257}Rf was unambiguously detected, with a branching ratio of b{sub Rf}{sup SF}=0.02{+-}0.01.

Excited states in (256)Rf were populated via the Pb-208(Ti-50,2n) fusion-evaporation reaction. Delayed gamma-ray and electron decay spectroscopy was performed and three isomeric states in (256)Rf h ...

The expanded level structure of $^{240}$Pu available from the present study highlights the role of strong octupole correlations in this nucleus. Besides a delayed alignment in the yrast band, the observations include the presence of both $I^{+}{\to}(I-1)^{-}$ and $I^{-}{\to}(I-1)^{+}$ E1 transitions linking states of the yrast and negative-parity bands at high spin and the presence of an additional even-spin, positive-parity band deexciting exclusively to the negative parity sequence. The observations appear to be consistent with expectations based on the recently proposed concept of octupole phonon condensation., Comment: Accepted by Physical Review Letters on February 20, 2009

The preparation techniques for producing targets of rare-earth isotopes depend greatly upon the chemical and physical properties of the particular rare-earth element. In most cases the isotope is supplied in the oxide form requiring a reduction to the metallic form. Collection efficiencies will be discussed.

We report on a study of the structure of the unbound nucleus {sup 7}He utilizing the proton-removal reaction {sup 2}H({sup 8}Li,{sup 3}He){sup 7}He. Combining the present results with those of our prior measurements of the neutron-adding reaction {sup 2}H({sup 6}He,p){sup 7}He, a consistent picture emerges for the low-lying excitations in {sup 7}He. Specifically, the negative-parity sequence of resonances, in order of excitation energies, is consistent with 3/2{sup -},1/2{sup -}, and 5/2{sup -}. The stable-beam reactions {sup 2}H({sup 7}Li,t){sup 6}Li and {sup 2}H({sup 7}Li,{sup 3}He){sup 6}He were also measured. The results are compared with the predictions of nuclear structure models, including those of ab initio quantum Monte Carlo calculations.

Lifetimes have been deduced in the intermediate/high-spin range for the three known rotational bands in $^{73}\mathrm{Kr}$ and the $T=0$ band in $^{74}\mathrm{Rb}$ using the residual Doppler shift method. This has enabled relative transition quadrupole moments to be studied for the first time in triaxial nuclei as a function of spin. The data suggest that the additivity principle for transition quadrupole moments is violated, a result that is in disagreement with predictions from cranked Nilsson-Strutinsky and cranked relativistic mean-field theory calculations. The reasons for the discrepancy are not understood but may indicate that important correlations are missing from the models.

Isomers have been populated in {sup 246}Cm and {sup 252}No with quantum numbers K{sup {pi}}=8{sup -}, which decay through K{sup {pi}}=2{sup -} rotational bands built on octupole vibrational states. For N=150 isotones with (even) atomic number Z=94-102, the K{sup {pi}}=8{sup -} and 2{sup -} states have remarkably stable energies, indicating neutron excitations. An exception is a singular minimum in the 2{sup -} energy at Z=98, due to the additional role of proton configurations. The nearly constant energies, in isotones spanning an 18% increase in Coulomb energy near the Coulomb limit, provide a test for theory. The two-quasiparticle K{sup {pi}}=8{sup -} energies are described with single-particle energies given by the Woods-Saxon potential and the K{sup {pi}}=2{sup -} vibrational energies by quasiparticle random-phase approximation calculations. Ramifications for self-consistent mean-field theory are discussed.

The United States military has been vigorously engaged throughout the full range of military operations during the course of the past two decades. Since gaining prominence during the withdrawal of U.S. forces in Somalia in 1995, non-lethal weapons have taken on an increasing role as our armed forces continue down the road toward doctrinal and technological transformation. While providing an option somewhere between the realm of "shoot" or "don't shoot", the utility of items such as rubber bullets, beanbag projectiles, and flash- bang grenades during looting, rioting, and similar unfavorable activities appears to be definitive and enduring. The need for non-lethal weapons during large- scale combat operations might not be so apparent. This leads to a fundamental question. Do non-lethal weapons have a legitimate battlefield role in major combat operations? This paper examines the need for non-lethal weapons in combat operations and considers the challenges towards their implementation.

We present some recent results from studies of light nuclei using exotic beams from ATLAS at Argonne National Laboratory. Light nuclei far from stability provide ideal testing grounds for modern theoretical methods, and may provide information about astrophysical environments. We focus on the nuclei Li-9 and He-7, populated with the (d,p) and (d,He-3) reactions.

High-spin states in the N=Z nucleus {sup 72}Kr have been populated in the {sup 40}Ca({sup 40}Ca, 2{alpha}){sup 72}Kr fusion-evaporation reaction at a beam energy of 165 MeV using the Gammasphere array for {gamma}-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in {sup 72}Kr were extended to an excitation energy of {approx}24 MeV and angular momentum of 30({Dirac_h}/2{pi}). Using the Doppler shift attenuation method the lifetimes of high-spin states were measured for the first time. Excellent agreement between the results of calculations within the isovector mean field theory and experiment is observed both for rotational and deformation properties. No enhancement of quadrupole deformation expected in the presence of isoscalar t=0 np pairing is observed. Current data do not show any evidence for the existence of the isoscalar np pairing.

We have demonstrated Zeeman slowing and capture of neutral $^{225}\mathrm{Ra}$ and $^{226}\mathrm{Ra}$ atoms in a magneto-optical trap. The intercombination transition $^{1}S_{0}\ensuremath{\rightarrow}^{3}P_{1}$ is the only quasicycling transition in radium and was used for laser-cooling and trapping. Repumping along the $^{3}D_{1}\ensuremath{\rightarrow}^{1}P_{1}$ transition extended the lifetime of the trap from milliseconds to seconds. Room-temperature blackbody radiation was demonstrated to provide repumping from the metastable $^{3}P_{0}$ level. We measured the isotope shift and hyperfine splittings on the $^{3}D_{1}\ensuremath{\rightarrow}^{1}P_{1}$ transition with the laser-cooled atoms, and set a limit on the lifetime of the $^{3}D_{1}$ level based on the measured blackbody repumping rate. Laser-cooled and trapped radium is an attractive system for studying fundamental symmetries.

High-spin states in $^{76}\mathrm{Sr}$ have been studied using Gammasphere plus Microball detector arrays. The known yrast band has been extended beyond the first band crossing, which involves the simultaneous alignment of pairs of ${\mathrm{g}}_{\frac{9}{2}}$ protons and neutrons, to a tentative spin of $24\ensuremath{\hbar}$. The data are compared with the results of cranked relativistic mean-field (CRMF) and cranked relativistic Hartree-Bogoliubov (CRHB) calculations. The properties of the band, including the ${\mathrm{g}}_{\frac{9}{2}}$ proton/neutron band crossing frequency and moments of inertia, are found to be well reproduced by the CRHB calculations. Furthermore, the unpaired CRMF calculations show quite good agreement with the data beyond the band crossing region, indicating that pairing is weak at these frequencies. The high spin results suggest that there is little evidence for an isoscalar $(t=0)$ $\mathit{np}$ pair field. Moreover, a systematic study of the band crossings in even-even $N=Z$ nuclei for the first time reveals that there is no evidence to support the existence of the Coulomb antipairing effect caused by the Coulomb exchange term.

The surrogate reaction method has been used to determine neutron-induced fission cross sections for the short-lived minor actinides 242,243 Cm and 241 Am. These cross sections are highly relevant for the design of fast reactors capable of incinerating minor actinides. Our results for the fission cross section of 242 Cm extend up to the onset of second-chance fission. None of the existing neutron-induced fission data for 242 Cm go as high in neutron energy. The latest direct neutron-induced measurement for the 243 Cm fission cross section is questioned by our results since there exist differences of more than 60% in the 0.7 to 7 MeV neutron energy range.

A Co-ordinated Research Project (CRP) entitled "Updated Decay Data Library for Actinides" was initiated in 2005 by the International Atomic Energy Agency (IAEA), with the primary aim of improving the quality of recommended decay data for actinides and their decay chains. Participants have attended two Research Coordination Meetings, and agreed on a list of important nuclides and evaluation methodologies to be adopted in work programmes dedicated to the preparation of a new database. Specific measurements were also proposed to address discrepancies between existing data, and some of these experimental studies are described in detail within this paper.

In a recent experiment at Argonne National Laboratory, new spectroscopic information was obtained for the mirror pair 67As and 67Se via the measurement of the lifetime of analogue 9/2I+ excited states. The nuclei of interest were populated via the fusion evaporation reaction of 32S on 40Ca, and selected by the combination of Gammasphere, Microball and the Neutron Wall arrays. The mirror B(E1) strengths were measured via the centroid shift method in analogue E1 transitions in 67As and 67Se. These findings are significant in determining the extent of conservation of isospin symmetry.

The half-life of $^{44}\mathrm{Ti}$ was determined by following the decay of $^{44}\mathrm{Ti}$ and $^{60}\mathrm{Co}$ for 14 yr. Mixed sources containing $^{44}\mathrm{Ti}$ and $^{60}\mathrm{Co}$ and pure sources of $^{44}\mathrm{Ti}$ and $^{60}\mathrm{Co}$ were prepared and their \ensuremath{\gamma}-ray spectra were measured with a Ge spectrometer once or twice a year. Counts in the 1157.0-keV \ensuremath{\gamma}-ray photopeak of $^{44}\mathrm{Ti}$ and the 1173.2- and 1332.5-keV \ensuremath{\gamma}-ray photopeaks of $^{60}\mathrm{Co}$ were used for this measurement. From the decay of the $^{44}\mathrm{Ti}$ and $^{60}\mathrm{Co}$ activity ratios, the half-life of $^{44}\mathrm{Ti}$ was determined. Using a value of 5.2711\ifmmode\pm\else\textpm\fi{}0.0004 yr for $^{60}\mathrm{Co}$ half-life, we determined the half-life of $^{44}\mathrm{Ti}$ as 58.9\ifmmode\pm\else\textpm\fi{}0.3 yr. Special efforts were made to check for systematic errors and these were found to be negligible within the quoted uncertainty.

The α -decay half-life of Cm 246 has been measured to be T 1 / 2 = 4706 (40) yr by means of the alpha-counting of ingrowth activity following the decay of a mass separated source of the Cf 250 parent nuclide. The α -decay emission probabilities of Cm 246 and Cf 250 have also been determined with high precision and have been compared with results from previous measurements. A new α -decay branch of Cm 246 to the 4 + level of the ground-state band of the Pu 242 daughter nucleus has been identified and characterized.

The $g$ factors of several low-lying excited states of the neutron-rich $^{101}\mathrm{Zr}$ and $^{103,105}\mathrm{Mo}$ nuclei have been measured for the first time. The isotopes were produced by the spontaneous fission of a $^{252}\mathrm{Cf}$ source, which was sandwiched between two magnetized iron foils and placed at the center of the Gammasphere spectrometer. The $g$ factors of excited states of fission fragments were inferred from Larmor precessions deduced from the measurement of time-integrated perturbed angular correlation functions. The magnitude and sign of the quantity $({g}_{K}\ensuremath{-}{g}_{R})/{Q}_{0}$ were determined from the mixing ratios measured for the 3/2[411] and 5/2[532] rotational bands in $^{101}\mathrm{Zr}$ and $^{103,105}\mathrm{Mo}$. The combination of this quantity with the measured $g$ factors permitted the separation of the particle-rotor parameters ${g}_{K}$ and ${g}_{R}$ for each band. The comparison of the extracted ${g}_{K}$ factors to Nilsson model predictions confirms current band assignments, and this agreement is consistent with an axially symmetric picture of these nuclei at low spins. The possible effect of triaxial deformation on the measured magnetic moments was investigated in the rigid triaxial rotor-plus-particle framework. The calculations suggest that triaxial deformation plays a stronger role in the Mo than in the Zr isotopes, but that triaxiality is likely to be dynamic. The extracted ${g}_{R}$ factors are consistently smaller than the $Z/A$ limit, in agreement with observations in neighboring even-even nuclei.

PACS; International audience; We present an original method that allows to determine neutron-induced cross sections of very short-lived minor actinides. This indirect method, based on the use of transfer reactions, has already been applied with success for the determination of the neutron-induced fission and capture cross section of 233Pa, a key nucleus in the 232Th-233U fuel cycle. A recent experiment using this technique has been performed to determine the neutron-induced fission cross sections of 242,243,244Cm and 241Am which are present in the nuclear waste of the current U-Pu fuel cycle. These cross sections are highly relevant for the design of reactors capable to incinerate minor actinides. The first results will be illustrated.

The {sup 44}Ti(t{sub 1/2}=59 yr) nuclide, an important signature of supernova nucleosynthesis, has recently been observed as live radioactivity by {gamma}-ray astronomy from the Cas A remnant. We investigate in the laboratory the major {sup 44}Ti production reaction {sup 40}Ca({alpha},{gamma}){sup 44}Ti (E{sub c.m.}{approx}0.6-1.2 MeV/u) by direct off-line counting of {sup 44}Ti nuclei. The yield, significantly higher than inferred from previous experiments, is analyzed in terms of a statistical model using microscopic nuclear inputs. The associated stellar rate has important astrophysical consequences, increasing the calculated supernova {sup 44}Ti yield by a factor {approx}2 over previous estimates and bringing it closer to Cas A observations.

Single‐neutron transfer with the (d,p) reaction in inverse kinematics has been used to study the properties of the light nuclei 9Li and 7He. The results for 9Li and 7Heg.s. are compared to the predictions of ab‐initio models of nuclear structure. Different possibilities for excited states in 7He are discussed in the context of other recent experimental studies of 7He.