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An experiment aimed at studying high-spin states in 190 Hg was performed with the Eurogam II array. The data have revealed the presence of cascades of magnetic dipole transitions with some unexpected properties. Unlike the M1 bands previously observed in the heavier Hg isotopes, these structures have extremely large B(M1)/B(E2) ratios. The observation of a third dipole band with much lower B(M1)/B(E2) values in the same spin/excitation energy regime suggests that the bands may represent configurations occurring in different minima in the potential energy surface. Configuration-dependent Cranked Nilsson–Strutinsky calculations predict the presence of a minimum in the nuclear potential energy surface at a deformation of e≈0.2, γ≈−90°, occurring when a proton is excited across the Z=82 shell-gap into an h9/2 orbital. It is suggested that the bands exhibiting anomalously large B(M1)/B(E2) ratios may be associated with this minimum. more...

For many nuclei beyond the proton drip line in the Z > 72, N > 82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Q α and Q p values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl and their daughters. more...

The yrast states of the beta-stable nucleus have been studied using the reaction at a beam energy of 65 MeV. Transitions in this nucleus were identified unambiguously using high-efficiency recoil-gated gamma-ray spectra obtained from the AYEBALL gamma-ray array in conjunction with the Argonne fragment mass analyser coupled to a split anode ionization chamber. The decay scheme is presented and it is hoped that such a study will shed light on the competition between core breaking and population of the neutron intruder orbitals in the generation of high angular momentum states in this region. more...

The excited states of the self-conjugate, odd-odd system, Ga have been investigated following the fusion-evaporation reaction at a beam energy of 65 MeV. Identification of candidate transitions in this nucleus were made using the AYEBALL -ray array following the selection of the recoil products with the Argonne fragment mass analyser (FMA) and a split anode ionization chamber. Spin assignments have been made on the basis of measured directional correlations from oriented states (DCO ratios). The resulting level scheme is presented and candidates for T = 1 and T = 0 structures suggested. more...

A technique for separating and identifying reaction products from radiative capture reactions induced by radioactive ion beams has been developed. The {sup 18}F(p,{gamma}){sup 19}Ne and {sup 18}O(p,{gamma}){sup 19}F reactions have been measured in inverse kinematics by identifying the {sup 19}F and {sup 19}Ne reaction products with respect to mass and charge at forward angles in the Fragment Mass Analyzer. A total detection efficiency of 30% and a suppression factor for the incident beam relative to the (p,{gamma}) reaction products of better than 10{sup 12}:1 was achieved. Details of the detection technique, the beam monitoring procedure as well as experience in the use of polypropylene targets in experiments with radioactive beams are discussed. more...

The highest-spin discrete states ( I ∼60 ℏ and E x ∼30 MeV) in normal deformed nuclei have been observed in the rare-earth isotope 156 Dy using the 124 Sn( 36 S,4n) reaction in conjunction with the GAMMASPHERE spectrometer. The positive parity yrast sequence appears to evolve smoothly from a prolate (collective) towards an oblate (non-collective) shape, in contrast to the sudden shape change observed in the isotone 158 Er. Terminating states are identified in the negative parity sequences at I π =52 − and 53 − and specific multi-particle-hole configurations are assigned by comparison with cranked Nilsson-Strutinsky calculations. An order of magnitude increase in the interaction strength between close lying high-spin weakly collective structures is determined compared with that found in the lower-spin strongly collective domain. These results give valuable insight into the interplay between collective and terminating structures, and their competition for yrast status in the 40−60 ℏ spin range. more...

Cross sections for multineutron transfer reactions in {sup 58}Ni+{sup 124}Sn collisions have been measured with good particle identification at four energies around the Coulomb barrier. The angle- and energy-integrated multineutron transfer cross sections exhibit an exponential falloff with increasing number of transferred neutrons. The elastic scattering and one-nucleon transfer reaction data can be reproduced well by coupled-channels calculations and distorted-wave Born approximation calculations, respectively, using the same optical potential. The transfer probabilities for each transfer channel, plotted as a function of the distance of closest approach, fall on a common exponential curve; the slopes of these exponential falloff curves are discussed. {copyright} {ital 1998} {ital The American Physical Society} more...

Quadrupole moments of the six known superdeformed (SD) bands of {sup 193}Hg and the yrast SD band of {sup 192}Hg have been determined by a Doppler-shift-attenuation-method measurement utilizing the gammasphere array. The quadrupole moments of all {sup 193}Hg SD bands were found to be similar, suggesting the active single-particle orbitals in the mass-190 region exhibit only small shape-driving effects. Additionally, there is evidence for an unexpected difference in the quadrupole moments of SD bands in {sup 192}Hg and {sup 193}Hg. {copyright} {ital 1998} {ital The American Physical Society} more...

An excited superdeformed band in {sup 194}Hg , observed to decay directly to both normal-deformed and superdeformed yrast states, is proposed to be a K{sup {pi}}=2{sup {minus}} octupole vibrational band, based on its excitation energies, spins, and likely parity. The transition energies are identical to those of the yrast superdeformed band in {sup 192}Hg , but originate from levels with different spins and parities. The evolution of transition energies with spin suggests that cancellations between pairing and particle alignment are partly responsible for the identical transition energies. {copyright} {ital 1997} {ital The American Physical Society} more...

One-step decay transitions linking the superdeformed (SD) bands 1 and 3 in194Hg to yrast levels are discussed. Inter-band transitions between bands 1 and 3 have also been identified. For the first time, the spin, parity and excitation energy have been determined for two SD bands in the same nucleus. The low excitation energy of the excited band supports the view that it is based on an octupole excitation. It is believed that Porter-Thomas fluctuations play a major role in determining the strength of the one-step transitions as suggested by the fact that only one other SD band has been linked in theA=190 mass region (194Pb) at the present time. When Porter-Thomas fluctuations prevent the observation of one-step or two-step linking transitions, as e.g. in the case of192Hg, the analysis of the quasi-continuous part of the decay-out spectrum provides an alternative method for the determination of the excitation energy and spin of an SD band. This method is discussed in detail. more...

In-beam γ-ray transitions in 181Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1 2 − [521] ground state was observed up to 29 2 − . A 5 2 − [512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i 13 2 orbitals and are proposed to decay to an i 13 2 isomeric state associated with an oblate state. more...

Excited states have been observed for the first time in the neutron-deficient {sup 176,178}Hg nuclei using the recoil-decay tagging (RDT) technique in which prompt {gamma} rays are associated with a particular isotope through a correlation with the characteristic ground state {alpha} decay. Below N=102, the excitation energy of a rotational band built on a prolate shape ({beta}{sub 2}{approximately}0.25) increases with decreasing mass to the point where there is no longer any evidence for its presence at low spin in {sup 176}Hg. The data are in qualitative agreement with recent mean field calculations. {copyright} {ital 1997} {ital The American Physical Society} more...

Gamma rays from the decay of states in the proton unstable nucleus {sup 147}Tm were observed for the first time following the {sup 92}Mo({sup 58}Ni,p2n){sup 147}Tm reaction at 260 MeV. Prompt {gamma} rays were detected with an array of Compton-suppressed Ge detectors, placed in front of the fragment mass analyzer at the ATLAS accelerator, and were assigned to individual reaction channels on an event-by-event basis using the recoil-decay tagging method. Gamma-ray transitions were associated with both the proton decay of the {pi}h{sub 11/2} ground state and the {pi}d{sub 3/2} isomeric state in {sup 147}Tm, even though the cross sections for populating these states were only {approx} 16 {mu}b and 2 {mu}b, respectively. The level scheme which was constructed for {sup 147}Tm is discussed and compared with the level structures for lighter N=78 isotones. {copyright} {ital 1997} {ital The American Physical Society} more...

High-precision lifetime measurements have been performed in superdeformed (SD) bands of {sup 192,194}Hg with the Doppler-shift attenuation method. Intrinsic quadrupole moments Q{sub 0} were extracted for three SD bands in {sup 194}Hg and for the yrast SD band in {sup 192}Hg. Within experimental uncertainties, all four SD bands have equal Q{sub 0} values. These results provide constraints on differences in Q{sub 0} values between the {open_quotes}identical{close_quotes} SD bands {sup 194}Hg(3) and {sup 192}Hg(1). {copyright} {ital 1997} {ital The American Physical Society} more...

Excited states in {sup 110}Sb have been identified for the first time in a series of {gamma}-spectroscopy experiments using both thin and backed targets, including neutron-fold and recoil-mass measurements to provide unambiguous channel identification. The three decoupled intruder bands observed in {sup 110}Sb are based upon configurations involving 2p-2h excitations across the Z=50 shell gap and show the features of smooth band termination. The yrast intruder band, which has been connected to the low-spin levels, is tentatively identified up to its predicted termination at I{sup {pi}}=45{sup +}. Excellent agreement with configuration-dependent cranked Nilsson-Strutinsky calculations is obtained for the high-spin states near termination. {copyright} {ital 1997} {ital The American Physical Society} more...

The new proton radioactivities ${}^{165,166,167}\mathrm{Ir}$ and ${}^{171}\mathrm{Au}$ have been observed. The Ir isotopes were produced via the ${}^{92}\mathrm{Mo}{(}^{78}\mathrm{Kr}{,pxn)}^{165,166,167}\mathrm{Ir}$ reactions at 357 and 384 MeV. ${}^{171}\mathrm{Au}$ was produced via the ${}^{96}\mathrm{Ru}{(}^{78}\mathrm{Kr}{,p2n)}^{171}\mathrm{Au}$ reaction at 389 MeV. The proton emitters were each identified by position, time, and energy correlations between the implantation of a residual nucleus into a double-sided silicon strip detector, the observation of a decay proton, and the subsequent observation of a decay alpha particle from the daughter nucleus (${}^{164,165,166}$Os and ${}^{170}\mathrm{Pt},$ respectively). Both ${}^{166}\mathrm{Ir}$ and ${}^{167}\mathrm{Ir}$ have proton-emitting ground and isomeric states, which also decay by alpha emission. The proton-decay rates have been reproduced by calculations using the WKB barrier penetration approximation and a low-seniority shell-model calculation of the spectroscopic factors. The alpha decays of the four nuclei are followed by chains of alpha decays, allowing the determination of single-particle orbital orderings. Mass information has also been obtained from the alpha-decay chains because a connection to a known mass can be obtained for one of the nuclei. Ground-state mass excesses are reported for ${}^{151}\mathrm{Tm},$ ${}^{154}\mathrm{Yb},$ ${}^{155}\mathrm{Lu},$ ${}^{158}\mathrm{Hf},$ ${}^{159}\mathrm{Ta},$ ${}^{162}\mathrm{W},$ ${}^{163}\mathrm{Re},$ ${}^{166}\mathrm{Os},$ ${}^{167}\mathrm{Ir},$ and ${}^{170}\mathrm{Pt}.$ The mass excess for ${}^{171m}\mathrm{Au}$ is also given. Proton separation energies are also deduced for the odd-$Z$ alpha daughter nuclei of the Ir proton emitters. more...

Proton radioactivities from {sup 157}Ta and {sup 161}Re are reported. Fusion-evaporation residues from the reaction of 270 MeV {sup 58}Ni ions on {sup 102}Pd and {sup 106}Cd targets were separated according to M/Q and implanted into a double-sided silicon strip detector. One line from {sup 157}Ta was observed with a proton energy of 927(7) keV [t{sub 1/2}=10.1(4) ms, b{sub p}=3.4(12){percent}] from the {pi}s{sub 1/2} ground state. A new alpha decay transition with energy 6117(4) keV was also observed from this state. Two proton lines from {sup 161}Re were observed with energies 1192(6) keV [t{sub 1/2}=0.37(4) ms, b{sub p}=100(7){percent}] and 1315(7) keV [t{sub 1/2}=16(1) ms, b{sub p}=4.8(6){percent}] from the {pi}s{sub 1/2} and {pi}h{sub 11/2} states, respectively. {copyright} {ital 1997} {ital The American Physical Society} more...

The contribution of the 18 F(p,γ) reaction to the production of 19 Ne which is the crucial isotope for the breakout from the hot CNO cycle into the rp process, has been investigated in experiments with 18 F beams. Measurements of the cross sections for the 18 F(p,α) 15 O and the 18 F(p,γ) 19 Ne reactions indicate that the contribution from the (p,γ) route to the formation of 19 Ne is small. more...

Excited states have been identified in ${}^{111}$Te using the ${}^{56}$Fe${(}^{58}$Ni,$2pn)$ reaction at 240 MeV. Assignment of transitions to ${}^{111}$Te was made via measurements of $\ensuremath{\gamma}$ rays in coincidence with both evaporation neutrons and mass-analyzed recoils. The observed cascade of $\ensuremath{\gamma}$ rays is assumed to feed an isomeric state with ${J}^{\ensuremath{\pi}}{=11/2}^{\ensuremath{-}}$, similar to the yrast structures observed in other odd-mass tellurium isotopes. more...

The gamma decay of high spin yrast states in {sup 83}Y up to I{sup {pi}}=59/2{sup +} and 53/2{sup {minus}} have been observed using the reaction {sup 58}Ni({sup 29}Si,3p) at 110 MeV and the Gammasphere Early Implementation Array. The level scheme has been substantially extended due to the observations of several new transitions in all of the bands. A sequence of transitions feeding into the positive parity yrast band above I{sup {pi}}=47/2{sup +} seems to be consistent with a noncollective oblate structure expected at these high spins. A similar cascade is found in the data for {sup 84}Zr. A new forking of the favored negative parity band is found which may be due to neutron alignment polarizing the core to a different shape. This suggests that the {open_quotes}isomeric{close_quote}{close_quote} band in {sup 83}Y, for which one more connecting transition was found, is of a similar nature to other high-K bands found in this region. Lifetime measurements in the unfavored negative parity band are consistent with cranking calculations which predict a nearly oblate shape with a deformation parameter {beta}{sub 2}{approx}0.2. A qualitative analysis of line shapes at very high spins suggests the persistence of collectivity in the yrast sequence to the highest excitationsmore » seen. {copyright} {ital 1997} {ital The American Physical Society}« less more...

An upper limit to the production of ${}^{19}\mathrm{Ne}$ through the ${}^{18}\mathrm{F}(p,\ensuremath{\gamma})$ reaction at the recently discovered $s$-wave resonance has been determined. The limit implies that in a hot stellar environment ${(T}_{9}g0.5)$ this reaction is not a significant gateway from the hot CNO cycle towards the production of heavier elements in stars. more...

Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the {sup 195}Hg nucleus. Two of the bands are interpreted as signature partners most likely based on N{sub osc}=6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j{sub 15/2} intruder orbital. These four bands do not exhibit a simple, {open_quotes}identical bands{close_quotes} relationship to other superdeformed bands in this mass region. {copyright} {ital 1997} {ital The American Physical Society} more...

A superdeformed band of 15 transitions has been found in the $^{155}\mathrm{Dy}$ nucleus. The measurement was performed with a backed target and the large deformation was inferred from the measured Doppler shifts. The new band displays an intensity pattern much different from typical superdeformed bands in this mass region. The dynamic moment of inertia is essentially identical to that of band 1 in $^{153}\mathrm{Dy}$ and is somewhat larger than those of the yrast superdeformed bands in $^{152,154}\mathrm{Dy}$, suggesting that the associated configuration has an additional N=7, ${\mathit{j}}_{15/2}$ intruder orbital occupied with respect to the $^{154}\mathrm{Dy}$ core. \textcopyright{} 1996 The American Physical Society. more...

The low-lying level structure of the neutron-deficient isotope $^{200}\mathrm{Rn}$ has been studied using the $^{176}\mathrm{Hf}$${(}^{28}$Si,4n) reaction at a beam energy of 142 MeV. Evaporation residues were selected using an in-flight recoil mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. Prompt \ensuremath{\gamma} rays in $^{200}\mathrm{Rn}$ were observed at the target position using the AYEBALL array of 19 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the strip detector. Isotopic assignments of the nuclei produced were made on the basis of the mass-to-charge ratio of the recoiling ion and the energy and half-life of its \ensuremath{\alpha} decay. Previous results concerning transitions in $^{202}\mathrm{Rn}$ were confirmed. The level scheme deduced for $^{200}\mathrm{Rn}$, compared with those of heavier radon isotopes, is not consistent with the onset of deformation predicted by theoretical calculations. The estimated production cross section for $^{200}\mathrm{Rn}$ in this reaction was 5 \ensuremath{\mu}b. \textcopyright{} 1996 The American Physical Society. more...

The presence of {Delta}{ital I}=2 staggering in the three known superdeformed (SD) bands of {sup 194}Hg has been reexamined in a new experiment with Gammasphere. A relative precision of better than 60eV was achieved for most transition energies. Staggering plots were extracted and their statistical significance was analyzed. No clear evidence was found for an extended regular {Delta}{ital I}=2 staggering in the three SD bands of {sup 194}Hg. However, statistically significant deviations from a smooth reference were observed in the two excited SD bands. Different scenarios are discussed but no firm conclusion about the origin of the observed deviations can be drawn. {copyright} {ital 1996 The American Physical Society.} more...

The decay-out spectrum of the superdeformed yrast band in {sup 192}Hg comprises a quasicontinuum, from which about 50 weak discrete transitions of energy between 1 and 3.2MeV are resolved. The fluctuations of the one-dimensional quasicontinuum spectrum are studied with the fluctuation analysis method, which shows that of the order of a few thousand different transitions are available in the first step of the decay-out cascades. The experimental effective number of transitions is compared to schematic theoretical calculations. {copyright} {ital 1996 The American Physical Society.} more...

Superdeformed (SD) states of {sup 190}Hg have been studied with the Eurogam Phase 2 {gamma}-ray spectrometer using the {sup 160}Gd({sup 34}S,4{ital n}) reaction. Two new excited SD bands have been found and identified as belonging to this nucleus, bringing the total number of SD bands in {sup 190}Hg to 4. One of the new bands has a dynamic moment of inertia that is very similar to that of the yrast SD band of {sup 190}Hg and most other SD bands in the {ital A}{approximately}190 region. In contrast, the other band has a dynamic moment of inertia which is mainly constant as a function of rotational frequency and exhibits a dramatic increase at the lowest frequencies. The observed dynamic moments of inertia are compared with the results of random phase approximation calculations based on the cranked shell model. Finally, the known excited SD band has been extended towards lower frequencies and new transitions have been found linking this band to the yrast SD band. The extracted {ital B}({ital E}1) values of the new linking transitions give further support for the possible octupole vibrational character of this band. {copyright} {ital 1996 The American Physical Society.} more...

In a series of $^{78}\mathrm{Kr}$ bombardments of $^{92}\mathrm{Mo}$ the new isotopes $^{166}\mathrm{Pt}$ and $^{167}\mathrm{Pt}$ were identified via their $\ensuremath{\alpha}$-decay properties. The $\ensuremath{\alpha}$-decay energies and half-lives of these two nuclides are as follows. (1) $^{166}\mathrm{Pt}$, ${E}_{\ensuremath{\alpha}}=7110(15)$ keV, ${T}_{\frac{1}{2}}=0.3(1)$ ms, and (2) $^{167}\mathrm{Pt}$, ${E}_{\ensuremath{\alpha}}=6988(10)$ keV, ${T}_{\frac{1}{2}}=0.7(2)$ ms. Also, the half-life of $^{168}\mathrm{Pt}$, which was previously unknown, was determined to be 2.0(4) ms. In a separate but concurrent experiment involving $^{78}\mathrm{Kr}$ + $^{96}\mathrm{Ru}$ reactions, $^{170}\mathrm{Pt}$ was made and a half-life of 14.7(5) ms was measured for it; the one published value is ${6}_{\ensuremath{-}2}^{+5}$ ms. Results for $^{162\ensuremath{-}164}\mathrm{Os}$ contained in the same data sets were also analyzed and by using mother-daughter correlations, the $\ensuremath{\alpha}$ branches of $^{162,163,164}\mathrm{Os}$ were established to be near 100%. more...

Four superdeformed bands have been confirmed in {sup 192}Tl. Two of these bands have I{sup (2)} dynamic moments of inertia which are nearly constant with rotational frequency {h_bar}{omega}. The other two bands show the characteristic rise of I{sup (2)} with increasing {h_bar}{omega} seen in most superdeformed bands of the {ital A} = 190 region of superdeformation. From comparisons with the odd-{ital A} neighbors, it was found that the alignments of these bands relative to a {sup 192}Hg core can be accounted for from the additive contributions of the assigned quasiproton and quasineutron orbitals. {copyright} {ital 1996 The American Physical Society.} more...

An excitation function for the {sup 18}F({ital p},{alpha}){sup 15}O reaction has been measured in the energy range {ital E}{sub c.m.}=600{endash}800 keV using a radioactive {sup 18}F beam. A resonant state with a spin value of 3/2{sup +} has been found at an energy of 652 keV above threshold. This {ital l}{sub {ital p}}=0 resonance is found to dominate the astrophysical reaction rate at temperatures {ital T}{sub 9}{approx_gt}0.5. {copyright} {ital 1996 The American Physical Society.} more...

Discrete {gamma} rays directly connecting states of a superdeformed (SD) band in {sup 194}Hg to the yrast states have been discovered. Thus, the excitation energies and spins of all members of the lowest SD band are established for the first time, together with their likely parity. The SD band decays from its 10{sup +} and 12{sup +} states, which lie 4204.8 and 4407.4 keV above the normal-deformed yrast states of the same spins. {copyright} {ital 1996 The American Physical Society.} more...

K-isomers are states in deformed nuclei whose {gamma}-decay is hindered by selection rules involving K, the projection of the angular momentum along the axis of symmetry of the nucleus. Previous work with the Argonne Notre Dame BGO Array delineated the existence of two K-isomers in {sup 176}W, one of which had a very unusual pattern of decay. A short description of this work was published as a letter, and a more complete account is being readied for submission. These results provided evidence that quantum-mechanical fluctuations in the nuclear shape may be responsible for some of the observed K-violating transitions. In addition, hints were present in the data of the existence of another K-isomer with an even higher in. An experiment was performed in September 1994 to observe this isomer, using the reaction {sup 50}Ti({sup 130}Te,4n), and a technique in which recoiling {sup 176}W nuclei were created 17-cm upstream of the center of the array and caught on a Pb catcher foil at the center. Intense ({approximately} 3 pnA) beams of {sup 130}Te were supplied by the ECR source using a new sputtering technique. The recoil-shadow geometry was highly successful at removing the background from non-isomeric decays, allowing the weakly populatedmore » K-isomers to be detected cleanly. In addition, the availability of pulsed beams from ATLAS and the timing data from the BGO array provided a second technique for isolating the decays of interest, by selecting events in which a given number of BGO detectors fired between beam pulses. This method was used in the previous experiment, and was also applied in this experiment as a second level of selection. As a result, gamma-ray transitions were detected in the present experiment with intensities as small as {approximately} 0.02 % of the {sup 176}W reaction channel. The existence of the new isomer was confirmed, and a partial level-scheme was constructed.« less more...

A detection system has been developed for experiments with radioactive beams which have considerable contamination from a stable isobar. The system uses the gas-filled magnet technique and identifies reaction products according to nuclear charge and mass with good resolution even at energies below 1 MeV/u. In a first experiment the device has been used to measure cross sections for the 18F(p, α)15O reaction in the energy range between 650 and 840 keV/u. more...

The new proton radioactivity ${}^{185m}\mathrm{Bi}$ has been observed, produced via the ${}^{95}\mathrm{Mo}{(}^{92}\mathrm{Mo},pn{)}^{185}\mathrm{Bi}$ reaction. Its decay proceeds from the low-lying ${\frac{1}{2}}^{+}$ intruder state in ${}^{185}\mathrm{Bi}$ to the ${}^{184}\mathrm{Pb}$ ground state with the emission of a proton of energy $1.585\ifmmode\pm\else\textpm\fi{}0.009\mathrm{MeV}$ and a half-life of $44\ifmmode\pm\else\textpm\fi{}16\ensuremath{\mu}\mathrm{s}$. This marks the first observation of proton radioactivity above the $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}82$ closed shell, and it has been used to obtain the admixture of a ${0}^{+}$ intruder state in ${}^{184}\mathrm{Pb}$ into the ${}^{184}\mathrm{Pb}$ ground-state wave function. more...

Prompt, in-beam γ rays following the reaction Yb170 + 142 MeV Si28 were measured at the ATLAS facility using 10 Compton-suppressed Ge detectors and the Fragment Mass Analyzer. Transitions in Po194 were identified and placed using γ-ray singles and coincidence data gated on the mass of the evaporation residues. A level spectrum up to J10 was established. The structure of Po194 is more collective than that observed in the heavier polonium isotopes and indicates that the structure has started to evolve toward the more collective nature expected for deformed nuclei. © 1995 The American Physical Society. more...

For the first time the $^{18}\mathrm{F}$(p,\ensuremath{\alpha}${)}^{15}$O reaction has been studied with a $^{18}\mathrm{F}$ beam at energies which are of interest to explosive nucleosynthesis. Utilizing the gas-filled magnet technique a clean identification of the reaction products was achieved. A resonance with spin 3/${2}^{+}$ at an equivalent c.m. energy of 660 keV dominates the yield. more...

We performed an experiment to search for the two-phonon octupole vibrational state in {sup 208}Pb. Thick targets of {sup 208}Pb, {sup 209}Bi, {sup 58,64}Ni, and {sup 160}Gd were bombarded with 1305 MeV beams of were bombard {sup 208}Pb supplied by ATLAS. Gamma rays were detected using the Argonne-Notre Dame BGO gamma-ray facility, consisting of 12 Compton-suppressed germanium detectors surrounding an array of 50 BGO scintillators. We identified some 30 known gamma rays from {sup 208}Pb in the spectra gated by the 5{sup -} {yields} 3{sup -} and 3{sup -} {yields} 0{sup +} transitions in {sup 208}Pb. In addition, after unfolding these spectra for Compton response, we observed broad coincident structures in the energy region expected for the 2-phonon states. Furthermore, we confirmed the placement of a 2485 keV line observed previously in {sup 207}Pb and find no evidence consistent with the placement of this line in {sup 208}Pb. We are currently in the process of investigating the origin of the broadened lines observed in the spectra, extracting the excitation probability of states in {sup 208}Pb, and determining the relative probability of mutual excitation and neutron transfer in this reaction. An additional experiment is also being performed to collect much highermore » statistics germanium-germanium coincidence data for the thick {sup 208}Pb target.« less more...

An experiment using the Eurogam phase II \ensuremath{\gamma}-ray spectrometer confirms the existence of an excited superdeformed (SD) band in $^{190}\mathrm{Hg}$ and its very unusual decay into the lowest SD band over 3--4 transitions. The energies of the transitions linking the two SD bands have been firmly established, and their angular distributions are consistent with a dipole character. Comparisons with calculations using random-phase approximation indicate that the excited SD band can be interpreted as an octupole-vibrational structure. more...

A superdeformed band has been found in the [sup 154]Dy ([ital N]=88) nucleus. The dynamic moment of inertia is identical to that of the yrast superdeformed band of [sup 152]Dy and the transition energies are similar to those of an excited superdeformed band in [sup 153]Dy. It is proposed that the two valence neutrons above the [ital N]=86 shell gap occupy the deformation-driving [514]9/2 orbital. more...

Isotopes in the light actinide region with [ital N][lt]126, [ital Z][gt]82 have been produced in the reaction of [sup 28]Si on [sup 182]W at beam energies of 164 and 170 MeV. Evaporation residues were selected using an in-flight mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. The charge-to-mass ratio of implanted ions, and energies and half-lives of correlated [alpha]-decay events have been used to make isotopic identifications. The [alpha] decay from the ground state of [sup 204]Ra has been observed with an [alpha]-particle energy of 7.488(12) MeV and a half-life of 45[sub [minus]21][sup +55] ms. Previous results concerning the decay of [sup 205]Ra were also confirmed. more...

The low-lying level structure of the neutron-deficient isotope [sup 202]Rn has been studied for the first time, using the [sup 181]Ta([sup 27]Al,6[ital n]) and [sup 192]Pt([sup 16]O,6[ital n]) reactions. Gamma-ray transitions between excited states in [sup 202]Rn were identified by mass tagging using a recoil mass separator, the Argonne Fragment Mass Analyzer, and by observation of coincident x rays. Transitions in [sup 203]Rn were also identified. The level scheme deduced from these data is consistent with the systematics of light radon isotopes below the [ital N]=126 shell closure and with theoretical calculations indicating that the ground-state shape should not be strongly deformed at [ital N]=116. more...

Considerable data have recently been collected on light zirconium isotopes. We present new measurements on [sup 84]Zr and some unpublished results on [sup 82]Zr. We have performed calculations on [sup 82,84,86]Zr using an extension to the IBM which allows a collective core to couple to up to four unpaired fermions (two broken pairs). The role of vibrational collectivity is clear in the [ital N]=44 and [ital N]=46 nuclei, but collective rotation becomes the dominant mode below [ital N]=44. The relative positions of the neutron and proton Fermi surfaces are crucial in determining the complexity of the decay path down the yrast states, being dominated by proton configurations for [ital N][le]44 but showing strong competition between neutron and proton structures when [ital N][gt]44. more...

High-spin states of the transitional nucleus {sup 1}{sub 47}{sup 01}Ag{sub 54} have been studied up to spin {ital J}=41/2 with the reaction {sup 70}Ge({sup 35}Cl,2{ital p}2{ital n}), using {gamma}-{gamma} coincidence and {gamma}-ray angular-distribution measurements. The low-spin states of this nucleus involve single-particle excitations, with little evidence of quadrupole collectivity. At high spins, a coupled band structure has been identified, consisting of a cascade of {Delta}{ital J}=1 transitions with stretched {ital E}2 crossover transitions, similar to high-spin negative-parity bands observed in the heavier odd Ag nuclei. Detailed cranked Nilsson-Strutinski calculations are presented, which predict deformed rotational states based on configurations involving {nu}{ital h}{sub 11/2} excitations, and agree well with the energy levels of these high-spin negative-parity band structures. The changing nature of collectivity in these nuclei above the {ital N}=50 shell closure is discussed. more...

The level scheme of 87Mo was investigated with the reaction Ni-58(S-32, 2pn) at projectile energies of 110-130 MeV and the reaction Ca-40(Cr-50, 2pn) at 170 MeV. Extensive spectroscopic information was collected including gamma-gamma and neutron-gated gamma-gamma-coincidences as well as coincidences with identified 87Mo residues. Level lifetimes were studied with the RDDS and DSA methods. The angular distributions of low-lying transitions were measured. The results indicate a sudden transition from single-particle-like to collective behavior which is caused by g9/2 particle alignment. The level scheme was constructed up to 12 MeV excitation energy and a probable spin of 49/2 HBAR. more...

We report on the observation of excited states in the niobium isotope with masses 84, 85 and 86. These nuclei lie in the shape transition region known to occur in nuclei with 35 less-than-or-equal-to Z less-than-or-equal-to 40 and N = 45. Unambiguous identification was achieved by detecting gamma-rays in coincidence with mass-separated recoils produced in heavy-ion fusion reactions. Rotational bands were observed in 84Nb and 85Nb which show decoupling schemes similar to those in the neighbouring nuclei. A rotational model was used to interpret these bands and the quasiparticle configurations involved. Two sequences of transitions were observed in 86Nb, at least one of which appears to be a rotational band. more...

The transitional nucleus $^{86}\mathrm{Zr}$ has been studied by the $^{60}\mathrm{Ni}$${(}^{30}$Si,2p2n) reaction, with \ensuremath{\gamma}-\ensuremath{\gamma} coincidence, angular correlation, Doppler-shift-attenuation and measurements. Band structures exhibiting strongly staggered M1 transition rates were found at high spins, with large B(M1) values but no significant E2 collectivity. The unusual behavior of this nucleus is interpreted within the framework of an interacting boson model incorporating two broken boson pairs. This new model for high-spin states is seen to be remarkably successful in describing the electromagnetic decay properties in the four-quasiparticle regime. more...

The gamma-decay of excited states in the neutron deficient isotopes Tc-87 and Tc-88 has been observed for the first time. The fusion-evaporation reactions Ni-58(S-32, p2n)Tc-87 and Ni-58(S-32, pn)Tc-88 at 110 MeV, Ca-40(Cr-50, p2n)Tc-87 and Ca-40(Cr-50, pn)Tc-88 at 170 MeV and Ni-58(Ar-36, alpha-pn)Tc-88 at 145 MeV beam energy were used. Unambiguous identification of these nuclei which are populated with less than 1 mb cross section was achieved with coincidences between the gamma-radiation and the evaporation residues detected in a recoil mass separator. From gamma-gamma-coincidence data, a decay scheme of 11 transitions was constructed for Tc-88, the ground state of which is suggested to have I-pi = 7- or 8+. Two transitions identified in Tc-87 follow the pattern of a g9/2 one-quasiparticle band. (Less) more...

The back-angle yields of the oxygen and carbon particles from the {sup 31}P+{sup 16}O reaction have been measured at {ital E}{sub lab}({sup 31}P)=135.6 MeV by using reverse kinematics. Comparison with similar data for the {sup 35}Cl+{sup 12}C reaction forming the same compound nucleus at the same excitation energy and with a very similar spin distribution shows very small entrance-channel dependence of back-angle yields. These results are in contrast to a similar study of the reactions {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O. It is evident that the oxygen and carbon yields from the {sup 31}P+{sup 16}O and {sup 35}Cl+{sup 12}C reactions have a predominantly compound nucleus origin in contrast to those from the {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed. more...

High spin states in the transitional nucleus87Nb up to 14 MeV excitation have been established for the first time via the reactions40Ca(50Cr, 3p)87Nb and58Ni (32S, 3p)87Nb. The87Nbγ-radiations have been identified throughγ-ray spectra taken in coincidence with the evaporation residues detected in the Daresbury recoil separator or with multiple proton emission. Gamma-gamma coincidences, DCO ratios,γ-ray angular distributions and lifetimes have been measured. A total of some 100 transitions have been placed into a level scheme comprising of sixty states. The one-quasiparticle (1qp) bands of either parity and several other band-like structures have been identified, some containing alignedg 9/2 nucleons. Moderately enhancedE2 in-band transitions of 13–48 W.u. as well as several weakE2 yrast transitions connecting bands with different quasiparticle numbers have been found. Similarities with respect to theN=46 isotones83Rb,84Sr,85Y,86Zr and88Mo are discussed. more...