Search

Cosmology with Type Ia supernovae heretofore has required extensive spectroscopic follow-up to establish a redshift. Though tolerable at the present discovery rate, the next generation of ground-based all-sky survey instruments will render this approach unsustainable. Photometry-based redshift determination is a viable alternative, but introduces non-negligible errors that ultimately degrade the ability to discriminate between competing cosmologies. We present a strictly template-based photometric redshift estimator and compute redshift reconstruction errors in the presence of photometry and statistical errors. With reasonable assumptions for a cadence and supernovae distribution, these redshift errors are combined with systematic errors and propagated using the Fisher matrix formalism to derive lower bounds on the joint errors in $\Omega_w$ and $\Omega_w'$ relevant to the next generation of ground-based all-sky survey., Comment: 23 pages, 6 figures

We investigate the ellipticity of the point-spread function (PSF) produced by imaging an unresolved source with a telescope, subject to the effects of atmospheric turbulence. It is important to quantify these effects in order to understand the errors in shape measurements of astronomical objects, such as those used to study weak gravitational lensing of field galaxies. The PSF modeling involves either a Fourier transform of the phase information in the pupil plane or a ray-tracing approach, which has the advantage of requiring fewer computations than the Fourier transform. Using a standard method, involving the Gaussian weighted second moments of intensity, we then calculate the ellipticity of the PSF patterns. We find significant ellipticity for the instantaneous patterns (up to more than 10%). Longer exposures, which we approximate by combining multiple (N) images from uncorrelated atmospheric realizations, yield progressively lower ellipticity (as 1 / sqrt(N)). We also verify that the measured ellipticity does not depend on the sampling interval in the pupil plane using the Fourier method. However, we find that the results using the ray-tracing technique do depend on the pupil sampling interval, representing a gradual breakdown of the geometric approximation at high spatial frequencies. Therefore, ray tracing is generally not an accurate method of modeling PSF ellipticity induced by atmospheric turbulence unless some additional procedure is implemented to correctly account for the effects of high spatial frequency aberrations. The Fourier method, however, can be used directly to accurately model PSF ellipticity, which can give insights into errors in the statistics of field galaxy shapes used in studies of weak gravitational lensing., Comment: 9 pages, 5 color figures (some reduced in size). Accepted for publication in the Astrophysical Journal

A Monte Carlo model has been developed for interrogation of fissionable material embedded in thick cargos when high-energy β-delayed γ-rays are detected following neutron-induced fission. The model includes the principal structural components of the laboratory, the neutron source and collimator assembly in which it resides, the assembly that represents cargo of given characteristics, a target of highly enriched uranium (HEU) and large external plastic scintillators for photon detection. The ability of this model to reproduce experimental measurements was tested by comparing simulations with measurements of the number of induced fissions and the number of detected photons when the HEU target was irradiated with 14.25-MeV neutrons in the absence of any cargo and while embedded in assemblies of plywood and iron pipes. The simulations agreed with experimental measurements within a factor of about 2 for irradiation of the bare target and when the areal density of intervening cargo was 33 g cm−2 (wood) and 61 g cm−2 (steel pipes). This suggests that the model can permit exploration of a large range in parameter space with reasonable fidelity.

▪ Abstract The axion, a favored dark matter candidate, is expected to have a very small mass and extraordinarily weak couplings. Although it has eluded discovery or exclusion for three decades, it remains the most compelling solution to the strong-CP problem. Axions may be detected by their resonant conversion to RF photons in a microwave cavity permeated by a magnetic field. Experiments have already set significant limits on the axion's mass and photon coupling; progress in photon detection schemes at or below the standard quantum limit will soon enable definitive searches. Similarly, axions produced in the solar burning core may be detectable by their conversion to X rays in a magnetic helioscope. Significant improvements in both mass range and sensitivity of the axion helioscope will likewise be forthcoming in the next few years.

New excited states built on the 11/2− isomeric states are identified in neutron-rich 121,123Cd, respectively, with gammasphere by measuring three-and higher-fold prompt coincidences following the spontaneous fission of 252Cf. The new data suggests that the 11/2− isomers in the odd-A Cd isotopes with N ≥ 75 have spherical shape similar to those in Te. It is suggested that the backbending observed at ω ≈ 0.445 MeV in 121Cd is because of the alignment of the h11/2 neutron pair.

High-spin states in 112Pd were studied using prompt γ-ray spectroscopy with Gammasphere following heavy-ion-induced fission in the reaction 18O + 208Pb at 91 MeV. A new 8+ level at 2638 keV was discovered with transitions connecting it to the yrast band and the quasi-gamma band. The three, now established, closely spaced 8+ states indicate a mixing between the ground-state band, s-band, and quasi-gamma band. Several high-spin structures with likely negative parity have been extended to higher spin and it is proposed that they are based on the νh 11/2(g 7/2 d 5/2) and νh 11/2(s 1/2 d 3/2) configurations.

Lifetimes of states in the two strongest superdeformed (SD) bands in 193Tl were measured using the Doppler-shift attenuation method. The reaction 176Yb(23Na,6n)193Tl at a beam energy of 129 MeV was used and γ-rays were detected by the Gammasphere array. Quadrupole moments of 18.3(10) eb and 17.4(10) eb were extracted for SD bands 1 and 2, respectively, using the fractional Doppler-shifts of the SD transitions. The previously reported linking transitions of these SD bands to normal deformed near yrast levels could not be confirmed. No other candidates for linking transitions could be established.

Lifetimes of states in a rotational-like $M1$ band in ${}^{110}\mathrm{Cd}$ have been determined through a Doppler-shift attenuation method measurement performed with the Gammasphere array. The deduced $B(M1)$ values, which agree well with the predictions of the tilted axis cranking model, clearly confirm that it has the character of a shears band. Using a semiclassical scheme of the coupling of two long $j$ vectors we deduce information on the strength and form of the effective interaction between the constituent nucleons. These results are the first definitive evidence of the shears mechanism and ``magnetic rotation'' in this mass region.

Several new high-spin states are observed in the prompt $\ensuremath{\gamma}$-rays emitted from the neutron-rich, odd-$Z$ ${}^{145,147}\mathrm{La}$ fragments produced in the spontaneous fission of ${}^{252}\mathrm{Cf}.$ Alternating parity bands are extended up to spins 41/2 and 43/2 in ${}^{145,147}\mathrm{La},$ respectively. A new band completes the evidence for two sets of parity doublets expected for octupole correlations. Eight $B(E1)/B(E2)$ ratios (four new) between two bands in ${}^{145}\mathrm{La}$ are all essentially constant and somewhat larger than similar ratios in ${}^{143,144}\mathrm{Ba},$ where stable octupole deformation and/or correlations are reported. The new ratios out of the ${31/2}^{\ensuremath{-}}$ levels in both nuclei show a sharp spike compared to other states, presumably from a strong reduction in $E2$ strengths in this backbending region. In ${}^{145}\mathrm{La},$ collective bands show competition and coexistence between symmetric and asymmetric shapes. Band crossings occur in both nuclei around $\ensuremath{\Elzxh}\ensuremath{\omega}\ensuremath{\approx}0.26--0.30 \mathrm{MeV}.$ Their backbends are associated with the alignment of two ${i}_{13/2}$ neutrons according to cranked shell model calculations.

We report a new measurement of the strength of the superallowed 0 + →0 + transition in the β -decay of 10 C. The experiment was done at the LBNL 88-inch cyclotron using forty-seven GAMMASPHERE germanium detectors. The technique used in this measurement was similar to that of an earlier experiment, but the systematic corrections were significantly different. The measured branching ratio: 1.4665±0.0038×10 −2 is used to compute the superallowed Fermi f t, which gives the weak vector coupling constant and the u to d element of the Cabibbo–Kobayashi–Maskawa quark mixing matrix.

Light-actinide nuclei in the octupole deformed region have been populated using multi-nucleon transfer from Th. The energy level schemes of several thorium isotopes with A = 228-234 have been extended up to and negative parity states have been observed for the first time in Th. A systematic study of the difference in alignment between the positive- and negative-parity bands in thorium nuclei in this mass region shows that Th behave like octupole vibrators, in contrast with Th, which are octupole-deformed in character. An intrinsic electric dipole moment has been measured for the first time in Th. The small value obtained is consistent with the vibrational description of this nucleus.

High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a 232 Th target and a 136 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin ( ∼28 h ) in 218,220,222 Rn, 222,224,226,228 Ra and 228,230,234 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational frequency. Measurement of the magnitude of the intrinsic electric dipole moment, D 0 , provides additional information concerning the strength of octupole interactions in these nuclei.

The Doppler shift attenuation method has been used to determined the transition quadrupole moment of a triaxial band belonging to the γ-soft nucleus,133Ce. Doppler broadened lineshape (DBLS) analysis has revealed the magnitude of theQt value, to be ∼ 2.4 eb. This contribution provides new information of (i) the transition quadrupole moment of this band (ii) the life-times of in-band and sidefeeding transition and (iii) the relative deformations of coexisting nuclear shapes.

An experiment designed to populate two-phonon vibrational states in {sup 208}Pb by Coulomb excitation was performed with a {sup 136}Xe beam at a bombarding energy of 650 MeV. The {gamma} rays from the decay of the excited states were measured with Gammasphere and scattered particles were detected in the compact heavy-ion counter CHICO. We have not been able to observe any state close to the expected harmonic energy of 5.2 MeV. However, we were able to extract the B(E3,3{sub 1}{sup {minus}}{r_arrow}6{sub 1}{sup +}) value for the lowest known 6{sup +} state at 4.424 MeV based on measured {gamma}-ray intensities. About 20{percent} of the expected total E3 strength can be found in this state, suggesting a large fragmentation of this second octupole phonon state in {sup 208}Pb. Upper limits for the B(E3) strength were determined for higher-lying, but unseen, 6{sup +} states ranging from 15{percent} of the harmonic value at 5.2 MeV to 100{percent} at 6.0 MeV. {copyright} {ital 1998} {ital The American Physical Society}

Lifetimes of states in at least one of the M1 bands in each nucleus from 193−197 Pb have been determined through Doppler-Shift Attenuation Method experiments performed with the Gammasphere array. The nuclei were populated under similar conditions allowing accurate relative measurements of the state lifetimes. The deduced B(M1) values display the characteristic decrease with increasing angular momentum which is a clear signature of the shears mechanism. Combined with the recent results for 198,199 Pb an impressive body of evidence now exists which supports the interpretation of these structures as examples of a new mode of nuclear behavior: `magnetic rotation'.

We present a technique for operating the Gammasphere segmented Ge detectors as γ-ray polarimeters. Using γ-rays of known polarization, we have measured the polarization sensitivity, Q ( E γ ), of these detectors in the energy range E γ =0.4–1.4 MeV. The experimentally obtained value of Q ranges from 5% at 415 keV to 4% at 1368 keV. The magnitude and energy dependence of Q ( E γ ) has also been determined theoretically by means of a Monte Carlo simulation, and the agreement between experiment and theory is within 20% over the energy range measured. In order to investigate the potential for operating Gammasphere as a γ-ray polarimeter in a high background environment (one which is typical of high-spin nuclear structure studies), we also discuss data that we have analyzed from the 176 Yb ( 26 Mg, 5n) 197 Pb reaction at E =135 MeV. Although the polarimeter performance of Gammasphere is seen to be relatively poor, we are still able to demonstrate, by way of γ-ray polarization measurements, that “Shears Band 1” in 197 Pb should have negative parity.

Lifetimes have been measured for states in five superdeformed yrast bands in 193−196 Pb using the Gammasphere spectrometer array. Centroid shifts and lineshapes of transitions showing attenuated Doppler shifts have been analyzed. Transition quadrupole moments are deduced for the five bands including, for the first time, bands of two odd-A Pb isotopes. The quadrupole moments are found to be remarkably similar for the yrast bands in 194 Pb (band 1), 195 Pb (bands 1 and 2) and 196 Pb (band 1) (Q t ≈20 b). However, for 193 Pb a smaller value, Q t =17.3(7) b, is obtained. This can be explained in terms of the occupation of the neutron N = 7 intruder orbitals.

From γ-γ-γ coincidence measurements in the spontaneous fission of252Cf, level energies were established for spins 14+ to 20+ in many neutron-rich nuclei. New isotopes160Sm and162Gd were identified. The yrast bands of152,154,156Nd,156,158,160Sm, and160,162Gd exhibit remarkably near-identical transition energies and moments of inertia which are shifted by the same constant amounts for every spin state from 2+ to 12+ or 14+ for nuclei differing by 2n, 4n, 2p, 4p, α, α+2p, and α+2n. These shifted identical bands (SIB) are a new phenomenon. Analysis of all known even-even proton- to neutron-rich nuclei from Ba (Z = 56) to Os (Z = 76) reveal no SIB for proton-rich nuclei and only a few additional cases of SIB for the most neutron-rich pairs aroundN = 98–102 separated by 2n and 2p. The levels in8107Mo were extended and levels in109Mo identified for the first time.

The phenomenon of cold (neutronless) alpha ternary fission in spontaneous fission of {sup 252}Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Correlated pairs of {sub 36}Kr-{sub 60}Nd, {sub 38}Sr-{sub 58}Ce, {sub 40}Zr-{sub 56}Ba, {sub 42}Mo-{sub 54}Xe, {sub 44}Ru-{sub 52}Te, and {sub 46}Pd-{sub 50}Sn were observed to be associated with {alpha} ternary fission of {sup 252}Cf. Yields of cold {alpha} ternary fission were extracted. {copyright} {ital 1998} {ital The American Physical Society}

By deriving the angle between the proton and neutron spin vectors ${j}_{\ensuremath{\pi}}$ and ${j}_{\ensuremath{\nu}}$ in the shears bands in ${}^{198,199}\mathrm{Pb},$ we present a semiclassical analysis of the $B(M1)$ and $B(E2)$ transition probabilities as a function of the shears angle. This provides a semiempirical confirmation of the shears mechanism proposed by Frauendorf using the tilted-axis-cranking model. In addition, we propose that the rotational-like behavior observed for these bands may arise from a residual proton-neutron interaction.

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}

The nucleus {sup 168}Yb, and its near neighbors, have been studied at the very highest angular momenta using the full Gammasphere array. The experiment was performed in order to search for evidence for the existence of hyperdeformed states, which have predicted nuclear axis ratios of {approx}3:1. After exhaustive searching for both discrete and continuum {gamma} rays associated with a hyperdeformed shape, using a wide variety of different analysis techniques, no evidence for the existence of hyperdeformation has been found. This search of unprecedented sensitivity has been carried out with the full Gammasphere, and was performed on arguably the best candidate nucleus. A maximum achievable observational limit of {approx}0.02{percent} of the {sup 168}Yb channel has been calculated for this particular experiment, using Monte Carlo simulations of the response of Gammasphere. {copyright} {ital 1997} {ital The American Physical Society}

An experiment was performed with the Gammasphere Ge-detector array, and the Microball charged particle detector, to search for transitions involved in the decay from the yrast superdeformed band in Eu-143. Sum spectra in coincidence with single, double, and triple gates on SD transitions were produced to search for previously reported two-step links between the superdeformed and the near-yrast ND levels. The sum spectra contained no evidence of peaks corresponding to sums of two-step linking transitions. Several discrete gamma rays were observed in coincidence with the yrast SD band. One previously reported single-step transition at 3361 keV was confirmed to decay out of the SD band.

We report on an experiment to search for the decay of two-phonon octupole vibrational states in ${}^{208}\mathrm{Pb}$ with GAMMASPHERE. A beam of ${}^{154}\mathrm{Sm}$ at a bombarding energy of 1 GeV was used to excite ${}^{208}\mathrm{Pb}$ via quasielastic as well as via deep-inelastic processes. To be independent of the lifetime of the two-phonon state a thin target was used, requiring the measurement of the position of the scattered particles to correct for the Doppler shift of the emitted \ensuremath{\gamma} rays. Scattered particles were detected by a silicon-strip detector covering forward angles. We did not observe any discrete \ensuremath{\gamma} transition in the expected energy range of 2\char21{}3 MeV down to a limit of 20% and 4% of the intensity in the ${5}^{\ensuremath{-}}\ensuremath{\rightarrow}{3}^{\ensuremath{-}}$ transition for quasielastic and deep-inelastic processes, respectively.

The phenomenon of cold (neutronless) binary and ternary fission in spontaneous fission of252 Cf was experimentally observed by triple gamma coincidence technique with Gammasphere with 72 gamma-ray detectors. Many correlated pairs for both binary and ternary (4He,10Be) fission were observed in the spontaneous fission of252 Cf. Yields of cold ternary and cold binary fission were extracted. These results are compared with the theoretical calculations using M3Y nucleon-nucleon potential and WKB approximation for barrier penetration.

Ten new transitions in {sup 107}Mo have been observed and levels in {sup 109}Mo are identified for the first time in a {gamma}-{gamma}-{gamma} coincidence study from the spontaneous fission of {sup 252}Cf with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by E1 transitions are observed in {sup 107}Mo and one such set in {sup 109}Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h{sub 11/2} and d{sub 5/2} neutron shells. {copyright} {ital 1997} {ital The American Physical Society}

Spontaneous fission of252Cm was studied with 72 large Compton suppressed Ge detectors in Gammasphere. New isotopes160Sm and162Gd were identified. Through X-ray-γ and γ-γ-γ coincidence measurements, level energies were established to spins 14+ to 20+ in152, 154, 15660Nd92, 94, 96156, 158, 16062Sm94, 96, 98 and160, 16264Gd96, 98. These nuclei exhibit a remarkable variety of identical bands and bands where the energies and moments of inertia are shifted by the same constant amounts for every spin state from 2+ to 12+ for various combinations of nuclei differing by 2n, 4n, 2p, 4p and α.

We have used the Ca-48+Yb-176 reaction to study the population of high-spin states in neutron-rich nuclei by deep-inelastic reactions. Using Gammasphere, we observed gamma transitions from nuclei s ...

Research and development is proceeding on a new /spl gamma/-ray detector array for nuclear physics: the Gamma-Ray Energy Tracking Array (GRETA). This array will consist of a spherical shell of highly segmented Ge detectors. By obtaining the energy and position of each interaction point, high efficiency and peak-to-total ratios can be obtained as compared with existing arrays. Here we discuss the computer algorithms that are needed to process the raw data and maximize the performance of the array. The results of these algorithms on Monte Carlo simulated data are presented.

From an experiment with Gammasphere and a 252 C spontaneous fission source, two bands with signatures -i and +i are identified in 153 Nd Also several new transitions in 149 Nd are observed for the first time. The band with signature -i in 153 Nd shows no back bending, similar to the one observed in 161 Er . The signature splitting observed in the ground band of 153 Nd is similar to the ones observed in N=93 isotones in this mass region. In 149 Nd the new transitions are placed into a band with a proposed configuration of [Formula: see text].

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}

Lifetimes of the 14{sup +}, 12{sup +}, 10{sup +} states and, for the first time, the 8{sup +} state in the yrast superdeformed (SD) band of {sup 194}Pb were measured at Gammasphere with the recoil-distance Doppler-shift method. Constant transition quadrupole moments with an average of 18.8 (11) eb were found at the bottom of the SD band. The decay out of the SD band can be viewed as governed by a small admixture of normal deformed (ND) states to the SD wave function which is assessed for the 8{sup +} and 10{sup +} SD states based on a simple mixing model. The electromagnetic properties of the ND states involved in the decay out are extracted for the first time by investigating the decay strength of the discrete linking transitions. Despite the large intensity of observed linking transitions, the new data show that the decay out of the SD band is statistical in nature. {copyright} {ital 1997} {ital The American Physical Society}

Lifetimes of states in four of the M1 bands in {sup 198,199}Pb have been determined through a Doppler-shift attenuation method measurement performed using the Gammasphere array. The deduced B(M1) values, which are a sensitive probe of the underlying mechanism for generating these sequences, show remarkable agreement with tilted axis cranking (TAC) calculations. The results represent clear evidence for a new concept in nuclear excitations: {open_quotes}magnetic rotation.{close_quote}{close_quote} {copyright} {ital 1997} {ital The American Physical Society}

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}

High-precision lifetime measurements have been performed in superdeformed (SD) bands of 151,152 Dy and 151 Tb with the Doppler-shift attenuation method. Differences found in the quadrupole moments Q 0 of the yrast SD bands are understood in terms of shape polarization effects by the high- N intruder orbitals. Q 0 moments are also presented for three excited SD bands in 151 Dy. Recent calculations can account for most of the observations.

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.}

A search was undertaken to look for evidence of hyperdeformation in Gd-146,Gd-147. Three experiments employing Gammasphere for gamma-ray detection coupled with the Microball for channel selection via charged particle detection were carried out with increasing detection sensitivity and statistics. No definitive evidence for band structures that could be assigned to hyperdeformation could be found. Candidates previously reported are shown not to have properties consistent with a band structure.

The {gamma} transitions in {sup 147}Ba, {sup 149}Ce, and {sup 151,153}Nd have been identified from {gamma}-{gamma}-{gamma}, {gamma}-{gamma}, {ital x}-{gamma}, and {ital x}-{gamma}-{gamma} coincidence studies of spontaneous fission of {sup 252}Cf. The yrast positive parity band in {sup 149}Ce is assigned to an {ital i}{sub 13/2}, neutron favored signature. The yrast negative parity band in {sup 149}Ce is assigned a {ital h}{sub 9/2} proton favored signature. The positive parity band in {sup 151}Nd corresponds to the positive parity band in {sup 149}Ce. The negative parity band in {sup 153}Nd corresponds to the negative parity bands of {sup 149}Ce and {sup 161}Er. The band observed in {sup 147}Ba is built on the {ital h}{sub 9/2} orbital. The plots for {ital J}{sub 1} in these isotopes are remarkably similar, supporting our assignments. {copyright} {ital 1996 The American Physical Society.}

Coincidence \ensuremath{\gamma}-ray data from the spontaneous fission of $^{242}\mathrm{Pu}$ were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of $^{242}\mathrm{Pu}$ and the yields from thermal-neutron-induced fission of $^{241}\mathrm{Pu}$ are also presented. \textcopyright{} 1996 The American Physical Society.

The quadrupole moments {ital Q}{sub 0} of five superdeformed bands in {sup 131,132}Ce have been established using the Doppler-shift attenuation method; for the first time, we can compare relative deformations of yrast and excited bands in different nuclei to an accuracy of {approx_equal}(57){percent}. Four of the five bands have very similar deformations, while the excited band in {sup 131}Ce has a somewhat larger quadrupole moment. Important new information is presented on the shape-driving force of the {nu}{ital i}{sub 13/2} orbital, the stability of the second minimum with respect to particle excitations, the relative deformations of identical bands, the nature of the sidefeeding, and the time scale of the decay process. {copyright} {ital 1996 The American Physical Society.}

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.}

New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

Six superdeformed bands have been observed in [sup 193]Pb following the [sup 174]Yb([sup 24]Mg,5[ital n]) reaction at a beam energy of 131 MeV. The in-beam [gamma] rays were detected with GAMMASPHERE early implementation. Two of the bands have dynamic moments of inertia which have an anomalously low increase with rotational frequency, and are interpreted as the favored and unfavored signature components of the [ital N]=7 neutron orbital. The other four bands have increasing dynamic moments of inertia typical of superdeformed bands in the [ital A]=190 region, and are interpreted as two pairs of signature partner bands based on high-[ital K] quasineutron excitations. The effects of the intruder [ital N]=7 neutron orbital on the superdeformed rotational characteristics are discussed.

A method for correcting target-thickness-induced Doppler broadening in gamma-ray spectra from weakly populated, very short-lived (femtosecond) states is presented. The method is illustrated by an a ...

We discuss the appearance of \ensuremath{\Delta}I=2 staggering effects in the \ensuremath{\gamma}-ray energies of some superdeformed bands as due to the mixing of a series of K bands. These bands are described by the rotational Hamiltonian of a symmetric top having a fourfold symmetry axis. Using the known properties of superdeformed bands we have found limits to the possible values of the model parameters by the analysis of effective moments of inertia, deviations from the I(I+1) rigid-rotor behavior and B(E2) values. Our results indicate that the value of ${\mathcal{I}}_{3}$, the moment of inertia due to the ${\mathit{Y}}_{44}$ deformation, is close to that expected for a rigid ellipsoid.

The Axion Dark Matter eXperiment (ADMX) was designed to detect ultra-weakly interacting relic axion particles by searching for their conversion to microwave photons in a resonant cavity positioned in a strong magnetic field. Given the extremely low expected axion-photon conversion power we have designed, built and operated a microwave receiver based on a Superconducting QUantum Interference Device (SQUID). We describe the ADMX receiver in detail as well as the analysis of narrow band microwave signals. We demonstrate the sustained use of a SQUID amplifier operating between 812 and 860 MHz with a noise temperature of 1 K. The receiver has a noise equivalent power of 1.1x10^-24 W/sqrt(Hz) in the band of operation for an integration time of 1.8x10^3 s., Comment: 8 pages, 12 figures, Submitted to Nuclear Inst. and Methods in Physics Research, A

Hidden U(1) gauge symmetries are common to many extensions of the standard model proposed to explain dark matter. The hidden gauge vector bosons of such extensions may mix kinetically with standard model photons, providing a means for electromagnetic power to pass through conducting barriers. The axion dark matter experiment detector was used to search for hidden vector bosons originating in an emitter cavity driven with microwave power. We exclude hidden vector bosons with kinetic couplings $\ensuremath{\chi}g3.48\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ for masses less than $3\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. This limit represents an improvement of more than 2 orders of magnitude in sensitivity relative to previous cavity experiments.