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A target was prepared for cyclic neutron activation analysis by heat sealing lithium-carbonate in polyethylene. The target was cyclically irradiated 50 times using a Thermo-Scientific accelerator based deuterium–tritium fusion neutron generator. During counting periods, gamma-rays emitted by 16 N were detected using three high-purity germanium detectors acquiring data in list-mode. Total counts acquired in each spectrum were compared between the three detectors to examine variability in geometric positioning of the target and variability of the generator intensity throughout the experiment. These two effects were determined to be the primary sources of variation in the measured counts. Variation in target positioning and generator intensity were found to increase the standard deviation by 34% and 33%, respectively. Transit times to the detector were found to be slower and more variable than transit to the generator but were well below the half second threshold needed to measure short-lived radionuclides with half-lives on the order of seconds. The standard deviation in irradiation time was found to be less than 1 milliseconds. The impact on statistical variability in the measured counts was negligible relative to the two primary sources of variation. Spectra acquired from each cycle were summed together. The sum of the peak areas from the 6.1 MeV gamma-ray and its corresponding single and double escape peaks were used to measure the half-life of 16 N. The result of 7.108(15) seconds derived from data suggests that the currently published value of 7.13(2) seconds has minimal systematic bias induced by background.

A highly portable high-speed CAMAC data acquisition system has been developed using Kmax software (Sparrow, Inc.) for Macintosh laptop and tower computers. It uses a USB-2 interface to the CAMAC crate controller with custom-written software drivers. Kmax permits 2D parameter gating and specific algorithms have been developed to facilitate the rapid evaluation of various multi-element nuclear detectors for energy and time-of-flight measurements. This includes tests using neutrons from 252Cf and a 2.5 MeV neutron generator as well as standard gamma calibration sources such as 60Co and 137Cs. In addition, the system has been used to measure gamma–gamma coincidences over extended time periods using radioactive sources (e.g., Ra-228, Pa-233, Np-237, and Am-243).

Accurate assays of radioactive materials by gamma-ray spectroscopy depend on many factors, the most obvious being accurate gamma-ray intensities. We have used radiochemical methods to prepare pure samples of actinides. One portion of each of these samples was used to measure disintegration rates (generally by liquid scintillation counting), and the remainder was used to obtain count rates of specific gamma-rays in a well-characterized HPGe spectrometer. These methods are illustrated by results from studies of neptunium isotopes 237, 238, and 239.

Solvent extraction was used to prepare pure solutions of 237 Np and 233 Pa. Portions were used for liquid scintillation counting (disintegration rates) and γ -ray spectroscopy with HPGe detectors. X- and γ -ray intensities observed in the 237 Np decay were verified, with a new result of 15.08 ± 0.04 % for the 29 keV γ -ray ( 5 σ higher than previous reports). K X- and γ -ray intensities observed in the 233 Pa decay were verified with new results for the L X-ray intensities ( ∼ 55 % total L intensity), approximately twice previously reported total intensity.

The reaction 12C(7Be,3He) has been studied at E(7Be) = 34 MeV. Angular distributions to levels with excitation energies up to 21 MeV in the residual 16O have been measured at θlab = 13–50 degrees. This reaction selectively populates states known to have a large 12C+α component in their structure, implying that direct processes dominates at this energy.

Intermediate-energy projectile Coulomb excitation of the unstable nucleus 18 F g.s. and its short-lived E x =1.1 MeV ( J π =5 + ) isomeric state ( t 1/2 =162 ns) 18 F m have been studied at 30 MeV per nucleon. Radioactive beams of 18 F g.s. and 18 F m nuclei were produced by nucleon transfer on a carbon production target and delivered to a secondary 197 Au target for Coulomb excitation. Photons emitted in the vicinity of the 197 Au target were detected in a large-solid-angle position-sensitive NaI(Tl) array, which allowed for the identification of the beam and target excited states populated by intermediate-energy Coulomb excitation. Two possible 18 F ground-state excitations were identified, and B (E λ ↑) values were deduced. Upper limits were established for reduced transition probabilities B (E1↑) and B (E2↑) of several predicted transitions from the 18 F m isomeric state, 5 + →4 + , 4 − , 3 + , and compared with values inferred from γ-decay lifetimes. An indication of an enhanced in-flight isomer decay, possibly due to the Coulomb interaction with the target is observed and discussed. The special detector configurations and analytical techniques needed for these types of measurements are described together with suggested improvements.

A stock solution of 238 Np was produced by the 237 Np(n,γ) reaction and was purified by solvent extraction. Three small portions were used to measure absolute activity by liquid scintillation counting, and two large portions were used to obtain γ-ray spectra with Ge detectors. Intensities for strong γ rays (e.g., 25.17±0.13% for 984.17 keV) agree within ∼1% with current evaluations, but several transitions previously assigned to and from the 968-keV level in 238 Pu are unlikely to be present. The β counting yielded a half-life of 2.1024±0.0005 days for 238 Np.

The β decay of 239 U populates at least 31 levels in 239 Np below 1100 keV, but the feeding of levels above 118 keV is weak (about 1%, total) and poorly characterized. We have prepared sources by neutron capture in 238 U followed by chemical purification. Spectra were obtained with Ge detectors, sometimes with absorbers. For energies above 120 keV, these spectra confirmed 94 and rejected 23 previously reported transitions, and revealed 43 new transitions.

The energies and emission probabilities (intensities) of gamma-rays emitted in radioactive decays of particular nuclides are the most important characteristics by which to quantify mixtures of radionuclides. Often, quantification is limited by uncertainties in measured intensities. A technique was developed to reduce these uncertainties. The method involves obtaining a pure sample of a nuclide using radiochemical techniques, and using appropriate fractions for beta and gamma measurements. The beta emission rates were measured using a liquid scintillation counter, and the gamma emission rates were measured with a high-purity germanium detector. Results were combined to obtain absolute gamma emission probabilities. All sources of uncertainties greater than 0.1% were examined. The method was tested with 38 Cl and 88 Rb.

We have reexamined the decay of 24 Na to reduce the uncertainty in the intensity of the 3866-keV γ-ray and to demonstrate the use of the nuclide in extending energy and efficiency calibrations of high-resolution Ge detectors beyond 2754 keV. We find 3866.22(15) keV and 0.067(2)% for the energy and intensity, respectively, of the γ-ray deexciting the 5235.20(8)-keV level in 24 Mg. For sources placed close to the detector, the 4122.66(2) sum peak is equivalent in statistical precision to a γ-ray of 5–10% intensity. The sum peak at 5234.9(2) keV is sufficiently well-resolved to confirm an energy calibration to ∼0.5 keV.

Activity determination by gamma-ray spectrometry is a valuable aid which is widely used where radioactive sources are applied. For the construction of an efficiency curve vs. energy in a standard geometry, the accuracy is limited not only by the uncertainty of peak area determination and the knowledge of the relevant emission probabilities but also by the uncertainties of the activity values applied to efficiency calibration with standard sources. Recently, a method to determine a relative efficiency function using selected radionuclides with gamma cascades of well known emission probabilities has been developed which yields very accurate efficiency values. Such a curve has to be converted into an absolute efficiency curve by calibration of the detector system with at least one source of very well known activity. Especially for this purpose, a set of Co-60 gamma-ray spectrometer sources was produced at the PTB. The activity values (10-45 kBq) were measured by the 4pi beta-gamma coincidence technique with a standard uncertainty of less than 0.1%. Production and measurement of these sources are described in the present paper. Special care was taken to include all contributions to the standard uncertainty of the activity value when establishing the uncertainty budget for the activity of each of these sources. The activity ratio of two of these sources, as obtained by the absolute measurements, was checked by independent gamma-ray counting at two other laboratories, where the precision achieved was less than 0.2%. The procedure described is considered to be a step towards more accurately determined efficiency functions in gamma-ray spectrometry.

Natural radioactivity was first confirmed by chemical means, and for many years it was the only known form of radioactivity. Chemical techniques remain necessary for obtaining samples of series components on which detailed studies can be made. These techniques must contend with features peculiar to or emphasized in the natural decay series—low specific activities of long-lived parents and trace quantities of short-lived intermediates, interferences from carriers (isotopic or non-isotopic), and rapid growth of impurities in initially pure fractions. Examples of each of these features (challenges) are given.

Yields of neutron-rich and other ions in the region of 10≤ Z ≤30, produced by a 30 MeV/u 136 Xe 24+ beam on a thick nat C target, are presented. The ions were collected and identified with the University of Michigan 7-Tesla solenoid device `BigSol' at 1.36 Tm. The yields are sufficient to make feasible gamma- and/or beta-decay studies of lifetimes and nuclear structure at the solenoid's focal position, or alternately with the fragments transported away for low-background studies. Small but usable amounts of ions close to or including the most n-rich ions produced anywhere to-date are produced and it is shown that if particle-by-particle identification is not continuously required, that the yields may be increased by over two orders of magnitude.

Several $\ensuremath{\gamma}$ transitions in ${}^{101--103}\mathrm{Nb},{ }^{98,100}\mathrm{Y},{ }^{146}\mathrm{La},$ and ${}^{149}\mathrm{Pr}$ are identified from spontaneous fission studies employing a ${}^{252}\mathrm{Cf}$ source and the Gammasphere detector array. In particular, the pairing-free bands in ${}^{100}\mathrm{Y}$ and ${}^{102}\mathrm{Nb}$ are extended, two rather highly deformed negative-parity bands feeding the 4.3-s $\ensuremath{\beta}$-decaying isomer of ${}^{102}\mathrm{Nb}$ are identified, and their possible bandhead configurations are discussed. In the case of ${}^{101,103}\mathrm{Nb},$ we have extended previously reported level schemes by over 20 transitions in each nuclide. For the fission partners ${}^{146}\mathrm{La}$ and ${}^{149}\mathrm{Pr}$ we have elucidated their previously unreported yrast level schemes.

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}

The question "How heavy can an atomic nucleus be?" is a fundamental problem in nuclear physics. The possible existence of island(s) of stable super-heavy nuclei has been an inspiring problem in heavy ion physics for almost four decades. This paper is focused on the experimental search of Super/Hyper Heavy Elements (SHE/HHE) conducted at the Cyclotron Institute, Texas A&M University. A novel experimental idea and experimental set up introduced for this research will be presented.

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}

Consistent, clean, and high chemical recovery is important for 63 Ni analysis of low-level radioactive waste samples from nuclear power reactors. These samples generally contain numerous radionuclides in high concentrations which can interfere with nickel measurements. Chemical recovery of approx. 90% can be achieved consistently using an optimized procedure. The use of 65 Ni as a chemical tracer was incorporated into such a procedure to provide sample-specific chemical recovery. eliminating error associated with using the average recovery value of several standards. Methods were also used to correct the contaminants of 55 Fe, 58 Co, and 60 Co should they be present in separated fractions for measurement of 63 Ni activity.

Coincidence spectra obtained from arrays of radiation detectors can be analyzed without resorting to projecting lower dimensional spectra. The techniques for two-dimensional analysis (peak searches and peak fitting) are described, and extensions to higher dimensions are discussed. Even for two-dimensional analysis it is most efficient to compare predictions from a model, such as a scheme for radioactive decay, with the data by backcalculating the data from the model.

49 Ca can be used to extend the efficiency calibration and rough energy calibration of a Ge γ-ray detector to almost 5 MeV. Spectra with good statistics can be obtained by multiple neutron irradiations of natural calcium. For calibration purposes the most useful γ-rays are 3084, 4072, and 4738 keV, for which we have obtained intensities of 90.72(4)%, 8.12(3)%, and 0.281(6)%, respectively. There is little coincidence summing of γ-rays in the decay. The absence of summing and the pattern of energies and intensities make 49 Ca particularly useful in measuring full energy and annihilation escape efficiencies for small source-to-detector distances. We have acquired over 50 spectra with a large, well-characterized Ge detector and have determined the intensities of all observable γ-rays, six of which have not been reported previously.

Transport times for volatile and nonvolatile fission products in a gas jet were determined using the facility at the Ford Nuclear Reactor of the University of Michigan. A mixture of ethylene and nitrogen was used to sweep the fission products from the target chamber in the gas jet. Activated charcoal traps [C] and quartz wool traps [QW] were used to collect the volatile and nonvolatile fission products respectively. The trap was positioned in front of a HPGe detector. A “stopped-flow” technique was used for the transport time measurement. The gas flow was controlled with electrically operated valves; the application of power to the valves also triggered the counting in multiscaler mode. Measurements were carried out for two target pressures. For each pressure a number of measurements were done with the charcoal and the quartz wool traps. For a target pressure of 4 psi above atmosphere transport times of 432 ± 41 and 432 ± 23 ms were obtained for the volatile [C] and nonvolatile [QW] fission products respectively; at about atmospheric pressure the corresponding values were 458 ± 33 and 443 ± 38 ms. The values indicated that there is no significant difference in the transport time for the volatile and nonvolatile fission products in a gas jet.

An understanding of the nature of the chemical reactions taking place between fission products and their carrier gases, and the designing of a fast separation procedure were the purposes of this investigation. Chemical reactions of short-lived (less than one minute half-life) fission products with carrier gases lead to various chemical species which can be separated in the gas phase. The Gas Jet Facility at the Ford Nuclear Reactor was used to study the yields of volatile selenium and bromine fission products of 235 U using a semi-automatic batch solvent extraction technique. Heptane and water were used as organic and inorganic solvents. A carrier gas mixture of ethylene to pre-purified nitrogen (1:3) was used to sweep the fission products from the target to the chemistry area for analysis. The results indicated that the volatile selenium products generated by the interaction of selenium fission fragments with ethylene were predominantly organic in nature (84%), possibly organoselenides. The selenium values were used to resolve the fractions of the bromine nuclides, which come from two major sources, viz., directly from fission and from the beta-decay of selenium. The data showed that the fractions of independent bromine fission products in the organic phase were much lower compared to selenium; the bromine values range from 10 to 22% and varied with mass number. Results indicated that the bromine products were inorganic in nature, as possibly hydrogen chloride.

A technique for producing 58 Co positron sources for use in slow positron beams has been developed. The method has been successfully tested at the μCi and mCi level. Scaling up of the technique is under way to consistently produce 1–2 Ci sources from 60 g of irradiated nickel.

We have constructed and installed at the Michigan State University National Superconducting Cyclotron Laboratory a 40 cm bore, 1 m long, superconducting solenoid ( B oz ≈ 7 T) for use as a large-solid-angle reaction-product collector lens. The device has been used to produce short-lived isomeric secondary beams and very neutron-rich nuclei ( A = 40–80). These initial tests and the magnet's performance are described.

In this article we present a new experimental approach for production of heavy and superheavy elements (HE, SHE). Nuclear reactions at low incident energies induced by heavy ion (HI) projectiles on fissile target nuclei are investigated. Dedicated detection setup is presented and the preliminary results for the reaction 197Au(7.5 MeV /u) + 232Th, studied at the Cyclotron Institute of Texas A&M University, are given.

A model for the rate at which various primary fission products stop in the gas of the source chamber of a gas jethas been constructed. It describes the absorption of fission fragments in AI foils placed between the 23 s U deposit and the gas chamber as well as the penetration of fragments through the gas. The model is based on reported ranges (mean values as. a function of A and the dispersion in ranges) and measured activities of Kr and Xe.

Extensive high-spin band structures in 82 Sr have been established using proton- γ - γ coincidence techniques. On the basis of the Woods-Saxon cranking calculations with pairing, four of these bands are interpreted to have prolate, oblate, or triaxial shapes. Pairing correlations are predicted to be very weak at high spins in this nucleus, and calculations with no static pairing successfully reproduce the experimentally observed crossing frequencies and alignments despite the fact that none of the bands displays a rigid-rotor behavior. It is concluded that observation of rigid-rotor behavior is neither necessary nor sufficient for the disappearance of static pairing in nuclei.

Stock solutions of (233)Th were produced by the (232)Th(n,gamma) reaction and multiple purifications were used to obtain relative intensities of weak transitions. Liquid scintillation counting (absolute disintegration rates) and gamma-ray spectroscopy with HPGe detectors yielded absolute photon intensities. Absolute intensities in % (with statistical uncertainties) of prominent radiations (L and K X-rays; 29, 86, and 459 keV gamma-rays) are 8.23(8), 1.32(10), 2.17(1), 1.843(2), and 0.989(2), respectively. These intensities are more precise and approximately 30% lower than previous results.

We have developed a two-dimensional fitting program which extracts coincidence intensities and their uncertainties from a γγ coincidence matrix. The data are fitted by peaks and ridges on a two-dimensional continuum. The continuum is described as the product of components of a presumed Compton distribution for the set of detectors contributing to each axis of the continuum. Peaks and ridges are based on simple Gaussians.

There are many important applications for very intense positron beams (≥ I Ci of e + ); however, the radioactive sources needed to produce these beams are not readily available. Two separate processes for fabricating inexpensive, intense positron sources from 22 Na and 58 Co have been investigated. Both procedures have been successfully tested with low levels (mCi) of activity.

Emission barriers and subbarrler anisotropies from a decay of Sn* and Y'b* compound nuclei are examined in the light of calculations incorporating deformation effects in the decay process. For the Yb* systems deformation which increases with spin is necessary to explain the data. For the Sn* systems the spectral shapes and auisotropies can be explained without deformation. For systems lighter than Sn this probe is not sensitive to the deformation. Energy spectra and angular correla52 34 82 tions of evaporated protons from the Cr( S, 2n2p) Sr reaction were measured in coincidence with discrete transitions. Large shifts in proton spectra were observed when high spin states in different rotational bands are populated. They are interpreted as due to near-yrast stretched proton emission preferentially populating the yrast hand by subbarrier protons. Simulations show that channel selected proton spectra cannot be used as probes of deformation.

Approximately 5% of the γ-ray transitions in fission fragments are internally converted, giving rise to X-rays. X-ray energies are characteristic of Z, but yields depend strongly and not smoothly on Z and A of the fragments and on time. If these biases can be accepted, X-rays can be used to identify the atomic number of fission fragments. More generally, internal conversion and X-ray emission must be interpreted in the context of detailed knowledge of γ-ray transitions.

Gamma-ray spectroscopy can be used to identify short-lived fission products in chemical fractions obtained by gas phase transport and liquid–liquid extraction. Volatile compounds of selenium and bromine fission products of 235U were studied using a semi-automatic batch solvent extraction technique. The resulting gamma-ray spectra of the heptane and water phases were consistent with the nuclides of interest (84Se, 85Se, 86Se and 86Br, 87Br, 88Br), activation products, and neutron reactions with the Ge in the detectors. The procedure used to identify these peaks is reported.

From an experiment with Gammasphere and a ${}^{252}\mathrm{Cf}$ spontaneous fission source, a new negative-parity band in ${}^{154}\mathrm{Nd}$ and new negative-parity levels in ${}^{152}\mathrm{Nd}$ were identified and the yrast bands were extended to ${18}^{+}$ in ${}^{154}\mathrm{Nd}$ and ${20}^{+}$ in ${}^{152}\mathrm{Nd}$ in a triple gamma coincidence study. These new negative-parity bands are consistent with octupole vibrational mode. There is a constant difference as a function of spin between the ${J}_{1}$ values for the negative-parity band in ${}^{152}\mathrm{Nd}$ and ${J}_{1}$ for the similar negative-parity band in ${}^{154}\mathrm{Nd},$ however, their ${J}_{2}$ values are essentially identical. These bands indicate a new kind of identical band.

The majority of practical radioactive materials decay by modes that include γ‐ray emission. For questions of “how much” or “how pure,” one must know the absolute intensities of the major radiations. We are using liquid scintillation counting (LSC) to measurements of disintegration rates, coupled with γ‐ray spectroscopy to measure absolute γ‐ray emission probabilities. Described is a study of the 227Th chain yielding absolute γ‐ray intensities with ∼0.5% accuracy and information on LSC efficiencies.

The cross section for \ensuremath{\alpha}-particle emission in the $^{6}\mathrm{He}+^{209}\mathrm{Bi}$ reaction at energies near the Coulomb barrier is remarkably large. Possible reactions that may produce the observed \ensuremath{\alpha} particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the \ensuremath{\alpha} particle and the outgoing neutron(s). A neutron-\ensuremath{\alpha}-particle coincidence experiment was performed to study two-neutron transfer to unbound states of $^{211}\mathrm{Bi}$. It is shown that approximately 55% of the observed \ensuremath{\alpha}-particle yield at and beyond the grazing angle is because of this process. This is more than 2.5 times the fraction attributable to single-neutron transfer. The corresponding 2n-transfer cross section is 0.4 \ifmmode\pm\else\textpm\fi{} 0.1 b.

Coincidence intensities and uncertainties are extracted at the statistical limits from γ-γ coincidence matrices. The matrices are decomposed into continuum, ridges and peaks. The continuum is successfully modeled by the product of two vectors which describe the Compton distributions in the coincident detectors or groups of detectors. The ridges are represented by the corresponding continuum vector scaled according to the intensity and energy of the associated γ-ray. The peaks are fitted as the product of two, one-dimensional Gaussians. This technique has been applied to the analysis of prompt gamma-rays from the spontaneous fission of 252 Cf and the high spin states in 163 Lu populated via the 122 Sn( 45 Sc, 4n) reaction.

High spin states of [sup 84]Sr nucleus excited through the [sup 52]Cr([sup 36]S,2[ital p]2[ital n]) reaction at 130 MeV energy were studied utilizing the Oak Ridge Compton-Suppression Spectrometer System. The level scheme has been extended up to probably [ital I][sup [pi]]=(24[sup +]) at 15 084 keV excitation energy for the positive parity band. The moment of inertia, for angular frequency higher than 0.58 MeV, presented an almost constant value.

Neutron-rich {sup 147,149,151}Pr nuclei, produced in the spontaneous fission of {sup 252}Cf, were studied using the Gammasphere array. Possible parity doublets in {sup 147}Pr with N=88 and {pi}h{sub 11/2} bands in {sup 149,151}Pr are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich {sub 59}{sup 147}Pr{sub 88} nucleus such as those observed in {sub 58}{sup 146}Ce{sub 88}, and also that the h{sub 11/2} bands in the {sup 149,151}Pr track in energy the yrast bands in {sup 148,150}Ce. The backbending related to the breaking of the neutron i{sub 13/2} pair is observed at {Dirac_h}{omega}{approx}0.27 (MeV) for the proton h{sub 11/2} band of {sup 149}Pr.

High spin states in neutron-rich odd-{ital Z} {sup 143,145}Ba nuclei have been investigated from the study of prompt {gamma} rays in the spontaneous fission of {sup 252}Cf by using {gamma}-{gamma}- and {gamma}-{gamma}-{gamma}- coincidence techniques. Alternating parity bands are identified for the first time in {sup 145}Ba and extended in {sup 143}Ba. A new side band, with equal, constant dynamic, and kinetic moments of inertia equal to the rigid body value, as found in superdeformed bands, is discovered in {sup 145}Ba. Enhanced E1 transitions between the negative- and positive-parity bands in these nuclei give evidence for strong octupole deformation in {sup 143}Ba and in {sup 145}Ba. These collective bands show competition and coexistence between symmetric and asymmetric shapes in {sup 145}Ba. Evidence is found for crossing M1 and E1 transitions between the s=+i and s={minus}i doublets in {sup 143}Ba. {copyright} {ital 1999} {ital The American Physical Society}

An overview of the Michigan Positron Microscope Program is presented with particular emphasis on the second generation microscope that is presently near completion. The design and intended applications of this microscope will be summarized.

Positron beams have proven very useful for condensed matter and surface research. The highest intensity of the current operating positron beams is ∼109 slow e+/second. The goal of our proposal is to build an Intense Slow Positron Source (ISPS) demonstration beam (Phase I) of unprecedented brightness at the Idaho National Engineering Laboratory, INEL (up to 1010 slow e+/s at 5 keV over a

The reaction 197Au + 232Th at 7.5 AMeV was studied using the BigSol spectrometer at Texas A&M. Theoretical calculations suggest that this reaction could be used as an alternative method to produce heavy and superheavy elements. During the short interaction time, heavy systems of interacting nucleons are formed and, due to the strong energy dissipation, a large number nucleons can be transferred. The larger the lifetime of the decaying giant system, the larger the possible number of transferred nucleons. Moreover shell effects may help in the formation of heavy nuclei in the region of the island of stability. Reaction products emitted in an angular range from 6 to 16 degrees were collected at the entrance of the BigSol spectrometer and detected at the focal plane using a segmented ionization chamber. Four position sensitive PPAC detectors placed along the ion's flight path were used to track the product trajectories and measure the times of flight. The experimental results are presented and compared with theoretical calculations performed with the Constraint Molecular Dynamics code.