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Beta-delayed neutron emission is being studied by detecting the β particles and recoiling ions emerging from the Beta-decay Paul Trap. For β decays to the ground state or γ -emitting states of the daughter nucleus, the fraction of recoiling ions which reach the ion detector in coincidence with a β particle has been determined for 134, 135Sb, 137, 138, 140I, and 144, 145Cs. This value is needed for the determination of the β -delayed neutron emission branching ratio solely from the recoil-ion time-of-flight (TOF) spectrum. The β -particle energy and recoil-ion TOF spectra were used to constrain a simple decay model, which can be used to determine the detection efficiency. The method is compared to simulations to estimate the uncertainty introduced by incomplete knowledge of the decay pattern. By fitting the simulation results to several β -ion coincidence properties measured during the experiment, the fraction of ions which reach the microchannel plate detector can be determined to within ± 4 % . This result opens the possibility of using the recoil-ion TOF spectra for high precision β -delayed neutron branching-ratio measurements.

We report a method for the precision measurement of the oscillator strengths and the branching fractions of the decay channels of the 6d7p 3F2o state in 226Ra. This method exploits a set of metastable states present in Ra, allowing a measurement of the oscillator strengths that does not require knowledge of the number of atoms in the atomic beam. We measure the oscillator strengths and the branching fractions for decays from the 6d7p 3F2o state to the 7s6d 3D1, 7s6d 3D2, and 7s6d 1D2 states and constrain the branching fraction to the 7s6d 3D3 state to be less than 0.4% (68% confidence limit). The lifetime of the 3F2o state is determined to be 15 ± 4 ns.

Radioisotopes, produced in stars and ejected into the Interstellar Medium, are important for constraining stellar and early Solar System (ESS) models. In particular, the half-life of the radioisotope, Fe-60, can have an impact on calculations for the timing for ESS events, the distance to nearby Supernovae, and the brightness of individual, non-steady-state Fe gamma ray sources in the Galaxy. A half-life measurement has been undertaken at the University of Notre Dame and measurements of the Fe-60/Fe-56 concentration of our samples using Accelerator Mass Spectrometry has begun. This result will be coupled with an activity measurement of the isomeric decay in Co-60, which is the decay product of Fe. Preliminary half-life estimates of (2.53 +/- 0.24) x 10(6) years seem to confirm the recent measurement by Rugel et al. (2009). (C) 2015 Elsevier B.V. All rights reserved.

Passivated, implanted, planar silicon (PIPS) detectors have been used for the measurement of electron spectra. The commercially available PIPS detectors, available in thicknesses of 100 μm, 300 μm, and 500 μm, have an energy resolution (FWHM) of ~ 2.2 keV , which is essentially the same as that of PIN diodes. Alpha and electron spectra of mass-separated 239 Pu and 240 Pu sources have been measured with a 300-μm thick PIPS detector and the electron to alpha ratios for the conversion lines of the 51.62- and 45.24-keV transitions have been determined. A procedure has been developed to determine the amount of 239 Pu and 240 Pu in a mixed source. The α-particle emission rate of the mixed source is measured, which is the sum of individual rates. From the electron spectrum of the mixed source, measured with the same setup as the alpha spectrum, the rates of 239 Pu electron lines are determined. Using the electron rate of the 239 Pu line and the electron to alpha ratio measured for the pure source, the α-particle emission rate of 239 Pu is determined. The difference from the total α-particle emission rate gives the α-particle emission rate of 240 Pu. In addition, electron intensities and conversion coefficients of the 239 Pu and 240 Pu transitions have been measured.

The γ - summing technique was successfully implemented for the first time in inverse kinematics using the NSCL Summing NaI(Tl) detector at the Nuclear Science Laboratory of the University of Notre Dame. This new method offers a way to measure (p,γ) and (α,γ) reactions on unstable nuclei, which are critical for an improved understanding of nucleosynthesis. As a proof of principle, the well-known resonances at E c . m . = 956 keV in the p(27Al,γ)28Si reaction and at E c . m . = 1400 keV in the p(58Ni,γ)59Cu reaction were measured and their resonance strengths were deduced. The values of the present work agree well with the reported literature values, demonstrating the viability of the technique.

International audience; In this paper, we provide a formalism for the characterization of tracking arrays with emphasis on the proper corrections required to extract their photopeak efficiencies and peak-to-total ratios. The methods are first applied to Gammasphere, a well characterized 4π array based on the principle of Compton suppression, and subsequently to GRETINA. The tracking efficiencies are then discussed and some guidelines as to what clustering angle to use in the tracking algorithm are presented. It was possible, using GEANT4 simulations, to scale the measured efficiencies up to the expected values for the full 4π implementation of GRETA.

The extinct p-process nuclide 146Sm (t1/2 = 103 ± 5 Myr) is known to have been present in the Early-Solar System and has been proposed as an astrophysical chronometer. 146Sm is also intensely used to date meteorite and planetary differentiation processes, enhancing the importance of an accurate knowledge of the 146Sm half-life. We are engaged in a new determination of the 146Sm half-life in which the 146Sm/147Sm atom ratio is determined by accelerator mass spectrometry at the ATLAS facility of Argonne National Laboratory. In order to reduce systematic errors in the AMS determination of the 146Sm/147Sm ratios (in the range of 10-7-10-9), 146Sm and 147Sm ions were alternately counted in the same detector in the focal plane of a gas-filled magnet, respectively in continuous-wave and attenuated mode. Quantitative attenuation is obtained with the 12 MHz pulsed and ns-bunched ATLAS beam by chopping beam pulses with an RF sweeper in a ratio (digitally determined) down to 1:106. The experiments and preliminary results are discussed. © 2012 Elsevier B.V. All rights reserved., SCOPUS: cp.j, info:eu-repo/semantics/published

A particle- γ coincidence technique has been used to measure the fusion cross-section in the system 12C+12C at low beam energies. Based on these results, it should be possible to measure this important fusion cross-section down to the 10 pb level within a week-long run.

The β - decay Paul trap is a linear radiofrequency-quadrupole ion trap that has been developed for precision β - decay studies. The design of the trap electrodes allows a variety of radiation detectors to surround the cloud of trapped ions. The momentum of the low-energy recoiling daughter nuclei following β decay is negligibly perturbed by scattering and is available for study. This advantageous property of traps allows the kinematics of particles that are difficult or even impossible to directly detect to be precisely reconstructed using conservation of energy and momentum. An ion-trap system offers several advantages over atom traps, such as higher trapping efficiencies and element-independent capabilities. The first precision experiment using this system is a measurement of β - decay angular correlations in the decay of 8Li performed by inferring the momentum of the neutrino from the kinematic shifts imparted to the breakup α particles. Many other β - decay studies that would benefit from a determination of the nuclear recoil can be performed with this system.

The use of the gas-filled magnet technique for the detection of intermediate mass ( A ∼ 20–40) recoil nuclei produced in (p, α ) reactions in inverse kinematics has been investigated. Through a series of calibration measurements with 27 Al, 28,29 Si and 33 S beams the optimum parameterization for calculating the average charge-state distribution in a gas-filled magnet has been determined. By measuring the magnetic rigidity, the time-of-flight and the differential energy loss of the particles at the focal plane of a gas-filled Enge Split Pole spectrograph it was possible to separate and identify the (p, α ) reaction products from elastically scattered particles at very small scattering angles. This technique was then tested by measuring the p( 33 S, 30 P) α and p( 37 K, 34 Cl) α reactions.

In this paper we discuss the properties of gas cell targets used for the production of radioactive beams via the in-flight technique as well as gas cell targets used for studies of nuclear reactions in inverse kinematics at the ATLAS heavy ion accelerator.

An interlock system is described that allows volatile targets to be prepared in an evaporator, sealed under vacuum, transported to the γ -array Gammasphere, and inserted into the reaction chamber for experiments, while maintaining a vacuum better than 10 - 5 torr . The performance of the system is demonstrated for lithium metal targets. A comparison is made between lithium targets covered by a gold evaporation to reduce oxidation and open metal targets transferred in the interlock.

Yield measurements from proton-induced fission have been performed on a number of actinide targets, both Th and U, at the on-line test facility at Oak Ridge National Laboratory. The results are discussed with a focus on the production process and physical and chemical properties of the targets.

The 242m Am isomer, a well-known candidate for photodepopulation research, has been studied in this first ever Coulomb excitation of a nearly pure (≈98%) isomer target. Thirty new states, including a new rotational band built on a K π = 6− state, have been identified. Strong K-mixing results in nearly equal populations of the K π=5− and 6− states. Newly identified states have been assigned to the K π=3− rotational band, the lowest states of which are known to decay into the ground-state band. Implications regarding K-mixing and Coulomb excitation paths to the ground state are discussed.

As part of an equipment grant provided by DOE for an upgrade to the target laboratory, the procurement of a new, general purpose, high-vacuum deposition system necessary to insure reliable and continued availability of high-purity targets was recognized as a priority item. Recommended specifications for this system included an automated, high-vacuum pumping station, a deposition chamber capable of handling large area foils or installation of a substrate planetary system for uniform coating capabilities and incorporating state-of-the-art thin film technologies. A newly manufactured system, although expensive, should be sought so as to take advantage of any warranty. Several vendors were approached so as to determine a range of price, capabilities and performance before proceeding with a purchase.

The heavy neutron-rich isotopes area is the least explored region of the nuclear landscape. Although sensitive techniques exist to gather the required information on these isotopes, they just have not been made available in sufficient quantity and with the right properties for many of the most basic studies. Recent measurements at the Canadian Penning trap (CPT) mass spectrometer, using isotopes produced from the fission of Cf 252 stopped in the CPT gas catcher system, have allowed the mass of a number of neutron-rich isotopes to be determined. This approach is being further pursued in the CARIBU project with the installation of a new dedicated heavily shielded source and gas catcher that will yield four orders of magnitude higher neutron-rich isotope yield at low energy for mass measurements and Coulomb barrier energy for nuclear structure studies.

A new focal-plane detector system has been designed and constructed for measuring very small heavy-ion induced fusion-evaporation cross sections with the Fragment Mass Analyzer (FMA) at Argonne National Laboratory. The system has been tested and successfully used in a fusion-evaporation excitation function measurement for 64 Ni + 100 Mo down to the 5 nb level. The design and performance of the detector system are described in detail with some examples from the latest data. Besides excellent tracking capabilities for each event measured in the detector, suppression of scattered beam background of the order of 4 × 10 - 17 has been demonstrated.

The r-process nuclide 244Pu (t1/2 = 80.8 Myr) was extant in the Early Solar System and is presently considered as extinct. However, fresh 244Pu produced in the Galaxy, may reach the Solar System and Earth through influx of interstellar dust or as direct ejecta from supernovae. Detection of such traces requires high sensitivity, discrimination power and efficiency. Accelerator mass spectrometry (AMS), despite low efficiency, is the method of choice. We report on the successful detection of 244Pu by AMS, using highly-charged positive ions produced in an Electron Cyclotron Resonance (ECR) ion source and accelerated with the superconducting heavy-ion linear accelerator ATLAS at Argonne National Laboratory. 244Pu34+,35+,36+ ions with a final energy of 0.7 MeV/u were dispersed in m/q using the Argonne Fragment Mass Analyzer (FMA) and are well discriminated from parasitic ions. A count rate of 0.7 244Pu counts/min was observed for a sample containing 2.7 × 108 244Pu atoms/mg. The technique described here is presently used, with improved setup and accelerator conditions, for the measurement of neutron capture cross sections in the actinide region.

A method for the production of well adhering thin film layers of oxide compounds was developed at Argonne National Laboratory using a wide-beam saddle field ion beam source. These deposits were to be subsequently exposed to alpha particle beams at the University of Notre Dame and the Weizmann Institute for nuclear astrophysics studies involving low-energy alpha capture cross-section measurements. The deposits produced had to be uniform, adhere well to the cooled substrates used, and withstand the high dose irradiation. A description of the apparatus, production method, and some preliminary results will be presented.

A new scattering chamber housing a large diameter rotating target wheel has been designed and constructed in front of the Fragment Mass Analyzer (FMA) for the production of very heavy nuclei (Z>100) using beams from the Argonne Tandem Linear Accelerator System (ATLAS). In addition to the target and drive system, the chamber is extensively instrumented in order to monitor target performance and deterioration. Capabilities also exist to install rotating entrance and exit windows for gas cooling of the target within the scattering chamber. The design and initial tests are described.

Sealed 252 Cf sources in the microCurie to milliCurie range are routinely used in industry and research. At present, no reliable analytical method is available for precise determination of the activity. Very strong sources can be analyzed by neutron counting but the error is large. We propose to use γ-ray spectroscopy for such analysis. In particular, high-energy γ rays (above 1 MeV ) of fission fragments in equilibrium with the source are very convenient because they have little absorption in materials surrounding the source. It is found that the 1435.8-keV γ-ray of 138 Cs and the 1596.5-keV γ-ray of 140 La are well isolated and sufficiently above the background under these peaks. We have measured the γ/α ratio for the 252 Cf with an uncertainty of better than 5%. The experiment involved the preparation of several thin 252 Cf sources, alpha pulse height analysis, determination of α decay rate, and the measurement of γ singles spectrum with a well-shielded germanium spectrometer. The measured ratio and the γ-ray spectroscopy of unknown samples can provide the activity of 252 Cf in these samples.

We report on the progress towards measuring the charge radius of 6 He and 8 He nuclei by performing laser spectroscopy on these helium atoms in a magneto-optical trap (MOT). First tests to produce neutral 6 He atoms via the 12 C( 7 Li, 6 He) 13 N reaction at the ATLAS accelerator have been successfully conducted. The MOT apparatus including the laser system and the discharge source to populate the metastable level are currently being set up.

A new approach to the production of low energy radioactive beams involves the stopping of fast beams produced by fragmentation, in-flight fission or fusion–evaporation reaction into a large gas catcher where the reaction products are thermalized in high-purity helium and extracted as singly charged ions for post-acceleration. This removes the limitation present in standard ISOL technique for species that are difficult to extract from the target/ion source assembly. This approach has been implemented at Argonne since 1998 to inject fusion–evaporation products in an ion trap system. Via a series of improvements since then, we now reach efficiencies for these devices of close to 50% with delay times below 10 ms. In preparation for the RIA project, a larger device for stopping fragmentation products is in preparation. The basic principles behind these devices together with results obtained and experience gained operating these devices will be presented. Preparation for a test of the large gas cell at the full RIA energy at GSI will also be presented.

The production of thin sulfur targets for nuclear physics, either in elemental or in compound form, is problematic, due to low melting points, high vapor pressures and high dissociation rates. Many sulfur compounds have been tried in the past without great success. In this paper, we report the use of spray coating molybdenum disulfide onto a thin carbon backing. The targets were of thickness 750 μg/cm 2 (∼300 μg/cm 2 of sulfur) on 15 μg/cm 2 carbon backings, and withstood 4 pnA (∼10 mW/cm 2 ) of deposited beam power for several days without apparent loss of sulfur content.

The preparation of ruthenium targets to be used in heavy-ion experiments has always presented challenges due to the physical properties of ruthenium and the cost of the separated isotopes. The straightforward approach of ion beam sputtering provides an efficient deposition technique, which allows for conservation of the isotopic starting material. A description of the target preparation will be presented along with results for several ruthenium isotopes.

Radiation damage caused by fission fragments to metal surfaces is an important research topic. Thin titanium foils were irradiated with a continuous wave beam of 132 MeV 132 Xe +29 at the current intensity of 2 pnA. Pre- and post-irradiated surface topologies were investigated using atomic force microscopy and the observed defects were quantified by root mean square roughness, depth profile of the disordered zones, size and areal density of the voids, and discussed as a function of the applied fluencies (1–9) × 10 13 Xe/cm 2 . The first ellipsoidal dislocation loops appeared at the fluence of 3.0 × 10 13 Xe/cm 2 with the areal density of 1.56 × 10 6 /cm 2 that increased to 2.0 × 10 7 cm −2 when the dose rose to 9.0 × 10 13 Xe/cm 2 . At this point also the first dislocation lines with the density of 1.3 × 10 7 cm −2 were seen. Our results suggest that the fission fragments might maximize large voids and dislocations and increase the degradation in depth resolution.

The Californium Rare Ion Breeder Upgrade (CARIBU) project was conceived to provide neutron rich beams originating from the 3% fission decay branch of a 252Cf source to be accelerated by the Argonne Tandem Linear Accelerator System (ATLAS). This 1Ci 252Cf source will be housed in a movable shielded cask, from which it can be directly transferred into a large helium gas stopper cell. Within the gas stopper, the CARIBU 252Cf source is positioned behind an aluminum degrader foil where the radioactive recoils of interest lose most of their energy before being stopped in the helium gas. To stop recoils over the full fission mass range effectively, three degraders of increasing thickness are required, one to cover the light fission peak and two for the isotopes in the heavy fission peak. The geometry of the source within the gas cell would ideally require a hemispherically shaped degrader foil for uniform energy loss of the fission products. The fabrication of a thin foil of such a shape proved to be exceedingly difficult and, therefore, a compromise “top hat” arrangement was designed. In addition, the ultra-high vacuum (UHV) environment necessary for the gas cell to function properly prevented the use of any epoxy due to vacuum outgassing. Handling, assembling of the foils and mounting must be done under clean room conditions. Details of early attempts at producing these foils as well as handling and mounting will be discussed.

Gamma-ray emission probabilities from the β − decay of 233 Pa were measured with planar (LEPS) and coaxial Ge detectors. A 233 Pa source was produced after radiochemical separation from a 237 Np sample in which the parent ( 237 Np) and daughter ( 233 Pa) nuclides were in secular equilibrium. Absolute γ ‐ ray emission probabilities per 100 α decays of the parent nuclide 237 Np were also measured in conjunction with the α - and γ ‐ ray spectroscopy techniques.

The performance of new scintillator detectors based on LaBr{sub 3}(Ce) technology was evaluated in conjunction with the Gammasphere spectrometer. Specifically, the lifetimes of states between 50 ps and 1 ns, populated in the decay of the {sup 177m}Lu isomeric state (T{sub 1/2} = 160 d), have been measured. Even though the decay scheme is rather complex, it is possible to perform precise measurements because of the superior energy resolution of the LaBr{sub 3}(Ce) detectors, compared to that of BaF{sub 2} scintillators, when used in combination with the power of the Gammasphere array to isolate a specific {gamma} cascade

For the detection of recoiling nuclei at the focal plane of the Argonne Fragment Mass Analyzer (FMA), a device employing position-sensitive micro-channel plates (MCP) was constructed. Heavy ions, when traversing a thin foil within the detector, produce secondary electrons, which are deflected by an electrostatic mirror onto the micro-channel plates where they are multiplied and counted. This thin foil serves the dual roles of producing these electrons as well as providing an electrode for the electric field. A further constraint placed upon the foil is that it should not interact detrimentally with the heavy-ion beam, and be strong enough to withstand the force produced by the potential gradient of the electric field. Preparation techniques for the thin metallized plastic films needed for this detector system are described and their performance is evaluated.

In a recently proposed study to resolve the discrepancy for the cross-section from the inverse reaction 21Ne(p,α)18F, important in calculations of asymptotic giant branch (AGB) stellar nucleosynthesis, a hydrogen target was required. Another important consideration for studying this reaction involves the isotopic abundance of Ne measured in stellar silicon carbide (SiC) grains found in meteorites. The measurement consists of the time-reversed reaction in inverse kinematics 1H(21Ne,α)18F at the resonance energy. Using a stable 21Ne beam, high currents are anticipated requiring a robust hydrogen-containing target. A metal hydride foil would be more apt to withstand the bombardment over a plastic polyethylene target. For this purpose we chose titanium hydride, as the easily produced titanium foils can be reacted with hydrogen to produce the needed targets. Details of the methods of production as well as target characteristics and performance are discussed.

Understanding the fate of heavy-metal contaminants in the environment is of fundamental importance in the development and evaluation of effective remediation and sequestration strategies. Among the factors influencing the transport of these contaminants are their chemical speciation and the chemical and physical attributes of the surrounding medium. Bacteria and the extracellular material associated with them are thought to play a key role in determining a contaminant's speciation and thus its mobility in the environment. In addition, the microenvironment at and adjacent to actively metabolizing cell surfaces can be significantly different from the bulk environment. Thus, the spatial distribution and chemical speciation of contaminants and elements that are key to biological processes must be characterized at micron and submicron resolution in order to understand the microscopic physical, geological, chemical, and biological interfaces that determine a contaminant's macroscopic fate. Hard x-ray microimaging is a powerful technique for the element-specific investigation of complex environmental samples at the needed micron and submicron resolution. An important advantage of this technique results from the large penetration depth of hard X-rays in water. This advantage minimizes the requirements for sample preparation and allows the detailed study of hydrated samples. This paper presents results of studies of themore » spatial distribution of naturally occurring metals and a heavy-metal contaminant (Cr) in and near hydrated bacteria (Pseudomonas fluorescens) in the early stages of biofilm development performed at the Advanced Photon Source Sector 2 X-ray microscopy beamline.« less

A technique for producing a high-quality radioactive 56 Ni (T 1/2 =6.1 d ) beam via the two-accelerator method has been developed. Beam intensities of 2×107 56Ni/s were extracted from the ion source and 2×104 56Ni/s were delivered to the target. For a study of neutron transfer reactions in inverse kinematics, a high-efficiency detection system was built consisting of a large solid angle (2.8 sr), high-granularity Si detector array for measuring the outgoing protons in coincidence with the heavy reaction products identified with respect to mass A and nuclear charge Z in the focal plane of a recoil mass separator.

Reactions with a heavy projectile incident on a light target can be used for the efficient in-flight production of secondary radioactive beams. An overview of this technique is given using data on 17F beams produced via the p(17O, 17F)n and d(16O, 17F)n reactions. With primary 16,17O beam currents of 100 pnA, intensities of up to 2×106 17F/s on target were achieved. Using this beam, the p(17F, α) 14O reaction was measured.

Molecular plating is now routinely used to prepare sources and targets of actinide elements. Although the technique is simple and fairly reproducible, because of the radioactive nature of the target it is very useful to record various parameters in the preparation of such targets. At Argonne, {approximately}200 {micro}g/cm{sup 2} thick targets of Pu and Cm were required for Coulomb Excitation (COULEX) Studies with the Argonne-Notre Dame BGO gamma ray facility and later with the GAMMASPHERE. These targets were plated on 50 mg/cm{sup 2} Au backing and were covered with 150 {micro}g/cm{sup 2} Au foil. Targets of {sup 239}Pu, {sup 240}Pu, {sup 242}Pu, {sup 244}Pu and {sup 248}Cm were prepared by dissolving the material in isopropyl alcohol and electroplating the actinide ions by applying 600 volts. The amount of these materials on the target was determined by alpha particle counting and gamma ray counting. Details of the molecular plating and counting will be discussed.

We give a description for the production of 13 C foils and the preparation of an approximately 1-mg/cm2 thick target. A recent experiment to measure the mass of 36 Ca , via the 40 Ca ( 4 He , 8 He ) 36 Ca reaction, required precise determination of the accelerated beam energy and calibration of the focal plane of a magnetic spectrometer to achieve the most accurate value for the 36 Ca mass. A 1 mg/cm2 13 C target was essential for these purposes. Target preparation and performance along with some preliminary results will be discussed.

Actinide targets on thick and thin backings are needed for experiments at heavy-ion accelerators. One of the efficient ways to prepare such targets is by molecular plating. Although many laboratories have successfully prepared targets on thick backings by this technique, it is quite difficult to make targets on thin backings (100 μg/cm2 up to 1 mg/cm2). In recent years, we have plated targets on thin Ni and carbon backings, for example 234U targets on a 200 μg/cm2 Ni backing. The Ni foils, evaporated on a copper substrate, are available commercially. We used these foils to plate 234U and afterwards we removed the copper by dissolving it in a mixture of ammoniacal trichloroacetic acid. In this way 400 μg/cm2 234U targets were prepared on a 200 μg/cm2 Ni backing. A 100 μg/cm2 243Am target was prepared by plating onto a 75 μg/cm2 carbon film left on its glass substrate for later floating. We found that a plating cell made from Teflon was difficult to use because it scratched the C film producing a liquid leak at the joint of the column and the C film. This sealing surface needs to be extremely smooth to avoid leakage. A column made of Delrin™ was then tried and did not produce any scratch on the carbon film surface. This column was used to prepare 100 μg/cm2 243Am targets. Details of the technique will be presented.

Due to the low melting point of tellurium metal, self-supporting Te targets degrade quickly when exposed to particle beams. This situation is greatly improved if the tellurium material is evaporated onto C foil backings. Elastic scattering in target and backing layers broadens the Te peak, making measurements difficult, while too little material reduces the reaction rate. Therefore, it is necessary to optimize the target thickness. Evaporated metallic and oxide Te targets were prepared at Argonne National Laboratory by vacuum deposition from a resistively heated source boat. The stability of the targets was then tested by exposing them to a varying intensity alpha beam with an energy range from 17 to 27 MeV using the FN Tandem Van de Graaff accelerator at the University of Notre Dame. Optimal target thicknesses and beam currents were then obtained for p-process experiments. A description of the apparatus and production method will be presented.

The half-life of 240 Pu has been determined by measuring its growth in a 244 Cm source. A thin source of 244 Cm was prepared by an electromagnetic isotope separator for this measurement, and the daughter nuclide 240 Pu was allowed to grow for 32.7 yr. The alpha spectrum of the 244 Cm source was measured with silicon detectors and the ratio of the 240 Pu and 244 Cm activities was determined. From this ratio and the previously known half-life of 244 Cm ( 18.11 ± 0.03 yr ) , the half-life of 240 Pu was determined to be T 1 / 2 = 6545 ± 19 yr . This is in excellent agreement with the value of 6564 ± 11 yr recommended by the US Half-Life Evaluation Committee.

We here report on recent experiments at GAMMASPHERE employing highly inverse, near-barrier reactions with silicon dioxide targets and use the Fragment Mass Analyzer (FMA) to collect the recoils. The 16O(58Ni,2n)72Kr reaction was studied with beams of 220 MeV 58Ni in excess of 15 pnA. Relatively few stable beam and target combinations are available to populate excited states in 72Kr, and the small cross sections of these reactions necessitate the use of targets that can withstand high intensity beam currents. A variety of oxygen containing targets were produced, with those made of silicon dioxide performing best. Over a period of 24 h of irradiation the oxygen content in these targets monotonically declined to about 1/3 of the original value. The silicon content did not appear to change. By inserting new sets of targets each 18-h-cycle an impressive data set was collected.

The wide-beam ion sputter source has several unique characteristics which make it very useful for producing, reducing the thickness or cleaning the surface of targets manufactured from expensive separated isotope. A discussion of these techniques as well as the sputter-source characteristics will be given. Sputter yields obtained utilizing this source are presented for a variety of materials common to nuclear-target production.

In conjunction with our experimental work on sputtering with a saddle-field ion source, the Monte-Carlo program TRansport of Ions in Matter (TRIM) was applied to calculate the sputter yields for a variety of noble gas sputtering applications. Comparison with experiments are shown. Information extracted from these analyses have proved useful in optimizing the experimental sputtering parameters. Calculated sputter yields obtained utilizing TRIM are presented for noble gas sputtering of a variety of materials common to nuclear target preparation.

A stack of titanium foils was irradiated with 136 MeV 136 Xe to study microstructure damage and phase stability of titanium upon irradiation. X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and atomic force microscopy were used to study the resulting microstructure damage and phase stability of titanium. We observed the phase transformation of polycrystalline titanium from alpha-Ti (hexagonally closed packed (hcp)) to face centered cubic (fcc) after irradiation with 2.2 × 10 15 ions/cm 2 . Irradiation of Ti with 1.8 × 10 14 –2.2 × 10 15 ions/cm 2 resulted in the formation of voids, hillocks, dislocation loops, dislocation lines, as well as polygonal ridge networks.

A rotating target wheel system built for the Atlas Positron Experiment (APEX) is described. It is designed so that targets could withstand the heating caused by the energy loss of intense heavy ion beams. A unique feature is the use of a digital encoder to provide logic trigger signals for beam sweeping and event-by-event target location information. Techniques for fabricating targets of tantalum, lead, thorium and uranium and the behaviour of the targets during beam exposure are also discussed.

A description is given of some recent developments at the target facility at Argonne National Laboratory. Highlights include equipment upgrades which enable us to provide enhanced capabilities for support of the Argonne Heavy-Ion Program. Work currently in progress is described and future prospects are discussed.

Targets of lead, tantalum, thorium and uranium have been produced for experiments with the APEX (Argonne Positron Experiment) apparatus at ATLAS (Argonne Tandem Linac Accelerator System). APEX is a device built at Argonne National Laboratory to investigate the anomalous positrons observed in collisions of very heavy ion beams on heavy targets. Both fixed and rotating targets have been used. The rotating target system involves a 4-quadrant wheel rotating at speeds up to 750 rpm with the position encoded into the data stream. In addition to the hundreds of targets produced for the heavy-ion reactions studied, a wide variety of targets were employed for beam diagnostics, detector calibration and target wheel development. The experiment used very heavy ion beams ( 238 U, 206 Pb and 208 Pb) from ATLAS and targets of 206 Pb, 208 Pb, 232 Th and 238 U produced in our laboratory.

A direct ion plasma sputtering effect has been observed in an electron cyclotron resonance ion source and developed into a reliable and simple method for producing ion beams from some solid materials. We describe the ion sputtering technique used with the Argonne Tandem Linac Accelerator System Positive Ion Injector Electron Cyclotron Resonance ion source to produce, to date, stable beams of nickel, silver, tellurium, gold, lead, and bismuth and present the results obtained in test cases.

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

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

For measurements of stellar reaction rates of proton rich nuclei involving resonance levels just above threshold, targets of Si-28 were used in studies of the Si-21(He-4, He-6)Si-26 reaction using the Research Center for Nuclear Physics (RCNP) Ring Cyclotron at Osaka University. Resonance structure observed in Si-26 above the 5.5 MeV proton threshold identified levels populated in the astrophysically important reaction Al-26(p,gamma) Si-26 and help to determine the yield of Al-26 gamma-rays seen in Novae. A few isolated states were also observed above the 9.2 MeV alpha threshold in the (He-4, He-6) reaction which can be used to improve the present stellar rate calculations. We describe here the involved preparation of large area Si-28 metal targets used for these experiments produced by the method of electron beam evaporation. The parting agent used was betaine. To obtain the 0.7 Mg/cm(2) Si-28 target thickness needed for the experiment, several mounted layers were assembled together by stacking. This formidable approach therefore required many foils. Two targets stacks of 0.7 Mg/cm(2) and 0.5 mg/cm(2) Si-28 were delivered to Osaka for the run. Published by Elsevier B.V.