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 design of high-power targets for production of intense beams of radioactive ions requires the following: a reliable determination of the power deposited, knowledge of the thermal properties of the materials incorporated in the design, and a comprehensive thermal analysis of designs to evaluate the conceptual approaches. From the thermal analysis, iterations in the design approaches can lead to effective target conceptual designs that can bypass a series of prototype tests. Emphasis will be made for conductive cooling approaches, for which comprehensive thermal conductivity data are required for all components. Additional thermal properties are needed if radiative cooling or shielding is incorporated in target concepts. The example is presented of a uranium/carbon target to produce fission-product activities, featuring sensitivities to power dissipation and thermal properties assumed in the analyses.

The two-step fission-product target concept is analyzed to design a prototype target for testing at the ISAC facility. A two-step target consists of an inner cylinder of heavy metal irradiated by an energetic light ion beam; neutrons produced emerge from the target into a coaxial secondary target (blanket) of fissionable material. With this approach, the production of fission product activities is enhanced compared to other products that can interfere in experiments, and significantly less energy is deposited in the secondary target than for direct irradiation. The design is mechanically simple and provides independent control of operating temperatures.The analysis determined appropriate target and blanket dimensions, and energy deposition profiles, temperature distributions and fission production rates. The production rates of some neutron-rich isotopes for selected elements are summarized. A conceptual design is presented, along with issues on cooling the primary target and heating of the secondary target. (C) 2002 Elsevier Science B.V. All rights reserved.

Development of a prototype two-step target to produce neutron-rich RIBS is presented, with particular emphasis on thermal analysis under high-power operation. The two-step target is an attractive concept for production of fission-product activities without interference by high-energy spallation reactions which occur in direct production targets. In this concept, a high-energy production beam interacts with a primary target of refractory metal, depositing beam energy in the primary target and producing low-energy neutrons that cause fissions in a surrounding secondary target of mixed UC2 and excess C. Thermal analysis of the composite target presents challenges in cooling the primary target while maintaining the secondary target at temperatures suitable for release of the fission products. The effects of fission energy deposition in the secondary target are discussed, along with the complexities resulting from the thermally insulating character of the secondary target material.

A short review is presented of target cooling approaches suggested for targets irradiated by intense high-energy proton beams to produce radioactive species for use in a broad range of physics studies, This work reports on conductive cooling approaches for operation at temperatures lower than effective for radiative cooling. The possibilities for conductive cooling are discussed, and a prototype test target is described. This target was constructed for an experiment, designed to validate the numerical analysis approaches, at the TRIUMF/ISAC facility. Fabrication issues and the results of the experiment are presented, followed by a discussion of the implications of the experiment outcome for future development of targets to produce intense beams of radioactive ions. (C) 2002 Elsevier Science B.V. All rights reserved.

Approaches to develop targets for production of intense radioactive ion beams (RIBs) have been evaluated over the past five years. It is acknowledged that many desired physics objectives using RIBs can be met only by using production beams of energetic protons with currents up to 100 μA. Such beams can be made available at future spallation neutron facilities. The production targets will require active cooling to control operational temperatures due to internal heating caused by the production beam. A target concept has been selected, and calculational analyses of the target concept have been performed to guide the design of a prototype target for an in-beam test of the actual thermal behavior. For this test, a high-power test facility is needed; fortunately, the beam currents required exist at the TRIUMF accelerator facility. An experimental proposal has been approved for such a test.

Issues are discussed in producing intense Radioactive Ion Beams (RIB) using the Isotope Separator On-Line (ISOL) approach, based on the use of thick targets employed at existing facilities. Some new physics studies may possibly be addressed by improving the performance of these existing targets through improvements in release and effusion properties to optimize the RIB yields. It is, however, acknowledged that many desired physics objectives using RTB can be met only by employing production beams of energetic light ions or protons with currents up to 100 mu A. Development of targets that use such intense production beams needs to address the requirement to control operational temperatures derived from internal production beam interactions with the target materials. In addition, issues arise for target materials in terms of their thermal characteristics, such as thermal conductivity and thermomechanical properties. A target concept is described for an in-beam test of a prototype target for actual thermal behavior under RIB production conditions. For such a test, a high-power test facility is needed; fortunately, the prototypical production beam currents required exist at. the TRIUMF accelerator facility. An experimental proposal has been approved for such a test.

Development of conceptual approaches for targets to produce intense radioactive ion beams is needed in anticipation of activity for a next-generation, intense ISOL-type radioactive beams facility, strongly recommended in the NSAC 1995 Long Range Plan for Nuclear Science. The production of isotopes in vapor form for subsequent mass separation and acceleration will depend on the ability to control target temperature profiles within the target resulting from interactions of the intense production beams with the target material. A number of earlier studies have identified promising approaches which need, however, to be carefully analyzed for specific target systems. A survey will be made of these earlier concepts employing various cooling techniques, including imposition of thermal barriers between the target materials and cooling systems. Some results of preliminary analyses are summarized.

Thermal analyses are presented of a cylindrical target concept for the production of radioactive beams by intense, high-energy proton production beams. The basic principle is to extract heat generated internally by the production beam interactions with the target material through appropriate thermal barriers. This approach allows the target material to be operated at an elevated temperature to enhance the release of radioactivities produced by the production beam bombardment, yet remove the heat generated initially. Three classes of targets are considered: high temperature and moderate heat generation; moderate temperature and low heat generation; and low temperature and high heat generation. Various thermal barriers approaches appropriate to the combined temperature and heat removal constraints are included, such as contact thermal resistance, refractory material interfaces, and porous metal interfaces. It is shown that suitable thermal barrier approaches exist to encompass the range of target conditions expected for the production of intense beams of radioactive ions.

Cylindrical targets used for the production of radioactive beams by high-energy protons are analyzed in terms of target interaction length for some typical target systems. The analysis, using the Monte Carlo based LAHET code system, first determined applicable parameters of the beam/target interaction at 500 MeV incident proton energy. The analysis was then extended to other commonly-available proton energies up to 1000 MeV.

Calculations have been made of energy deposition distributions for “thick” targets (∼1 mole/cm2) employed in on-line production of exotic nuclei using the Monte Carlo based LAHET code system for high-energy charged particle transport. A variety of target materials and incident proton beam energies have been examined. For 600 MeV protons, the results are compared to those from a similar study reported in the literature. The agreement between the two studies for total energy deposition is reasonably good for monatomic targets, but the results differ in some details of the energy deposition distributions. Target cooling, both radiative and conductive, is examined to assess the suitability of existing target concepts exposed to bombardment by intense (up to 100 μA), energetic (500 MeV to 1.2 GeV) proton beams to produce exotic nuclei. Implications of cooling requirements to target material selection and design are discussed.

Studies of the low-velocity stages of a radioactive beams accelerator are summarized, highlighting the limitations of existing RFQ technology when applied to the specifications of the IsoSpin Laboratory.

Levels in 110Ru have been studied via the gamma-rays following the beta- -decay of 1.0-s Tc-110. The emitted gamma-rays have been investigated by gamma-singles and gamma-gamma(t) coincidence measurements. The technetium activity was separated from the Cf-249-fission products using the on-line centrifuge system SISAK. A level scheme for 110Ru is proposed based on 15 gamma-transitions. In addition, the beta- -decay of 0.9-s Tc-109 has been studied and six gamma-lines could be assigned to this nuclide.

The total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T=2.9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ to 0.16 GK. For thermal neutrons the cross sections to the ground state (${p}_{0}$) and the first excited state (${\mathit{p}}_{1}$) of $^{7}\mathrm{BLi}$ are 38 400\ifmmode\pm\else\textpm\fi{}800 b and 420\ifmmode\pm\else\textpm\fi{}120 b, respectively. This result for the total $^{7}\mathrm{Be}$(n,p${)}^{7}$Li thermal cross section is about 25% lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/v shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the ${2}^{\mathrm{\ensuremath{-}}}$ threshold state and for a possible nearby ${2}^{\mathrm{\ensuremath{-}}}$ state. The astrophysical reaction rate, ${N}_{A}$〈\ensuremath{\sigma}v〉, was calculated from the measured cross sections for the combined ${p}_{0}$ and ${p}_{1}$ transitions. The resulting reaction rate is approximately 60--80 % of the rate currently in use. This reduction in the $^{7}\mathrm{Be}$(n,p${)}^{7}$Li reaction rate could result in a calculated increase in the production of $^{7}\mathrm{Li}$ during the big bang by as much as 20%.

A two-stage isotope separator is proposed to operate on-line with a He-jet coupled ion source installed at LAMPF. As a special feature, the design of this separator employs a preseparation stage to remove the intense He+ component of the ion source output. This feature allows the low-intensity radioactive ion beam to be transported throughout the two separator stages, and at the same time makes possible monitoring and control of the ion source performance. A design goal is to achieve a resolving power sufficient to provide isobar separation for nuclei far from stability, especially important becuase of the elemental nondiscrimination obtained using the He-jet approach.

Two patients with mononucleosis, one due to cytomegalovirus (CMV), and the other due to Epstein-Barr virus (EBV), presenting with high fever, malaise and hepatitis, had granulomas in the bone marrow but not in the liver. In patients who have unexplained fever, bone marrow granulomas may be a clue to CMV or EBV infection and need not initially raise the fear of prognostically more severe illness.

The thermal-neutron fission cross section of $^{235}\mathrm{U}^{\mathrm{m}}$ has been measured relative to the ground-state cross section. A rapid radiochemical separation procedure was developed to provide sizeable (${10}^{10}$ to ${10}^{11}$ atom) samples that were reasonably free of the parent $^{239}\mathrm{Pu}$. From a series of eight measurements, the value of 1.42\ifmmode\pm\else\textpm\fi{}0.04 was obtained for the ratio ${\ensuremath{\sigma}}_{m}$/${\ensuremath{\sigma}}_{g}$.