Bismuth Targets Research Articles

Experimental studies and cascade-exciton model analysis of negative pion induced fission in gold and bismuth

Fission induced by energetic negative pions in gold and bismuth has been studied experimentally and theoretically. CR-39 dielectric track detectors in 4 π-geometry were used to determine experimental cross sections, and the computer code CEM95 has been used for theoretical calculations. Experimental fission cross sections for gold have been determined at energies of 500, 672, 1068 and 1665 MeV, and for bismuth at energies of 500, 672 and 1068 MeV. The targets and detectors were irradiated at the AGS of Brookhaven National Laboratory (USA). Theoretical fission cross sections were calculated from 50 MeV to 2500 MeV to compare with a wider range of measurements. Good agreement is observed among the measured and computed results. For validation of the code CEM95 and our methodology, we also benchmarked fission cross sections induced by protons and neutrons on targets of lead and bismuth, and for pions on gold and bismuth over a wide energy range.

Evidence of microscopic effects in fragment mass distribution in heavy ion induced fusion–fission reactions

Our measurements of variances (σm2) in mass distributions of fission fragments from fusion–fission reactions of light projectiles (C, O and F) on deformed thorium targets exhibit a sharp anomalous increase with energy near the Coulomb barrier, in contrast to the smooth variation of σm2 for the spherical bismuth target. This departure from expectation based on a statistical description is explained in terms of microscopic effects arising from the orientational dependence in the case of deformed thorium targets.

Experimental study of the cross-sections of α-particle induced reactions on 209Bi

α-particle-induced nuclear reactions for generation of 211At used in therapeutic nuclear medicine and possible contaminants were investigated with the stacked foil activation technique on natural bismuth targets up to E α = 39 MeV . Excitation functions are reported for the reactions 209Bi( α,2n) 211At, 209Bi( α,3n) 210At and 209Bi( α,x) 210Po. Results obtained from direct α-emission measurements and γ-spectra from decay products are compared and correspond well with earlier literature values. Thick target yields have been deduced from the experimental cross-sections and optimised production pathways for minimal contamination are presented. A comparison with the results of the theoretical model code ALICE-IPPE is discussed.

Target cooling for high-current experiments at SHIP

In order to further increase the intensity of ion beams used in high-current experiments, e.g. the synthesis of heavy and superheavy elements, it is necessary to develop methods for cooling the targets sufficiently below the melting point which is particularly low in the case of metallic lead and bismuth targets. In this paper we describe measurements for various fixed targets and rotating target wheels in vacuum as well as in a stationary He-gas and a He-gas flow as cooling medium. As a result improvements of the target system are suggested, which will allow for a considerable increase of the beam intensity.

Calculation of the energy deposition in the targets from C to U irradiated with intermediate energy protons

AbstractThe energy deposition was calculated for the targets from carbon to uranium irradiated with intermediate energy protons with the help of different models incorporated in the MCNPX code package (Bertini, CEM and ISABEL) and with the help of the CASCADE/INPE code. The values obtained using the different models and codes are in a good agreement for all targets except uranium. The comparison with the available experimental data for the heat deposition for 0.8, 1.0 and 1.2 GeV protons has been performed. The good agreement is observed for copper, lead and bismuth target. The best result is obtained with the help of the ISABEL model. The systematic dependence of the heat deposition from atomic number of the target was investigated. The contribution of different particles and energy ranges in the heat deposition has been studied at the primary proton energies from 0.3 to 2.5 GeV.

Summary of third workshop on materials science and technology for the spallation neutron source at KEK, March 2002

The third workshop on the Materials Science and Technology for Spallation Neutron Source was held on 14–15 March, 2002 at KEK to discuss the present status and problems concerning the material issues for the spallation neutron source designs and associated R&D. There were 62 in attendance. The following six topics were energetically discussed: general presentations, radiation damage, solid target, cladding techniques, corrosion tests and accelerator-driven systems. Conclusions were reached in several areas: the basic technology of solid targets, including a Ta-clad tungsten block with the HIP method might be well-established, but irradiation and fatigue data are not yet sufficient. Liquid-target technology seems to have several problems: the urgent problem of mercury targets for neutron-scattering facilities is pitting by pressure waves induced by pulsed protons. The PIE of the STIP experiments is expected to prove the irradiation data. Problems of materials and coolant under irradiation, such as IASCC, should be investigated with the STIP and ion irradiation. Further, R&D for a lead–bismuth target is needed to design an ADS.

Extraction separation of No-carrier-added astatine from bismuth target

SummaryAlpha particle activation of natural Bi2O3results in the formation of astatine radionuclides. A simple and rapid separation method of astatine is presented from the bulk target matrix bismuth by employing liquid-liquid extraction (LLX) method using methylisobutylketone (MIBK) and hydrochloric acid. Back extraction of astatine was performed by ethylenediaminetetraacetic acid (EDTA) solution at pH 10.

Concept design of a new liquid metal target station for high power neutron scattering facilities

A new liquid metal target station without a window wall for high power charged particle beams to pass through is proposed for neutron-scattering sources and/or neutron-spallation sources. The beams are irradiated directly from above into the free surface of the liquid metal in a target tube soaked vertically in a reservoir tank of the liquid metal. A large hollow chamber is located above the target tube. This chamber works as a getter pump to evacuate the system and as a heat siphon to remove the heat fed by the beams, where the liquid metal works as the working liquid for both functions. Bismuth, Bi in the liquid state at temperatures above 300 °C, is chosen as the target medium. Experimental data for a cylindrical bismuth target are used to calculate the temperature distribution along the liquid metal target column. The evaporation rate of Bi atoms due to boiling under reduced pressure is calculated under a simple assumption in order to evaluate its activity as the working medium of a getter pump and a heat siphon.

The accelerator driven system strategy in Japan

Recent status of study on accelerator driven system (ADS) in Japan is presented. The double-strata fuel cycle concept has been proposed by Japan Atomic Energy Research Institute (JAERI) under the `OMEGA' program as a system for partitioning and transmutation (P&T) of long-lived radioactive nuclides. The ADS dedicated to transmutation is the key technology of the double-strata fuel cycle concept. The proposed system is a lead–bismuth cooled, nitride fuel 800 MW ADS for transmutation of minor actinides and long-lived fission products. JAERI has carried out a conceptual design study under the joint project between JAERI and KEK (High Energy Accelerator Research Organization) on high-intensity proton accelerators. In addition to a high-intensity proton accelerator complex, two experimental facilities are planned for development and demonstration of accelerator driven transmutation technology: The major objective of an ADS physics experimental facility is to obtain reactor physics data of hybrid subcritical system. The major objective of an ADS engineering experimental facility is to accumulate material data for the design of a lead–bismuth target system.

Current status of JAERI spallation target material program

In the joint project of spallation neutron source between JAERI and KEK, material technology has been developed for the mercury target in the neutron source facility, the lead–bismuth target in the transmutation test facility, superconducting accelerator, post-irradiation examination and the ion beam test. Design of target system is progressing for the mercury spallation target: a pressure test of moderator, an impacting test in mercury and a corrosion test have been carried out. For nuclear transmutation with ADS an engineering facility is proposed. A material corrosion test loop is built-up and SS316 and F82H steels are to be tested in a flowing Pb–Bi. Fracture toughness of superconducting cavity material was found to be considerably large at 4 K. Irradiated samples at SINQ are to be transported to JAERI Hot Laboratory. For simulating radiation damage small disk specimens were irradiated in single, dual and triple ion beam modes.

MEGAPIE, a 1 MW pilot experiment for a liquid metal spallation target

Megawatt pilot target experiment (MEGAPIE) is an initiative launched by Commisariat à l'Energie Atomique, Cadarache (France) and Forschungszentrum Karlsruhe (Germany) together with Paul Scherrer Institut (Switzerland), to demonstrate, in an international collaboration, the feasibility of a liquid lead bismuth target for spallation facilities at a beam power level of 1 MW. Such a target is under consideration for various concepts of accelerator driven systems (ADS) to be used in transmutation of nuclear waste and other applications world wide. It also has the potential of increasing significantly the thermal neutron flux available at the spallation neutron source SINQ for neutron scattering. SINQ's beam power being close to 1 MW already, this facility offers a unique opportunity to realize such an experiment with a reasonably small number of new ancillary systems. The paper describes the basic features of the experiment and its boundary conditions, the technical concept of the target and underlying research carried out at participating laboratories.

Dry-distillation of astatine-211 from irradiated bismuth targets: a time-saving procedure with high recovery yields

Astatine-211 was produced via the 209Bi( α,2n) 211At reaction. The radionuclide was isolated with a novel procedure employing dry-distillation of the irradiated target material. The astatine was condensed as a dry residue in a PEEK-capillary cryotrap. Distillation was completed within 1–2 min with isolation yields of 92±3%. Subsequent work-up of the nuclide resulted in final recovery yields of 79±3%.

Thermal-hydraulic investigations on a pilot liquid metal target

Accelerator Driven Systems (ADS) promise to play an important role in nuclear power future due to their ability to enhance both the neutronics of reactors as well as safety physics. The target where neutrons are generated by a proton beam is one of the most important units of such a system. To achieve high thermal-hydraulic performance, different target concepts have been proposed in the past. One of the most favourable concepts is the so-called liquid-metal target. To master the operation technology of a liquid-metal target system, a pilot liquid lead–bismuth target of 1 MWth has been designed and fabricated at the Institute of Physics and Power Engineering (IPPE) in the framework of an ISTC project. At the Forschungszentrum Karlsruhe (FZK) theoretical investigations are being carried out on the thermal-hydraulic behaviour of the liquid lead–bismuth target. The main purpose of this investigation is to provide basic information for the target design, initially, from the viewpoint of optimizing the window cooling.

The discovery of the heaviest elements

The nuclear shell model predicts that the next doubly magic shell closure beyond ${}^{208}\mathrm{Pb}$ is at a proton number between $Z=114$ and 126 and at a neutron number $N=184.$ The outstanding aim of experimental investigations is the exploration of this region of spherical superheavy elements (SHE's). This article describes the experimental methods that led to the identification of elements 107 to 112 at GSI, Darmstadt. Excitation functions were measured for the one-neutron evaporation channel of cold-fusion reactions using lead and bismuth targets. The maximum cross section was measured at beam energies well below a fusion barrier estimated in one dimension. These studies indicate that the transfer of nucleons is an important process for the initiation of fusion. The recent efforts at JINR, Dubna, to investigate the hot-fusion reaction for the production of SHE's using actinide targets are also presented. First results were obtained on the synthesis of neutron-rich isotopes of elements 112 and 114. However, the most surprising result was achieved in 1999 at LBNL, Berkeley. In a study of the reaction ${}^{86}{\mathrm{K}\mathrm{r}+}^{208}{\mathrm{Pb}\ensuremath{\rightarrow}}^{294}{118}^{*},$ three decay chains were measured and assigned to the superheavy nucleus ${}^{293}118.$ The decay data reveal that, for the heaviest elements, the dominant decay mode is alpha emission, not fission. The results are discussed in the framework of theoretical models. This article also presents plans for the further development of the experimental setup and the application of new techniques. At a higher sensitivity, the exploration of the region of spherical SHE's now seems to be feasible, more than 30 years after its prediction.

Synthesis of heavy and superheavy elements

In two series of experiments at SHIP, six new elements (Z = 107–112) were synthesized via fusion reactions using lead or bismuth targets and 1n-deexcitation channels. The isotopes were unambiguously identified by means of α-α correlations. Not fission, but alpha decay is the dominant decay mode. Cross-sections decrease by two orders of magnitude from bohrium (Z = 107) to element 112, for which a cross-section of 1 pb was measured. Based on our results, it is likely that the production of isotopes of element 114 close to the island of sphericalSuperHeavy Elements (SHE) could be achieved by fusion reactions using208Pb targets. Systematic studies of the reaction cross-sections indicate that the transfer of nucleons is an important process for the initiation of fusion. The data allow for the fixing of a narrow energy window for the production of SHE using 1n-emission channels. The likelihood of broadening the energy window by investigation of radiative capture reactions, use of neutron deficient projectile isotopes and use of actinide targets is discussed.

Preparation of 211At-Labeled Humanized Anti-Tac Using 211At Produced in Disposable Internal and External Bismuth Targets

These studies describe the production and purification of 211At as well as the procedure for labeling humanized anti-Tac, the antibody to the α-chain of the IL-2 receptor (IL-2Rα), which has been shown to be a useful target for immunotherapy. The optimized protocol combines the advantages of the two-stage dry distillation procedure with the astatination of trialkylstannyl substances as labeling compounds for proteins. The 211At was produced by bombarding either an external or a recently developed disposable internal bismuth target with α-particles from a Cyclotron Corporation CS-30 cyclotron. The 211At was found to contain less than 0.01% 210At. The production rate for the external target was 0.15 mCi ± 0.056 μA −1 h −1 ( n = 9) (5.55 MBq μA −1 h −1). The production rate for the internal target was 0.44 ± 0.14 mCi μA −1 h −1 ( n = 16) (16.28 MBq μA −1 h −1).

Dynamics of erosion plasma formation and formation of a plasma flame with a condensed disperse phase when quasi-continuous laser radiation acts on bismuth

The dynamics of near-surface plasma formation and the formation of an erosion plasma flame was investigated for quasi-continuous laser radiation (λ=1.06 μm, q=0.1–10 MW/cm2, τ∼1.5 msec) acting on bismuth targets in air. The absence of low-threshold plasma formation at q<2 MW/cm2 was established and explained. Instabilities in the plasma formation were revealed and the range of laser radiation power densities (2≤q≤4 MW/cm2) at which these instabilities take place was determined. At q≥5.4 MW/cm2, brightening of the flame was noted. The dependence of the luminescence temperature of the flame on the laser radiation power density q was determined.

Techniques for the discovery of new elements

Search for new elements is part of the broader field of investigations of nuclei at the limits of stability. In two series of experiments at SHIP, six new elements ( Z = 107–112) were synthesized via fusion reactions by 1n-deexcitation channels using lead or bismuth targets. The isotopes were unambiguously identified by means of αα correlations. Alpha decay, and not fission, is the dominant decay mode due to strong shell effects. Cross sections drop by two orders of magnitude from nielsbohrium ( Z = 107) to element 112, for which a cross section of 1 pb was measured. The development of intensive beam currents and sensitive detection methods is a necessity, aiming at production and identification of still heavier elements and new isotopes of already known elements, as well as small α-, β- and fission-branching ratios. An equally sensitive set-up is needed for measurement of excitation functions at low cross sections. Our results give hope that isotopes of element 114 close to the island of spherical superheavy elements could be produced by fusion reactions using 208Pb or 209Bi targets. Systematic studies of the reaction cross sections indicate that transfer of nucleons is the important process to initiate the fusion process.

Calorimetric measurements of the spatial component of heat deposition in targets from lead and bismuth bombarded by medium-energy protons

Abstract A calorimeter for the determination of the radial component of energy deposition has been developed and applied to measurements on 20 cm diameter lead and bismuth targets bombarded by 0.8, 1.0, and 1.2 GeV protons. The experimental parameters of the spatial component have been estimated.

Yield of near-target product interaction of 47 MeV/A12C ions with bismuth targets

Formation cross sections of near-target products from the reaction of 47MeV/A12C with209Bi targets have been measured. Their independent yields were obtained from their cumulative and partially cumulative yields according to the experimental data measured in this work and correction for mother-daughter decay. From the yield distribution curves of Pt, Au and Hg isotopes constructed it was found that for their peak positions at mass numbers A=188.1, 190.9 and 195.8, the widths of charge distributions are σ = 3.08, 2.80 and 3.74, respectively. The formation cross sections for some near-target neutron-rich new isotopes were extrapolated from the isotopic yield distribution curves.