In-flight Fission Research Articles

Calculated intensity of high-energy neutron beams

Abstract The flux, energy and angular distributions of high-energy neutrons produced by in-flight spallation and fission of a 400 MeV / A 238 U beam and by the break-up of a 400 MeV / A deuteron beam are calculated. In both cases very intense secondary neutron beams are produced, peaking at zero degrees, with a relatively narrow energy spread. Such secondary neutron beams can be produced with the primary beams from the proposed rare isotope accelerator driver linac. The break-up of a 400 kW deuteron beam on a liquid-lithium target can produce a neutron flux of >10 10 neutrons / cm 2 / s at a distance of 10 m from the target.

Development and operation of gas catchers to thermalize fusion–evaporation and fragmentation products

Abstract 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.

In-flight RI beam separator BigRIPS at RIKEN and elsewhere in Japan

Abstract Presented are features of the in-flight radioactive isotope (RI) beam separators in Japan as well as of a next-generation separator BigRIPS being built at RIKEN for the RI-beam factory project. Characteristic features and present status of the existing separators are reviewed for the RIPS at RIKEN, the Secondary Beam Line at RCNP, the Secondary Beam Course at NIRS, the CRIB at CNS and the RMS at JAERI. Design features are outlined for the BigRIPS, which is characterized by two major features: large acceptances and a tandem (or two-stage) separator scheme. The large acceptances allow one to produce RI beams efficiently by using in-flight fission of uranium ions, being achieved by using superconducting quadrupoles with a large aperture. The tandem separator scheme allows one to deliver tagged RI beam. The integrated capability of the BigRIPS and the accelerators of the project can significantly enlarge the scope of future RI-beam experiments. A low-energy course following the BigRIPS can provide energy-degraded and -bunched RI beams to be applied for a gas catcher system with an RF ion guide, aiming at realizing a projectile fragmentation based ISOL system.

Yield calculations for a facility for short-lived nuclear beams

Yields for a broad range of radioactive nuclei produced by spallation reactions, neutron-induced fission, in-flight projectile fragmentation and in-flight fission have been calculated for beams of stable nuclei at energies of 100–1000MeV/u. Calculations of cross-sections and yields, attenuation effects due to absorption, production from secondary reactions, and transport efficiencies for mass selection are discussed. Rare isotope yields as functions of bombarding energies for both reaccelerated and directly produced fast-fragmentation beams are presented. This information provides a foundation for a cost-effective design of a next generation rare isotope accelerator.

The fission systematics of [formula omitted] Au ions in polymer CR-39

It has been demonstrated that high-energy heavy ions undergo ssion while propagating in dielectric solids. Since these materials act as particle detectors because of their ability to retain primary ionization damage that can be xed and enlarged with chemical etching, therefore, in principle, a complete kinematical analysis of ssion events is possible. The crucial point in this regard is the availability of a well-calibrated range-energy relation, which is necessary for mass identi cation. We have developed an analytical method to convert the geometrical parameters of ssion fragment tracks into physical parameters using an equation that expresses velocity as a polynomial of mass and range. A set of nine di<erent polynomials was used to represent small regions of mass and range in order to improve accuracy. In the case of (15:9 MeV=u) Au ions incident normally on CR-39, we have found about 200 events which could be categorized as in-=ight ssion of Au ions inside the body of the detector. Mass distributions and cross sections of ssion events have been calculated. c

The in-flight fission of 3.2 GeV uranium ions in polymer CR-39

Abstract The transparent solid materials with high resistivity can be used to register and visualize the tracks of heavily ionizing charged particles. During the passage of incident ions in the detector material, it is possible that nuclear reactions are also triggered. For uranium projectiles of energy 3.2 GeV penetrating CR-39 polymer (allyldiglycol carbonate), we have detected a large number of events in which uranium tracks are found to split in two prongs. We have measured the geometrical parameters of the bifurcated tracks and converted them into kinematical quantities such as masses and velocities of the ions associated with these tracks. The values of masses, relative velocities and opening angles of the final fragments, have been shown to be consistent with the hypothesis that the uranium ions undergo in-flight binary fission while interacting with the atoms of CR-39 polymer.