Design study of 10 kW direct fission target for RISP project

Abstract

Abstract. We are developing Isotope Separation On-Line (ISOL) target system, which consists of 1.3 mm-thick uranium-carbide multi-disks and cylindrical tantalum heater, to be installed in new facility for Rare Isotope Science Project in Korea. The intense neutron-rich nuclei are produced via the fission process using the uranium carbide targets with a 70 MeV proton beam. The fission rate was estimated to be ∼1.5 × 10 13 /sec for 10 kW proton beam. The target system has been designed to be operated at a temperature of ∼2000 • C so as to improve the release efficiency.Production and delivery of high purity intense of Rare Isotope Beam (RIB) have been a major concern for fundamental research fields such as astro− and nuclear−physics as well as applied research field such as material and bio-medical science. Rare Isotope Science Project (RISP) of Korea has proposed to construct Isotope Separation On-Line (ISOL) facility in order to provide the intense rare isotopes. The ISOL target enables us not only to produce the nuclei with the medium mass neutronrich region but also to obtain their high production rates. A uniform 70 MeV proton beam with a maximum current of 500 µA, which is delivered from a cyclotron driver, will impinge on an uranium carbide target. The neutron-rich isotopes are produced via proton-induced fission. A singly charged (1+) RIB is produced and extracted from the target and the ion source, respectively, then the beam emittance is reduced by a RF-cooler to be 3 πmm mrad before injecting to the high resolution mass separator (HRMS). The isotopes selected by the HRMS are delivered to an electron beam ion source (EBIS) or an electron cyclotron resonance (ECR) type charge breeder so as to breed the charge from the 1 + charge state to a n + charge state for efficient and economical post-acceleration. An A/q separator is installed at the downstream of the charge breeder to purify the ion beam contaminated during charge breeding. Here, we report on the results of the ISOL target design for 10 kW proton beam.The main issues concerning the design of the ISOL target can be divided into three categories; intarget fission rate, release time, and temperature of the target. Firstly, a total effective thickness of the target should be as thick as possible in order to maximize the in-target fission rate. This requires a large size of the target. Secondly, release time should be as short as possible so as to minimize the losses by the decay of isotopes. A small size of the target helps to reduce the release time by decreasing the flight length of the isotopes. However, it should be noted here that the small size can lead to melt down of the target due to the reduced radiant cooling. Lastly, the temperature of the target should be as high as possible to increase the thermal velocity of the isotopes, which leads to the reduction of the release time. Therefore, the correlations between the three points mentioned above should be investigated so as to find the optimum condition for the ISOL target. a

Characterization of uranium carbide target materials to produce neutron-rich radioactive beams

“…Finding optimal properties of the uranium refractory compound target materials constitutes a key ingredient for the production of a wide variety of isotope beams using the ISOL (Isotope Separator Online) technique. Different developments have been achieved in various facilities [1][2][3] and today uranium carbides with an excess of graphite (with variable stoichiometries, UC x , since uranium dicarbide UC 2 and uranium monocarbide UC phases can be both stabilized depending on the amount of graphite added) are used by the different operating facilities throughout the world [4][5][6][7][8].…”