Radioactive ion beams produced by neutron-induced fission at ISOLDE

Abstract

The production rates of neutron-rich fission products for the next-generation radioactive beam facility EURISOL are mainly limited by the maximum amount of power deposited by protons in the target. An alternative approach is to use neutron beams to induce fission in actinide targets. This has the advantage of reducing: the energy deposited by the proton beam in the target; contamination from neutron-deficient isobars that would be produced by spallation; and mechanical stress on the target. At ISOLDE CERN, tests have been made on standard ISOLDE actinide targets using fast neutron bunches produced by bombarding thick, high-Z metal converters with 1 and 1.4 GeV proton pulses. This paper reviews the first applications of converters used at ISOLDE. It highlights the different geometries and the techniques used to compare fission yields produced by the proton beam directly on the target with neutron-induced fission. Results from the six targets already tested, namely UC 2 /graphite and ThO 2 targets with tungsten and tantalum converters, are presented.To gain further knowledge for the design of a dedicated target as required by the TARGISOL project, the results are compared to simulations, using the MARS code interfaced with MCNP libraries, of the neutron flux from the converters interacting with the actinide targets. Victoria, B.C. Canada, 6-10 May, 2002 Geneva R. Catherall ** , J. Lettry, S. Gilardoni, U. Köster and the ISOLDE collaboration Paper presented at the 14th International Conference on Electromagnetic Isotope Separators and Techniques Related to their Application CERN, CH-1211 Genève 23, Switzerland AbstractThe production rates of neutron-rich fission products for the next-generation radioactive beam facility EURISOL [1] are mainly limited by the maximum amount of power deposited by protons in the target. An alternative approach is to use neutron beams to induce fission in actinide targets. This has the advantage of reducing: the energy deposited by the proton beam in the target; contamination from neutron-deficient isobars that would be produced by spallation; and mechanical stress on the target. At ISOLDE CERN [2], tests have been made on standard ISOLDE actinide targets using fast neutron bunches produced by bombarding thick, high-Z metal converters with 1 and 1.4 GeV proton pulses.This paper reviews the first applications of converters used at ISOLDE. It highlights the different geometries and the techniques used to compare fission yields produced by the proton beam directly on the target with neutron-induced fission. Results from the six targets already tested, namely UC 2 /graphite and ThO 2 targets with tungsten and tantalum converters, are presented.To gain further knowledge for the design of a dedicated target as required by the TARGISOL project [3], the results are compared to simulations, using the MARS [4][5][6][7] code interfaced with MCNP [8,9] libraries, of the neutron flux from the converters interacting with the actinide targets.

βdecay ofAr47

“…The tape was moved 2 s after every proton pulse to remove the long-lived decay products before the next implantation. The lower statistics in the neutron-converter spectrum correspond to the shorter collection time and the generally lower yield due to the geometrical efficiency factor [12].…”

“…Recently, irradiation of targets by spallation neutrons, produced by bombarding thick metal converters with 1 and 1.4 GeV proton beams, has become common practice at the ISOLDE [12]. The advantage of the use of a neutron converter is the significant reduction of the energy deposited in the targets, and hence, the reduction of the mechanical and thermal stress of the target material.…”

“…The leakage of nongaseous isobars through the cooled line was found to be negligible. A tungsten converter (12.7 mm diameter, 125 mm length) was placed parallel to the target at a distance of 22 mm axis to axis [12], that allowed one to switch to the neutron irradiation of the target by changing the focus of the proton beam from the target to the converter. The implantation point was surrounded by four 125 m Kapton windows transparent to high-energy ␤ particles.…”

Simple Nuclear Structure inCd111–129from Atomic Isomer Shifts

“…Most of the measurements were conducted in the cadmium ion in order to benefit from an exceptionally high sensitivity in the 5s 2 S 1=2 → 5p 2 P 3=2 transition at 214.5 nm [17]. Beampurity improvement by multiple orders of magnitude was achieved by the use of a neutron converter [18], a quartz transfer line [19], and by resonant laser ionization [20]. Significant background suppression in the fluorescence measurements derived from ion-beam bunching [21,22].…”

Approaching theN=82shell closure with mass measurements of Ag and Cd isotopes

“…All experiments employed the neutron converter (n-conv.) [31] for the production of neutron-rich fission products and in the case of all Cd measurements, a temperature-controlled quartz transfer-line (QTL) was used [21]. Ionization was performed using the RILIS [19,20].…”