The Preparation of Carrier-Free Chlorine-36 via Ligand Recoil in K₂[ReCl₆] and K₃[RhCl₆]

Abstract

The wide use of »C1 (T = 3.1 · 10 6 a) in tracer applications and the demand for high specific activities necessitates special separation techniques. The longlived ^Cl is generally produced via the ^Cl (n, yJ^Clprocess by extended pile irradiation at high neutron flux densities. The obtainable specific activities, however, are limited even in Szilard-Chalmers separations because of the accompanying radiation decomposition. Neutron irradiations of chlorates and Perchlorates have been shown to give rise to high chloride yields [1, 2, 3], but the lack of radiation stability of these compounds imposes a serious limitation to their use in the production of the longlived ^Cl. Similarly, the application of Szilard-Chalmers separations in organic systems does not seem to provide a good tool for the production of Μ 01 in the mCi-range even in favorable cases [4].In our studies on the ligand recoil behaviour in hexahalo-complexes of Re(IV) and Rh(III) [5], we found that the hexachlororhenates and -rhodates show a remarkable radiation stability. Furthermore, the radiochlorine activity appears in only two chemical forms, the labelled parent complex and the carrierfree chloride, e. g. : R 15% 36 C1 (N, Y) 36 CL R K 2 [ReCl e ] • ae Cl" 85% • [itecyci] 2 -In the case of K 3 [RhCl 6 ] an additional alumina column was necessary to separate iridium activity resulting from impurities [5]. The separation procedure and the stability of the complexes were checked with corresponding tracers. For the determination of the ^Cl-activity chloride carrier was added to aliquots of the separated fractions and precipitated as AgCl. The ^Cl-activity of both the chloride fraction and the total chlorine was then measured in a methane flow counter under identical conditions. The radiochemical purity was established by ^-spectroscopy and measurement of the ^-absorption curve. The specific activity of the separated 36 C1 _ -fraction was determined by neutron activation analysis via the short-lived 38 C1. Neutron -irradiated K 2 [ReCl 6 ] dissol. i. 0.1 Ν CHjCOOH Determination of 36 Cl~ -fractionThe six-chlorine-containing complex seemed to be particularly well suited for the preparation of practically carrier-free ^Cl, due to its radiation resistance and simplicity of the product spectrum, despite the relatively low yield of 15% for the chloride fraction. Experimental K 2 [ReCl e ] and K 3 [RhCl e ] (Heraeus GmbH, Hanau)were recrystallized several times from water solution by adding isopropanol. The purity of the material was checked by Differential Thermal Analysis and by chemical analysis. The samples, sealed in quartz ampoules in vacuo, were irradiated in the FRJ-1 at different positions and neutron flux densities (see below, Fig. 3). The irradiation temperature in each case was < 50 °C. The irradiated ampoules were stored for several months to allow the decay of shorterlived activities and then crushed under the surface of O.INCH3COOH for dissolution. The analytical procedure used for the separation of the chloride fraction from the labelled par...

Production of Some Medically Important Short-Lived Neutron-Deficient Radioisotopes of Halogens

“…For medical applications 34m Cl was produced via the 3S Cl(p, pn) 34m Cl reaction [39]. A K 2 ReCl 6 target was irradiated with 24 MeV protons at beam currents of a few μ A, and practically carrier-free 34m Cl was separated by the Szilard-Chalmers process [40]. The chloride yield is around 15 % and is strongly dependent on the temperature.…”

Study of Gamma Radiolysis and Annealing Reactions of Radiolytic Products in Sodium Ethylenediaminetetraacetate Co (III) Crystals

“…The recoil atoms, which normally are highly energetic, are often ejected away from their original site. In contrast to this, the radiolysis species remain in the immediate vicinity of their product site and thus have a much greater chance of reentering their parent ligand sphere [24,25]. Thus, it is conceivable that the model which is found satisfactory in recoil chemistry may be not directly applicable to radiation decomposition study even though the chemical system is the same.…”