Radiochemical separation and purification of non-carrier-added silicon-32

32Si (T 1/2 = 153(19) y) is an extremely rare, naturally-occurring isotope that has been considered as a geochronometer suitable for radiometric dating over the time span from 100 to 1000 years ago – a time span that has proved rather difficult to explore in this manner. Past attempts to determine the 32Si half-life have resulted in a wide range of values possessing significant uncertainties because only low-activity samples could be made available for such measurements. Utilizing the 590 MeV ring cyclotron at PSI, megabecquerel quantities of 32Si have been produced by exposing metallic vanadium discs to high-energy protons in order to induce spallation. A radiochemical separation procedure has been successfully developed and applied to the irradiated discs as part of the SINCHRON project, based on a combination of ion-exchange and extraction resins. The process was shown to be reliable and robust with a high chemical yield. Radiochemically pure 32Si solutions with activity concentrations of up to several kBq/g can be produced to perform individual measurements (AMS, ICP-MS, LSC) for various studies. Thus, a careful redetermination of the 32Si half-life has become feasible to begin the first steps toward the confident implementation of this radionuclide for geochronological purposes.

Arsenic for potential diagnostic imaging and radiotherapy

Targeted agents hold promise for non-invasive in vivo imaging, therapy, and monitoring of diseases. Foundational work focused on imaging and therapy of cancer has centered primarily on the use of 18F, 90Y, 99mTc, and 131I radionuclides. Use of these agents often requires conjugation to a biological targeting vector, a peptide or monoclonal antibody (mAb), to investigate biological processes. To truly be effective the physical properties of the radionuclide must be suitably matched to the time required for chemical derivatization, conjugation, to reach maximal uptake of the targeting vector at the targeting site. Radioisotopes of arsenic, 72, 77As, have half-lives well-matched for conjugation to peptides or mAbs. Even with favorable decay characteristics, production, and separation pathways, the ability to use radioarsenic has largely remained undeveloped. It is the aim of this work to address this issue through the identification and synthesis of no-carrier added radioarsenic complexes. Macroscopic synthesis of AsPh(S-Rn-S) precursors to no-carrier added 72,77AsPh(S-Rn-S) complexes, synthesis and no-carrier added radioarsenic labelling of a simple trithiol ligand, and two linkable trithiocyanate precursors, a carboxylic acid and “clickable” alkyne, are described in detail. The development of a radiochemical separation procedure to separate no-carrier arsenic, 77As, from a neutron irradiated germanium dioxide target, evaluation of a novel copper selective resin, and synthesis of any additional unmentioned compounds are found in the attached appendices.