On the categorization of uranium materials using low resolution gamma ray spectrometry.

In order to characterize uranium materials during e.g. nuclear safeguards inspections and in initial stages of nuclear forensic investigations, hand-held low resolution gamma ray detection instruments with automatic uranium categorization capabilities may be used. In this paper, simulated response curves for a number of matrices applied on NaI(Tl) scintillation detector spectra show that the result of the categorization is strongly dependent on the physical properties of the uranium material. Recommendations on how to minimize the possibility of misclassification are discussed.

Closed source experimental system for soft x-ray spectroscopy of radioactive materials.

An instrumental and experimental setup for soft x-ray spectroscopy meeting the requirements of a closed source for radioactivity is described. The system consists of a vacuum sealed cell containing the sample, mounted on a tubing system to ensure compatibility with most standard manipulators. The soft x rays penetrate a thin x-ray window separating the interior of the cell from the vacuum in the experimental chamber. Our first results for single crystal PuO(2) confirm the feasibility of experiments using the setup. The results are consistent with results of first principles calculations and previously recorded spectra obtained using a standard open source setup. The results show that the closed source experimental system can be used to collect valuable experimental data from radioactive materials.

A method for preparation and purification of 234Th.

An improved method to recover 234Th from depleted uranium has been developed. The method is based on solvent extraction and ion-exchange separations. The final thorium fraction has a high specific activity, about 1-3 PBq/mol Th, which makes it well suited for investigations, where a low thorium concentration is essential. The method is comparably fast, with a total processing time of 2 days. Another advantage is that the uranium fraction can be used as a 234Th generator for several years.

Low-energy electron emitters for targeted radiotherapy of small tumours.

The possibility of using electron emitters to cure a cancer with metastatic spread depends on the energy of the emitted electrons. Electrons with high energy will give a high, absorbed dose to large tumours, but the absorbed dose to small tumours or single tumour cells will be low, because the range of the electrons is too long. The fraction of energy absorbed within the tumour decreases with increasing electron energy and decreasing tumour size. For tumours smaller than 1 g, the tumour-to-normal-tissue mean absorbed dose-rate ratio, TND, will be low, e.g. for 131I and 90Y, because of the high energy of the emitted electrons. For radiotherapy of small tumours, radionuclides emitting charged particles with short ranges (a few microm) are required. A mathematical model was constructed to evaluate the relation between TND and electron energy, photon-to-electron energy ratio, p/e, and tumour size. Criteria for the selection of suitable radionuclides for the treatment of small tumours were defined based on the results of the TND model. In addition, the possibility of producing such radionuclides and their physical and chemical properties were evaluated. Based on the mathematical model, the energy of the emitted electrons should be < or = 40 keV for small tumours (< 1000 cells), and the photon-to-electron energy ratio, p/e, should be < or = 2 to achieve a high TND. Using the selection criteria defined, five low-energy electron emitters were found to be suitable: 58Co, 103mRh, 119Sb, 161Ho, and 189mOs. All of these nuclides decay by internal transition or electron capture, which yields conversion and Auger electrons, and it should be possible to produce most of them in therapeutic amounts. The five low-energy electron-emitting radionuclides identified may be relevant in the radiation treatment of small tumours, especially if bound to internalizing radiopharmaceuticals.

High-efficiency astatination of antibodies using N-iodosuccinimide as the oxidising agent in labelling of N-succinimidyl 3-(trimethylstannyl)benzoate.

Monoclonal antibodies C215, reactive with colorectal carcinomas, and MOv18, reactive with most of the ovarian carcinomas, were radiohalogenated with [211At]astatine. The radiohalogen was conjugate coupled to antibodies via the intermediate labelling reagent N-succinimidyl-3-(trimethylstannyl)benzoate (m-MeATE) in a two-step, single-pot reaction. Optimisation of the labelling of the reagent was achieved using N-iodosuccinimide, NIS, as the oxidising agent. The yields ranged from 69-95% in the labelling of 0.1-1.0 nmole of the m-MeATE precursor. Subsequent conjugation to antibodies resulted in yields of 58+/-7%. In vitro binding to tumour cells showed that the immunoreactivity of both antibodies was retained after astatine labelling.

Chloramine-T in high-specific-activity radioiodination of antibodies using N-succinimidyl-3-(trimethylstannyl)benzoate as an intermediate.

Monoclonal antibodies C215 and MOv18 have been radiohalogenated, using a single-batch method employing N-succinimidyl-3-(trimethylstannyl)benzoate, m-MeATE. Labelling to the stannyl ester was optimized using chloramine-T as oxidizing agent. The results show that the stannyl ester is effectively labelled with short reaction times giving reproducible yields from 85% to 95%. Subsequent antibody conjugation, 10 to 80 microg MAb, resulted in biologically active, labelled antibodies with overall radiochemical yields of 50% to 80%, with corresponding specific activities of 490-50 kBq(125I)/microg.