Irradiated Target Material Research Articles

Direct implantation of Ge ions produced by high-energy low-intensity laser pulses into SiO2 films prepared on Si substrates

Due to the development and growing demands for implantation techniques, the laser plasma as a source of multiply charged ions has been investigated. With focusing the laser beam on the solid target it is possible to produce higher current densities of ions than with other currently available ion sources. Kinetic energy and the charge state of ions depend on the properties of the irradiated target material and the parameters of the laser radiation used. Selection of proper laser beam characteristics is very important for efficiency of the ion implantation technology. Several experiments on the implantation of different kinds of laser-produced ions have been performed at the Institute of Physics ASCR and at the PALS Research Center, ASCR in Prague. During these experiments 0.4 ns iodine laser pulses of energies up to 750 J at a wavelength of 1315 nm or up to 250 J at a wavelength of 438 nm have been used for generation of ions. The significant part of these experiments concerned the characterization and optimization of laser-produced Ge ion fluxes as well as the analysis of the direct implantation of these ions into SiO2 films prepared on the surface of a Si single crystal. In this paper we present the results, analysis and conclusions of these experiments which include ion collector and ion analyser measurements and the bulk profiles of Ge ion implantation with maximum depth of ∼450 nm.

Preparation of [61Cu]pyruvaldehyde-bis (N 4-methylthiosemicarbazone) complex as a possible PET radiopharmaceutical

Summary Copper-61 (T1/2= 3.33 h) produced via the natZn(p,x) 61Cu nuclear reaction using natural zinc target, was separated from the irradiated target material by a two-step method developed in our laboratory and was used for the preparation of [61Cu]-pyruvaldehyde- bis (N4-methylthiosemicarbazone) ([61Cu]-PTSM) using an in house-made PTSM ligand. An electroplated natural zinc layer on a gold-coated copper backing (zinc and gold layer thicknesses were 80 and 50 μm respectively) was irradiated with 22 MeV; protons (22−12 MeV; on the target). 61Cu was separated by a two-step chromatography method using a cation and an anion exchange column which gave satisfactory results. After 180 μA irradiation of the target for 3.2 hours, about 6.006 Ci of 61Cu2+ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of more than 99% (60Cu as impurity). Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The solution of [61Cu]-PTSM was prepared with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and specific activity of about 246 Ci/mmol.

Preparation of [ 61Cu]-2-acetylpyridine thiosemicarbazone complex as a possible PET tracer for malignancies

Due to the interesting anti-proliferative properties of copper–thiosemicarbazone complexes, the production of a 61Cu-labeled thiosemicarbazone, i.e. 2-acetylpyridine thiosemicarbazone (APTS) was investigated. Copper-61 ( T 1 / 2 = 3.33 h ) was produced via the 64Zn(p,α) 61Cu nuclear reaction using a natural zinc target irradiated with 22 MeV protons for 500 μAh. The 61Cu was separated from the irradiated target material by a two-step method and converted to acetate; this yielded a final activity of 222 GBq (6.0 Ci), with a radiochemical yield of >95%. The 61Cu–acetate was mixed with 2-acetylpyridine thiosemicarbazone for 30 min at room temperature to yield [ 61Cu]APTS with a radiochemical yield of more than 80%. Colorimetric methods showed that residual chemical impurities in the product were below the accepted limits. Radio thin layer chromatography (RTLC) showed a radiochemical purity of more than 99% after C 18 column chromatography. A specific activity of about 370–740 MBq/mmol (10–20 Ci/mmol) was obtained. The stability of the final product was checked in the absence and presence of human serum at 37 °C for up to 3 h. The partition coefficient of the final complex was also determined.

The role of diffusion in ISOL targets for the production of radioactive ion beams

On-line isotope separation techniques (ISOL) for production of ion beams of short-lived radionuclides require fast separation of nuclear reaction products from irradiated target materials followed by a transfer into an ion source. As a first step in this transport chain the release of nuclear reaction products from refractory metals has been studied systematically and will be reviewed. High-energy protons (500–1000 MeV) produce a large number of radionuclides in irradiated materials via the nuclear reactions spallation, fission and fragmentation. Foils and powders of Re, W, Ta, Hf, Mo, Nb, Zr, Y, Ti and C were irradiated with protons (600–1000 MeV) at the Dubna synchrocyclotron, the CERN synchrocyclotron and at the CERN PS-booster to produce different nuclear reaction products. The main topic of the paper is the determination of diffusion coefficients of the nuclear reaction products in the target matrix, data evaluation and a systematic interpretation of the data. The influence of the ionic radius of the diffusing species and the lattice type of the host material used as matrix or target on the diffusion will be evaluated from these systematics. Special attention was directed to the release of group I-, II- and III-elements. Arrhenius plots lead to activation energies of the diffusion process. Results: 1. A strong radius determined diffusion behaviour was found: D IIIB> D IIA> D IA> D VIIIA, ( D Y> D Sr> D Rb> D Kr). Rare earth elements diffuse as Me 3+-species. 2. Within the host elements of one period of the periodic table the diffusion of the trace elements changes in the following order: D IIIB> D IVB≫ D VB> D VIB. 3. In a given target trace elements of group I and II of a lower period diffuse faster than the corresponding elements of the higher period of the periodic table. D 2ndperiod> D 5thperiod> D 6thperiod, ( D Be≫ D Sr> D Ba). The diffusion determined transport rate of nuclear reaction products in solid target materials is often satisfactory, and consequently several refractory metals are suited as targets for fast on-line separation of short-lived nuclear reaction products. The delay times measured in on-line mode at ISOLDE, however, are significantly shorter. An enhancement of the diffusion under radiation condition is considered, subject for further systematic studies. The results obtained in this systematic study may also be applied in the development of alternative separation technologies in medical radionuclide production.

A novel, very compact 1.0 MV singletron™ accelerator

Recently, a novel 1 MV terminal voltage, single ended accelerator has been put into operation at the Institute of Advanced Energy, Kyoto University, Japan. The coaxial Singletron™, in which three new technologies are made successfully for practical use, is characterised by a very small footprint of 1×2 m 2 and has been designed by High Voltage Engineering Europa B.V. It is part of an experimental set-up called DuET. The accelerator will be applied to simulate atom transmutation in neutron irradiated target materials in nuclear fusion material research. The accelerator is capable of delivering high brightness beams of e.g. hydrogen and helium. A typical brightness of >10 A m −2 rad −2 eV −1 was measured for a∼20 μA, 1 MeV H + beam. Initial test showed stable operation at 1 MV terminal voltage for three consecutive days with currents of 20 μA He + when the terminal was cooled directly.

Dry-distillation of astatine-211 from irradiated bismuth targets: a time-saving procedure with high recovery yields

Astatine-211 was produced via the 209Bi( α,2n) 211At reaction. The radionuclide was isolated with a novel procedure employing dry-distillation of the irradiated target material. The astatine was condensed as a dry residue in a PEEK-capillary cryotrap. Distillation was completed within 1–2 min with isolation yields of 92±3%. Subsequent work-up of the nuclide resulted in final recovery yields of 79±3%.

Quality assurance of iodine-124 produced via the nuclear reaction124Te (d, 2n)124I

For more than a year,124I (T=4.15 d) has been produced routinely with a compact cyclotron by irradiation of124TeO2 with 14 MeV deuterons, followed by dry distillation of the iodine radioisotopes formed from irradiated target materials. The following by-products have been measured and compiled in each charge: 13.2-d123I, 60-d125I, 13.0-d126I, 12.4-h130I and 8.02-d131I. The data show that after 45 h decay time, the sum of the activities of these nuclides is less than 5% of the124I activity. Observation of this limit has been required by the Swiss Regulatory Agencies for a PET study of cell proliferation in human brain tumors using [124I] IUdR.

Comparison of radioactive ion-beam intensities produced by means of thick targets bombarded with neutrons, protons and heavy ions

Target and ion-source techniques which allow rapid separation of thermalized radioactive nuclei from 1–500 g cm 2 thick irradiated target material and continuously convert them into a mono-isotopic ion beam have been proven to be a powerful method of radiochemical separation. These techniques combine nuclear reactions with high-temperature chemistry, metallurgy, solid-state diffusion, and ionization phenomena. Developed at the many mass separators on-line to various accelerators or reactors they are today widely used to produce low-energy (10–60 keV) radioactive ion-beams for physics experiments. Since some years they have reached a stage of development that allows the production of high-intensity beams of up to 10 12 ions/s of radioactive isotopes of most elements in the periodic system. Such on-line mass separators seem to be excellent injectors to a second accelerator which accelerates up to 20 MeV/u. This paper discusses the radioactive beam intensities that may be injected into proposed or working European radioactive ion-beam facilities which make use of such injectors. First a short introduction is given to the technique of on-line mass separation. This is followed by a detailed discussion of the three factors that determine the production rates in the target, i.e. reaction cross-sections, primary beam properties, and target thicknesses, and by a discussion of the more decisive factors that control the efficiency with which the radioactive nuclei produced in the target can be transformed into an injection ion-beam of typically 10–60 keV energy. Throughout the discussion the influence of new developments is assessed. Finally, selected examples of realistic beam intensities are given, which are used for intercomparison of the different production methods used by the various European projects.

Spectroscopic studies of XeCl-laser-induced plasma on Ti targets in nitrogen containing atmospheres

This work deals with the study of a plasma produced by intense XeCl-excimer-laser irradiation of a titanium surface in nitrogen-containing atmospheres. We observed that the optical emission spectra resulting from irradiation of Ti targets in various ambient atmospheres (N2, NH3, N2+H2 mixtures) contain lines of atomic and ionized species of the irradiated target material only. The spectra are almost independent of the ambient atmosphere. The expansion velocities of atomic and ionic species in the plasma plume were obtained by time-of-flight measurements at different distances from the target. Mass spectrometry measurements are also performed at low background pressure to identify non-emitting species.

Development of myocardial perfusion tracers for positron emission tomography

Six positron-emitting cations were investigated as possible perfusion tracers: [ 13N]NH 4, 38K, 51Mn, 52 m Mn, 81Rb, and 82Rb. Aspects of the production of the radionuclides and their separations from the irradiated target materials were addressed. The thick target, saturated yields of several nuclear reactions leading to these radionuclides were studied theoretically and experimentally in the energy range 6–10 MeV. A figure-of-merit describing the production aspects of each tracer was calculated, and tomographic imaging results in normal human subjects were reported.

Measurement of the product mass distributions from heavy-ion-induced nuclear reactions: I: Gamma-ray spectrometric product identification

A system for the measurement of the product mass yield distributions from heavy-ion-induced nuclear reactions has been developed. This system is based on the gamma-ray spectrometric identification of product radioactivities in the irradiated target materials or in separated chemical fractions derived from the target. Gamma-ray spectra are collected as a function of time and all peaks and peak areas are identified and measured with a modified version of SAMPO. Decay curves for all gamma-rays observed in two or more spectra are constructed by the computer code TAU1. A current table of all the known gamma-ray transitions is then used to match a known gamma-ray energy and half-life to each measured decay curve. This is done interactively with the computer code TAU2 and a Tektronix graphics terminal. Examples of the various options are given. Nuclear reaction cross-sections are calculated on weighted average of all the observed gamma-rays for each product nuclide after the identifications have been screened for duplicate or erroneous identifications and for self-consistency.

RADIOCARBON-LABELED COMPOUNDS PRODUCED BY THE NEUTRON IRRADIATION OF GUANIDINE HYDROCHLORIDE

Crystalline guanidine hydrochloride was irradiated by neutrons and studies were made on the Cu-labeled compounds present when the target material was dissolved in water. The results indicate that the cyanamide radical plays an important role in the production of the final chemical species incorporating the recoil C/sup 14/ atom. The production of the cyanamide radical may occur by a replacement reaction of the C/sup 14/ atom with a guanidine molecule within the solid matrix, after the recoil atom has been alowed down to the point where it is stable toward recombinations. This results in the rupture of a C-NH/sub 2/ bond and leads to the formation of the radiocarbon labeled cyanamide radical, which may then undergo reactions with other molecules of the matrix to produce the final chemical compounds observed. Significant amounts of activity were found in cyanoguanidine (12%), acetamidine (11%), guanylguanidine (18%), and melamine (22%). There appeared to be no significant interaction of the solvent with the irradiated target material. (P.C.H.)