The International journal of applied radiation and isotopes最新文献

A bacterial count of 10⁷–10⁸/g present in pepper corn could be reduced to 10³/g by a radiation dose of 7 kGy. The effect of ionizing radiation on piperine, starch, sugar and some volatile oil was investigated. In irradiated pepper quantitative changes were observed in the carbohydrates and some of the oil constituents. Qualitative changes were observed in piperine from irradiated pepper.

The cycloidal mass spectrometer design of Andrew⁽¹⁾ has been adapted to dual ion collection for hydrogen isotope analysis. Difficulties experienced by Andrew with thermal expansion of the wire used to produce uniform electric fields were overcome by using 0.05 mm diameter tungsten wire. The focal lengths for ion beams M/e = 2 and 3, are 2 and 3 cm respectively. The sensitivity is about two orders of magnitude higher than for magnetic sector mass spectrometers of similar size. Under normal operating conditions the H₃⁺ production is 10% of the total ion current HD⁺ and H₃⁺, and the reproducibility of δD measurements is better than ±0.5 per mil. Increase of the resolving power to 600 for separation of ³He⁺ from HD⁺ and H₃⁺ ions appears feasible.

Five indolealkylamines (N,N-dimethyltryptamine, N-methyltryptamine, bufotenine, O-methylbufotenine, N,N,N-trimethyltryptamine iodide) were labeled with ¹¹C by use of ¹¹CH₃I. The labeled compounds were synthesized with a radiochemical yield of 2–50% (based on trapped ¹¹CH₃I) in 20–35 min with radiochemical purities of more than 92%. The tissue distributions of these labeled compounds were investigated in rats. In all cases, the accumulations in the liver, lung and small intestine were high. [¹¹C]DMT and [¹¹C]OMB also accumulated to a large extent in the brain, where their accumulation was retained. Brain uptake of three other radiopharmaceuticals was low. [¹¹C]DMT is the radiopharmaceutical of choice for the study of the serotonin action mechanism in the brain, because it has the highest radiochemical yield and the highest brain uptake of these ¹¹C-labeled compounds.

TAMS has extended the scope of radiocarbon dating but improved sample target preparation techniques are still required. In this paper a quick and reliable method for the conversion of CO₂ into graphite targets suitable for radiocarbon dating is presented. In the outlined procedure a single operator can produce 20 graphite targets a day.

The materials studied in the present work as high-dose dosimeters are members of a large class of molecular crystals which are organic conductors of electricity. Very different from each other in the details of their molecular and crystal structures, they all behave in the same way when subjected to increasing high doses of radiation, at least from the point of view of their electronic transport properties, because of the quasi-one-dimensional character of the conduction process. Their resistivities increase exponentially with the absorbed dose while their electron spin resonance (ESR) linewidths decrease exponentially. Very small single crystals less than 10 μm thick can be used as dosimeters in the dose range 0.01–50 MGy for γ rays as well as for electron irradiations, by applying four probe resistance measurements. Only a few compounds over a large number of candidates have been irradiated in the present work with γ-rays, low energy x-rays and electrons. In some favourable cases the energy and temperature dependences of the dosimeters have been checked experimentally. Their mass energy absorption coefficients and electron stopping powers have been also calculated. It is hoped to extend this kind of dosimetry to lower and higher doses by trying new compounds from the large family of organic conductors or by improving the resistivity and ESR measurement techniques.

A study on the measurements of proton current density profiles determined by the scattering process in natural krypton gas resulted in the development of a quantitative autoradiographic technique for the determination of a proton induced activity distribution on a Cu foil. Application of this technique showed that a 24 MeV, 1 μA proton beam with a FWHM of 7.3 mm was enlarged to a beam with a FWHM of about 43.5 mm for a target length of 50 cm and a Kr gas pressure of 400 kPa. For a comparison the target was also filled with Xe gas resulting in a larger FWHM value than for krypton under the same experimental conditions.

The specific radioactivity of ¹⁴CO₂ (> 3 nCi mol⁻¹) can be determined by conversion to an insoluble carbonate followed by re-evolution of the gas, using a mineral acid, through a proprietary organic sample oxidiser (Packard 306 Oxidiser, Packard Instruments Ltd, Caversham, Berks, U.K.).