Distribution Of Radioactive Isotopes Research Articles

Distribution of radioactive isotopes in the mountain and piedmont regions of Central Tajikistan Varzob river valley

The Varzob Valley in the Central Tajikistan, due to its proximity to the Gissar mountains range, acts like a funnel for the air mass transported by the southern winds. For a better understanding this local phenomenon, the gross alpha and beta as well as 40K, 137Cs, 232Th and 238U activity concentrations together with the Th/U ratio were studied. The results showed the existence of a deposition process of the airborne dust on the southern slope of Gissar Mountains. The influence of the Odjuk pegmatite outcrop on the natural radioactivity along the Varzob valley was evidenced too. At the same time, no traces of radioactive contamination from local anthropogenic sources were found.

Polarization of MeV gamma-rays and 511 keV line shape as probesof SNIa asymmetry and magnetic field

We discuss gamma-ray signatures associated with an asymmetric explosion and transport of positrons in SN Ia ejecta. In particular, Compton scattering of gamma-ray line photons can induce polarization in the continuum, which would be a direct probe of the asymmetries in the distribution of radioactive isotopes and/or of the scattering medium. Even more interesting would be a comparison of the shapes of $\gamma$-ray lines and that of the electron-positron annihilation line at 511 keV. The shapes of $\gamma$-ray lines associated with the decay of Co56 (e.g., lines at 847 and 1238 keV) directly reflect the velocity distribution of Co56. On the other hand, the 511 keV line arises from the annihilation of positions, which are also produced by the Co56 decay but can propagate through the ejecta before they slow down and annihilate. Therefore, the shape of the annihilation line might differ from other gamma-ray lines, providing constraints on the efficiency of positrons propagation through the ejecta and, as consequence, on the topology of magnetic fields in the ejecta and on the fraction of positrons that escape to the interstellar medium. We illustrate the above effects with two models aimed at capturing the main predicted signatures.

Distribution of radioactive isotopes in rock and ore of Arkhangelskaya pipe from the Arkhangelsk diamond province

The contents of radioactive elements and the uranium isotopic composition of kimberlite in the Arkhangelskaya pipe at the M.V. Lomonosov deposit and of nearby country rocks have been studied. A surplus of 234U isotope has been established in rocks from the near-pipe space. The high γ = 234U/238U ratio is controlled by the geological structure of the near-pipe space. A nonequilibrium uranium halo reaches two pipe diameters in size and can be regarded as a local ore guide for kimberlite discovery. The rocks in the nearpipe space are also characterized by elevated or anomalous U, Th, and K contents with respect to the background.

Distribution of natural and anthropogenic radioactivity in samples of soil and dust haze in the south of Tajikistan

The study results of the elemental composition of soil and dust aerosol samples from Aivanj vil. and Dushanbe are presented. Data on the distribution of radioactive isotopes of uranium and thorium series, K-40 and other anthropogenic isotopes are analyzed.

Position-Sensitive Radiation Detector with Flexible Light Guide and Liquid Organic Scintillator to Monitor Distributions of Radioactive Isotopes

Position-sensitive detectors consisting of optical fibers such as scintillating fibers, normal optical plastic fibers, and liquid light guides have been developed as radiation sensors to monitor long-range distributions of radioactive isotopes. Because of losses of optical transmission due to radiation damage in high-level radiation environments, however, both scintillating fibers and normal optical plastic fibers are less applicable to areas of high dose rate. In order to develop a flexible fiber-type radiation sensor with good radiation hardness, we propose to use a liquid light guide, the core of which is replaced by a liquid organic scintillator. A liquid light guide consists of flexible cladding material, and can be easily bent. A liquid organic scintillator can generate a much larger number of photons than the original liquid material, leading to a better detection efficiency than a simple liquid light guide; furthermore, it is not significantly damaged by incident radiation. In preliminary experiments using a fast neutron beam, we confirmed that our prototype system can be operated as a position-sensitive radiation detector. Fundamental characteristics such as spatial resolution, detection efficiency and attenuation length of light propagation were examined with two detectors of 2 m and 10 m length. Optical transmission losses due to radiation damage were examined using 60Co gamma rays; no significant transmission loss was observed up to a dose of 1.5 × 104 Gy.

The isotopic characterization of carbon monoxide in the troposphere

The distributions of stable isotopes in trace atmospheric species are controlled mainly by the isotopic compositions of precursor molecules and isotope fractionation effects during production and removal of the species. Distributions of radioactive isotopes are controlled mainly by the isotopic compositions of precursor molecules and radioactive decay processes. As a result, through their isotopic compositions, atmospheric species are traceable to sources and sinks. Thus, isotopic compositions provide useful information for estimating source strengths and for understanding the importance of removal processes in the cycling of the species. The use of radioactive 14C and the stable isotopes ( 13C and 18O) are reviewed here for understanding production and removal processes of CO in the troposphere. Carbon monoxide is a critical component in atmospheric chemistry because of its large effect on levels of OH, the principal oxidant in the atmosphere. In the troposphere, this is due to relatively high concentrations of CO and a short lifetime (2–4 months). Initially, 14CO measurements were instrumental in estimating accurately the tropospheric lifetime. Since seasonal 14CO variation is controlled largely by OH, 14CO serves as an important surrogate measure of tropospheric OH. Global 14CO measurements have also been used to estimate the biogenic component of the global CO budget, specifically contributions from biomass burning, oxidized non-methane hydrocarbon (NMHC) emissions, oceans and plants. Research using 14CO measurements is also active in quantifying fossil and non-fossil urban emissions. Kinetic isotopic fractionation during production of 13CO and C 18O from reduced precursors allows one to distinguish, at least qualitatively, different varieties of CO based on seasonal tropospheric isotopic measurements. Difficulties in interpreting the stable isotopic record arise from large fractionation effects that obscure source isotopic signatures (in particular the oxygen kinetic isotope effect for the CO+OH reaction), and large seasonal/latitudinal variability in source fluxes. While dual-isotopic CO source signatures do not allow a direct mathematical determination of contributions from several sources, plots of δ 18O vs δ 13C may help estimate relative proportions of dominant sources. In addition to understanding CO sources, the pressure dependence of the carbon kinetic isotope effect (KIE) has helped elucidate pathways for the CO+OH reaction. Since formaldehyde (HCHO) is an important intermediate in hydrocarbon oxidation to CO and CO 2, the stable carbon and oxygen isotopes in atmospheric HCHO may help distinguish different hydrocarbon sources to regional CO budgets and elucidate the importance of different oxidative reaction pathways.

The preparation and use of radioactive tracers for the study of comminution processes. Part I. homogeneous materials

As part of an investigation of the radioactive tracer method for the study of comminution processes, the distribution of radioactive isotopes in various particle sizes after grinding was investigated. It is found that certain apparently homogeneous materials break down into fragments of different elemental compositions upon comminution. Moreover, comminution also affects the average elemental composition of the unbroken particles. Under such circumstances the gross counting of all radioisotopes produced by irradiation in a nuclear reactor is not applicable as a tracer method in the study of comminution. Refinement of this technique using gamma-ray spectroscopy may reveal the presence of suitable specific elements which can be used individually as tracers.

Histoautoradiographic Studies of Herbicidal Translocation

AN understanding of the physiological action of various herbicides 1A is based in part upon a knowledge of (1) the exact path of movement of the substance in the plant, (2) the rapidity of transfer from one tissue to another, and (3) the relative proportion of the total conductive tissue that is effective in transfer under any given set of conditions. Although the intercellular distribution of radioactive isotopes in both plant and animal tissues has been studied by the use of histoautoradiography (6), only one brief paper (8) describes the use of this method with plant growth regulators. A histoautoradiograph is obtained by bringing a thin tissue section (1 to 25 [t) containing a radioisotope into close contact with a photographic emulsion which is exposed and later developed. Microscopic examination is then made to correlate the pattern of developed emulsion grains with the tissues of the section. Two of the major problems encountered in this procedure are the loss of labeled substance from the tissue and diffusion from the initial location to other locations within the tissue during fixation and dehydration. These artifacts can be minimized by (1) the use of precipitants that react with the herbicide to form insoluble and immovable deposits, together with fixatives that do not dissolve the compound being studied (15, 17); (2) by the application of a freeze-drying technique of the Altmann-Gerch type (9, 10, 12); or (3) by a combination of these two methods. The present paper deals with the evaluation of these techniques in the study of the intercellular movement of labeled 2,4-dichlorophenoxyacetic acid (2,4-D) and 3-amino-1,2,4-triazole (amitrole).

DISTRIBUTION OF RADIOACTIVE ISOTOPES

>The present position and the methods used in the distribution of radioactive isotopes at home and abroad are discussed. Types of isotopes produced in various countries and the range of labeled chemical compounds are described. (tr-auth)