Radioactive Layer Research Articles

Thin film radiation sources by radiofrequency sputtering

The preparation of thin film radiation sources using radiofrequency-sputtering techniques has been demonstrated. 241Am alpha photon and photon radiation sources have been prepared using a radiofrequency-sputtering system, installed in a glove box designed to maintain radioisotope containment. Sources prepared using radiofrequency sputtering to deposit the radioactive layer and also the isotope containment layer have been evaluated for uniformity, activity, and integrity with generally positive results. Up to 25 radiation sources having a 0.5 in. diam. active layer have been prepared in a single run. Planar ring sources and other geometry sources may be conveniently prepared. The use of sputtering for source preparation is most applicable when several sources are prepared in a run, and when there is a continuing demand for sources containing a given radioisotope.

A critical study of the thin layer method in thermomigration: Application to gold

During a thermomigration anneal, a thin radioactive layer is displaced and distorted. The velocities of its maximum and of its center of mass have been calculated without any approximation. A re-analysis of earlier data shows the heats of transport of Au and Sb ions in gold to be, respectively, 0.5 ± 0.3 eV and -3.5 ± 0.5 eV. An interpretation is proposed.

A radioactive layer over Barrow, Alaska, attributed to the Chinese nuclear test of October 16, 1964

A profile of atmospheric radioactivity taken over Barrow, Alaska, on November 12, 1964, showed a relatively diffuse radioactive layer extending from 4.0 to 7.0 km. This layer has been attributed to debris from the Chinese nuclear test conducted at Lop Nor (40°N, 90°E) in Sinkiang Province on October 16, 1964. The profile was obtained by using a balloon-borne scintillation detector (designated a Gigi for gross-gamma detector) designed and built by the U. S. Atomic Energy Commission's Health and Safety Laboratory in New York [HASL, 1962]. The detector consisted of a cylindrical NaI crystal 1 inch in diameter by 1½ inches in length optically coupled to a 6199 photomultiplier tube. The detector was set to respond to photons and charged particles that lost more than 0.3 Mev in the crystal. The total count rate of such events was transmitted to ground by a conventional 1680-Mc/s radiosonde transmitter, the carrier of which was modulated according to the count rate. The instrumentation was powered by standard Weather Bureau radiosonde batteries—the entire package including batteries weighed slightly less than 2½ kg—and was carried aloft by a 1200-g balloon. On the ground the modulated 1680-Mc/s signal was received by a WBBT-57 (Weather Bureau radio-the-odolite) receiver-tracking antenna system with count rate recorded on a strip chart recorder.

Radioactive contamination of the atmosphere

This article is a review of foreign works on the study of radioactive contamination of the atmosphere due primarily to diffusion of fission fragments from atomic tests. Several properties of fission fragment activity, namely its decay rate and the composition of its radiation, are considered, and methods are described for monitoring the fallout from the atmosphere and calculating the resulting radiation dose. The dose is almost everywhere much less than the permissible limit. At several places, however, fallout densities and activity concentrations are observed which are close to the allowable limit. A method for constructing the trajectories of air masses is briefly described, and it is shown that radioactive clouds migrate over the whole world, producing a radioactive layer in the atmosphere at an altitude of 8–12 km consisting primarily of the long-lived nuclides Sr90, Ce144, and Pu239. Of the fission fragments contaminating the earth's surface the most dangerous is Sr90 which has the property that it accumulates in the organisms of domesticated animals and thus enters the human organism. The radiation level at points fat from the test areas is at present far below the allowable limit in the sense of the possible occurrence of somatic diseases, although even at the present radiation level, effects on posterity cannot be excluded.

The Thermal State of the Earth's Crust

THE product of the rate of increase of temperature with depth in the earth's crust into the thermal conductivity of the surface rocks gives the rate of loss of heat from the interior. When allowance is made for the residual effects of the original heat, this gives a most important datum concerning the rate of generation of heat below, and hence, if the radioactivity of the rocks is known, to an estimate of the thickness of the radioactive layer. Hitherto it has been good enough, in discussions of this problem, to adopt mean values of the temperature gradient, the conductivity, and the radioactivity. It has now, however, become worth while to allow for variation of conductivity with depth, and to attend more to details in the vertical distribution of radioactive matter. When this is done as well as is at present possible, the agreement of the results with those obtained from the study of near earthquakes is practically perfect (Gerlands Beitrage z. Geophysik, 18, 1-29; 1927).