Environmental air sampling uses fiberglass filters to collect particulate matter from the air and then a gas flow detector to measure the alpha and beta activity on the filter. When counted, the filter is located close to the detector so the alpha and beta particles emerging from the filter travel toward the detector at angles ranging from zero to nearly 90 degrees to the normal to the filter surface. The particles at small angles can readily pass through the filter, but particles at large angles pass through a significant amount of filter material and can be totally absorbed. As a result, counting losses can be great. For 4 MeV alpha particles, the filter used in this experiment absorbs 43% of the alpha particles; for 7.5 MeV alphas, the absorption is 13%. The measured beta activities also can have significant counting losses. Beta particles with maximum energies of 0.2 and 2.0 MeV have absorptions of 44 and 2%, respectively.
Open-faced and diffusion-barrier charcoal canisters were individually exposed to a fixed temperature, humidity, and radon concentration in a chamber for a period of 7 d. The radon progeny activity in the canister under study was measured every 3 h. A total of 15 runs were made for the open-faced canisters and nine runs for the barrier canisters with temperatures and absolute humidities ranging from 15-30 degrees C and 0-15 g m-3, respectively. In addition, several runs were made with the radon, temperature, and humidity changing during the 7 d. Results show that open-faced canisters adsorb radon up to 60% more efficiently at 15 degrees C than at 30 degrees C while the barrier canisters show little temperature dependence. The barrier canisters are much less sensitive to humidity effects than the open-faced canister. When used to measure the radon concentration in air, the open-faced canister integrates over a period of only approximately 48 h while the barrier canister integrates over a period of approximately 96 h. The short integration time and the interference of water adsorption by open-faced canisters indicate that the open-faced canisters should be used for exposure times of 48 h and no longer.
An apparatus that uses readily available material to measure the relativistic mass increase of beta particles from a radioactive 204 Tl source is described. Although the most accurate analysis uses curve fitting or a Kurie plot, students may just use the raw data and a simple calculation to verify the relativistic mass increase.
Measured differential cross sections are reported for 30-MeV 3 He ions elastically scattered from 27 A1, 51 V, 69 Co, 60 Ni, 89 Y, 114 Cd, 115 In, and 116 Sn for angles between 6° and 165° and for 35-MeV 8 He ions elastically scattered from 69 Co, 60 Ni, 116 In, and 116 Sn for angles between 6° and 140°. The data are compared with predictions of the nuclear optical model, and potential parameters that produce optimum fits with a leastsquares computer routine are reported. Good fits at back angles for 27 A1, 51 V, 59 Co, and 60 Ni are obtained only with the inclusion of a spin-orbit interaction with a magnitude between 2 and 5 MeV for most cases. The back-angle data for these nuclei also tend to suppress discrete ambiguities in the potential well depths. A continuous ambiguity between the radius and the diffuseness parameters is found to be related to a constancy of the root-mean-square radius. Effects of experimental uncertainties on the potential parameters are also presented.
Gas lantern mantles contain thorium to produce incandescence when lantern fuel is burned on the mantle. Although only thorium is initially present on the mantle, the thorium daughters build up, some over a period of weeks and some over a period of years, and significant quantities of these daughters are present when the mantle is used. Some of these daughters are released when the lantern fuel is burned on the mantle. The amounts of radioactivity released during burning is studied by measuring the gamma radiation emitted by the daughters. Results of this study show that some of the radium (224Ra and 228Ra) and more than half the 212Pb and 212Bi is released during the first hour of a burn. The actual amounts release depend on the age of the mantle.
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