Design criteria and performance parameters of an alpha irradiation device for cell studies

An alpha irradiation device is described that utilises a commercially available disc-shaped americium-241 source of 8 cm diameter. The alpha particles traverse a moving collimator and the source is rotated to reduce the influence of source inhomogeneities. Source, collimator and a shutter disc are mounted in a container which is flushed with helium to reduce energy losses of the alpha particles before reaching the exit foil. The shutter disc is activated by a computer-controlled step motor. The broad beam of alpha particles emerges from the exit window of the container with a remaining range in tissue of about 15 mu m. An intermittent computer-controlled use of a preabsorber makes it possible to reduce dose differences within a depth up to 12.5 mu m to not more than +or-3%. With the commercially available americium sources a dose rate of 0.2 Gy min-1 is reached; this can be increased by utilising a somewhat wider collimator

Ferromagnetic/superconducting bilayer structure: A model system for spin diffusion length estimation

We report detailed studies on ferromagnet--superconductor bilayer structures. Epitaxial bilayer structures of half metal--colossal magnetoresistive La$_{\mathrm{2/3}}$Ca$_{\mathrm{1/3}}$MnO$_{\mathrm{3}}$ (HM--CMR) and high--$T_{\mathrm{c}}$ superconducting YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta}}$(HTSC) are grown on SrTiO$_3$ (100) single--crystalline substrates using pulsed laser deposition. Magnetization $M$(T) measurements show the coexistence of ferromagnetism and superconductivity in these structures at low temperatures. Using the HM--CMR layer as an electrode for spin polarized electrons, we discuss the role of spin polarized self injection into the HTSC layer. The experimental results are in good agreement with a presented theoretical estimation, where the spin diffusion length $\xi_{\mathrm {FM}}$ is found to be in the range of $\xi_{\mathrm{FM}} \approx$ 10 nm.Comment: 6 pages, 7 figures, Accepted for publication in Phys. Rev.

His+ reversions Caused in Salmonella typhimurium by different types of ionizing radiation

The yield of his+ reversions in the Ames Salmonella tester strain TA2638 has been determined for 60Co γ rays, 140 kV X rays, 5.4 keV characteristic X rays, 2.2 MeV protons, 3.1 MeV α particles, and 18 MeV/U Fe ions. Inactivation studies were performed with the same radiations. For both mutation and inactivation, the maximum effectiveness per unit absorbed dose was obtained for the characteristic X rays, which have a dose averaged linear energy transfer (LET) of roughly 10 keV/μm. The ratio of the effectiveness of this radiation to γ rays was 2 for inactivation and about 1.4 for the his+ reversion. For both end points the effectiveness decreases substantially at high LET, i.e., for the α particles and the Fe ions. The composition of the bottom and the top agar was the one recommended by Maron and Ames [Mutat. Res. 113, 173-215 (1983)] for application in chemical mutagenicity tests. The experiments with the less penetrating radiations differed from the usual protocol by utilization of a technique of plating the bacteria on the surface of the top agar. As in an earlier study [Roos et al., Radiat. Res. 104, 102-108 (1985)] greatly enhanced yields of mutations, relative to the spontaneous reversion rate, were obtained in these experiments by performing the irradiations 6 h after plating, which differs from the conventional procedure to irradiate the bacteria shortly after plating