[en] This symposium sought to raise ethical issues bound with the development and use of nuclear energy. The approach was to challenge the common assumption that nuclear decision making should be left to technicians

[en] The performance characteristics of several propulsion technologies applied to piloted Mars missions are compared. The characteristics that are compared are Initial Mass in Low Earth Orbit (IMLEO), mission flexibility, and flight times. The propulsion systems being compared are both demonstrated and envisioned: Chemical (or Cryogenic), Nuclear Thermal Rocket (NTR) solid core, NTR gas core, Nuclear Electric Propulsion (NEP), and a mirror fusion space propulsion system. The proposed magnetic mirror fusion reactor, known as the Mirror Fusion Propulsion System (MFPS), is described. The description is an overview of a design study that was conducted to convert a mirror reactor experiment at Lawrence Livermore National Lab (LLNL) into a viable space propulsion system. Design principles geared towards minimizing mass and maximizing power available for thrust are identified and applied to the LLNL reactor design, resulting in the MFPS. The MFPS' design evolution, reactor and fuel choices, and system configuration are described. Results of the performance comparison shows that the MFPS minimizes flight time to 60 to 90 days for flights to Mars while allowing continuous return-home capability while at Mars. Total MFPS IMLEO including propellant and payloads is kept to about 1,000 metric tons. 50 refs

No abstract available

[en] Alpha-irradiation to the bronchial airways from inhaled radon progeny increases the risk of developing lung cancer. The molecular mechanism of radon-induced lung cancer is not clear, but one of the most important genetic effects of ionizing radiation is the induction of gene mutation. Mutations, especially those associated with visible chromosome abnormalities in humans, have been associated with cancer. Therefore, our objective is to use a well-defined model system to determine the mutagenic potential of alpha particles in normal human skin cells and to define this action at the molecular level. Normal human skin fibroblasts were irradiated with alpha particles (3.59 MeV, LET 115 keV μm^-1) emitted from the decay of ²³⁸Pu. Mutagenicity was determined at the X-linked hypoxanthine guanine phosphoribosyl transferase (HPRT) locus. Results from this study indicate that beta particles were more efficient in mutation induction than gamma rays. Based on the initial slopes of the dose-response curves, the RBE for mutation is about 8 for alpha particles. HPRT-deficient mutants which are resistant to 6-thioguanine have been isolated and analyzed by the Southern blot technique. To date, we have characterized 69 gamma-ray-induced and 195 alpha-particle-induced HPRT-deficient mutants. Our data indicate that more than 50% of all gamma-ray-induced mutants have band patterns identical to that observed for the normal structural HPRT gene, whereas the remaining mutants (45%) contain either a rearrangement, partial deletion, or total deletion of the HPRT gene. In contrast, only 30% of alpha-particle-induced human HPRT mutants contain a normal Southern blot pattern, and about 50% indicate total deletion of the HPRT gene. Our results support the notion that high-LET radiation produces more unrepaired or misrepaired DNA damage than do gamma rays

[en] Two thousand rads of gamma irradiation delivered to the lower legs of ten day old normal and x-chromosome linked muscular dystrophy (mdx) mice caused significant inhibition of tibial bone and soleus muscle fiber growth. In the irradiated mdx solei, there was a major loss of muscle fibers, lack of central nucleation, and some endomysial fibrosis. These features were caused by a failure of regeneration of muscle fibers due to impaired proliferative capacity of satellite cells. Gamma irradiation transforms the late pathological phenotype of mdx muscles, so that in one major aspect (muscle fiber loss) they resemble muscles in Duchenne muscular dystrophy. However, extensive endomysial fibrosis which is another characteristic feature of Duchenne muscular dystrophy did not develop. This experimental model could be useful for the functional investigation of possible beneficial effects of therapeutic interventions in mdx dystrophy

[en] Cell survival was studied for V79 hamster, 10T1/2 mouse, and human skin fibroblast cell lines, using carbon K (0.28 keV), copper K (8.0 keV), and 250 kVp x rays. Because of the rapid attenuation of the carbon x rays, cellular dimensions at the time of exposure were measured using optical and electron microscopy, and frequency distributions of mean dose absorbed by the cell nucleus were obtained. The results indicate that the differences in cell killing between ultra-soft and hard x rays may depend on the nuclear thickness of the cells. Studies of the effects of hypoxia on V79 and 10T1/2 cells using carbon K, aluminum K (1.5 keV), and copper K x rays show decreasing OER values with decreasing x-ray energy and no difference between the two cell lines. Age response studies with V79 cells show similar cell-cycle variation of survival for carbon K and aluminum K x rays as for hard x rays

[en] The goal of this program is to elucidate the principal physical, chemical, and biological mechanisms of radiation action in cells. The basic experiments for this program involve selected low- and high-energy x-ray sources and include studies of cell killing, both with and without modifiers (for example, hypoxia), determination of cellular age response, and measurement of induced DNA strand breaks, mutations, and chromosome aberrations. The theoretical effort involves Monte Carlo-based radiation track simulation codes to generate energy-deposition events and to follow the subsequent diffusion of chemical species. By combining the experimental and theoretical results, the authors plan to test assumptions used in existing models and to determine important parameters that should be included in any model. Ultrasoft x-rays (less than a few kiloelectron volts) provide a unique tool for studying induced biological lesions because x-rays produce photoelectrons with ranges much shorter than cellular dimensions but equivalent to the size of DNA strands and metaphase chromosomes

[en] Cultured Chinese hamster cells (V79) were exposed to ²³⁸Pu α particles or 250 kVp x rays at doses resulting in similar cell survivals (i.e., 50, 10, and 1%). The DNA distributions of cells at different times after radiation exposure were measured using flow cytometry. Results indicated that after exposure to α particles, V79 cells showed significantly prolonged late S phase delay compared to x rays for comparable cell-killing doses. Retention of cells in late S subsequent to α-particle exposure caused a longer mitotic delay compared to x rays for a given survival level, consistent with the observation that for the endpoint of mitotic delay the RBE for high-LET radiation is higher than the RBE for cell killing

[en] The experimental results of cell killing by ultrasoft x-rays (0.28 and 1.5 keV) is presented. Cell lines V79, 10 T 1/2 and human skin fibroblasts that have different cellular dimensions due to difference in their attachment properties were used in these studies. Cellular dimensions at the time of exposure to ultrasoft x-rays were carefully measured by optical and electron microscopy. The results indicate that the differences in cell killing by ultrasoft x-rays and hard x-rays may be dependent on nuclear configurations of cells. The implications of these results to theories of radiation action are discussed

[en] In the first paper of this series, using V79 cells, we reported that the relative biological effectiveness (RBE) of ultrasoft X rays was found to increase with decreasing energy, and the oxygen enhancement ratio (OER) was found to decrease with decreasing energy. In this report, we present RBE and OER results for 10T1/2 cells that are known to grow uniformly flat and are considerably thinner than V79 cells. Thus the variation in dose across the cell nucleus is considerably reduced. The OER results agree well with our earlier V79 results. However, the RBE values for 10T1/2 cells compared to V79 cells are systematically less for all soft X rays and especially for 0.28 keV carbon-K (1.3 compared to 3.4 for V79 cells). Some plausible explanations are presented to reconcile the apparent discrepancy between V79 and 10T1/2 results