RESUMO
The application of a xenon-filled multiwire proportional counter to photon absorptiometry of bone mass is described. Performance characteristics obtained from a prototype system are discussed and future developments indicated.
Assuntos
Osso e Ossos , Osso e Ossos/análise , Cálcio/análise , Humanos , Técnicas In Vitro , Métodos , Tamanho do Órgão , Radiometria/instrumentação , Análise Espectral , XenônioRESUMO
HeLa cells were irradiated at liquid nitrogen temperature with negative pions from Nimrod at the Rutherford Laboratory and then assayed for survival of colony-forming ability. Complete dose-response curves were obtained from repeated determinations at 14 different positions along the depth-dose profile and survival curves were fitted to the data by computer programme. A depth-damage profile was thus established in terms of the final slopes of these survival curves. This confirmed the expected RBE value of 1.84 at the ionization peak. Although a value of unity was found in the main plateau region, the "entrance" positions showed significantly higher values.
Assuntos
Sobrevivência Celular/efeitos da radiação , Partículas Elementares , Relação Dose-Resposta à Radiação , Células HeLa/efeitos da radiação , Humanos , Doses de Radiação , Eficiência Biológica RelativaRESUMO
The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on board the Mars Express spacecraft found that solar wind plasma and accelerated ionospheric ions may be observed all the way down to the Mars Express pericenter of 270 kilometers above the dayside planetary surface. This is very deep in the ionosphere, implying direct exposure of the martian topside atmosphere to solar wind plasma forcing. The low-altitude penetration of solar wind plasma and the energization of ionospheric plasma may be due to solar wind irregularities or perturbations, to magnetic anomalies at Mars, or both.