ABSTRACT
The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1,2,3), an irregularly shaped body with approximate dimensions of 34 x 13 x 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of 'ejecta blocks'. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a 'pond'. Properties of the 'ponds' are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.
Subject(s)
School Health Services/standards , Adolescent , Child , Disabled Persons , Drug Therapy/standards , First Aid , Forms and Records Control/standards , HIV Infections/prevention & control , Humans , Immunization , Inservice Training , Interprofessional Relations , Mass Screening/standards , Oral Health , Organizational Objectives , Program Evaluation , School Health Services/organization & administration , School Nursing/education , School Nursing/standards , United States , Universal PrecautionsABSTRACT
A survey of radiation doses received by infants having radiography in a neo-natal unit was undertaken at Aberdeen Maternity Hospital. Options for dose reduction recommended by the CEC Lake Starnberg Group were investigated. Techniques were implemented for clinical evaluation after assessments of image quality with test objects and phantoms. Clinical image quality of radiographs was evaluated by paediatric radiologists using CEC criteria. Results revealed a clear relationship between entrance dose and patient weight, indicating that reference doses for infants could be linked to weight. At the start of the study the mean entrance dose for chest anteroposterior (AP) radiographs was 65 microGy and the dose-area product 12.3 mGy cm2 for a system with 2.5 mm aluminum filtration using 50 kVp X-rays with a 200 speed class film/screen system. A 400 speed class film/screen combination was investigated but not evaluated clinically, because the image quality was not considered acceptable. Addition of 0.1 mm copper to the filtration of the X-ray tube reduced entrance doses by 50%, but the technique was not adopted, because of a poorer image quality with only 72% of features in clinical images being reproduced to an acceptable standard, compared with 87% with the original system. Use of faster processing chemicals, an increase in filtration to 3.5 mm aluminium and a tube potential of 60 kVp resulted in a 40% reduction in mean entrance dose to 37 microGy with satisfactory clinical image quality.
Subject(s)
Technology, Radiologic/methods , Body Weight , Humans , Infant, Newborn , Radiation DosageABSTRACT
Entrance doses and dose-area products have been measured for paediatric X-ray examinations in a dedicated paediatric department. Dose-area products for barium meal and micturating cystourethrogram examinations involving fluoroscopy were substantially less than results from other studies. A number of factors contribute to this, including a high gain image intensifier used without a grid, shorter screening times, smaller numbers of films, exclusive use of a 100 mm camera and careful collimation of the X-ray field. Entrance air kerma has been measured for pelvis, abdomen, chest and skull radiographs. The relationship between dosimetric quantities and an equivalent patient diameter derived from data on patient height and weight has been studied. The results show a linear relationship between the logarithm of entrance air kerma and equivalent patient diameter for radiographic examinations performed on a single X-ray unit. Application of exponential correction factors could allow entrance doses for radiographs of children of different ages to be compared with appropriate reference doses.
