后装治疗机真(假)源参考点故障的维修

后装机在使用过程中最常见的故障就是真（假）源参考点故障。下面以国产威达ＷＤ -ＨＤＲ１８型后装机为例 ,介绍一下真（假）源参考点故障的维修。工作原理在治疗机储源铅罐放射源出口处有一个检测放射源是否在铅罐中（安全位置）的装置 ,叫参考光源。它是一个有机玻璃圆盘 ,中间穿有两个孔 ,真、假放射源分别从其中通过。在每个孔孔壁的两侧各装有一个发光二极管（Ｌ１）和一个光敏三极管（ｔ）组成的光电耦合器。放射源在铅罐内时 ,ｔ接收到来自Ｌ１的发光 ,比较器输出 ５Ｖ ,发光二极管Ｌ２发光 ,表示放射源在安全位置 ,同时这个信号经…     

Predicting population dental disease experience at a small area level using Census and health service data

BACKGROUND: Information on the dental disease patterns of child populations is required at a small area level. At present, this can be provided only by expensive whole population surveys. The aim of this study was to evaluate the ability of Census data combined with health service information to provide estimates of population dental disease experience at the small area level. METHOD: Clinical dental data were collected from a large cross-sectional survey of 5-year-old children. A preliminary series of bivariate linear regression analyses were undertaken at ward level with the mean number of decayed, missing or filled teeth per child (dmft) as the dependent variable, and the Census and health service and lifestyle variables suspected of having a strong relationship with dmft as independent variables. This was followed by fitting a multiple linear regression model using a stepwise procedure to include independent variables that explain most of the variability in the dependent variable dmft. RESULTS: All deprivation indicators derived from the Census showed a highly significant (p<0.001) bivariate linear relationship with ward dmft. The Jarman deprivation score gave the highest R2 value (0.45), but the Townsend index (R2=0.43) and the single Census variable 'percentage of households with no car' (R2 = 0.42) gave very similar results. The health and lifestyle indicators also showed highly significant (p<0.001) linear relationships with dmft. The R2 values were generally much lower than the deprivation-related Census variables, with the exception of the percentage of residents who smoked (R2 = 0.42). None of the health or lifestyle variables was included in the final dental disadvantage model. This model explained 51 per cent of the variability of ward dmft. CONCLUSIONS: The results demonstrate the strong relationship between dental decay and deprivation, and all of the commonly used measures of deprivation exhibited a similar performance. For this population of young children health and health services shelf data did not improve on the ability of deprivation-related Census variables to predict population dental caries experience at a small area level.     

Predicting small area health-related behaviour: a comparison of multilevel synthetic estimation and local survey data

A recent paper in Social Science and Medicine (Twigg et al. 50 (2000) 1109) outlined an approach to the estimation of prevalences of small-area health-related behaviour using multilevel models. This paper compares results from the application of the multilevel approach with those derived using the more traditional strategy of the local 'lifestyle' survey. Estimations of smoking prevalence and high alcohol consumption are examined and critical assessments made of both estimation approaches. It is concluded that the alternative method is more suited towards the prediction of smoking rates as opposed to unsafe alcohol consumption.     

Photon shielding for 241Am surface and point sources.

To determine radiation protection requirements for work with actinide elements, a method for rapidly estimating effective dose-equivalent rates from low-energy photons has been developed. This paper describes results obtained from a personal computer program that incorporates the point kernel technique to predict radiation fields from shielded and unshielded sources containing 241Am. Information generated has been used to determine procedures and to design facilities for handling actinides at Argonne National Laboratory's site at the Idaho National Engineering Laboratory. Area or point sources can be treated; effects of Compton scattering in air and in solid shields are considered. Users can select an appropriate response function; their choice has a strong influence on predicted dose rates from unshielded sources.     

Human teratogenic and mutagenic markers in monitoring about point sources of pollution

For most pollutants a full range of short-term adverse reproductive outcomes should be considered as possible markers in monitoring populations. These include sex ratio, birth-weight, intrauterine growth retardations, neonatal mortality, birth defects manifest at birth or very shortly thereafter, embryonic and fetal deaths (EFD), germinal chromosome abnormalities in EFD and in livebirths, specific locus mutations detectable at birth, and indicators of somatic mutation including chromosome breakage and sister chromatid exchange. It is suggested (in the absence of a defined expected effect) that the highest priority be given to study of rates of EFD and of somatic chromosome rearrangement. Monitoring not involving direct evaluation of human morbidity and mortality may be considered, including examination of human sperm, examination of human body fluids for toxicological and biochemical evidence of mutagenesis, the study of wild animal populations in polluted areas, and the use of caged experimental mammals placed in locations of concern. Where possible, data on reproductive and mutagenic outcomes in the potential target population should be sought systematically before a putative pollution source comes into operation. Reference data on human mutagenic and teratogenic outcomes are presented.     

Endovascular brachytherapy: dosimetry and dose-area analysis of various radiation sources

With the increase in popularity of endovascular brachytherapy for prevention of restenosis following coronary angioplasty, it remains to be determined which isotope and isotope form is the most ideal. An issue concerning the use of wire sources is the influence of the centering of the wire on dose uniformity across the artery wall and the potential problems this can lead to in terms of underdosage of the target tissues. In this investigation, the dosimetric characteristics of three currently used sources (gamma-emitting 192Ir wire; beta-emitting 32P wire; and beta-emitting 188Re solution) were determined with EGS4 Monte Carlo. The dose results were then used to determine the dose-area relationships for the three sources in arteries with concentric and non-concentric lumens/walls, including situations in which the wire sources are moved away from the centre of the artery. It is found that, in order to ensure dose uniformity, centering is substantially more important for beta-emitting wire sources. This is highlighted most significantly in the case of an example large irregular artery. Although the suitability of a source depends on many criteria (e.g., cost, availability, radiation protection, possible radiation-induced late effects), the problem of centering a wire source in possibly large and/or irregular arteries is greatly eased by the use of a gamma-emitting source.     

探究4种临床CT扫描方式对受检者辐射剂量的影响及胸部扫描辐射场的空间分布

目的 探究4种临床CT扫描方式对受检者常见组织吸收剂量的影响及胸部扫描的辐射场空间分布,以期为受检者与机房内空间辐射防护提供依据。方法 利用热释光探测器（TLD）测量仿真体模的眼晶体、甲状腺、性腺、胸部和腹部皮肤在4种CT扫描方式下的吸收剂量。利用TLD监测胸部螺旋扫描时距离CT诊断床不同位置处的空气比释动能。结果 仿真体模的眼晶体、甲状腺、性腺、胸部和腹部皮肤在4种CT扫描方式下的吸收剂量分别为0.040～64.818 mGy、0.154～10.155 mGy、0.028～0.154 mGy、0.443～17.141 mGy和0.093～14.346 mGy。胸部扫描时空间辐射场的空气比释动能最大值为0.049 mGy,且与CT球管距离越大数值越小。结论 4种CT扫描方式对受检者常见组织的吸收剂量一般不会超过阈剂量。单次CT胸部扫描时陪检者所受剂量较小。为减少辐射危害,在CT扫描中可采取屏蔽措施来减少受检者组织吸收剂量,同时陪检者应适当增加与球管和诊断床的距离。     

Cluster detection diagnostics for small area health data: with reference to evaluation of local likelihood models

The focus of this paper is the development of a range of cluster detection diagnostics that can be used to assess the degree to which a clustering method recovers the true clustering behaviour of small area data. The diagnostics proposed range from individual region specific diagnostics to neighbourhood diagnostics, and assume either individual region risk as focus, or concern areas of maps defined to be clustered and the recovery ability of methods. A simulation-based comparison is made between a small set of count data models: local likelihood, BYM and Lawson and Clark. It is found that local likelihood has good performance across a range of criteria when a CAR prior is assumed for the lasso parameter.     

Epidemiology,public health,and health surveillance around point sources of pollution

In industrial society a large number of point sources of pollution exist, such as chemical plants, smelters, and nuclear power plants. Public concern has forced the practising epidemiologist to undertake health surveillance of the usually small populations living around point sources. Although not justifiable as research, such epidemiologic surveillance activities are becoming a routine part of public heath practice, and this trend will continue. This introduction reviews concepts of epidemiologic surveillance, and institutional problems relating to the quality of such applied research.     

新生儿疾病筛查临界值选取与筛查效率

目的:探讨武汉市新生儿疾病筛查临界值选取方法和运用此临界值的筛查效果,总结经验、提高筛查效率,降低漏诊率。方法:新生儿出生后72 h,采足跟末稍血制成滤纸干血片,用FEIA法检测血片中TSH和Phe含量,根据季节和标本采集时间选择不同临界值,并将初筛阳性新生儿召回确诊。结果;5年来,共筛查新生儿137826例,使用新临界值后,CH和PKU初筛阳性率由7.14‰和1.27‰增加到9.98‰和1.99‰,同时,CH和PKU发病率分别由0.49‰和0.60万/提高到0.78‰和1.05万/。结论:新生儿疾病筛查实验室应根据自身实际情况,制定适合本地区临界值,最大限度地减少漏诊,同时,避免过高假阳性给社会带来的负担,实验室要加强全面质量控制,推动新生儿疾病筛查工作向深层次发展。     

A comparison between gross and net count methods when searching for orphan radioactive sources

Different numerical strategies in searching for orphan radioactive sources in the environment by means of a mobile detector system have been evaluated. A carborne 3- by 3-inch NaI(Tl) spectrometric system was used with an unshielded 2 GBq 137Cs source as a test source. In this paper, a previous method (MB method), based on a moving average algorithm applied on the gross count rate, was extended and compared with three moving average algorithm methods involving different natural background subtraction strategies. For each method the distance from the road that an orphan source can be detected with a probability of 50% (the critical distance, CD) when driving by is determined. The CD for a 2 GBq 137Cs source improved from 105 m to 130 m when the interference from 40K was subtracted from the 137Cs spectral window. However, when the contribution of other natural gamma-emitting nuclides also was subtracted, the ability to find the 137Cs source was reduced.     

小分子肽产生菌培养基碳源与氮源的优化

目的:探讨不同碳源、氮源对乳酸杆菌小分子肽产量及抑菌效果的影响。方法:用1%的不同碳源和2%的不同氮源替换基础培养基中的葡萄糖、酵母膏和蛋白胨,同时改变基础培养基中的葡萄糖浓度,分别在相同条件下发酵,双层平板法检测抑菌效果,同时测定发酵液的OD值和PH值。结果:不同碳源均能促进LB-9菌株的生物量增加,生物量从高到低依次为葡萄糖、果糖、蔗糖、乳糖、木糖、糊精、玉米浆、可溶性淀粉,其中葡萄糖为碳源的发酵液的生物量最大。各有机氮源均可促进小分子肽的产生,而无机氮源不能。有机氮源发酵液的抑菌效果从高到低依次为酵母膏、牛肉膏、多胨、鱼蛋白胨、胰蛋白胨、大豆胨。结论:葡萄糖是本实验最好的碳源。葡萄糖为碳源的发酵液的生物量最大,小分子肽产量随葡萄糖浓度的增加而增加。菌体细胞生长最好的氮源是酵母膏,有机氮源均可促进小分子肽的产生,而无机氮源不能。     

Asthma prevalence and deprivation: a small area analysis

STUDY OBJECTIVE: To investigate the relation between the prevalence of asthma symptoms in adults and deprivation in the area of residence. DESIGN: Two complementary surveys carried out between 1991-1993 yielding adult asthma symptom prevalence throughout New Zealand. Deprivation is measured by the NZDep91 index of deprivation for small areas. SETTING: New Zealand. PARTICIPANTS: A random sample of 25,042 adults aged 20-50 years. MAIN RESULTS: After controlling for possible confounding by age, gender, and ethnicity, the 12 month period prevalence rates of asthma in this representative sample of New Zealand adults are significantly higher in the three most deprived area categories than in the least deprived (tenth) category. The prevalence ratio for the most deprived category compared with the least deprived category is 1.29 with 95% confidence intervals (CI) 1.14, 1.47. There is a linear increase in asthma prevalence with increasing area deprivation (chi 2(1) = 32.20, p < 0.001). Independently, the rates are also 1.41 (95% CI 1.29, 1.54) times higher among Maori and 1.29 (95% CI 1.10, 1.52) times higher among the Pacific Island group than among the remaining, mostly European, respondents. CONCLUSIONS: The relation between asthma in adults and area deprivation is unlikely to be attributable to study biases or confounding. Further work should examine the possible role of modifiable deprivation factors in this relation.     

Unemployment and mortality: a small area analysis.

It has been claimed that unemployment affects the health and thus the mortality of the unemployed, their families, and other members of their communities. This paper examines the relation between mortality and the unemployment experiences of small areas which vary in the extent to which their unemployment levels have changed in recent years. Quarterly numbers of unemployed, classified by age, sex, duration of unemployment, and unemployment office for 1977-81, have been aggregated to correspond to Family Practitioner Committee areas (FPCs), for which population and mortality data had been collected for a different study. There was little variation in long term (greater than 6 months) unemployment trends prior to July 1980, but subsequently there were large variations between FPCs in the rate of increase in unemployment rates. Mortality data for suicide, ischaemic heart disease, cerebrovascular disease, and all causes were examined for the period 1975-83. When the mortality trends of FPCs with different unemployment experiences were compared, no statistically significant differences in trends were found, although areas with greater increases in unemployment appeared to have slightly worse mortality trends for suicide, ischaemic heart disease, cerebrovascular disease, and total mortality for men in the younger age groups. If changes in the level of unemployment do have an effect on changes in trends in mortality levels, this effect is not of sufficient magnitude to be statistically significant with the sample available, in spite of the fact that it included the whole of England and Wales.