β表面污染测量的探测限及γ剂量率影响分析

目的 讨论了β表面污染监测仪对γ剂量率的响应问题、β表面污染本底测量及探测下限问题。方法 在不同γ剂量率水平的环境中进行β表面污染测量,并就γ剂量率较低场所的(本底水平)测量值讨论探测限的计算。结果 β探头对γ射线的响应具有线性正相关,在不同γ剂量下测量β表面污染的本底不一样,相应的探测限也随之改变。结论 γ剂量率对β表面污染测量结果的影响不容忽视,根据监测任务要求、本底计数(率)来选择仪器,确定测量时间或重复测量次数,使探测限满足评价指标/标准的需要。     

食品和饮用水放射性监测时测量时间与探测限关系初步研究

目的 比较不同测量时间食品和饮用水中放射性核素的探测限值,为应对核与辐射突发事件提供参考。方法 使用同一台γ谱仪分别测量水、牛奶和菠菜的马林杯样品,每种样品测量的活时间分别为2、4、8、12、24、72 h,将分析得到的探测限值与国际原子能机构(IAEA)推荐的操作干预水平以及世界卫生组织(WHO)推荐的饮用水水质标准进行比较。结果 饮用水和牛奶样品2~72小时¹³¹I、¹³⁷Cs和¹³⁴Cs测量结果范围分别为0.04~0.30 Bq/kg,0.05~0.34 Bq/kg和0.05~0.36 Bq/kg,新鲜菠菜样品的探测限略高于饮用水和牛奶样品。三种样品2~72 h测量结果均符合相关标准要求,但所得探测限值均随测量时间延长而减小。结论 在时间许可的条件下,尽量采用较长的探测时间可以增强检测能力,提高样品的检出率,但在应急情况下,应当进行代价利益分析,选择与可探测到的最低活度匹配的最佳测量时间。     

LB6008型六路低本底α、β测量仪的性能评估

目的掌握LB6008型六路低本底α、β测量仪性能指标,准确测量样品中总α、总β放射性体积活度。方法使用239Pu、90Sr-90Y工作源和241Am、40K粉末源对仪器进行效率刻度,对本底计数率、串道比及效率稳定性进行分析,依据GB/T 11682—2008和厂家指标进行评价。结果α本底计数率≤0.07计数/(cm2·h),β本底计数率≤5.1计数/(cm2·h),各路α探测器2π探测效率比均80%,β探测器2π探测效率比均50%;241Amα源探测效率为(5.62±0.33)%,40Kβ源探测效率为(26.22±2.11)%,5 d内探测效率变化≤4.58%;α射线对β道的串道比≤1.6%,β射线对α道的串道比≤0.12%;本底月稳定性实际测量值均在N_b±3δ可接受范围内,95%的测量值在N_b±2δ目标值范围内。结论该测量仪的基本性能指标均达到国家规定的Ⅱ级标准,适于样品总放射性水平的常规测量。     

固体径迹法测量氡及子体的判断阈和探测限

目的 研究利用固体径迹技术测量氡及子体的瓶颈技术问题,探讨本底氡对个人监测可靠性的影响及有效控制方法。方法 依据统计学规律,参考相关文献,结合剂量学分析,推导固体径迹技术测量氡及子体的判断阈和探测下限,进行辐射剂量估算。结果 利用应用举例方式,给出了具体实例的判断阈和探测下限。结论 发生β错误的概率不仅与判断阈L_C有关,而且与净径迹计数有关。净径迹计数值越大,β错误的概率就越小,可给出最小可探测径迹计数,估计最小可探测氡浓度,提高了氡个人剂量监测的可靠性。     

用两种效率刻度方法测量比对土壤介质放射性核素

目的 为了检验和提高γ谱仪测量准确性。方法 本实验室参加了由IAEA组织的土壤介质放射性核素测量比对活动。结果 分别采用由标准源刻度的和无源模拟刻度的效率曲线法,使用低本底高纯锗γ谱仪对土壤样品进行测量,通过相对偏差、Z检验、U检验、准确度和精确度等综合检验方法对测量结果进行了比对测试。结论 此次比对数据结果为"可以接受",从而验证了效率曲线刻度来源(包括无源模拟)的可靠性。     

反符合方法用于降低内照射直接测量系统探测下限的研究

目的 目前肺部计数器在超铀核素的内照射直接测量方面存在探测下限较高的问题，本文采用反符合方法降低系统的本底，进一步降低系统探测下限。方法 在肺部计数器系统内建立宇宙射线探测器，采用反符合方法，研究宇宙射线中μ子等硬成分对肺部计数器系统本底的影响。该宇宙射线探测器主要由140 cm（长）×110 cm（宽）×5 cm（高）的大面积塑料闪烁体和反符合电路组成。结果 在6~2 MeV能量段，增加反符合探测器后系统的本底计数率由2.5 cps降至2.2 cps。测量时间1 800 s，系统对²⁴¹Am（59.5 keV）和²³⁹Pu（13.6 keV）的探测下限可达1.4 Bq和1 700 Bq。结论 用肺部计数器直接测量超铀核素的过程中，采用反符合方法降低宇宙射线硬成分可以较好地降低部分系统本底，在降低核素探测下限方面起到一定作用。     

人类的限食研究

<正> 20世纪30年代,美国营养学家麦凯等人研究了一个有意义的实验现象,小鼠“吃得少些,活得长些”。他们通过严格的实验,发现限食不仅能使小白鼠增寿,对大白鼠、荷兰猪、兔子和其他实验动物也同样能增寿,对猴子的实验已进行10多年,目前观察的结果与鼠类的限食实验结果基本吻合,据报道,适量限食对人类健康长寿也有重要的作用。国内外老年医学都     

BH1227型低本底α、β测量仪性能期间核查

目的 BH1227型低本底α、β测量仪属于弱放射性测量装置,应定期进行期间核查。方法本文对本底及其稳定性、效率比及其稳定性、和影响量进行测试,又结合本底质控图对仪器性能进行综合评价。结果该仪器α、β平均本底计数率:α≤0.05计数·min~(-1)cm~(-2),β≤0.15计数·min~(-1)cm~(-2);效率比:η_γ(α)≥0.70,η_γ(β)≥0.40;效率稳定度R_α5%,R_β15%;α对β影响量:(F_(α→β))3%;β对α影响量:(F_(β→α))1%;本底计数率在平均本底计数率的3倍变异系数范围内波动。另外,本底质控图中20个月本底值均落在警戒线范围内。结论以上各项性能的结果均符合国家标准~([1]),本α、β测量仪在检定周期内性能稳定,能够满足工作需要。     

三门核电站宁海毗邻区域辐射水平本底调查

目的了解三门核电站运行前宁海毗邻区域环境γ辐射剂量和环境介质的放射性水平,建立环境辐射本底基线数据。方法采用碘化钠闪烁体探测法和热释光累积剂量法测定监测区域环境γ外照射剂量率和环境辐射累积剂量,采用低本底α/β探测装置测定监测区域水源水总α和总β辐射剂量,食品样品放射性核素采用γ能谱仪测定。结果监测区域居民人均年有效剂量为0.928 mSv;原野γ外照射剂量率为(98.32±21.08)nGy/h;环境辐射年累积剂量为(1.040±0.044)mSv。原野γ外照射剂量率和环境辐射累积剂量均有季节性差异。20 km范围内监测区域环境γ外照射剂量率和环境辐射累积剂量与10 km和30 km范围的测量结果差异无统计学意义。食品样品放射性核素检出值均远小于国家标准,水源水样品总放射性指标符合国家饮用水标准。结论三门核电站宁海毗邻区域放射性本底在正常水平范围内,环境放射性本底有季节性差异。本次调查为三门核电站运行前宁海毗邻区域放射性本底建立了基线数据,~(90)Sr、~(137)Cs、~(131)I等人工放射性核素是今后食品样品监测的重点。     

居民限盐控油行为影响因素分析

目的了解影响广州市居民限盐控油行为的因素,为促进限盐控油行为的形成提供参考。方法将4 461名明确是否使用限盐勺以及4 426名明确是否使用控油壶的调查对象分为使用组和未使用组,对两组的基本特征、油盐相关知信行等进行调查及比较分析。结果限盐勺使用组食盐推荐摄入量知晓率(41.52%)、食盐摄入过量与高血压相关知晓率(59.97%)、与中风有关知晓率(17.77%)、支持全民减少摄盐量人数(91.61%)等均高于未使用组(分别是34.91%,χ2=18.88,P<0.01;55.52%,χ2=8.52,P<0.01;15.14%,χ2=5.18,P=0.02;81.57%,χ2=98.38,P<0.01),饮食口味很咸和较咸的构成比(7.50%)低于未使用组(10.22%,χ2=9.93,P<0.01)。控油壶使用组食用油推荐摄入量知晓率(39.44%)、食油摄入过量与高血压相关知晓率(55.61%)、与肿瘤相关知晓率(11.85%)、支持全民减少摄油量构成比(91.43%)均高于未使用组(分别是30.95%,χ2=33.19,P<0.01;50.87%,χ2=9.90,P<0.01;9.38%,χ2=6.97,P<0.01;84.21%,χ2=54.65,P<0.01)。结论油盐相关知识知晓程度及态度、个人的饮食习惯对限盐控油行为有一定的影响。     

Evaluation of eight decision rules for low-level radioactivity counting.

In low-level radioactivity measurements, it is often important to decide whether a measurement differs from background. A traditional formula for decision level (DL) is given in numerous sources, including the recent ANSI/HPS N13.30-1996, Performance Criteria for Radiobioassay and the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM). This formula, which we dub the N13.30 rule, does not adequately account for the discrete nature of the Poisson distribution for paired blank (equal count times for background and sample) measurements, especially at low numbers of counts. We calculate the actual false positive rates that occur using the N13.30 DL formula as a function of a priori false positive rate a and background Poisson mean mu = rhot, where rho is the underlying Poisson rate and t is the counting time. False positive rates exceed a by significant amounts for alpha < or = 0.2 and mu < 100 counts, peaking at 25% at mu approximately equal to 0.71, nearly independent of alpha. Monte Carlo simulations verified calculations. Currie's derivation of the N13.30 DL was based on knowing a good estimate of the mean and standard deviation of background, a case that does not hold for paired blanks and low background rates. We propose one new decision rule (simply add 1 to the number of background counts), and we present six additional decision rules from various sources. We evaluate the actual false positive rate for all eight decision rules as a function of a priori false positive rate and background mean. All of the seven alternative rules perform better than the N13.30 rule. Each has advantages and drawbacks. Given these results, we believe that many regulations, national standards, guidance documents, and texts should be corrected or modified to use a better decision rule.     

Exact calculation of probabilities of false positives and false negatives for low background counting.

The purpose of this paper is to demonstrate the derivation and use of exact formulas, and their algorithms, for calculating the probabilities alpha of Type I errors, and beta of Type II errors, for low blank total counts (Poisson-distributed). The calculations are carried out to examine the alpha and beta probabilities at low blank levels of the decision level (DL) and minimum detectable amount (MDA) formulations as adopted in the Health Physics Society Standard, "Performance Criteria for Radiobioassay." These formulations are consistent with those published by L.A. Currie, which have received wide acceptance in defining lower limits of detection (LLD). Although Currie's formulation was derived assuming a normal distribution in net counts, the behavior of the distribution of net counts at low count levels, which is a distribution of the difference between two Poisson variates, is such that the MDA formulation in the standard could be considered acceptable for the purpose of providing one simple formulation of MDA. The derivations in this note can also be useful in other problems involving differences in Poisson variates, such as those in certain population studies.     

Minimum detectable activity when background is counted longer than the sample.

This note discusses the use of blank or background counting data that are measured for times that differ from times used for the sample counts. The correct formula for the minimum detectable activity, under this condition, is given as follows: MDA = [3 + 3.29 square root of Rbtg(1 + tg/tb)]/epsilon tg, where Rb denotes background count rate, tb and tg denote background and gross count times, and epsilon denotes counting efficiency. Counting backgrounds for a long time reduces decision levels, uncertainties, and minimum detectable activities. These benefits are fully available only when there is no other source of variability than random fluctuations in count rates.     

环境生物样品中氚分析测量方法研究

目的 建立一种环境生物样品中氚的分析测量方法，并对方法的适用性进行验证，为环境生物中氚分析方法标准的制定提供技术支持。方法 真空冷冻分离生物鲜样制得组织自由水氚试样和生物干样；生物干样与氧气反应后制得有机结合氚试样。用低本底液体闪烁计数器测量氚活度浓度。结果 该方法对组织自由水氚和有机结合氚测试结果的相对标准偏差分别为8.50%和16.3%；组织自由水氚加标测试的加标回收率为96.7%，已知活度浓度试样有机结合氚测试结果的相对误差为-2.38%；组织自由水氚和有机结合氚的探测下限分别为1.07 Bq/kg·鲜和0.0539Bq/kg·鲜。结论 该方法可用于环境生物样品中氚的分析测量。     

脑出血预后与血白细胞数及血糖的关系分析

目的　分析脑出血预后与血白细胞数、血糖的关系。方法　测定５１ 例急性脑血管病中的脑出血患者，在起病４８ 小时内的外周血白细胞计数与血糖值。结果　外周血白细胞计数升高和血糖高于正常值者预后相对较差。结论　脑出血病死率与外周血白细胞计数和血糖值相关。     

Limits and uncertainties--with special regard to radon measurements.

The concept of limits was introduced to assure a commonly tolerated low health risk from the exposure to radioactivity or chemicals. In most countries concentration limits are given by the authorities and are fixed to certain values. The question is how to prove compliance with limits, keeping in mind that all measurements are subject to uncertainties. This means there is always a certain probability for a wrong decision. Generally, the authorities demand only the answer "below" or "above" the limit and will not accept statements on probability. Advantages and disadvantages of different decision making philosophies are discussed.     

Using exact Poisson likelihood functions in Bayesian interpretation of counting measurements

A technique for computing the exact marginalized (integrated) Poisson likelihood function for counting measurement processes involving a background subtraction is described. An empirical Bayesian method for determining the prior probability distribution of background count rates from population data is recommended and would seem to have important practical advantages. The exact marginalized Poisson likelihood function may be used instead of the commonly used Gaussian approximation. Differences occur in some cases of small numbers of measured counts, which are discussed. Optional use of exact likelihood functions in our Bayesian internal dosimetry codes has been implemented using an interpolation-table approach, which means that there is no computation time penalty except for the initial setup of the interpolation tables.     

Generation of airborne fly body particles by four electrocution fly traps and an electronic fly trap

Five commercially available fly traps were tested with laboratory reared house flies in a chamber for 15 minutes, to determine the sizes and number of respirable particles generated during the course of fly capture. Four of the five traps electrocuted the flies, while one trap captured the flies on a sticky pad after disorienting them with a periodic low d.c. voltage. The electrocution resulted in a respirable particle count level increasing 10 to 500 times over the background (flies with no trap), while the non‐electrocution technique resulted in particle count levels near or below the mean background level. For three of the four electrocution traps, a simple linear regression model indicated that particle counts increased with an increasing number of flies killed. Statistically significant correlation between particle counts and fly kills could not be obtained for the other two traps.     

Antimalarial efficacy of chloroquine, amodiaquine, sulfadoxine-pyrimethamine, and the combinations of amodiaquine + artesunate and sulfadoxine-pyrimethamine + artesunate in Huambo and Bie provinces, central Angola

We studied three antimalarial treatments in Caala and Kuito, Angola, in 2002 and 2003. We tested chloroquine (CQ), amodiaquine (AQ) and sulfadoxine-pyrimethamine (SP) in Caala, and AQ, SP and the combinations AQ+artesunate (AQ+AS) and SP+artesunate (SP+AS) in Kuito. A total of 619 children (240 in Caala, 379 in Kuito) with uncomplicated Plasmodium falciparum malaria were followed-up for 28 days, with PCR genotyping to distinguish recrudescence from reinfection. PCR-corrected failure proportions at day 28 were very high in the CQ group (83.5%, 95% CI 74.1-90.5), high in the SP groups (Caala: 25.3%, 95% CI 16.7-35.8; Kuito: 38.8%, 95% CI 28.4-50.0), around 20% in the AQ groups (Caala: 17.3%, 95% CI 10.0-27.2; Kuito: 21.6%, 95% CI 14.3-30.6) and very low in the artemisinin-based combination groups (1.2%, 95% CI 0.0-6.4 for each combination AQ+AS and SP+AS). These results show that CQ and SP are no longer efficacious in Caala and Kuito and that the moderate efficacy of AQ is likely to be compromised in the short term if used as monotherapy. We recommend the use of AQ with AS, though this combination might not have a long useful therapeutic life because of AQ resistance.