Increased radon detection sensitivity: extraction from 200 ml of water and liquid scintillation counting

To increase detection sensitivity in a radon ground-water monitoring program, radon is extracted and transferred from 200 mL of water to a liquid scintillator by bubbling and circulating air through the two liquids in a closed system using a peristaltic pump. This results in a count rate that is 11 times higher than for samples prepared by the most widely used method, where 10 mL of water are added to 10 mL of scintillator. Preparation of counting samples is simple and takes 4 min. Standard deviation in radon concentration is 5% and minimum detectable activity is 5 mBq L(-1), using a counter with a background of 3 counts per hour and a counting time of 3 h. This method is also suitable for the measurement of radium in water.     

Retrospective determination of the contamination in the HML's counting chambers

The original documentation surrounding the purchase of the Human Monitoring Laboratory's (HML) counting chambers clearly showed that the steel contained low levels of radioactivity, presumably as a result of A-bomb fallout or perhaps to the inadvertent mixing of radioactive sources with scrap steel. Monte Carlo simulations have been combined with experimental measurements to estimate the level of contamination in the steel of the HML's whole body counting chamber. A 24-h empty chamber background count showed the presence of 137Cs and 60Co. The estimated activity of 137Cs in the 51 tons of steel was 2.7 kBq in 2007 (51.3 microBq g(-1) steel) which would have been 8 kBq at the time of manufacture. The 60Co that was found in the background spectrum is postulated to be contained in the bed-frame. The estimated amount in 2007 was 5 Bq and its origin is likely to be contaminated scrap metal entering the steel production cycle sometime in the past. The estimated activities are 10 to 25 times higher than the estimated minimum detectable activity for this measurement. These amounts have no impact on the usefulness of the whole body counter.     

An evaluation of germanium detectors employed for the measurement of radionuclides deposited in lungs using an experimental and Monte Carlo approach.

A study was undertaken to evaluate the performance of an advanced design broad energy germanium detector for the in vivo measurement of radionuclides in lungs. Relative counting efficiency, background, and sensitivity for lung counting arrays consisting of four, three, and two 80-mm-diameter by 20-mm-thick (80 x 20 mm) broad energy germanium detectors were simulated by collecting spectra with the single 80 x 20 mm broad energy germanium at each of four locations over a humanoid torso phantom. Regions of interest were evaluated for photon energies ranging from 17 to 1,500 keV. The 80 x 20 mm detector arrays were then benchmarked against a standard array of four 70-mm-diameter by 20-mm-thick (70 x 20 mm) broad energy germanium detectors. Since testing new equipment can be an expensive and time consuming process, an alternative approach, using Monte Carlo simulations instead of physical measurements, was also evaluated and compared to experimental data. With this approach, counting efficiency and minimum detectable amount were simulated for two sizes of germanium detectors (70 mm and 80 mm diameter) at four different crystal thicknesses (15, 20, 25, and 30 mm). For the experimental measurements, arrays consisting of three and four 80 x 20 mm broad energy germanium detectors resulted in an increase in counting efficiencies, relative to the standard array, at all photon energies. The greatest relative increase was observed for the four-detector array (24-35%). In contrast, counting efficiency decreased, relative to the standard array, by 24-28% with a two-detector array. Arrays consisting of two and three 80 x 20 mm broad energy germanium detectors resulted in decreased relative background at all photon energies, with the exception of the 946 keV photon for the three-detector array. The most significant decrease in background occurred with the two-detector array (28 to 40%), while background was increased by 18-43% for the four-detector array. Arrays consisting of three and four 80 x 20 mm broad energy germanium detectors resulted in increased relative sensitivity at all photon energies. The three-detector array provided the greatest sensitivity at photon energies below 344 keV. The four-detector array provided slightly better measurement sensitivity at photon energies greater than 344 keV. The two 80 x 20 mm detector array provided sensitivity unexpectedly comparable to the standard array. Monte Carlo predictions on how size affects counting efficiency and minimum detectable amount agreed well with the experimental results. From the Monte Carlo predictions, the effect of detector thickness on counting efficiency was unimportant at photon energies up to 60 keV and independent of detector diameter. At higher photon energies for both detector diameters, the counting efficiency decreased as the thickness decreased. The values of minimum detectable amount for the 70-mm and 80-mm diameter detectors did not differ by more than 15% at 17 keV or 20% at 60 keV when compared to detectors of equivalent thickness. Minimum detectable amount increased slightly at 17 keV and rose by approximately 52% at 660 keV, with decreases in thickness from 30 mm to 15 mm.     

Use of alpha spectroscopy for conducting rapid surveys of transuranic activity on air sample filters and smears

This paper demonstrates the utility of a portable alpha Continuous Air Monitor (CAM) as a bench top scalar counter for multiple sample types. These include using the CAM to count fixed air sample filters and radiological smears. In counting radiological smears, the CAM is used very much like a gas flow proportional counter (GFPC), albeit with a lower efficiency. Due to the typically low background in this configuration, the minimum detectable activity for a 5-min count should be in the range of about 10 dpm which is acceptably below the 20 dpm limit for transuranic isotopes. When counting fixed air sample filters, the CAM algorithm along with other measurable characteristics can be used to identify and quantify the presence of transuranic isotopes in the samples. When the radiological control technician wants to take some credit from naturally occurring radioactive material contributions due to radon progeny producing higher energy peaks (as in the case with a fixed air sample filter), then more elaborate techniques are required. The techniques presented here will generate a decision level of about 43 dpm for such applications. The calibration for this application should alternatively be done using the default values of channels 92-126 for region of interest 1. This can be done within 10 to 15 min resulting in a method to rapidly evaluate air filters for transuranic activity. When compared to the 1-h count technique described by , the technique presented in the present work demonstrates a technique whereby more than two thirds of samples can be rapidly shown (within 10 to 15 min) to be within regulatory compliant limits. In both cases, however, spectral quality checks are required to insure sample self attenuation is not a significant bias in the activity estimates. This will allow the same level of confidence when using these techniques for activity quantification as is presently available for air monitoring activity quantification using CAMs.     

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。     

An evaluation of two sample preparation methods for measuring 3H and 14C in incinerator ash and spent lime.

This paper compares the performance of two methodologies, oxidation and gel suspension, for measuring the 3H and 14C specific activity in incinerator ash and lime. The two methods were judged on the basis of the count time needed to achieve a specified minimum detectable concentration. Both methods involve pretreatment of the sample matrix followed by liquid scintillation counting. Both methods perform adequately for measuring 3H in spent lime, but only oxidation delivers adequate sensitivity for the more demanding 14C case. In addition, the gel suspension method fails to detect over 95% of the 3H seen by the oxidation method in incinerator ash.     

A proposed method to determine the decision level for radioactivity measurements

When measuring radioactivity, the problem rises of deciding whether or not a sample contains radioactivity in excess of background and above which value the result is meaningful. This decision process is why the notion of decision level was introduced. Whereas there is unanimity about its definition, this is not the case for its calculation, and many expressions have been proposed. This article contains a comparison of several decision level models by means of the calculation of actual false positive probability. First, three models are compared for the case of a well-known background, then a proposed model is developed and the four models are compared for the case of a poorly-known background. It appears from this study that, in order to be valid, the formula of the decision level must verify three conditions. First, the counting times have to appear symmetrically in the formula of the decision level; second, for long background counting times, the expression has to be equivalent to the one obtained with the corrected normal distribution corresponding to the Poisson law for the case of a well-known background; and, third, for large background, the expression has to be equivalent to those given by the three former models. It will be demonstrated that only the proposed model fulfills these requirements.     

Evaluating current policy for detecting mosaicism in amniotic fluid cultures: implications for current cell counting practices

Chromosomal mosaicism is one of the most vexing problems for clinical cytogenetic laboratories and personnel time used for analysis at the microscope is one of the principle costs in cytogenetic laboratories. We use data collected from 26 cytogenetic laboratories to evaluate whether the American College of Medical Genetics guidelines for minimum number of cells to count to exclude mosaicism in amniotic fluid specimens is appropriate. An accurate estimate of the number of mosaics that are missed by current cell counting practices is an important step in this process. Thus, we present a new method for estimating the number of mosaics that are missed and we use computer simulation to evaluate this new method. Our results indicate that if the clinical significance of mosaicism is suspected to be minimal for certain cytogenetic anomalies when the percentage of abnormal cells is 15 per cent or less, then it may be sufficient to use a 15-cell counting-rule-for-detection along with a minimum total cell count of 30 regardless of whether abnormal cells or normal cells are in the minority.     

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.     

Analysis of 228Ra and 226Ra in public water supplies by a gamma-ray spectrometer

Methods for measuring 228Ra were reviewed to select a brief and simple screening procedure under NIPDW Regulations for public water supplies. A two-step method was considered to concentrate Ra by evaporation or co-precipitation and to count it with a gas ionization detector, a liquid-scintillation detector, or a Ge detector with multichannel analyzer. Gross beta particle counting appears to be feasible for screening to meet the 0.04 Bq L-1 detection limit. One can utilize the same sample volume as currently collected and measure radiation with commonly available equipment in reasonable time. The required sample volumes were estimated on the basis of known counting efficiencies and background count rates. Gamma-ray spectral analysis is the recommended option, however, because 226Ra and 228Ra can be determined directly and simultaneously. Several aspects of the method were examined to assure that the concentration procedure is nearly quantitative and that the detection limit can be reached with a 3.8-L sample in a 6000-s counting period. The method was tested with Ra tracer solutions and EPA intercomparison samples over the range of 0.04 to 1 Bq L-1. It was found appropriate for 228Ra and 226Ra analyses.     

An application of decision theory to patient screening for an autologous tumour vaccine trial

Patients are eligible for accrual onto a phase I autologous tumour vaccine clinical trial if their resected and dissociated tumour achieves a minimum viable cell count. Because tumour pre-processing and cell count determination are expensive, there has been developed a screening procedure based on tumour mass to screen out those tumours unlikely to yield sufficient viable cells. If θ is the ratio of the expected benefit of an accrual onto the study to the cost of tumour pre-processing and cell counting, then we maximize long-run benefit by pre-processing and counting only those tumours whose masses exceed a cutoff m_c, such that Pr {sufficient tumour cells mass = m_c} = 1/θ. We derive algorithms for estimating m_c and evaluate them under a variety of assumptions concerning the cell count/mass relationship. These include explicit equations for m_c under parametric assumptions as well as more general algorithms based on non-parametric smoothing techniques. We show that when θ deviates substantially from 2, these methods outperform simple inverse interpolation.     

全髋关节置换后髋关节前屈后伸活动范围计算

目的探讨全髋关节置换术后髋关节前屈后伸活动范围的计算方法。方法1、用数学方法推导人工全髋关节前曲和后伸时股骨假体柄上臼柄撞击点位置的数学表达式:(1)设股骨假体前倾角a,股骨假体颈干角的补角的余角J,股骨假体颈柄的半径为L。(2)通过函数求导数的方法确定股骨假体柄上头颈结合圆上距矢状面距离最小点位置。(3)人工髋关节前曲和后伸时股骨假体柄上臼柄撞击点位于头颈结合截面圆上距该圆圆心距离h=L(1-sin2a)/(1+sin2a)的水平弦与圆在后方的交点。2、求出人工髋关节屈伸活动时臼柄撞击点所具有的外展角或前倾角b=arcsin[cosa2k2-2-2(1+sin2a)]/2k(k为头颈比)。3、根据髋臼外展角和前倾角动态变化规律得出全髋关节置换术后髋关节前屈后伸活动范围数学表达式。结果全髋关节置换术后髋关节前屈后伸活动范围ROM=180°-arcsin[tg2Atg2B-(tg2A+tg2B)(tg2b-tg2A)-tgAtgB]/(tg2A+tg2B)-arcsin[tg2Atg2B-(tg2A+tg2B)(tg2b-tg2B)-tgAtgB]/(tg2A+tg2B)(A和B分别为髋臼杯前倾角和外展角)。结论全髋关节置换术后髋关节前屈后伸活动范围与头颈比呈正相关,与股骨假体颈前倾角呈负相关。髋臼杯外展角与后伸活动度正相关与前屈活动度呈负相关、髋臼杯前倾角与后伸活动度负相关与前屈活动度呈正相关,该公式准确、可靠,值得临床参考。     

Use of green fluorescent protein-expressing Aspergillus fumigatus conidia to validate quantitative PCR analysis of air samples collected on filters

This study used green fluorescent protein (GFP)-expressing Aspergillus fumigatus conidia to compare quantitative PCR (qPCR) enumeration with direct epifluorescent microscopic filter counts of conidia collected on filters in a test chamber. In separate experiments this study initially compared white versus fluorescent light microscopy for counting A. fumigatus conidia, then compared fluorescent microscopy counting of corresponding filter halves, and finally compared qPCR enumeration to counting by fluorescent light microscopy. The use of GFP-expressing conidia with epifluorescent microscopy yielded significantly higher conidia counts (p = 0.026, n = 41, mean of 4.1 conidia per counting field) and 40% faster counting times when compared to conventional counting using white light microscopy. GFP-expressing conidia were aerosolized in a test chamber and collected onto filters. Filters were divided in half and GFP-expressing conidia enumerated. There was no significant difference in the average conidia count per field between corresponding filter halves (p = 0.3, n = 9 filters, mean of 7.8 conidia per counting field). Thus, one filter half could be counted optically and would provide a reliable estimate of filter loading of the corresponding half, which could then be analyzed by qPCR. Filters (n = 38) loaded with GFP conidia in the aerosol chamber were divided in half and analyzed by either fluorescent microscopy or qPCR. The estimated filter loadings ranged from 15-30,000 conidia per filter. There was a linear relationship with a nearly 1:1 ratio between qPCR and direct microscopic estimates of filter loading (y = 1.06x + 404; R(2) = 0.91) showing that the outlined qPCR analysis method is in agreement with an external reference method and is reliable for enumerating A. fumigatus conidia collected on filters. The comparative data derived using GFP-expressing conidia confirmed that qPCR provides sensitive and accurate quantification of DNA from airborne conidia collected on filters.     

Continuous monitoring for airborne alpha emitters in a dusty environment

Disposal of radioactive wastes in underground facilities requires continuous monitoring for airborne radioactive materials, both on the surface and underground. In addition to a natural background of nonradioactive and radioactive aerosols, there may be a sizeable dust contribution from ongoing work such as mining and vehicular traffic. In the monitoring of alpha-emitting radionuclides, these aerosols may lead to self-absorption in the source and a deterioration of the energy spectrum of the detected alpha particles. In this paper, the influence of a realistic background aerosol on the performance of an alpha monitoring system is evaluated theoretically. It is shown that depositing alpha emitters and background aerosol on a surface for counting leads rapidly to a considerable loss of counts, a deterioration of the alpha spectra, an eventual saturation of the count rates, and interference from the natural background of Rn daughters.     

结核分枝杆菌菌悬液光密度值与菌落计数的关联性

目的建立一种基于光密度值计算结核分枝杆菌菌落数的可靠方法。方法利用低频超声和玻璃珠研磨两种方法制备H37Ra菌悬液,菌悬液2倍梯度稀释后,分别测定各个稀释度菌悬液在600 nm处的光密度值（OD600值）,并分析OD600值与稀释倍数曲线,确定最佳的菌悬液制备方法,OD600线性范围,以及OD600值与CFU关联曲线。结果OD600值为0.1～0.6,线性范围内OD600值与稀释倍数线性回归分析结果显示,玻璃珠研磨法和低频超声法相关系数（R2）分别为0.98、1.00,均呈良好的相关性,且低频超声法比玻璃珠研磨法的相关性好,其菌液分散更均匀。OD600值与CFU值线性回归分析结果显示,玻璃珠研磨法和低频超声法回归方程分别是：CFU=2.35×107×OD600+4.42×105、CFU=3.26×107×OD600+6.89×105。结论低频超声法是一种较好的结核分枝杆菌菌悬液制备方法,结合OD600值测定,可成为一种可靠、快速的结核分枝杆菌定量方法。     

低本底反康测量系统屏蔽体的设计研究

目的 根据天然辐射来源，设计一套低本底反康测量系统的屏蔽体。方法 通过Geant4蒙卡程序建立探测器与屏蔽体模型，将主要的天然本底辐射作为源项输入到程序中，模拟优化低本底反康测量系统的屏蔽体的结构和尺寸，并通过实验测量对模拟结果进行了验证。结果 确定了由外到内依次为10 cm铅、8 cm含硼聚乙烯、2 cm铅和1 mm无氧铜内衬的屏蔽结构，各屏蔽层实验测量和模拟结果较为符合，规律体现出一致性，测量得到的50~2 000 keV能量范围内的积分本底计数率为1.72 cps。结论 优化设计了低本底反康测量系统屏蔽层的结构和尺寸，并通过增加含硼聚乙烯夹层来降低热中子和快中子所致本底，实验测量结果验证了设计方案的合理性和可行性。     

Radium-226 body burden in U miners by measurement of Rn in exhaled breath

Uranium miners were made to inhale Rn-free medical O2 and exhale through a 5.2-1 A1 chamber before reporting to work. The chamber was sealed and isolated from the sampling circuit. An electrostatic plate collected the freshly formed Rn-decay products. The subsequent programmed alpha counting of the plate yielded a Rn concentration in the exhaled breath. Assuming that the exhaled breath represents a certain fraction of the Rn produced inside the body, the body burden of 226Ra was calculated. Standardisation of this procedure and the data collected on 310 miners are discussed. The procedure is simple and applicable for routine measurements. The miner needs to be in the laboratory for only 10 min. The system is also portable for field application. For routine use, the minimum detectable concentration is 3.87 Bq X m-3 which corresponds to a body burden of 0.26 kBq in a typical miner, if one assumes the Rn release fraction from the body as 84%. The system offers a more convenient and sensitive alternative to whole-body counting of workers for 226Ra.     

Design and operation of a whole-body monitoring system for the Goiania radiation accident

With as many individuals involved in the Goiania 137Cs accident who had high levels of internal contamination, it was necessary to improvise a whole-body counter installation in loco. The in-vivo counting system was located in a 4.0 X 3.5 X 3.5-m room, where seven layers of 2-mm lead sheets with dimensions of 2.0 m X 1.0 m were overlaid on the floor at loci that were equidistant from the walls. A 20-cm diameter NaI (Tl) detector was installed at a height of 2.05 m above the floor at the center of the room. The detector was shielded and collimated with 5 cm of lead. The enormous amounts of activity in the subjects required the detector to be positioned at a height of 2.05 m. Subjects were required to wear disposable clothing and lie on a reclining, fiberglass chair. Counting time for the subjects was 2 min (live-time). The minimum detectable 137Cs activity for this counting time was 7.3 kBq* (0.05 significance level). Besides the accident victims, all individuals who had direct or indirect contact with contaminated people or areas were also monitored. More than 300 people of both sexes, with ages varying from a few months to 72 y, were measured for whole-body radioactivity. The observed activities ranged from less than the minimum detectable activity (MDA) to 59 MBq.     

食品中单增李斯特菌国标定量方法实验室验证结果与分析

目的对食品中单增李斯特菌国标定量方法进行实验室验证。方法将单增李斯特菌标准菌株活化,经一系列稀释后染菌样品。再用单增李斯特菌国标定量方法讨论稿中平板计数和MPN法检测样品中单增李斯特菌浓度。使用3种分离培养基鉴定,对比检测效果,确定检出限。结果平板计数法的检出限为100CFU／250ml和10CFU／250ml。MPN计数法的检出限为10CFU／250ml和1CFU／250ml。平板计数法中科玛嘉单增李斯特菌显色培养基检出限低于PALCAM分离培养基,而MPN计数法中,3种分离培养基鉴定结果一致。结论平板计数法和MPN计数法均适合于食品中单增李斯特菌定量检测,MPN计数法灵敏度更高。平板计数法中科玛嘉单增李斯特菌显色培养基普遍优于PALCAM分离培养基,3种培养基都适合MPN计数法,鉴定符合率高。科玛嘉和ALOA上生长典型菌落较PALCAM容易判别。     

Determination of gross alpha, 224Ra, 226Ra, and 228Ra activities in drinking water using a single sample preparation procedure

The current federal and New Jersey State regulations have greatly increased the number of gross alpha and radium tests for public and private drinking water supplies. The determination of radium isotopes in water generally involves lengthy and complicated processes. In this study, a new approach is presented for the determination of gross alpha, 224Ra, 226Ra, and 228Ra activities in water samples. The method includes a single sample preparation procedure followed by alpha counting and gamma-ray spectroscopy. The sample preparation technique incorporates an EPA-approved co-precipitation methodology for gross alpha determination with a few alterations and improvements. Using 3-L aliquots of sample, spiked with 133Ba tracer, the alpha-emitting radionuclides are isolated by a BaSO4 and Fe(OH)3 co-precipitation scheme. First the gross alpha-particle activity of the sample is measured with a low-background gas-flow proportional counter, followed by radium isotopes assay by gamma-ray spectroscopy, using the same prepared sample. Gamma-ray determination of 133Ba tracer is used to assess the radium chemical recovery. The 224Ra, 226Ra, and 228Ra activities in the sample are measured through their gamma-ray-emitting decay products, 212Pb, 214Pb/214Bi, and 228Ac, respectively. In cases where 224Ra determination is required, the gamma-ray counting should be performed within 2-4 d from sample collection. To measure 226Ra activity in the sample, the gamma-ray spectroscopy can be repeated 21 d after sample preparation to ensure that 226Ra and its progeny have reached the equilibrium state. At this point, the 228Ac equilibration with parent 228Ra is already established. Analysis of aliquots of de-ionized water spiked with NIST-traceable 230Th, 224Ra, 226Ra, and 228Ra standards demonstrated the accuracy and precision of this method. Various performance evaluation samples were also assayed for gross alpha as well as radium isotope activity determination using this procedure and the results were in close agreement with the assigned values. In addition, method comparison results of actual sample analyses agreed well with the ones performed using EPA-approved procedures. With a 3-L sample aliquot and 1,000-min counting time, the average gross alpha minimum detectable concentration (MDC) was about 0.002 Bq L(-1). The average MDC's for 224Ra, 226Ra, and 228Ra were 0.034 Bq L(-1), 0.017 Bq L(-1), and 0.036 Bq L(-1), respectively, based on a 3-L sample aliquot, 85% chemical yield, 40% intrinsic Ge detector, and 1,000-min count time. This method combines and simplifies the analytical procedures and reduces labor while achieving the precision, accuracy, and minimum detection limit requirements of EPA regulations.