γ能谱无源效率模拟中食品样品成分分析研究

目的 通过分析常见食品的成分,利用无源效率刻度与有源验证相结合的方法,为食品γ能谱无源效率刻度分析推荐参考成分。方法 对全国食品放射性污染监测中30种常见食品样品进行分析,统计出粮食类和蔬菜类的参考成分,结合白藜麦标准源的自身参数,应用LabSOCS进行白藜麦标准源不同成分的无源效率模拟,计算白藜麦标准源测量活度与其证书活度的相对偏差并进行分析。结果 30种 食品样品的检测结果表明,C、H、O、N、S这5种元素占食品组成的77.0% ~ 93.7%, 是食品的主要成分。将白藜麦自身成分和粮食类参考成分应用于白藜麦标准源的无源效率模拟,进行活度计算,与其证书活度的相对偏差绝对值分别在0.37% ~ 5.86%和0.38% ~ 5.87%。结论 白藜麦自身成分和粮食类参考成分应用于白藜麦标准源的无源效率模拟,计算的测量活度与标准源证书活度的相对偏差基本一致,若使用γ能谱无源效率模拟测量未知成分的食品样品且不便进行食品样品成分分析时,特别是在应急情况下,可参考使用本研究得到的参考成分。     

Correction factors determination in large samples gamma assay using its own multi-gamma lines spectrum

An easy and simple method for gamma assay of large multi-gamma lines samples was introduced in this work. This method performs the assay using point source calibration. The correction factors for volume and self-attenuation are experimentally deduced from the spectra of different thicknesses samples utilizing the following two simple well known facts: large and small samples of the same homogenous material have identical specific activities; the self-attenuation of gamma line decreases as its energy increases. The method was successfully applied to naturally occurring radioactive material (NORM) large samples. This method does not require complicated mathematical procedures. Neither sample matrix data nor detector unit composition is needed.     

Determination of detection efficiency curves of HPGe detectors on radioactivity measurement of volume samples

An efficiency calibration method has been developed to measure radioactivity of volume samples with HPGe detectors. The method has two main procedures. One is a point-source calibration at a representative point near the detector. The position of the representative point is determined by Monte Carlo simulations. The other is correction for absorption by a sample matrix and a sample container. This paper presents application of the method for obtaining efficiency curves for volume samples in the energy range from 22 to 1836 keV. In addition to the standard volume sources of cement and water matrices, measurement was made with some kinds of environmental samples that are often used in environmental monitoring for radiation control works. The composition of the environmental sample was determined by elemental analysis. For these samples, measured absorption correction factors were compared with those by the Monte Carlo simulations. As a result, detection efficiency curves were obtained with good accuracy for variety types of volume samples.     

Perceived brightness of incandescent and LED aviation signal lights

INTRODUCTION: Aviation signal lights using light emitting diodes (LEDs) are commonly perceived as brighter than those using incandescent sources, even at the same measured intensity. In general, saturated colors, like those produced by LEDs, appear brighter than less saturated lights, like those produced by incandescent sources. METHODS: We describe a series of experiments quantifying the brightness of simulated blue, white, and green LED signal lights relative to incandescent signal lights of the same hue. Simulated signal lights and arrays were compared against dark and against dimly lighted backgrounds, and through simulated fog. RESULTS: The results confirm that LED signal lights are brighter than incandescent signals at matched luminous intensities. Brightness relationships were unaffected by background light level, and by the number of signals viewed, but the simulated fog reduced the brightness difference between the incandescent and LED signal lights. CONCLUSIONS: The present results could not be accurately predicted by several previously published models of brightness appearance, probably because of differences in experimental conditions. We present a new model that can be used to predict signal light brightness for blue, white, and green signal colors. Except for very short-wavelength blue signal lights, the model was able to accurately predict the present brightness data as well as those from previously published independent experiments. This validation lends confidence to the generality of the model for predicting blue, white, and green signal light brightness, but different colors (e.g., yellow or red) remain to be tested and modeled using this approach.     

Sample preparation method with ultrafiltration for whole blood thiosulfate measurement

Quantitative analysis of thiosulfate is useful for diagnosing hydrogen sulfide poisoning. Liquid chromatography-tandem mass spectrometry (LC–MS/MS) enables more rapid and sensitive measurements than previous methodologies. As simple measurements of blood thiosulfate concentration are affected by the blood matrix, blood is used as the solvent to prepare the standard solution for calibration curve generation. Thus, a large amount of blood devoid of thiosulfate is required. We developed a preparation method by incorporating an ultrafiltration step to overcome this limitation and generate a calibration curve using a standard solution prepared with pure water. We used this improved method to investigate the stability of thiosulfate in refrigerated samples. To compare the effects of refrigeration, blood samples were prepared using the following two methods: one sample was treated with a 50-kDa exclusion ultrafiltration membrane and the other was not treated. The samples were stored at 4 °C, and then measured at 0, 3, 6, 24, 48, and 96 h. The incorporation of the ultrafiltration step in the measurement procedure enabled the quantification of thiosulfate, by plotting a calibration curve using a standard of pure water; it did not require a blood standard. Additionally, the reduction in whole blood thiosulfate concentration was within 10% during 2 days of refrigeration. Thus, the need for a large amount of blood to prepare the standard solution was resolved by the ultrafiltration step in test sample preparation. This method is useful to measure thiosulfate concentration and is not hindered by sample refrigeration for a few days.     

CREPT-MCNP code for efficiency calibration of HPGe detectors with the representative point method

The representative point method for the efficiency calibration of volume samples has been previously proposed. For smoothly implementing the method, a calculation code named CREPT-MCNP has been developed. The code estimates the position of a representative point which is intrinsic to each shape of volume sample. The self-absorption correction factors are also given to make correction on the efficiencies measured at the representative point with a standard point source. Features of the CREPT-MCNP code are presented.     

A method for calculation of true coincidence summing correction factors for extended sources.

In gamma-ray spectrometry, true coincidence summing correction factors for an extended sample can be calculated from full-energy-peak and total efficiencies as if the sample were a point source, if the so-called linear-to-square- (LS) curve, introduced by Blaauw and Gelsema, is known and properly applied. A method is described for obtaining the efficiencies and the corresponding LS-curve for an arbitrary cylindrical sample from calibration measurements in a reference geometry. The approach is aimed at the analysis of samples measured on p-type HPGe detectors in environmental gamma-ray spectrometry and was successfully verified against experimental data.     

Comparison of air kerma rate between the S7500 and S7600 xoft axxent sources

PURPOSEThe purpose of this work was to evaluate differences in air-kerma rate of the older, S7500 water-cooled Xoft Axxent source and newer, S7600 Galden-cooled source.METHODS AND MATERIALSThe Attix Free Air Chamber (FAC) at the UWMRRC was used to measure the air-kerma rate at 50 cm for six S7600 Xoft Axxent sources. The average measured air-kerma of the S7600 sources was compared with the measured average air-kerma rate from five S7500 sources. The air-kerma rates of the S7500 sources were measured in a Standard Imaging HDR 1000+ well chamber. The FAC measurements were used to determine a well chamber calibration coefficient for the S7600 source. The S7500 calibration coefficients were incorrectly applied to the S7600 sources to indicate the magnitude of error that can occur if the incorrect calibration coefficient is used.RESULTSA 10.3% difference was observed between the average air-kerma rates of the two sources although a 17% difference was observed between their calibration coefficients. The application of the S7500 calibration coefficient to the S7600 sources resulted in measured air-kerma rates that were 20% greater than the true value.CONCLUSIONSThis work indicates the need for a new air-kerma rate standard for the S7600 sources, and the results presented in this work are indicative of values that would be obtained at National Institute of Standards and Technology.     

Determination of an air kerma-rate correction factor for the S7600 Xoft AxxentⓇ source model

PurposeThe purpose of this work was to provide guidance for the lack of an air-kerma rate standard for the S7600 Xoft Axxent® source by providing a correction factor to apply to the National Institute of Standards and Technology (NIST) traceable S7500 well chamber (WC) calibration coefficient before the development of an S7600 standard at NIST.METHODS AND MATERIALSThe Attix free air chamber (FAC) at the University of Wisconsin Medical Radiation Research Center was used to measure the air-kerma rate at 50 cm for six S7500 and six S7600 sources. These same sources were then measured using five standard imaging HDR1000+ WCs. The measurements made with the FAC were used to calculate source-specific WC calibration coefficients for the S7500 and S7600 source. These results were compared to the NIST traceable calibration coefficients for the S7500 source. The average results for each WC were then averaged together, and a ratio of the S7600 to S7500 WC calibration coefficients was determined.ResultsThe average S7600 air-kerma rate measurement with the FAC was 7% lower than the average air-kerma rate measurements of the S7500 source. On average, the S7500 determined WC calibration coefficients agreed within ±1% of the NIST traceable S7500 values. The S7600 WC calibration coefficients were up to 16% less than the NIST traceable S7500 values. The final correction factor determined to be applied to the NIST traceable S7500 value was 0.8415 with an associated uncertainty of ±8.1% at k = 2.ConclusionsThis work provides a suggested correction factor for the S7600 Xoft Axxent source such that the sources can be accurately implemented in the clinical setting.     

Neurosurgical microscopic solid laser-based light inhibits photobleaching during fluorescence-guided brain tumor removal with 5-aminolevulinic acid

BackgroundFluorescence image guided surgery (FIGS) with 5-aminolevulinic acid for malignant gliomas improves surgical outcome. One of the problems during FIGS is photobleaching under surgical microscopic white light. A solid laser-based white light source for neurosurgery that we developed does not include light with a wavelength of around 405 nm, which is strongly absorbed by protoporphyrin IX. In the present study, we examined the efficacy of this light source to prevent the photobleaching of protoporphyrin IX-induced fluorescence.MethodsFilter papers transfused with protoporphyrin IX solution and a coronally sectioned F98 glioma rat model pretreated with 50 mg/kg 5-aminolevulinic acid were continuously exposed to white light. One group was exposed to conventional xenon-based white light and another group was exposed to laser-based white light. Fluorescence at a wavelength of 635 nm was measured with a radiospectrometer (in vitro study) and the relative fluorescence brightness was also measured in digital images (in vivo study) under excitation from violet blue light emitted from diodes every 5 min.Results and conclusionEstimated time for 50% photobleaching was prolonged about two times in the laser-based white light exposure group compared with that in the xenon-based white light exposure group (9.1/18.7 min). In the brain tumor rat model, it was also prolonged about 2.7 times (15.1/40.7 min). A laser-based white light source may inhibit photobleaching during FIGS for malignant gliomas. This light source for neurosurgical microscopy has the potential to prolong the prognosis of malignant glioma patients.     

New numerical algorithm method to calibrate the HPGe cylindrical detectors using non-axial extended source geometries

The knowledge of the full-energy peak efficiency for a specific source–detector arrangement is often required in various fields of research and applications, such as the analysis of nuclear waste or environmental samples, where both require modeling because it is not practical to prepare a standard that matches the physical and nuclear properties of every waste or environmental item. Therefore, a new numerical algorithm method (NAM) is proposed in the present work to calibrate the co-axial HPGe cylindrical detectors. Cylindrical sources are used in the calibration process placed perpendicularly to the detector’s axis. The self-attenuation and the coincidence summing effects at low source–detector distance are also included in the algorithm. A remarkable agreement between the measured and the calculated efficiencies is achieved with discrepancies less than 3%.     

Combination of chemical separation and data treatment for 55 Fe, 63 Ni, 99 Tc, 137 Cs and 90 Sr/90Y activity determination in radioactive waste by liquid scintillation.

Routine operations involving nuclear reactors and decommissioning activities require numerous chemical analyses. Most of the procedures developed for these chemical characterisations involve several separation steps to prepare the sample for measurement. Chemical treatments are time- and manpower-consuming, labour intensive and produce significant quantities of waste. In order to address this problem, we evaluate a data treatment procedure (multivariate calibration--PLS), which we propose as a substitute to some of these separation steps. Mixtures of beta emitter radionuclides of increasing complexity ((90)Sr/(90)Y--(99)Tc, (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs and (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs--(55)Fe) have been measured by liquid scintillation (LS) counting. The influences of quenching and level of activity was evaluated and the activity of unknown samples determined. Despite the spectra overlapping and low resolution of LS, relative errors in the activities quantification of unknown samples inside the range covered by the calibration matrix are lower than 15% whatever the number of radionuclides included in the solution was.     

LabSOCS效率刻度方法在应急监测实验室快速分析中的应用

目的 探讨LabSOCS效率刻度方法在"涉核"事件应急监测实验室分析中的应用.方法 用LabSOCS效率刻度方法模拟应急监测中采集的3种环境样品的探测效率,并与这3种样品的有源效率刻度的实测探测效率进行比较.结果 LabSOCS效率刻度方法模拟的探测效率(共20组比对值)与实测效率最大的相对偏差<15%,其中相对偏差小于5%的占70%.结论 LabSOCS效率刻度方法可以代替实测标准刻度源得到效率的方法,满足"涉核"事件应急监测实验室快速分析的需求.     

A hybrid method to determine efficiency curve of HPGe detectors

A method was developed for determining the efficiency calibration curve of HPGe detectors between 26 and 1770 keV. A simple simulation based on the attenuation of gamma-rays in pure germanium was used together with efficiency calibrations performed for three detector–source distances: 5, 12 and 30 cm. The simple simulation model required an energy dependent term with three parameters and these parameters were determined from the fit of the simulated data to the measured efficiency of the detector. The efficiency response of the detector determined this way was then tested with other certified sources to verify the validity of the method.     

A simple method for calibrating force plates and force treadmills using an instrumented pole

We propose a new method for calibrating force plates to reduce errors in center of pressure locations, forces, and moments. These errors may be caused by imperfect mounting of force plates to the ground or by installation of a treadmill atop a force plate, which may introduce distorting loads. The method, termed the Post-Installation Least-Squares (PILS) calibration, combines features of several previous methods into a simple procedure. It requires a motion capture system and an instrumented pole for applying reference loads. Reference loads may be manually applied to the force plate in arbitrary locations and directions. The instrumented pole measures applied load magnitudes through a single-axis load cell, and load directions through motion capture markers. Reference data and imperfect force plate signals are then combined to form a linear calibration matrix that simultaneously minimizes mean square errors in all forces and moments. We applied the procedure to standard laboratory force plates, as well as a custom-built, split-belt force treadmill. We also collected an independent set of verification data for testing. The proposed calibration procedure was found to reduce force errors by over 20%, and moment errors by over 60%. Center of pressure errors were also reduced by 63% for standard force plates and 91% for the force treadmill. The instrumented pole is advantageous because it allows for fast and arbitrary load application without needing a precise fixture for aligning loads. The linear calibration matrix is simpler than nonlinear correction equations and more compatible with standard data acquisition software, yet it yields error reductions comparable to more complex methods.     

Consistent non-cartesian off-axis MRI quality: calibrating and removing multiple sources of demodulation phase errors.

The consistency of off-axis MRI with non-Cartesian sequences across a large number of scanners is highly variable. Improper timing alignment of the gradient fields, data acquisition system, and real-time frequency demodulation reference signal, which are necessary for off-axis imaging, is an important source of this variability. In addition, eddy currents and anisotropic gradient delays cause deviations in k-space trajectories that in turn make the demodulation reference signals inaccurate. A method is presented to quickly measure the timing error in the frequency demodulation reference signal and separate it from anisotropic gradient delays. k-Space deviations, as measured with a previous gradient calibration technique, are shown to be a second source of demodulation phase errors that degrade image quality. Using the timing delay and k-space deviations, a retrospective phase correction is applied to each k-space sample before the data are regridded during reconstruction. The timing delays of four MR scanners were measured to be 4.2-7.5 micros below the manufacturer's suggested delay. Significant degradation in 3D radial (3D projection reconstruction (PR)) knee and breast images are retrospectively corrected while a partial prospective correction is applied for spiral imaging. The method allows for more consistent performance of non-Cartesian sequences across multiple scanners without operator intervention.     

LabSOCS效率刻度方法在应急监测实验室快速分析中的应用

目的 探讨LabSOCS效率刻度方法在"涉核"事件应急监测实验室分析中的应用.方法 用LabSOCS效率刻度方法模拟应急监测中采集的3种环境样品的探测效率,并与这3种样品的有源效率刻度的实测探测效率进行比较.结果 LabSOCS效率刻度方法模拟的探测效率(共20组比对值)与实测效率最大的相对偏差<15%,其中相对偏差小于5%的占70%.结论 LabSOCS效率刻度方法可以代替实测标准刻度源得到效率的方法,满足"涉核"事件应急监测实验室快速分析的需求.

Abstract：

Objective To explore the effeetiviness of the method of LabSOCS(Laboratory sourceless calibration software)efficiency calibration in laboratory rapid analysis for emergency monitoring of nuclear incidents.Methods The detection efficiency of three kinds of environmental samples in emergency monitoring Wag calculated bY using the LabSOCS efficiency calibration method,and compared with the values that were obtained by way of radioactive source calibration method.Results The maximum relative deviation of the detection efficiency between the two methods was less than 15%,and the values with relative deviation less than 5%accounted for 70%.Conclusions The LabSOCS efficiency calibration method might take the place of radioactive source efficiency calibration method,and meet the requirement of rapid analysis in emergency monitoring of the nuclear incidents.     

Proficiency tests for radionuclide laboratories supporting the network of IMS stations.

A tailored proficiency test programme in high-resolution gamma-spectrometric analysis has been established for the radionuclide laboratories designated to support the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). It entails certified reference samples that contain fission products relevant to the CTBT. The sample geometries and materials correspond to aerosol filter samples from the high-volume samplers of the radionuclide stations of the International Monitoring System (IMS) and the related calibration sources are matrix and geometry matched to the reference samples.     

Precise image-receptor calibration and monitoring of beam quality with a step wedge.

OBJECTIVE: To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality. METHODS: Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source. RESULTS: The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential. CONCLUSIONS: The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.     

In vivo O‐Space imaging with a dedicated 12 cm Z2 insert coil on a human 3T scanner using phase map calibration

Recently, spatial encoding with nonlinear magnetic fields has drawn attention for its potential to achieve faster gradient switching within safety limits, tailored resolution in regions of interest, and improved parallel imaging using encoding fields that complement the sensitivity profiles of radio frequency receive arrays. Proposed methods can broadly be divided into those that use phase encoding (Cartesian‐trajectory PatLoc and COGNAC) and those that acquire nonlinear projections (O‐Space, Null space imaging, radial PatLoc, and 4D‐RIO). Nonlinear projection data are most often reconstructed with iterative algorithms that backproject data using the full encoding matrix. Just like conventional radial sequences that use linear spatial encoding magnetic fields, nonlinear projection methods are more sensitive than phase encoding methods to imperfect calibration of the encoding fields. In this work, voxel‐wise phase evolution is mapped at each acquired point in an O‐Space trajectory using a variant of chemical shift imaging, capturing all spin dynamics caused by encoding fields, eddy currents, and pulse timing. Phase map calibration is then applied to data acquired from a high‐power, 12 cm, Z2 insert coil with an eight‐channel radio frequency transmit‐receive array on a 3T human scanner. We show the first experimental proof‐of‐concept O‐Space images on in vivo and phantom samples, paving the way for more in‐depth exploration of O‐Space and similar imaging methods. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.