Count Loss Research Articles

Correction for counting losses in X-ray diffractometry

Non-extended and extended dead-time models, a pulse-height analyser (PHA) windowing model, and a model intermediate between the non-extended and extended models for losses in counting methods are compared. The validities of the methods are examined by application to the analysis of powder diffraction peak intensity profiles measured by a foil method. The intermediate model including parameters for the dead-time and degree of extension can reproduce both the non-extended and the extended models and also intermediate dependence between the two models. A convenient approximate formula for the intermediate model, the maximum relative deviation of which is 0.0003, is also proposed. The determination of the parameters and a correction for the measured intensities can easily be achieved by applying the approximate model, because it provides simple formulae for the correction function expressed as a combination of elementary functions. Experimental and analytical methods for precise evaluation of the parameters to specify the counting losses are also presented. Systematic deviations of the observed dependence from the non-extended and extended dead-time models have been detected by the precise analyses of experimental data, while the PHA windowing model, intermediate model and its approximation have reproduced the observed dependence within the experimental errors.

CVD diamond detectors for nuclear and dosimetric applications

The recent availability of single crystal (sc) CVD diamond samples of very good quality and suitable thickness and surface area has opened new application fields in nuclear detection and dosimetry such as hadron radiotherapy and neutron spectrometry in fusion reactors. At the same time, dot, strip, and pixel detectors with unprecedented performances have been successfully realized and exploited in the framework of high energy physics (HEP). While the goal of a charge collection distance (ccd) of 200 μm was reached with polycrystalline (pc) samples in the year 2000, values of ccd up to 0.42 mm at 0.2 V/μm are now reported for the new sc samples. From the point of view of “detector quality,” the mobility–lifetime product for carriers is now approaching that of one of the best nonsilicon detector materials like CdTe, but it seems still far from that of Si. The most important point seems to be related to the homogeneity of new sc samples, which now in some cases displays an energy resolution down to 0.4% for Am-241 alpha particles and of 2.9% for 14.1 MeV neutrons. CVD single crystal beam monitors are now currently running in HEP experiments and their performances are compared with more recent radiation hard Si detectors. CVD diamond detectors are quoted to be capable to withstand particle fluxes over 10 15 cm −2 (which corresponds to a 10-year experiment run) with no counting losses and only a small reduction in S/N ratio. A more intriguing question is concerning priming, which is very important for detector performances: while no priming seems necessary for sc samples, in the case of pc samples, a simple priming with blue light instead of X-rays or beta-rays is possible, with the issue of different or better detector performances. The paper will review the more recent history of CVD diamond nuclear detectors with respect to material quality and priming. Some detectors and dosimeter performances in different top level fields will be quoted and possible future scenarios will be described.

A neutron activation analyzer

Dubbed “Analyzer” because of its simplicity, a neutron activation analysis facility for short-lived isomeric transitions is based on a low-cost rabbit system and an adaptive digital filter which are controlled by a software performing irradiation control, loss-free gamma-spectrometry, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic flow of operations. Designed for TRIGA reactors and constructed from inexpensive plastic tubing and an aluminum in-core part, the rabbit system features samples of 5 ml and 10 ml with sample separation at 150 ms and 200 ms transport time or 25 ml samples without separation at a transport time of 300 ms. By automatically adapting shaping times to pulse intervals the preloaded digital filter gives best throughput at best resolution up to input counting rates of 106 cps. Loss-free counting enables quantitative correction of counting losses of up to 99%. As a test of system reproducibility in sample separation geometry, K, Cl, Mn, Mg, Ca, Sc, and V have been determined in various reference materials at excellent agreement with consensus values.

The Effect of Capsular Tension Ring on Posterior Capsular Opacity in Cataract Surgery

This study was performed to evaluate the efficacy and safety of the capsular tension ring on posterior capsular opacity in comparison with cases undergoing intraocular lens (IOL) implantation alone. We analyzed 127 eyes which had undergone cataract surgery, including capsular tension ring insertion, along with 127 eyes which had undergone IOL implantation alone by the same surgeon from September 1998 to March 2003. In the insertion group, 41 eyes (group A) had been followed up for more than one year after silicone IOL implantation, as had 40 eyes (group B) in the control group. We compared the incidence, type, and degree of capsular opacity between A and B groups and also endothelial cell loss after surgery between the two groups. For insertion group A, the frequency of posterior capsular opacity was lower(7.3%), the duration to development was longer, and the energy required for Nd-Yag capsulotomy of PCO was less than for control group B (25%) (p=0.037). The endothelial cell count loss rate was not significantly different between the two groups (p=0.522). The capsular tension ring is associated with a significantly reduced incidence of posterior capsular opacity and is a safe procedure.

Macrophages from Mice with the Restrictive Lgn1 Allele Exhibit Multifactorial Resistance to Legionella pneumophila

Although Legionella pneumophila can multiply in diverse cell types from a variety of species, macrophages from most inbred mouse strains are nonpermissive for intracellular replication and allow little or no growth of the bacteria. This phenomenon is likely genetically controlled by the mouse naip5 (birc1e) gene located within the Lgn1 locus. In this study, we have investigated the resistance of C57BL/6J macrophages to L. pneumophila infection by examining the fate of both the bacterium and the infected cells compared to that in macrophages from the permissive A/J strain. Our results indicate that although the trafficking of the L. pneumophila-containing vacuole is partially disrupted in C57BL/6J macrophages, this cannot account for the severity of the defect in intracellular growth observed in this strain. Infected macrophages are lost shortly after infection, and at later times a larger fraction of the C57BL/6J macrophages in which L. pneumophila undergoes replication are apoptotic compared to those derived from A/J mice. Finally, a loss of bacterial counts occurs after the first round of growth. Therefore, the resistance mechanism of C57BL/6J macrophages to L. pneumophila infection appears to be multifactorial, and we discuss how early and late responses result in clearing the infection.

Compensation by the CIEMAT/NIST-method of long-term effects in LSC measurements of beta emitters

A systematic evaluation of activity concentrations of 3H, 63Ni and 14C by using the CIEMAT/NIST method has been carried out over time intervals of 4, 2.4 and 2.3 years, respectively. It proves that the CIEMAT/NIST method can compensate, with no need for additional checking sources or procedures, for count losses and quench parameter reduction in long-term measurements with LSC spectrometers and allows one to obtain very accurate activity concentration values by using a quench curve close to the nuclide measurements. If this requirement of the method is not fulfilled, significant discrepancies, up to 5.6% for 3H, 1.5% for 63Ni and 0.35% for 14C, can be obtained in only 1-year time difference.

Breastfeeding and maternal HIV-1 disease progression and mortality.

To examine the association between breastfeeding and disease progression among HIV-infected women in Dar es Salaam, Tanzania. Cohort study design with Cox proportional hazards models. The relative risk of death comparing women who recently had been breastfeeding to those who were not breastfeeding was 0.47 (95% confidence interval, 0.18-1.20). Neither breastfeeding status nor the duration of exclusive or partial breastfeeding was associated with HIV-1 disease progression, represented by death or development of a low CD4 cell count, anemia or excessive weight loss, in multivariate analyses. These associations remained insignificant when women with relatively low and high CD4 cell counts were analyzed separately. There is insufficient evidence to support the hypothesis that breastfeeding is detrimental to the health of HIV-infected women.

Measurement of resonant x-ray magnetic scattering from induced Cu polarizations inexchange-coupled Co/Cu multilayers

An avalanche photodiode detector has been commissioned to measure weakresonant x-ray magnetic scattering (RXMS) from induced magnetic polarizationsin Cu layers in exchange-coupled Co/Cu multilayers using circularly polarizedx-rays from synchrotron sources. The detector can count x-rays at rates of107 photons s−1, giving good estimates of the RXMS at superlattice Bragg peaks in areasonably short time when count losses due to the time structure of thesynchrotron x-rays are corrected for. RXMS superlattice Bragg peaks as small as1 × 10−4 in flipping ratio have been measured from a Co/Cu multilayer at the K absorption edge ofCu. The data are fitted by an oscillatory model magnetization profile in the Cu layersderived from a Ruderman–Kittel–Kasuya–Yosida theory of exchange coupling adapted to aplanar geometry.

Precise measurement of the positive muon lifetime at the RIKEN-RAL muon facility

New method is adopted for the precise muon lifetime measurement at the RIKEN-RAL muon facility. About 1010 data have already accumulated. Analysis, especially count loss correction, is now in progress.

Dosimetric Impact of Correcting Count Losses due to Deadtime in Clinical Radioimmunotherapy Trials Involving Iodine-131 Scintigraphy

This study describes the use of a new method for correcting count losses due to deadtime in the context of quantitative imaging of patients undergoing scintigraphy after a 4 GBq therapeutic injection of iodine-131. This method, based on measuring the count rate observed throughout the spectrum detected (50-750 keV), had been validated in a previous study and was applied here to 10 patients. Imaging was performed 3, 6, 8 and 10 days after injection. Whole-body images were acquired in six steps in energy-indexed list mode. Before reconstruction of the whole-body image, each step was processed to obtain an appropriate correction. Three days after injection, corrective factors ranged between 1.01 (feet) and 1.20 (liver), and the increase in whole-body activity was estimated at around 10%. The difference between whole-body activities calculated from images corrected for deadtime and those estimated by urine collection was around 1% when urine collection was complete. Correction for count losses led to an 11% increase in whole-body cumulated activity. These results indicate that it is possible to integrate this correction into dosimetric studies in order to allow count rate variations to be taken into account as a function of the regions imaged. Although the complexity of acquisitions in energy-indexed list mode limits the systematic use of this method, it can be simplified if corrections are made only for those steps in which the correction factor exceeds a threshold value. However, this implies a selection of the regions to be corrected. Another possibility consists in acquiring spectrometric images in several windows, which also allows correction for count losses.

Focus on Magnetics

Focus on Magnetics

Experimental tests of dead-time corrections

Experimental tests of dead-time-induced counting losses in radiation or particle detection using a relatively simple electronic device are described. A calculated correction described earlier, applicable in certain cases of pulsed radiation, is confirmed up to high fractional counting losses. The well-known correction formulae for constant, extending or non-extending dead times in the case of continuous radiation can as well be confirmed within the precision limits of the device. The technique may be useful in instruction laboratory courses.

Practical correction of dead time effect in variance-to-mean ratio measurement

A practical technique to correct the dead time effect in the variance-to-mean ratio measurement is proposed. A correction formula used in the technique is derived based on a simple mechanism of count loss due to a non-extending dead time. The technique was verified with a Monte Carlo simulation and an experiment in Deuterium Critical Assembly. It was confirmed that the formula can make a reasonable correction to the case that the count loss is as large as 50%. This correction technique is extremely simple and can make the correction only with data obtained in the original measurement.

Dead-Time Effects on Counting Statistics in Subcritical Nuclear Systems

The analysis of the fluctuations of signals coming from detectors in the vicinity of a subcritical assembly of fissile materials is commonly used for the control and safeguard of nuclear materials and might be used for the surveillance of an accelerator driven system. One of the stochastic techniques is the measurement of the probability distributions of counts in time intervals Δt (gates); the departure of the ratio of the variance and the mean value with respect to 1 (the correlation) is directly related to the amount of fissile material and its subcriticality. The measurement of this correlation is affected by dead-time effects due to count losses because of the finite-time resolution of the detection system. We present a theory that allows (a) the calculation of the probability of losing n counts (P(n)) in gate Δt, (b) the definition of experimental conditions under which P(2) << P(1), and (c) a methodology to correct the measured correlation because of losing one count in any gate. The theory is applied to the analysis of experiments performed in a highly enriched subcritical assembly.

An automatic attenuator device for x-ray detectors at high counting rate

In this article we describe an attenuator device for reducing/controlling the pulse detector counting losses at a high counting rate. The electronics are based on a direct measure of the detector dead time from the analog output signal at the end of the detection chain. Taking into account this parameter the attenuator device decides to reduce/enhance the number of photons that arrive at the detector by inserting/extracting the necessary number of attenuation foils in the x-ray beam path. In that way the number of events in the incoming signal are reduced and the “apparent dynamic range” of the detector is increased.

Mammary Pathogens and Their Relationship to Somatic Cell Count and Milk Yield Losses in Dairy Ewes

A total of 9592 samples of half udder milk were collected monthly throughout lactation for bacteriological and somatic cell count (SCC) study from 1322 Churra ewe lactations from seven separate flocks enrolled in the recording scheme of the National Association of Spanish Churra Breeders in the Castile-León region of Spain. Statistical analyses were carried out from a mixed model with random factor half udder or ewe for repeated measures. Test of significance of fixed effects of this mixed model showed significant effects of organisms, flock, parity, lactation stage, and birth type on SCC. Special reference must be made to novobiocin-sensitive coagulase-negative staphylococci, which represented more than 50% of the isolates and which elicited SCC geometric means of around 106/ml. In addition, the analysis of 4352 monthly test-day records for milk yield, SCC, and bacteriology showed that the ewes that were uninfected and infected by minor pathogens had the lowest SCC and the highest milk yields, whereas those infected by major pathogens had high SCC and milk yield losses between 8.8 and 10.1% according to the uni- or bilateral character of the infection. Finally, ewes infected by novobiocin-sensitive coagulase-negative staphylococci elicited SCC values similar to those of infections by major pathogens and milk yield losses ranging between those caused by minor and major pathogens. As a result, emphasis should be put on prevention of subclinical mastitis, particularly mastitis caused by novobiocin-sensitive coagulase-negative staphylococci in dairy sheep herds to improve microbiological and hygienic milk quality and to minimize losses in milk yield.

Correction of count losses due to deadtime on a DST-XLi (SMVi-GE) camera during dosimetric studies in patients injected with iodine-131

In dosimetric studies performed after therapeutic injection, it is essential to correct count losses due to deadtime on the gamma camera. This note describes four deadtime correction methods, one based on the use of a standard source without preliminary calibration, and three requiring specific calibration and based on the count rate observed in different spectrometric windows (20%, 20% plus a lower energy window and the full spectrum of 50–750 keV). Experiments were conducted on a phantom at increasingly higher count rates to check correction accuracy with the different methods.The error was less than +7% with a standard source, whereas count-rate-based methods gave more accurate results. On the assumption that the model was paralysable, preliminary calibration allowed an observed count rate curve to be plotted as a function of the real count rate. The use of the full spectrum led to a 3.0% underestimation for the highest activity imaged. As count losses depend on photon flux independent of energy, the use of the full spectrum during measurement allowed scatter conditions to be taken into account. A protocol was developed to apply this correction method to whole-body acquisitions.

Monte Carlo calculation of the efficiency response of a low-background well-type HPGe detector

Well-type HPGe detectors are well suited for the analysis of small amounts of environmental samples, as they can combine both low background and high detection efficiency. A low-background well-type detector is installed in the Modane underground Laboratory. In the well geometry, coincidence-summing effects are high and make construction of the full energy peak efficiency curve difficult with the usual calibration standard, especially in the high energy range. Using the GEANT code, taking into account a detailed description of the detector and the source, efficiency curves have been modelled for several filling heights of the vial. With a special routine, taking into account the decay schemes of the radionuclides, corrections have been computed for coincidence-summing effects that occur when measuring samples containing 238U, 232Th or 134Cs. The results are found to be in good agreement with experimental data. It is shown that triple coincidences effect on counting losses accounts for 7–15% of pair coincidences effect in the case of the 604 and 796 keV lines of 134Cs.

Increased protection against bovine tuberculosis in the brushtail possum (Trichosurus vulpecula) when BCG is administered with killed Mycobacterium vaccae

Setting: The Australian brushtail possum is the major wildlife reservoir for Mycobacterium bovis infection in New Zealand. Development of an effective tuberculosis vaccine for possums will reduce the spread of infection to cattle and farmed deer.Objectives: To determine whether killed M. vaccae can improve the efficacy of vaccination with M. bovis bacillus Calmette Guerin (BCG) against bovine tuberculosis in the possum.Design: Groups of possums (n=6–8) were vaccinated via intranasal and intraconjunctival routes with BCG alone or BCG in combination with heat-killed M. vaccae. Controls were non-vaccinated or vaccinated with heat-killed M. vaccae alone. After challenge with virulent M. bovis, protection was assessed by a reduction in loss of body weight and bacterial counts in lungs and spleens. Blood lymphocyte proliferative responses to M. bovis purified protein derivative were monitored throughout.Results: The earliest lymphocyte responses following vaccination were from animals inoculated with BCG plus 100 μg heat-killed M. vaccae. Loss of body weight was significantly reduced in all BCG-vaccinated groups compared control groups. Spleen bacterial counts were significantly lower in animals vaccinated with M. vaccae plus BCG compared to the non-vaccinated group. Furthermore, vaccination with 100 μgM. vaccae plus BCG significantly reduced spleen bacterial counts compared to vaccination with BCG alone.Conclusion: The possum infection model is one of the first to show that novel vaccine strategies may offer better protection against tuberculosis than BCG alone.

Analytical calculations of counting losses in internal gas proportional counting

In internal gas proportional counting, the evaluation of counting losses is important in order to obtain high accuracy measurement results. In this paper, counting losses due to the wall effect not counted and beta particles with very low energy are evaluated by analytical calculations. The calculated and experimental results are compared and a very good agreement is found.