Count Rate Ratio Research Articles

Depth dependent element ratios in fluid inclusion analysis by laser ablation ICP-MS

Ratios of element count rates used for quantification of LA-ICP-MS analysis of fluid inclusions inside minerals change between shallow inclusions, ablated at crater depth to diameter aspect ratios 4, by up to a factor of 2.5. The Cl/Na and the Pb/Na ratios were found to be affected the most. Ablating a scapolite sample with homogeneous Na, Pb and Cl concentrations showed a similar pattern but of smaller magnitude. Such strong fractionation behaviour of chlorine has not been reported to date for LA-ICP-MS analysis. This aspect ratio dependent elemental fractionation is likely due to condensation–deposition and remobilisation effects within the laser ablation crater and may account for some of the scatter obtained when analysing a homogeneous assemblage of fluid inclusions located at variable depths below the surface.

99mTc Sulfur Colloid and 99mTc Mebrofenin Hepatobiliary Functional Liver Imaging in Normal and Diabetic Rats

Objectives: To use ^99mTc sulfur colloid (^99mTc-SC) and ^99mTc mebrofenin (^99mTc-BrIDA) to study liver function in normal and diabetic rats. Materials and Methods: Radionuclide imaging was performed on 2 groups of rats, using ^99mTc-SC for one group and ^99mTc-BrIDA for the other (20 rats per group) before and after induction of diabetes mellitus (DM) using streptozotocin administration (55 mg/kg i.p.). Dynamic acquisition was obtained for 1 h after the injection of 37 MBq of radiotracer. For the ^99mTc-SC group, organ/tissue uptake was determined by drawing regions of interest (ROI) over the heart, liver, spleen and also the whole body (WB). The ratio of the ROI of each organ to the WB ROI was calculated. For ^99mTc-BrIDA, ratios of cumulative count rates in liver, liver parenchyma, biliary tree and abdomen ROI to a WB ROI were also calculated. Statistical analysis was performed to compare the ratios of organ/tissue uptake to WB uptake before and after DM induction using the paired t test. Results:^99mTc-SC uptake ratios (means ±SD) showed a lower liver-to-WB uptake ratio (0.75 ± 0.05) in the rats after DM induction compared to baseline (0.81 ± 0.06), while the cardiac blood pool showed higher uptake ratios in the rats after DM induction (p = 0.026). For ^99mTc-BrIDA, there was no significant difference in radiotracer uptake ratios obtained from the rats before and after DM induction (p = 0.41). Conclusion: Using functional liver imaging, there was a statistically significant decrease in the liver phagocytic/reticuloendothelial system function after DM induction, as evidenced by decreased ^99mTc-SC liver uptake and increased blood pool compared to prediabetes, while the hepatobiliary function remained unchanged after DM induction using ^99mTc-BrIDA imaging.

Internal cancellation of spikes using two avalanche photodiodes in series for single photon detection

We propose a method of improving the performance of InGaAs/InP avalanche photodiodes by using two avalanche photodiodes in series as single photon detectors for 1550-nm wavelength. In this method, the raw single photon avalanche signals are not attenuated, thus a high signal-to-noise ratio can be obtained compared with the existing results. The performance of the scheme is investigated and the ratio of the dark count rate to the detection efficiency is obtained to be 1.3×10−4 at 213 K.

Modeling the spectral evolution in the decaying tail of gamma-ray bursts observed by Swift

The detailed study of the spectral evolution during the steep decay phase of early X-ray light curves of gamma-ray bursts (GRBs) is a very important task that can give us information on different emission components contributing to the prompt-to-afterglow transition and help to understand the link between these two stages. Time resolved spectral analysis of bright GRBs detected by Swift has shown that a good modeling of the early X-ray light curves can be obtained with Band or cut-off power-law broad band spectra with evolving parameters (e.g., decaying peak energy). We developed a procedure to simultaneously fit the temporal evolution of all the spectral parameters of a GRB during the prompt-to-afterglow transition based on the analysis of the Swift Burst Alert Telescope (BAT) and the Swift X-ray Telescope (XRT) count rate and hardness ratio light curves. The procedure has been tested on GRB 060614 and GRB 090618, two very peculiar bright GRB detected by Swift that show a long exponentially decaying tail with strong softening and peak energy crossing the XRT energy band.

Radioactive point source localization in one, two, and three dimensions within a bulky medium

The major objective of this study has been to investigate methods of radioactive point source localization within an object. Count rate ratios from two opposite detectors around an object are used for localization. Potentially useful mathematical non-linear equations are derived and solved by MATHEMATICA-based program to identify activity position in multidimensions.

METHODS FOR ESTIMATING FLUXES AND ABSORPTIONS OF FAINT X-RAY SOURCES

X-ray sources with very few counts can be identified with low-noise X-ray detectors such as ACIS onboard the Chandra X-ray Observatory. These sources are often too faint for parametric spectral modeling using well-established methods such as fitting with XSPEC. We discuss the estimation of apparent and intrinsic broad-band X-ray fluxes and soft X-ray absorption from gas along the line of sight to these sources, using nonparametric methods. Apparent flux is estimated from the ratio of the source count rate to the instrumental effective area averaged over the chosen band. Absorption, intrinsic flux, and errors on these quantities are estimated from comparison of source photometric quantities with those of high S/N spectra that were simulated using spectral models characteristic of the class of astrophysical sources under study. The concept of this method is similar to the long-standing use of color-magnitude diagrams in optical and infrared astronomy, with X-ray median energy replacing color index and X-ray source counts replacing magnitude. Our nonparametric method is tested against the apparent spectra of 2000 faint sources in the Chandra observation of the rich young stellar cluster in the M17 HII region. We show that the intrinsic X-ray properties can be determined with little bias and reasonable accuracy using these observable photometric quantities without employing often uncertain and time-consuming methods of non-linear parametric spectral modeling. Our method is calibrated for thermal spectra characteristic of stars in young stellar clusters, but recalibration should be possible for some other classes of faint X-ray sources such as extragalactic AGN.

Recognition of pigment layers in illuminated manuscripts by means of Kα/Kβ and Lα/Lβ ratios of characteristic X-rays

X-ray fluorescence analysis with an evaluation of the Kalpha/Kbeta or Lalpha/Lbeta count rate ratios enables a layered structure to be recognized, because the measured ratio of two lines of one element depends on the depth distribution of this element in the analyzed objects. Several specimens consisting of layers of various pigments were analyzed to demonstrate the possibilities of the proposed technique. Then the Lalpha/Lbeta technique was applied in an investigation of cinnabar distribution in mediaeval manuscripts.

Quantification of methylamine in the headspace of ethanol of agricultural origin by selected ion flow tube mass spectrometry

Selected ion flow tube mass spectrometry, SIFT-MS, has been used to investigate if absolute levels of trace compounds in the headspace of ethanol/water vapour mixture can be quantified. This case study was directed towards the analysis of methylamine in distilled ethanol of agricultural origin because of its relevance to quality control legislation in the distillery industry. This has required a detailed study of the ion chemistry occurring – initiated by H 3O + precursor ions – when ethanol/water vapour mixtures are introduced into the H 3O +/helium carrier gas swarm and has resulted in the construction of a full scheme of the complex ionic reactions that occur. It has been found that under the SIFT-MS flow reactor conditions (He pressure 130 Pa and temperature 299 K) the terminating ions of the several parallel and sequential reactions that occur are the proton bound ethanol clusters ions, C 2H 5OH 2 +(C 2H 5OH) n , with n = 1,2,3, proton bound trimer ( n = 2) being the dominant species. These ethanol cluster ions can be used as precursor (reagent) ions for the chemical ionisation of the methylamine present in the ethanol/water vapour, which produces two characteristic product ions CH 3NH 2H +(C 2H 5OH) 1,2 that are used for the methylamine analysis. The ratio of the product ion count rate to the precursor ion count rate is used in an analogous way to the routinely used for SIFT-MS analyses to quantify the methylamine concentration. The results of calibration experiments show that using SIFT-MS it is possible to quantify methylamine in liquid ethanol/water mixtures at levels of 0.1 mg/L or greater.

Determination of 235U/ 238U atom ratio in uranium samples using liquid scintillation counting (LSC)

A correlation has been developed for the determination of 235U/ 238U atom ratio in uranium samples using liquid scintillation counting (LSC). The 235U/ 238U atom ratio determined by thermal ionization mass spectrometry (TIMS) was correlated to the ratio of (i) α-count rate and (ii) Cerenkov count rate due to 234mPa in the sample; both measured by LSC. This correlation is linear over the range of 235U/ 238U atom ratio encountered in the nuclear fuel samples, i.e. the low enriched uranium (LEU) samples with 235U < 20 atom%. The methodology based on this correlation will be useful for the quick determination and verification of 235U/ 238U atom ratios in fuel samples using cost effective technique of LSC.

Kα/Kβ Ratios of Fluorescence X-rays as an Information Source on the Depth Distribution of Iron in a Low Z Matrix

This paper describes how the K(alpha)/K(beta) count rate ratio of the characteristic X-rays of a given element can be applied to determine the depth at which a layer or a grain of that element is located. The theoretical background and a basic description of the K(alpha)/K(beta) technique are given in the introduction. The experimental part of the paper deals with measurements of thick standard pure iron, intermediately thick iron foils, and layers prepared with a powder of Prussian blue. All these specimens were analyzed alone, and they were also analyzed overlaid with a low Z matrix. The light matrix consisted of sheets of paper of known thickness. Paper was chosen, because we take into account the subsequent application of this technique to surveys of historical monuments. The relation between the K(alpha) count rate, the K(alpha)/K(beta) count rate ratio, and the distribution of iron in the paper matrix are presented here.

First experiments on the observation of gamma resonance of a long-lived 109m Ag isomer using a gravitational gamma spectrometer

The first measurements of the resonant Mossbauer self-absorption of the long-lived 109m Ag isomer gamma rays as a function of the declination angle of the gamma beams from the horizontal direction are presented for a gamma source that represents a single-crystal silver plate doped with a parent 109Cd nuclide. The resonant absorption is manifested as a minimum of the counting rate ratio of the 109m Ag and 241Am (control gamma source) gamma-line intensities at a zero-declination angle for one of two detectors and an angle of about 1° for another detector. The magnitude of the effect is in agreement with the results of our previous experiments performed on another setup. It follows, from the data obtained, that the angular width of the gamma-resonance profile is less than two degrees, which corresponds to a broadening factor of the Mossbauer gamma line of less than five. The value of this factor calculated from the measured relative magnitude of the 109m Ag gamma-ray resonant absorption is 6.3 −1.9 +5.2 .

Improved localization of a 'hot spot' in the lungs for an array of four HPGe detectors--the isotopic ratio effect

Considerable errors in the determination of radioactivity in lungs are caused by the usual assumption of homogeneous distribution, while actually the radioactive contamination can be distributed, and even in the form of a 'hot spot'. Modern lung counter systems use several HPGe detectors, and the ratio of the different count rates of the detectors can be used to locate a 'hot spot' and apply correction algorithms for activity calculation. In the present work it is shown that the variability of the isotopic composition of the uranium source has a major effect on the process of localization of the 'hot spot' in the lungs. A way to eliminate this effect is proposed by separate normalization of the count rates of each energy peak.

Identification of New M Dwarfs in the Solar Neighborhood

We present the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating the Two Micron All Sky Survey and ROSAT catalogs. We have derived the spectral types and estimated distances for all of our stars. The spectral types range between K5 and M6. Nearly half of our stars lie within 50 pc. We have measured the equivalent width of the Hα emission line. Our targets show an increase in chromospheric activity from early to midspectral types, with a peak in activity around M5. Using the count rate and hardness ratios obtained from the ROSAT catalog, we have derived the X-ray luminosities. Our stars display a relation between the chromospheric and coronal activity. The relation is such that log LX/Lbol remains at a value of approximately -3 for varying Hα equivalent width. We have found 568 matches in the USNO-B catalog and have derived the tangential velocities for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher vtan have lower Hα equivalent widths. The coronal emission, however, remains saturated at a value of log LX/Lbol ~ -3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age. We do not find any break in the saturation-type relation at the spectral type at which stars become fully convective (~M3.5). Most of the stars in our sample show more coronal emission than the dMe stars in the Hyades and Praesepe and have vtan < 40 km s-1, suggesting a young population.

A novel method of quantitative assay of PuBe neutron sources by neutron coincidence technique

Using a simple model for PuBe neutron sources, in which the neutrons were assumed to be randomly emitted from the centre of a spherical source, and induce neutron-producing secondary reactions in the material, calculation shows that the ratio of the real coincidence count rate R to the total count rate T, measured by neutron coincidence technique, is proportional to the Pu content of the sample. Therefore, measuring the ratio R/ T can be considered a method for determining the Pu content of PuBe neutron sources. The effect of the moderator of a neutron coincidence collar on the count rate of doubles was investigated experimentally using uranium samples of different enrichment (0.7–2.7% 235U). An important conclusion from the data of the experiments is that the influence of the neutrons backscattered from the moderator for the secondary reaction rate can be neglected during measuring PuBe neutron sources. This result leads to an empirical formula for determining the Pu content of PuBe neutron sources, which is independent of the type of the detector. The accuracy of the method is about 15%.

Improved localization of a “hot spot” in the lungs for an array of four HPGe detectors—the simultaneous use of two gamma energies

Significant errors in the determination of radioactivity in lungs are caused by the usual assumption of homogeneous distribution, while actually the radioactive contamination can be in the form of a “hot spot”. Modern Lung Counter systems use several HPGe detectors, and the ratio of the different count rates of the detectors can be used to locate the “hot spot” and apply correction algorithms for activity calculation. An average error of only 9.5%, can be obtained when using this information for detection of a natural uranium point source in the lungs, when the analysis is based on either the 186 or the 92 keV peaks. In the present paper it is shown that the uncertainty can be further reduced to about 3.8%, if the two gamma energy peaks (186 and 92 keV) are analyzed simultaneously for the localization of the uranium point source.

Attenuation correction of SPECT images based on separately performed CT

Summary Aim: A new software approach uses separately acquired CT images for attenuation correction after retrospective fusion with the SPECT data. This study evaluates the effect of this CT-based attenuation correction on indium- 111-pentetreotide-SPECT images. Methods: Indium- 111-pentetreotide-SPECT imaging using a dual-head gamma camera e.cam (Siemens Medical Solutions, Erlangen, Germany) as well as separate spiral computed tomography (CT) was performed in 13 patients. After fusion of SPECT and CT data, the bilinear attenuation coefficients were calculated for each pixel in the CT image volume using their Hounsfield unit values and attenuation- corrected images were reconstructed iteratively (OSEM 2D). Regions of interest (ROIs) were drawn on 24 suspicious foci and background, and target to background ratios were calculated for corrected (TBAC) and uncorrected (TBNAC) images. The shortest distance from the centre of the lesion to the surface of the body (DS) was measured on the corresponding CT slice. Furthermore, ROIs were drawn over the rim and the centre of the liver. Ratios of hepatic count rates for corrected (LRAC) and uncorrected (LRNAC) images were also compared. Results: In lesions located more centrally, TBAC was up to 52% higher, whereas in peripherally located lesions, TBAC was up to 63% lower than TBNAC. The TBAC/TBNAC quotient was linearly correlated with DS. In the liver, attenuation correction resulted in a 35% increase of LRAC compared with LRNAC. Conclusions: Attenuation correction of SPECT images performed by separately acquired CT data is quick and simple. It improves the contrast between target and background for lesions located more centrally in the body and improves homogeneity of the visualisation of tracer uptake in the liver.

Lymph kinetics with technetium-99m labeled radiopharmaceuticals

Summary Aim of this study was to characterize suitable technetium- 99m labeled tracers for lymphoscintigraphy by comparative animal tests. Animals, methods: To evaluate the influence of the particle size and the organ tracer-uptake on lymphtransport animal experiments were performed on six different agents (including one control group). Activity distributions were examined in Sprague-Dawley-rats by lymphoscintigraphy; the maximum uptake (count-rate) of the whole body and in lymph nodes were analyzed by regions- of-interest-technique, respectively. Additionally, for characterization of lymphatic and extralymphatic traceruptake an intra-individual relative count-rate ratio of the liver, lung, kidneys, and spleen has been calculated following organ extraction. Results: Organ specific differences of distribution were clearly demonstrated. Our results indicate that the kinetics of lymphoscintigraphic 99mTc-bound agents substantially depends on particle size. Reliable transport from the interstitium to initial lymph vessels and lymph node uptake suggested for tracers suited for lymphoscintigraphy a median size of about &lt;100 nm. Conclusion: Our data could improve standardization of diagnostic methods and lead to an objective consideration of therapeutic procedures.

Fluorine-18-fluoro-deoxyglucose positron emission tomography follow-up in Erdheim Chester disease: comparison with X-ray, scintigraphy, CT and MRI

Purpose: Erdheim Chester disease is a rare form of histiocytosis, affecting the skeleton and various inner organs. One hundred and twenty-five publications have reported radiographic and bone scintigraphic studies in the English speaking literature. We present a patient who underwent an initial as well as a follow-up fluorine-18-fluoro-deoxyglucose positron emission tomography (FDG-PET) study. Materials and methods: Whole-body PET studies with attenuation correction were performed at the time of diagnosis and two years later. The quantification was done with isoactivity-ROIs in the coronal slices of the limbs. For the humeri, standardized uptake values (SUV) values were calculated additionally. The results were compared to scintigraphic and radiological findings, including CT and MRI. Results: FDG-PET showed an increased metabolism in the limbs with SUV values up to 5.01. Initially, the count rate ratio of lower/upper limbs showed a predominance of both femora, according to the pain localization predominantly in the legs. In the follow-up study, the ratio decreased, corresponding to the pain, which had shifted to the arms. Conclusion: This study shows that also in Erdheim Chester disease, PET is able to detect the pathognomonic changes in bone metabolism. In addition, PET may be helpful for determination of the extent of the disease, since a good correlation between PET findings and the clinical symptoms could be demonstrated.

F-35 Comparison of Computed Absolute Fluorescence Photon Counts with Data from Fully Calibrated Beamlines and Detectors at PTB/BESSY-II

Quantitative analysis is in general based on ratios of count rates from the unknown and a reference sample. Thereby several common factors cancel, particularly the geometrical beam and sample sizes, the acceptance angle and detection efficiency of analyzer and detection system, and the scaling factor of the primary spectral distribution function. In addition, in the theoretical methods, various errors in fundamental coefficients which cause a parallel bias in the photon counts of the unknown and reference sample (for example the transition probabilities, fluorescent yields, and absorption edge jump ratios), are effectively reduced.

Locating a “hot spot” in the lungs when using an array of four HPGe detectors

Considerable errors in the activity determination in lungs can be induced for the case of a “hot spot”. Modern lung counter systems use several HPGe detectors, and the count rate ratios of the detectors can be used to locate the “hot spot” and apply correction algorithms. Some criteria for location determination of a point source in the lungs were investigated, and it is shown that an average error of up to about 10% can be achieved.