Determination of purple corn husk anthocyanins

Components of the purple corn husk anthocyanin complex as a rich inedible source for the preparation of natural dyes were analyzed by reversed-phase HPLC with spectrophotometric and mass-spectrometric detection. The wide speciation of anthocyanins was found and its main components were identified as malonylation products of cyanidin-3-glucoside, 3″,5″-dimalonate (31.0%), 5″-monomalonate (32.2%), and 3″-monomalonate (7.3%), with low concentrations of similar pelargonidin and peonidin derivatives. The total accumulation level of anthocyanins in the samples under study exceeded 3.5 g per 100 g of an air-dry material. The results of the study of anthocyanin complexes of other purple corn parts are presented for comparison. Based on the studies performed, supplements to differential spectrophotometric and chromatographic methods for the determination of anthocyanins were proposed, which gave reproducible data for two alternative methods of their determination.     

Construction of a light-emitting diode fluorescence detector for high-performance liquid chromatography and its application to fluorometric determination of L-3-hydroxybutyrate

This study employed a new light source, a light-emitting diode (LED), for fluorescence detection of high-performance liquid chromatography to measure the concentration of trace constituents in biological fluids. Using l-3-hydroxybutyrate ( l-3HB) as a tested trace compound, the function of the new system was compared with that of the current commercially available model. A detailed schematic diagram of the path of the detection rays in the LED detector is given. A voltage-stabilizer for the drive circuit was designed with an input of 10 V and an output of 8 V, and another voltage regulator was used to maintain a constant 8 V. Then the regulator was used to set the output voltage for the LED at 2.8 V by two external resistors. Replacing the xenon lamp with LED, this system provided higher photon density and a narrow spectrum at a wavelength of 491 nm. At room temperature (22.1°C), the average temperature of six places in the chamber of LED detector was 22.1°C compared with 51.1°C in the xenon detector. The spectra of the excitation light sources were measured. Compared with the xenon lamp, approximately 1.32 times higher excitation intensity was obtained by the LED source. The accuracy of detection of l-3HB in 50 μL of rat serum was 99.85-100.85%, and the intra-day and inter-day precision values were within 8.99 and 13.90%, respectively. The limit of detection of l-3HB was approximately 0.73 μM (signal-to-noise ratio 3). The sensitivity of the proposed LED detector was comparable to that of traditional fluorescence detectors using xenon arc lamps; however, the cost and operating temperature of LED lamps were far lower. This assay system could be further used to detect trace constituents in various samples.     

An economical fluorescence detector for lab-on-a-chip devices with a light emitting photodiode and a low-cost avalanche photodiode

An economical fluorescence detector was developed with an LED as the exciting source and a low-cost avalanche photodiode (APD) module as a photon sensor. The detector was arranged in an epifluorescence configuration using a microscope objective (20× or 40×) and a dichroic mirror. The low-cost APD was biased by a direct current (DC) high voltage power supply at 121 V, which is much lower than that normally used for a PMT. Both DC and square wave (SW) supplies were used to power the LED and different data treatment protocols, such as simple average for DC mode, software based lock-in amplification and time specific average for SW mode, were tested to maximize the signal-to-noise ratio. Using an LED at a DC mode with simple data averaging, a limit of detection of 0.2 nmol L(-1) for sodium fluorescein was attained, which is among the lowest ever achieved with an LED as an excitation source. The detector was successfully used in both capillary and chip electrophoresis. The most significant advantages of the detector are the compact size and low cost of its parts. The aim of the work is to prove that widely available, low-cost components for civilian use can be successfully used for miniaturized analytical devices.     

Recent experimental studies of photon–atom scattering in the X-ray energy region

We present a review of our recent measurements of large angle elastic and inelastic scattering differential cross-sections in the photon energy range 14–88 keV (momentum transfer ranging 1.135 to 6.310 Å⁻¹ covering large number of elements in the atomic region Z=1–92, with special emphasis on the elements having K/Li shell/subshell binding energy in the vicinity of the incident photon energy. These measurements were performed using energy dispersive X-ray fluorescence (EDXRF) setup involving radioisotope as a photon source and a solid-state photon detector arranged in an annular geometry. The measured scattering differential cross-sections were compared with the theoretical values based on the state-of-art relativistic second order S-matrix calculations and those based on the form factor approximations in order to check their reliability. The KL and KM resonant Raman scattering (RRS) at 59.54 keV incident photon energy was also investigated for some heavy elements.     

Dissociative double photoionization of singly deuterated benzene molecules in the 26-33 eV energy range

This work provides new experimental and theoretical results about the formation and dissociation of benzene dication. The experiment has been carried out by using a vacuum ultraviolet radiation from a synchrotron source together with a time-of-flight spectrometer and a position sensitive ion detector. Isotopically labeled benzene molecules with a single deuterium atom have been used in order to study the symmetric dissociation of the benzene dication, not well evident in previous experiments. A threshold of 30.1 ± 0.1 eV has been observed for this dissociation reaction. Moreover, the lifetime of the dissociation of the benzene metastable dication producing CH(3)(+) and C(5)H(3)(+) has been obtained as a function of the photon energy, by the use of a Monte Carlo trajectory analysis of the coincidence distributions. The determined lifetime is independent of the photon energy and has an average value of 0.75 ± 0.22 μs. Theoretical calculations of the energy and structure of dissociation product ions have been also performed to provide crucial information about the dynamics of the charge separation reactions following the photoionization event.     

Determination of depth of a radionuclide source in a tissue equivalent phantom

Hydrophilic materials which refer to a group of cross-linked polymers originally developed in the 60s to produce soft contact lenses are characterised by an equilibrium water uptake in the range 15–95 % by wet weight when hydrated in water or normal saline solution at 25 °C. This ability to absorb controlled amounts of water makes them suitable human tissue substitutes. Four types of hydrophilic materials of different composition and thickness were placed between a ²²Na calibrated point source and a single LaBr₃: Ce (5 %) detector (Saint-Gobain) at a fixed distance between source and detector. The scatter-to-peak ratio was determined by selecting five scatter angle windows between 25 and 50^° (467–376 keV), at 5^° intervals, to study how the ratio varied with attenuating material, thickness and composition. From photon spectra recorded a ‘best’ estimate of the depth of the source in the hydrophilic material was obtained by finding the most sensitive scattering window. Theoretical and practical models of the source-to-detector geometries are included and discussed.     

Characterization of an energy dispersive X-ray fluorescence imaging system based on a Micropattern Gaseous Detector

An energy dispersive X-ray fluorescence (EDXRF) imaging system based on a Micropattern Gas Detector has already shown good results for different applications. An X-ray tube, a pinhole camera and a Micro-Hole and Strip Plate (MHSP) based detector are the main components of the experimental system. The detector uses an MHSP in a Xe atmosphere at 1 bar, and acting as a photon counting device, i.e., it is capable to record each single event retaining the energy and the interaction position (2D-sensitive detector) information of the incident photon, demonstrating to be a promising device for EDXRF imaging applications. This work presents studies of energy resolution, energy linearity and spatial resolution/elemental mapping as a function of image magnification of the system.     

An inexpensive, portable and microcontrolled near infrared LED-photometer for screening analysis of gasoline

A microcontrolled, portable and inexpensive photometer is proposed. It uses a near infrared light emitting diode (NIR LED) as radiation source, a PbSe photoresistor as infrared detector and a programmable interrupt controller (PIC) microcontroller as control unit. The detector system presents a thermoresistor and a thermoelectric cooling to control the detector temperature and keep the noise at low levels. The microcontroller incorporated total autonomy on the proposed photometer. As its components are inexpensive and of easy acquisition, the proposed NIR LED-photometer is an economical alternative for chemical analyses in small routine, research and/or teaching laboratories. By being portable and microcontrolled, it also allows carrying out field chemical analyses. The instrument was successfully applied on the screening analysis to verify adulteration in gasoline samples.     

Enhancement of low energy photon intensity caused by coherent scattering with collimator

The low energy photon counting rate normalized to the source-detector geometry showed an enhancement in intensities, when the source was placed in the vicinity of the detector. Isotopic X-ray source of known output /^93mNb,⁵⁵Fe and⁴⁹V/ was used. This enhancement is interpreted to be due, at least, to the occurrence of diffractional coherent scattering with the lead collimator.     

Absolute-scale measurement of compton backscattering in germanium at 105.3 keV

The differential cross section d²σ/dEdΩ was measured at an incident photon energy of 105.3 keV in germanium on absolute scale. The measurements were made using two high purity Ge detectors that operated in a coincidence mode. One detector served as the target and detector of ejected electrons, and another as the detector of Compton-scattered photons. It was found that fast (multiple) cascades have little influence on the data of the 105.3 keV crossover transition. An improved determination of the detector efficiency was made. The calculated values of the cross-section d²σ/dEdΩ using the impulse approximation (IA) with Hatree–Fock (HF) wave functions are in excellent agreement with the experimental cross-sections, while the IA with hydrogen like (HL) wave functions give fair agreement. A comparison of the calculated values of the cross-sections obtained with HF and HL wave functions for each subshell in germanium gives new values for effective charges, which improve agreement between the results of IA with HL and experimental values.     

EDXRF imaging of Pb in glazed ceramics using a micropattern gas detector

A new system for energy-resolved X-ray fluorescence imaging using a microhole and strip plate (MHSP), a new type of micropattern gas detector (MPGD), is proposed. It works as a single photon counting detector with position and energy detection capability. The interaction of X-rays with the gas medium produces electrons via the photoelectric effect, and the number of electrons is proportional to the absorbed X-ray energy. These electrons are further multiplied in the MHSP. Position detection is achieved using the charge division method. The detector has an active area of 28?×?28 mm² and shows good position resolution, about σ?=?125 μm, an intrinsic energy resolution of about 14% FWHM for 5.9 keV X-rays, and a counting rate capability of up to 0.5 MHz. The system has shown good properties for energy-dispersive X-ray fluorescence (EDXRF) applications, since it allows efficient energy and position detection of fluorescence X-rays from multielemental samples. In this work, the system was used to study lead depth distributions in eighteenth-century Portuguese faiences from the Santa Clara-a-Velha monastery. The fluorescence images were obtained by irradiating the samples, with a pinhole placed between the sample and the detector to focus the radiation into the detector. The results are presented here, including the elemental map distributions for different samples.     

A new method for detecting hemoglobin directly in whole blood using photon attenuation techniques

The objective of the proposed work is focused on measuring iron concentration directly in whole blood as tool for estimating hemoglobin and anemic conditions in patients across the world. The investigated method depends on theory of photon attenuation through transmission of low energy in whole blood sample. The mathematical expressions for calculating hemoglobin and iron deficit on blood using photon attenuation are derived. Calculations are carried out for estimating concentration of iron in blood samples taken from children, adults and old patients and therefore measuring their hemoglobin and iron deficit from normal values. Theoretical mass attenuation coefficient values were obtained using the XCOM program. A high-resolution gamma-ray spectrometry based on high purity germanium detector was employed to measure attenuation of strongly collimated monoenergetic gamma beam through blood samples.     

Experimental comparison of the relative yield of 3γ/2γ positron annihilation using semiconductor and scintillation detectors

The yield of three photon positron annihilation is measured using semiconductor and scintillation detectors in a comparison for applications in positron emission tomography, particularly in the exploitation of three photon positron annihilation imaging where good energy resolution and good efficiency are required. In this experimental study four detectors, High-purity Germanium (HPGe), Sodium Iodide (NaI(Tl)), Lanthanum Chloride (LaCl₃:10%Ce³⁺) and Lanthanum Bromide (LaBr₃:5%Ce³⁺) were used. The peak-to-peak method was used with a ²²Na source to determine these yields. Aluminium was employed as a reference material as its high electron density reduces positronium formation and lifetimes. Teflon was also used in order to enhance the formation of ortho-positronium, since quenching is low, leading to increased three photon positron annihilation. The relative 3γ/2γ yields obtained were (3.04±0.11)·10⁻², (2.17±0.11)·10⁻², (3.26±0.10)·10⁻² and (2.03±0.11)·10⁻² for LaBr₃:Ce, LaCl₃:Ce, NaI(Tl) and HPGe detectors, respectively. Among these detectors LaBr₃:Ce proved to be the detector of choice for three photon imaging applications as it has both good energy resolution and efficiency.     

Transversely illuminated liquid core waveguide based fluorescence detection Fluorometric flow injection determination of aqueous ammonium/ammonia

The analytical performance of a new type of fluorescence detector, based on a transversely illuminated liquid core waveguide (LCW), has been investigated using the determination of NH(3)/NH(4)(+) as the 1-sulfonatoisoindole. With a very inexpensive combination of a miniature Hg blacklight as an excitation source, a colored plastic sheet as the emission filter, and an integrated blue sensitized photodiode-operational amplifier as the detector (totaling <$100 in hardware cost), we were able to achieve a limit of detection (LOD) of 35 nM (1.6 pmol) NH(3) with a linear dynamic range up to 60 muM NH(3). Details of detector construction and performance are given.     

New method to measure the K-shell absorption jump factor in some rare-earth elements

The Compton scattering of 59.54 keV gamma rays by an Al scatterer has been used as a primer source at scattering angles from 48 to 118° by using a Si(Li) detector, and this primer gamma ray has been send to absorbers including Gd, Tb, Dy, Ho and Er. A new method has been developed to determine the K-shell absorption jump factor of elements and compounds. This method is based on simultaneous measurement of fluorescence radiation and scattered radiation, thus avoiding the problems with measuring the source strength and source-to-detector solid angle. In this method, the jump factor is effected from the scattering angle. Evident energies near to K-absorption edges of each lanthanide element have been determined for chosen angles, after the incident photon energy (59.5 keV) is exposed to Compton scattering from Al (secondary source). The experimental absorption jump factors are compared with the theoretical estimates and literature experimental values.     

REMPI studies in the Lewis-Rayleigh afterglow of nitrogen

The resonance-enhanced multiphoton ionization (REMPI) technique has been used to detect the presence of highly vibrationally excited nitrogen (to at least ν″ = 26) in the Lewis-Rayleigh afterglow of nitrogen using photoionization via the intermediate a ¹Π_g state (Lyman-Birge-Hopfield bands). For the ν″ = 23, 24 and 25 levels in their Δν = −11 sequence, the REMPI process involves one photon to excite and one to ionize in contrast to the 2 + 2 process required to detect the ν″ = 0 level. The power dependences of the various processes have been measured and provide further confirmation of the assignments.     

Utilization of phoswich detectors for simultaneous,multiple radiation detection

Summary A phoswich radiation detector is comprised of a phosphor sandwich in which several different phosphors are viewed by a common photomultiplier. By selecting the appropriate phosphors, this system can be used to simultaneously measure multiple radiation types (alpha, beta, gamma and/or neutron) with a single detector. Differentiation between the signals from the different phosphors is accomplished using digital pulse shape discrimination techniques. This method has been shown to result in accurate discrimination with highly reliable and versatile digital systems. This system also requires minimal component count (i.e., only the detector and a computer for signal processing). A variety of detectors of this type have been built and tested including: (1) a triple phoswich system for alpha/beta/gamma swipe counting, (2) two well-type detectors for measuring low levels of low energy photons in the presence of a high energy background, (3) a large area detector for measuring beta contamination in the presence of a photon background, and (4) another large area detector for measuring low energy photons from radioactive elements such as uranium in the presence of a photon background. An annular geometry, triple phoswich system optimized for measuring alpha/beta/gamma radiation in liquid waste processing streams is currently being designed.     

Performance of CdTe detector in the 13–1333 keV energy range

The photopeak efficiency, peak to valley ratio and energy resolution of a 3×3×1 mm³ CdTe detector were determined experimentally for 13–1333 keV photon energy by using polyester coated radioisotopes ²⁴¹Am, ²²Na, ⁵⁴Mn, ⁵⁷Co, ⁶⁰Co, ¹⁰⁹Cd, ¹³⁷Cs and ¹³³Ba. The data were analyzed by using PX4 from Amptek. The experimental values were fitted to an analytical function of photon energy, and an agreement was observed for the entire range of the studied energies. The results have shown that the CdTe detector has a high performance due to both the improved charge collection efficiency comparable with that of SI GaAs detectors (Vittone et al., 1999), and the low leakage current. Also, CdTe detector is very attractive for field application as it works at room temperature.     

Photopeak profile of full energy and escape peaks in neutron capture prompt-gamma ray spectra

This paper describes effect of base profile for precise measurement of photon energy in prompt -ray analysis (PGA). The base profile has been examined in the vicinity of full energy (FE), single escape and double escape peaks. Major origins of step-wise base profiles are single and double escape events for triple photon annihilation and single and double Compton escape events for double photon annihilation in the detector, in addition to general events for the FE peak. A formula has been proposed for the quantitative characterization of the base profile.     

The production rates of rare earth nuclides by 70 MeV bremsstrahlung for photon activation analysis

The combination of photon activation and solid state γ-ray detection provides a very effective method of analysis of rare earths. The present report describes the production rates of almost all of the product nuclides found in yttrium and 14 rare earths irradiated with 70 MeV bremsstrahlung photons from an electron synchrotron. A 20 cm³ lithium-drifted germanium diode was used as a detector. Sensitivities of this method have been summarized for photon activation analysis, and experimental reaction yields have been obtained in order to discuss the reactivity of high-energy photons with nuclei in the rare earth region. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2556