Anticosmic-shielded ultralow-background germanium detector systems for analysis of bulk environmental samples

A low-level gamma-ray counting system has been developed which reduces system background, relative to other typical low-background systems, by a factor of ten in the energy region below one MeV, and by as much as a factor of forty at higher energies. This germanium-diode gamma-ray spectrometer was constructed for a modest investment above that required for a conventional germanium detector. The techniques involved use: (1) materials of known radiopurity to surround the diode, (2) an active external anticosmic shield to reduce the background continuum due to interactions of cosmic particles with the detector and passive lead shielding, and (3) nitrogen exhausted from the cryogenic dewar to minimize the introduction of ubiquitous radon decay nuclei into the sample counting chamber. A novel method for handling samples prior to counting is presented. Also; some of the difficulties encountered in calibrating a system intended for bulk samples are discussed.Operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.     

Low-level gamma-ray spectrometry for environmental samples

Low-level gamma-ray spectrometry with large volume HPGe detectors has been widely used in analysis of environmental radionuclides. The reasons are excellent energy resolution and high efficiency that permits selective and non-destructive analyses of several radionuclides in composite samples. Although the most effective way of increasing the sensitivity of a gamma-ray spectrometer is to increase counting efficiency and the amount of the sample, very often the only possible way is to decrease the detector’s background. The typical background components of a low-level HPGe detector, not situated deep underground, are cosmic radiation (cosmic muons, neutrons and activation products), radioactivity of construction materials, radon and its progenies. A review of Monte Carlo simulations of background components of HPGe detectors, and their characteristics in coincidence and anti-Compton mode of operation are presented and discussed.     

7Be analyses in seawater by low background gamma-spectroscopy

Oceanographers use the cosmogenic radionuclide ⁷Be (T _1/2 53 days) as a tracer for atmospheric input and a conservative tracer of mixing in the open ocean. This paper elucidates a method for improving the analysis of ⁷Be from seawater. The scavenging efficiency of Fe(OH)₃ for each sample is measured by ICP-MS using stable ⁹Be as a yield monitor. Samples are gamma-counted in a large diameter (28 mm) well detector. The high purity germanium well detector is coupled with an active anti-coincidence cosmic guard to reduce the spectra background. The improved overall accuracy of the method and lower detection limit of the detector results in a lower volume of seawater needed for analyses. Results will be shown from a study of ⁷Be in the Sargasso Sea.     

Future advances in near infrared Fourier Transform Raman spectroscopy

The probable directions in which the technique of near infrared Fourier Transform Raman spectroscopy will advance are discussed. The analysis considers the limitations of the method and the instrumental balances which may be found for different applications. Discussion is from an instrumental viewpoint, including filtering, detection, excitation, sampling techniques and data analysis. Applications of these advances in the analytical environment are suggested. Spectra are presented from a system which employs Q-switched Nd:YAG excitation and a gated detector in order to discriminate against long-lived spectral backgrounds. Dramatic reductions in the background from hot samples are demonstrated.     

Cosmic dust in the earth's atmosphere

This review discusses the magnitude of the cosmic dust input into the earth's atmosphere, and the resulting impacts from around 100 km to the earth's surface. Zodiacal cloud observations and measurements made with a spaceborne dust detector indicate a daily mass input of interplanetary dust particles ranging from 100 to 300 tonnes, which is in agreement with the accumulation rates of cosmic-enriched elements (Ir, Pt, Os and super-paramagnetic Fe) in polar ice cores and deep-sea sediments. In contrast, measurements in the middle atmosphere - by radar, lidar, high-flying aircraft and satellite remote sensing - indicate that the input is between 5 and 50 tonnes per day. There are two reasons why this huge discrepancy matters. First, if the upper range of estimates is correct, then vertical transport in the middle atmosphere must be considerably faster than generally believed; whereas if the lower range is correct, then our understanding of dust evolution in the solar system, and transport from the middle atmosphere to the surface, will need substantial revision. Second, cosmic dust particles enter the atmosphere at high speeds and undergo significant ablation. The resulting metals injected into the atmosphere are involved in a diverse range of phenomena, including: the formation of layers of metal atoms and ions; the nucleation of noctilucent clouds, which are a sensitive marker of climate change; impacts on stratospheric aerosols and O(3) chemistry, which need to be considered against the background of a cooling stratosphere and geo-engineering plans to increase sulphate aerosol; and fertilization of the ocean with bio-available Fe, which has potential climate feedbacks.     

Environmental radioactivity in the ground water at the Gran Sasso National Laboratory (Italy): a possible contribution to the variation of the neutron flux background

The possible sources analyzed up to now for the neutron flux background at the Gran Sasso National Laboratory are the natural radioactivity in the rock, the concrete, as well as the induced part coming from interaction of cosmic ray muons with the rock or the detector material itself. Water was considered only as moderator in concrete, due to its variable concentration and its radioactivity as additional source for neutron flux modulation. Therefore, the water–rock interaction and its spatial-temporal variation induced by hydrological pattern of the Gran Sasso aquifer are taken into account.     

Non-dispersive measurements by magneto-optic rotation using a graphite furnace

The signal to background ratio of magneto-optic measurements can be substantially improved by use of a suitable optical masking system. A numerical simulation is used to determine the optimum configuration for such an arrangement. The simulation works well enough to allow experimental non-dispersive measurements to be made at comparable sensitivity to that obtained when a monochromator is used to further limit the atomiser background which reaches the detector. The simulation also allows estimates to be made of the sensitivity reductions caused by the use of standard components whose dimensions are not necessarily optimal.     

Monte Carlo simulations of low background detectors

An implementation of the Electron Gamma Shower 4 code (EGS4) has been developed to allow convenient simulation of typical gamma ray measurement systems. Coincidence gamma rays, beta spectra, and angular correlations have been added to adequately simulate a complete nuclear decay and provide corrections to experimentally determined detector efficiencies. This code has been used to strip certain low-background spectra for the purpose of extremely low-level assay. Monte Carlo calculations of this sort can be extremely successful since low background detectors are usually free of significant contributions from poorly localized radiation sources, such as cosmic muons, secondary cosmic neutrons, and radioactive construction or shielding materials. Previously, validation of this code has been obtained from a series of comparisons between measurements and blind calculations. An example of the application of this code to an exceedingly low background spectrum stripping will be presented.Pacific Northwest Laboratory is operated by Battelle Memorial Institute for the US Department of Energy under Contract DE-AC06-76RLO 1830.     

Application of the photoionization detector for the determination of ethanol in aqueous solutions and human breath

A determination of ethanol is described, which is based on a purging system in conjunction with a photoionization detector. With that system a fast and reliable determination of ethanol in aqueous solutions is possible. The system has been used for the analysis of wine. The 3delta-detection limit has been 0.005% ethanol, the relative standard deviation 4.8 to 6.0% and the time constant of the entire analytical system 20 s. The photoionization detector has been also applied to the analysis of artificial and genuine human breath. A comparison with gas-chromatography and non-dispersive IR-detection has been proven the reliability of results.     

A capillary electrophoretic system with an improved gas-phase chemiluminescence nitrogen detector.

A new, rugged nebulizer interface was designed to couple a capillary electrophoretic system to a gas-phase nitrogen chemiluminescence detector. By hydraulically decoupling the separation capillary from the nebulizer of the gas-phase nitrogen chemiluminescence detector, the interface-related loss of separation efficiency could be limited to a mere 10%. The ozone reaction chamber of the gas-phase nitrogen chemiluminescence detector has been redesigned leading to a threefold improvement in detection sensitivity over the old design. In combination with a field-amplified sample stacking procedure, the new system was used to detect 0.25 ppm concentrations of UV chromophore-free aminoglycosides.     

Compton suppression system at Penn State Radiation Science and Engineering Center

A Compton suppression system is used to reduce the contribution of scattered gamma-rays that originate within the HPGe detector to the gamma-ray spectrum. The HPGe detector is surrounded by an assembly of guard detectors, usually NaI(T1). The HPGe and NaI(T1) detectors are operated in anti-coincidence mode. The NaI(T1) guard detector detects the photons that Compton scatter within, and subsequently escape from the HPGe detector. Since these photons are correlated with the partial energy deposition within the detector, much of the resulting Compton continuum can be subtracted from the spectrum reducing the unwanted background in gamma-ray spectra. A commercially available Compton suppression spectrometer (CSS) was purchased from Canberra Industries and tested at the Radiation Science and Engineering Center at Penn State University. The PSU-CSS includes a reverse bias HPGe detector, four annulus NaI(T1) detectors, a NaI(T1) plug detector, detector shields, data acquisition electronics, and a data processing computer. The HPGe detector is n-type with 54% relative efficiency. The guard detectors form an annulus with 9-inch diameter and 9-inch height, and have a plug detector that goes into/out of the annulus with the help of a special lift apparatus to raise/lower. The detector assembly is placed in a shielding cave. State-of-the-art electronics and software are used. The system was tested using standard sources, neutron activated NIST SRM sample and Dendrochronologically Dated Tree Ring samples. The PSU-CSS dramatically improved the peak-to-Compton ratio, up to 1000:1 for the ¹³⁷Cs source.     

Capillary electrophoresis with solid-state electrochemiluminescence detector

We report capillary electrophoresis coupling to a solid-state electrochemiluminescence (ECL) detector for the first time. The solid-state ECL detector was fabricated by immobilizing the ECL reagent tris(2,2'-bipyridyl)ruthenium (TBR) in poly-(p-styrenesulfonate)-silica-poly(vinyl alcohol) grafting 4-vinylpyridine copolymer films. The excellent stability of the solid-state ECL detector in the phosphate solution satisfied application in CE. The CE with solid-state ECL detector system was characterized using tripropylamine (TPA) and proline. The influences of detection potential, the concentration of TBR in the film, and pH value of ECL buffer were investigated. The linear range for TPA and proline was 0.005-10 microM and 5-10 mM with correlation coefficients of 0.997 and 0.998, respectively. The detection limit (signal-to-noise ratio S/N = 3) was estimated to be 0.002 and 2.0 microM for TPA and proline, respectively. The relative standard deviations for 1.0 microM TPA and 1.0 mM proline were 8.7% and 7.5% with theoretical plate numbers of 70 000 and 16 000, respectively. Compared with the CE-ECL of TBR in aqueous solution, the CE coupling with solid-state ECL detector system gave the same sensitivity of analysis.     

A new low noise detector for Ft-Raman

A germanium photodiode has been used to record FT-Raman spectra excited by an NdYag laser at 1.06m. Since photon noise appears much smaller than detector noise, reduced detector noise leads directly to improved spectral signal-to-noise ratio. A new InGaAs photodiode with about seven times lower noise equivalent power indeed improves the spectrum signal-to-noise ratio by a factor of seven. When compared with a particularly sensitive Ge photodiode prepared by the North Coast Detector Corp. the InGaAs detector appears to have about the same noise level, but with a higher electrical bandwith, which is needed in FT-Raman, and the absence of so-called cosmic ray spikes.     

Application of the photoionization detector for the determination of ethanol in aqueous solutions and human breath

A determination of ethanol is described, which is based on a purging system in conjunction with a photoionization detector. With that system a fast and reliable determination of ethanol in aqueous solutions is possible. The system has been used for the analysis of wine. The 3-detection limit has been 0.005% ethanol, the relative standard deviation 4.8 to 6.0% and the time constant of the entire analytical system 20 s. The photoionization detector has been also applied to the analysis of artificial and genuine human breath. A comparison with gas-chromatography and non-dispersive IR-detection has been proven the reliability of results.     

Evaluation of high-performance liquid chromatography with a dual working-electrode electrochemical detector for the determination of catecholamines in human cerebrospinal fluid

A procedure is described for quantifying norepinephrine [1(3,4-dihydroxyphenyl)-2-aminoethanol] and dopamine (4-(2-aminoethyl)-1,2-benzenediol] in cerebrospinal fluid by high-performance liquid chromatography (h.p.l.c.) with dual working-electrode electrochemical detection. An ion-pairing reversed-phase h.p.l.c. technique is used after clean-up and preconcentration of the fluid on alumina. The dual working-electrode electrochemical detector used provides amplification in the electrochemical response per unit concentration of material passing through the detector. This is achieved by locating two working electrodes on the opposite walls of a thin-layer cell, holding them close together and at potentials that will induce a sequence of oxidation/reductions. The greater the number of oxidation/reduction cycles, the greater the amplification of the electrochemical response. Peak height ratios are linear over the range expected and detection limits are 3 pg for norepinephrine and 5 pg for dopamine. The concentrations of norepinephrine and dopamine in human cerebrospinal fluid were found to be 141 pg ml^?1 and 262 pg ml^?1 with relative standard deviations of 6.8 and 5.8%, respectively.     

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.     

Determination of water by flow injection analysis with the karl fischer reagent: Minization of effects caused by differences in physical properties of the samples

In the previously described flow-injection method for the spectrophotometric determination of water with the Karl Fischer reagent, problems can arise from the rather large variation between the calibration curves for different types of samples. Different combinations of flow-injection arrangements and detector types are described here, to establish a system which levels out this undesirable spreading between the calibration curves. One necessary condition for attaining a low spread is shown to be the use of a spectrophotometric detector especially constructed to minimize refractive index effects. The best results, including samples with large differences in refractive indices and viscosities, were obtained by a combination of peak area measurements and the use of this detector. For example, the relative mean deviation for a sample containing 0.1% water was about 2%.     

手持式智能光度计的研制及应用

本文研制了手持式智能光度计。该仪器集成了光源、进样系统和检测器,体积小巧,采用吸入式进样系统取代比色皿设计,试剂消耗量仅为比色皿的10%。使用该仪器进行了甲醛标准样品测定,标准曲线回归系数为0.9979,相对标准偏差1.02%(n=5)。用于水发牛百叶等三种水发产品中甲醛含量的测定,结果令人满意。     

Indirect determination of iron in a flow-injection system with amperometric detection

The change in peak current resulting from the reaction of Fe(II) with nitroso-R salt in a flow-injection system is used to quantify Fe(II) with either single- or dual-electrode amperometric detectors. The current change varies linearly with Fe(II) concentration from 0 to 200 mg 1^?1. The relative standard deviation was about 5% with the single-electrode detector and about 10% with the dual-electrode detector. The method is evaluated for the determination of iron in dietary supplements.