Stilbene composite scintillators as detectors of fast neutrons emitted by a 252Cf source

The results of the measurements are presented of the relative efficiency ε for ²⁵²Cf fast neutron detection by composite detectors based on stilbene crystalline grains. The effects of the grain size and height of the composite detector on its scintillation properties were studied. It is shown that the efficiency of fast neutron detection of stilbene composite scintillators ranges up to 60% of that of bulk single crystals. The results are also presented for relative light output measurements of stilbene composite detectors irradiated by gamma photons of ¹³⁷Cs, as well as transmittance data of samples in the range of their transparency absorption.     

Monitoring of the thermal neutron flux in the EDELWEISS II dark matter direct search experiment

The results from measurements of thermal neutron flux in the EDELWEISS II experiment aimed at the direct detection of WIMPs (weakly interacting massive particles) by means of cryogenic germanium bolometers are described. Detailed knowledge of the neutron background is of crucial importance for the experiment, since neutrons with the MeV energy range of scattering seem to be hard to distinguish from the expected WIMP signal within the bolometers. Monitoring of the thermal neutron flux is performed using a mobile detection system with a low background proportional ³He counter. The neutron flux measurements were performed both outside and inside the device’s shielding, in the direct proximity of a cryostat with built-in germanium detectors. The sensitivity of the created thermal neutron detection system is on the level of 10⁻⁹ neutron (cm² s)⁻¹.     

Comparison of Detection Limits in Atomic Fluorescence and Absorption Spectroscopy

Dagnall, Taylor, and West have recently compared detection limits for a number of metals in atomic fluorescence and absorption spectroscopy and have concluded that “atomic fluorescence measurements using an electrodeless discharge tube are inherently more sensitive than those obtainable by atomic absorption measurements”. Likewise West and Williams have compared the two techniques for magnesium²and silver³, using high-intensity hollow-cathode lamps as sources, and have found much lower detection limits in fluorescence than in absorption.     

Photoacoustic spectroscopy for trace gas detection with cryogenic and room-temperature continuous-wave quantum cascade lasers

The main characteristics that a sensor must possess for trace gas detection and pollution monitoring are high sensitivity, high selectivity and the capability to perform in situ measurements. The photacoustic Helmholtz sensor developed in Reims, used in conjunction with powerful Quantum Cascade Lasers (QCLs), fulfils all these requirements. The best cell response is # 1200 V W⁻¹ cm and the corresponding ultimate sensitivity is j 3.3 × 10⁻¹⁰ W cm⁻¹¹ Hz^−11/2. This efficient sensor is used with mid-infrared QCLs from Alpes Lasers to reach the strong fundamental absorption bands of some atmospheric gases. A first cryogenic QCL emitting at 7.9 μm demonstrates the detection of methane in air with a detection limit of 3 ppb. A detection limit of 20 ppb of NO in air is demonstrated using another cryogenic QCL emitting in the 5.4 μm region. Real in-situ measurements can be achieved only with room-temperature QCLs. A room-temperature QCL emitting in the 7.9 μm region demonstrates the simultaneous detection of methane and nitrous oxide in air (17 and 7 ppb detection limit, respectively). All these reliable measurements allow the estimated detection limit for various atmospheric gases using quantum cascade lasers to be obtained. Each gas absorbing in the infrared may be detected at a detection limit in the ppb or low-ppb range.     

A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers

We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 μm, where strong fundamental absorption bands occur for the considered species and their isotopomers. The detection technique is based on audio-frequency and radio-frequency modulation of laser radiation. First experimental tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of ¹³C/¹²C, ¹⁸O/¹⁶O, ¹⁷O/¹⁶O and ¹⁵N/¹⁴N isotope ratios.     

A pure rotational Raman lidar using double-grating monochromator for temperature profile detection

A pure rotational Raman lidar is constructed for measurements of vertical temperature profiles of atmosphere. A fiber-coupled, double-grating monochromator is used as the filter system so that a high spectral resolution of <0.23 nm and an out-of-band rejection rate of 10⁷ are achieved. Comparison with in-situ measurements indicates that the accuracy of atmospheric temperature measurements using this lidar system is better than 1.1 K up to an altitude of 10 km. Different effects on signal accuracy resulting from various noise sources are analyzed and uncertainties in temperature due to detection noises are estimated.     

Resonance ionization mass spectroscopy for trace analysis of neptunium

Resonance ionization mass spectroscopic (RIMS) measurements for trace analysis and spectroscopy of ²³⁷Np, the ecologically most important isotope of neptunium, are described. The chemical procedure for the separation of neptunium from aqueous samples as well as the preparation of filaments for RIMS are outlined. Several two- and three-step excitation schemes have been investigated in order to find suitable conditions for the sensitive detection of ²³⁷Np. Using a three-step, three-color excitation and ionization scheme an overall detection efficiency of 3×10^–8 was obtained, resulting in a detection limit of 4×10⁸ atoms (160 fg) of ²³⁷Np. The hyperfine structure splittings of the levels under investigation, which influence the detection limit, were measured. A new method to determine the first ionization potential (IP) was applied to neptunium yielding a value of IP=6.2655(2) eV.     

Simultaneous measurements of atmospheric HONO and NO<Subscript>2</Subscript> via absorption spectroscopy using tunable mid-infrared continuous-wave quantum cascade lasers

Nitrous acid (HONO) is important as a significant source of hydroxyl radical (OH) in the troposphere and as a potent indoor air pollutant. It is thought to be generated in both environments via heterogeneous reactions involving nitrogen dioxide (NO₂). In order to enable fast-response HONO detection suitable for eddy-covariance flux measurements and to provide a direct method that avoids interferences associated with derivatization, we have developed a 2-channel tunable infrared laser differential absorption spectrometer (TILDAS) capable of simultaneous high-frequency measurements of HONO and NO₂. Beams from two mid-infrared continuous-wave mode quantum cascade lasers (cw-QCLs) traverse separate 210 m paths through a multi-pass astigmatic sampling cell at reduced pressure for the direct detection of HONO (1660 cm⁻¹) and NO₂ (1604 cm⁻¹). The resulting one-second detection limits (S/N=3) are 300 and 30 ppt (pmol/mol) for HONO and NO₂, respectively. Our HONO quantification is based on revised line-strengths and peak positions for cis-HONO in the 6-micron spectral region that were derived from laboratory measurements. An essential component of ambient HONO measurements is the inlet system and we demonstrate that heated surfaces and reduced pressure minimize sampling artifacts.     

Determination of radon concentration in soil gas by gamma-ray spectrometry of olive oil

Measurements of radon concentration in soil gas have been carried out using a bubbling system in which the soil gas is drawn through an active pumping to bubble a liquid absorber (olive oil) for the deposition of the soil gas in it. After the bubbling process, the absorber is then taken for gamma-ray measurements. Gamma-ray photopeaks from the ²¹⁴Pb and the ²¹⁴Bi radon progeny are considered for the detection of the ²²²Rn gas to study the concentration levels for radon soil gas. Results for some field measurements were obtained and compared with results obtained using AlphaGuard radon gas monitor. The technique provides a possible approach for the measurements of radon soil gas with gamma-ray spectrometry.     

Implantation of impurity ions into He II for optical spectroscopy purposes

An experimental arrangement for implantation and handling of high densities of alkaline earth ions in He II is described. First results, including mobility measurements of Sr⁺, Ba⁺, Zn⁺and Cd⁺ ions as well as optical detection of Ba⁺ ions, are reported.     

Monte Carlo studies of the resonance fluorescence technique for atmospheric atomic oxygen measurements

The resonance fluorescence of the O (³P³S) triplet has been used extensively for rocket-borne measurements of atomic oxygen in the mesosphere and lower thermosphere. The accuracy and compatibility of different experimental configurations are however still a subject of controversy. In order to better quantify the measurements, we have developed a 3-dimensional Monte Carlo model which simulates the radiative transfer inherent to atom detection by means of resonance lamps. Angle-dependent partial frequency redistribution describes the fluorescence process, natural broadening becoming significant when the line center optical thickness exceeds 10. Applying the model to a recently flown rocket instrument, a strong temperature dependence and nonlinear relations between atomic oxygen abundance and fluorescence signal are found at densities above 5.10¹⁰ cm⁻³. Above 1.10¹² cm⁻³, the signal gradually saturates and useful measurements cannot be obtained. The spatial distribution of the scattering events and effects of the payload motion are analyzed. A discussion of the results is applied to different calibration techniques for rocket instruments.     

Progress in the development of cryogenic detectors for GNO

An improvement of the statistical and systematic uncertainty beyond the level achieved in GALLEX is an essential prerequisite for GNO. As major contributions to these errors are associated with the detection of the EC-decay of ⁷¹Ge in miniaturized gas counters, low temperature calorimetric detectors might provide a promising alternative for a later phase of GNO. We report first results achieved in measurements of the EC-decaying isotopes ⁷¹Ge and ³⁷Ar with cryogenic calorimeters.     

Measurements of long atomic lifetimes at an ion storage ring

Millisecond lifetimes of excited levels in multicharged ions may be measured at ion storage rings. At the Heidelberg ion storage ring TSR, particle detection after collisions between the circulating ions and electrons of the cooler has been used to obtain dielectronic recombination spectra as well as time curves of ionization and recombination for four-electron ions, with the aim of measuring transition probabilities for magnetic dipole and for electric dipole intercombination decays. The measurements on the 2s2p³P ₁ ^o level in the Be-like ions of N and O indicate lifetime values of =(1.6±0.2) ms for N³⁺ and of =(0.5±0.1) ms for O⁴⁺. Problems of these experiments are discussed as well as the prospects for improved measurements on other such ions of astrophysical interest, planning for state-specific optical detection.     

Multiple quantum NMR transitions of8Li (T 1/2=0.84 s) in single crystals and powders of LiTaO3, and the quadrupole moment of8Li

Multiple quantum nuclear magnetic resonance (NMR) transitions were observed on polarized⁸Li nuclei, which were produced by capture of polarized neutrons in a single crystal of LiTaO₃. The asymmetric⁸Liβ-radiation distribution was used for the detection of NMR. A quadrupole moment ratio ¦Q(⁸Li)/Q(⁷Li)¦=0.78(1) was determined. Saturation of multiple quantum transitions in nuclear radiation detected NMR may lead to a reduction in measuring time of up to two orders of magnitude, as compared to single quantum detection methods. The measured spectra agree well with an exact lineshape calculation. The same measurements were also performed on a LiTaO₃ powder sample. This was done to test a method to obtain quadrupole coupling constants from high field NMR multiple quantum powder patterns, which are easily detectable, also for higher nuclear spins. This latter method may be applicable also to conventional NMR detection techniques.     

The investigation of ion implanted layers by scanning electron microscopy

SEM signals were used to image ion-implanted surfaces and to quantitatively analyze implanted layers. Silicon was used as substrate material for implantation, but some measurements on GaAs are also reported. Various ion species were implanted and the dependence of the signals upon fluence was studied. Electron backscattering and absorbed current were found to be influenced by the radiation damage rather than by the species of implanted ions. The degree of damage could be characterized by absorbed current measurements. The ion fluence necessary to produce amorphous layers was determined for N, P, and As in Si using this technique. This fluence was found to correspond to an energy deposition of 2.8×10²¹ keV/cm³. For the detection of very small amounts of implanted ions by characteristic X-rays, the electron energy must be fitted to the penetration depth of the ions under conditions maintaining reasonable excitation cross sections. The lowest value of the normalized detectability obtained in our measurements was 2.5×10¹³ Ions/cm² for 45 keV phosphorus.     

Photoacoustic monitoring of gases using a novel laser source tunable around 2.5 μm

We present the first spectroscopic measurements using a tunable solid state Cr²+:ZnSe laser emitting at wavelengths between 2.2 μm and 2.8 μm. Photoacoustic measurements on various gases such as methane, carbon monoxide, carbon dioxide, water vapour, nitrous oxide, and ambient air were carried out. In this paper, we present measurements on methane, nitrous oxide, and ambient air. The deduced detection limits are in the low ppm or sub-ppm range, e.g., 0.2 ppm for carbon dioxide, 0.8 ppm for methane and 2.7 ppm for carbon monoxide.     

Fiber Optic Spectroelectrochemical Sensing for in situ Determination of Metal Ions

In situ chemical sensing techniques are increasingly used for a variety of applications, including industrial process control, on‐site environmental assessment, and detection of explosives and chemical and biological weapons. A common category of sensors for such purposes entails the use of optical fibers for making spectral measurements of target compounds or species derived from these compounds via physical, chemical, enzymatic, or immunologic reactions. A less common but potentially advantageous approach involves the electrochemical conversion of the analyte subsequent to its spectroscopic detection. These spectroelectrochemical schemes represent versatile, essentially reagent‐free analyses that could provide superior alternatives to existing methods. Reported here is a summary of progress made by the authors' group toward the development of fiber optic spectroelectrochemical sensors for in situ measurements. The aqueous copper (II)/copper (0) couple was chosen as a model system to investigate the merit of an analytical scheme involving (i) cathodic preconcentration of Cu²⁺ as Cu⁰ followed by (ii) anodic stripping of Cu⁰ to Cu²⁺, (iii) complexation of Cu²⁺ by an appropriate ligand, and finally (iv) absorbance determination of the copper–ligand complex or fluorescence determination of the unbound ligand. Results are encouraging and indicate the need for further refinement of the sensor's design and the experimental protocol in order to improve the method's sensitivity.     

Spectroscopic monitoring of NO traces in plants and human breath: applications and perspectives

Optical methods based on quantum cascade lasers (QCLs) are becoming popular in many life science applications. We report on two trace gas detection schemes based on continuous wave QCLs for on-line detection of nitric oxide (NO) at the sub-part-per-billion level by volume (ppbv, 1:10^?9), using wavelength modulation spectroscopy (WMS) and Faraday rotation spectroscopy (FRS) at 1894 cm^?1 and 1875.73 cm^?1, respectively. Several technical incremental steps are discussed to further improve the sensitivity of these methods. Examples are included to demonstrate the merits of WMS-based sensor: direct monitoring of NO concentrations in exhaled breath, and from plants under pathogen attack. A simple hand-held breath sampling device that allows single breath collection at various exhalation flows (15, 50, 100 and 300 mL/s, respectively) is developed for off-line measurements and validated in combination with the WMS-based sensor. Additionally, the capability of plants to remove environmental NO is presented.     

A Streak Camera System for Quantitative Fluorimetry

In conventional and laser excited molecular fluorescence spectrometry,^1,2 the excitation scatter and luminescence from the blank have been shown to be the major factors controlling the limits of detection. However, because of their high intensity, an increase in sensitivity (signal/concentration) is often noted with laser excitation as compared with conventional sources. From theoretical calculations,^3,4 as well as experimental results,⁵ pulsed source excitation with gated detection, using time resolution, can be used to improve the signal to noise ratio, S/N, in certain instances. Pulsed lasers are very well suited for these measurements because of their high intensities and short pulse widths.     

Photon production in Au+Au collisions at \sqrt {s_{NN} } = 130 GeV

We report raw photon, neutral pion and eta measurements at RHIC. Photons in the energy range from 100MeV ? 4GeV were detected by reconstructing e ⁺ e ^? pair production, γ+Z→e ⁺+e ^?+Z, with the STAR Time Projection Chamber (TPC). Along with the photon detection technique we discuss the purity of the photon candidates and measurements of hadronic decays via their electromagnetic decay channels. The π⁰→γ and η→γγ decay channels are addressed.