Multichannel Scaler Research Articles

Three-dimensional surface analysis of iron-based materials using synchrotron Mössbauer source

A novel three-dimensional surface analysis system for iron-based solid materials has been developed. This system is composed of a synchrotron Mössbauer source, an X-ray focusing device, a precision stage, a gas flow proportional counter for conversion electron measurements, and multiple multichannel scalers. The performance was evidenced by determining the spatial distribution of the iron oxide abundance on a laser-ablated iron foil surface. This system can be widely utilized as a powerful analytical tool in steel science for corrosion, welding, and laser surface modification.

Development of Time- and Energy-Resolved Synchrotron-Radiation-Based Mössbauer Spectroscopy

Synchrotron-radiation based Mössbauer spectroscopy has become a useful technique capable for investigating various Mössbauer isotopes. For a typical experimental setup, the information associated with the pulse height (that is, energy) in an avalanche photodiode (APD) detector has not been used effectively. By using a system for simultaneous measurement system of time and energy associated with the APD signal, a system for the time- and energy-resolved Mössbauer spectroscopy has been developed. In this system, the pulse height information was converted to the time information through an amplitude-to-time converter applied to one of the divided signals from the APD. The corresponding time information was processed separately from another one of the divided signals. Both signals are recorded by a multi-channel scaler in an event-by-event data acquisition process. The velocity information from the Mössbauer transducer was also recorded as a tag for each signal event. Thus, the Mössbauer spectra with any time- and energy-window can be reconstructed after the data collection process. This system can be used for many purposes in time- and energy-resolved Mössbauer spectroscopy, and shows significant promise for use with other fast detectors and for various types of experiments.

Multichannel Photon Counting Lidar Measurements Using USB-based Digital Storage Oscilloscope

We present a simple method of making multichannel photon counting measurements of weak lidar signal from large ranges, using commonly available USB-based digital storage oscilloscopes. The single photon pulses from compact photomultiplier tubes are amplified and stretched so that the pulses are large and broad enough to be sampled efficiently by the USB oscilloscopes. A software interface written in Labview is then used to count the number of photon pulses in each of the prescribed time bins to form the histogram of LIDAR signal. This method presents a flexible alternative to the modular multichannel scalers and facilitate the development of sensitive lidar systems.

Kinetic Measurements of Singlet Oxygen Phosphorescence in Hydrogen-Free Solvents by Time-Resolved Photon Counting.

Solvents lacking hydrogen atoms are very convenient models for elucidating the properties of singlet oxygen, since the lifetime of singlet oxygen in these solvents reaches tens milliseconds. Measuring intrinsic infrared (IR) phosphorescence of singlet oxygen at 1270 nm is the most reliable method of singlet oxygen detection. However, efficient application of the phosphorescence method to these models requires an equipment allowing reliable measurement of the phosphorescence kinetic parameters in the millisecond time range at low rates of singlet oxygen generation, which is a technically difficult problem. Here, we describe a highly sensitive LED (laser) spectrometer recently constructed in our laboratory for the steady-state and time-resolved measurements of the millisecond phosphorescence of singlet oxygen. In the steady-state mode, this spectrometer allows detection of singlet oxygen phosphorescence upon direct excitation of oxygen molecules in the region of dark-red absorption bands at 690 and 765 nm. For kinetic measurements, we used phenalenone as a photosensitizer, microsecond pulses of violet (405 nm) LED for excitation (irradiance intensity, ≤50 μW/cm2), a photomultiplier and a computer multichannel scaler for time-resolved photon counting. The decays of singlet oxygen in air-saturated CCl4, C6F6, and Freon 113 and quenching of singlet oxygen by phenalenone and dissolved molecules of triplet oxygen were measured. The relative values of the radiative rate constants of singlet oxygen in these media were determined. The results were compared with the absorption coefficients of oxygen measured by our group using the methods of laser photochemistry. Critical discussion of the obtained results and the data of other researchers is presented.

Fluorescence Lifetime Spectroscopy of the Cornea using a Multichannel Scaler

An interface based on Multichannel scaler (MCS; SR430; Stanford Research Systems, USA) has been tested for enabling fluorescence lifetime measurements of pO2-sensitive fluorophores with a custom-made confocal scanning microfluorometer (CSMF) for transcorneal pO2 measurements. SR430 served as a transient photon counter. A trigger pulse, coincident with the rising edge of an excitation pulse for fluorescence, was coupled to accumulate emission pulses detected by a photomultiplier tube (PMT; R928 HA, Hamamatsu, Inc). The pulse started the photon counting and segmented the photon count data into consecutive time bins (ranging from 1 up to 32k), the width of which could be varied from 5 ns to 10.486 ms. With no dead time between bins, photon counting with the fluorescence decay is seamless. Silica-bound Ruthenium phenanthroline, dispersed in silicone rubber, was employed as a fluorophore sensitive to pO2. The test interface for CSMF-MCS system showed sensitive pO2 measurements and hence is suitable to measure local pO2 at any depth across the cornea.

Lifetime of the metastable P1/22 state of F-like Ar9+ isolated in a compact Penning trap

Multiply ionized atoms of a single charge state can be captured at low energy in a compact Penning trap, allowing the measurement of the radiative lifetime of an atomic state that decays via weakly allowed transitions. Such a measurement is reported here for the radiative decay lifetime of the metastable $^{2}P_{1/2}$ state in fluorinelike ${\mathrm{Ar}}^{9+}$, wherein the $n=2$ shell has only one vacancy (hole) in a $2p$ orbital. Highly ionized atoms are extracted from an electron beam ion trap and guided into the ion capture apparatus. Upon capturing the ${\mathrm{Ar}}^{9+}$ ions, light from the magnetic-dipole transition is detected with a photomultiplier tube and counted with a multichannel scaler. Using this technique, the radiative lifetime of the metastable $^{2}P_{1/2}$ state in ${\mathrm{Ar}}^{9+}\phantom{\rule{4pt}{0ex}}1{s}^{2}\phantom{\rule{0.16em}{0ex}}2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{5}$ is measured to be $\ensuremath{\tau}=9.31\ifmmode\pm\else\textpm\fi{}0.08$ ms, consistent with a previous intra-EBIT measurement.

Ion beam induced luminescence spectra of lithium fluoride at high-and low-temperature

A new ion beam induced luminescence (IBIL) measuring setup, equipped with a custom-made heating/cooling sample stage (the attainable temperature ranges from 80 K to 900 K), has been established on the GIC4117 tandem accelerator in Beijing Normal University. As the yield of back scattering ions is proportional to the beam flux, an Au-Si surface barrier detector is employed to count the back scattering ions synchronously with collecting the IBIL spectra under the multi-channel scaler (MCS) mode of the multichannel analyzer, making it possible to online monitor the beam current. Then, the yield of back scattering ions is used to correct the intensity of the IBIL spectrum and calculate the ion fluence, for eliminating the influence of the beam current fluctuation. IBIL spectra of pure lithium fluoride (LiF) at different temperatures (100, 200, 290, 450, 550 K) under the 2 MeV H+ irradiation are acquired and the significant influence of temperature on luminescence centers is observed. The emission bands relating to exciton recombination (296 and 340 nm) and impurities (400 nm) are more prominent at low temperatures and present quite lower intensities at high temperatures. Moreover, these luminescent intensities decay with ion fluence increase obviously at high temperatures after initially increasing in the early period of irradiation. The initial increase of the disturbed exciton peak at 296 nm can be attributed to the strained bonds produced by nuclear elastic scattering at a low fluence, which was not observed in previous IBIL measurements under high ionization energy density or high ion beam flux. This observed increase indicates that the emission feature may also originate from the emitting centers relating to point defects, not just from exciton transition near lattice or impurities. The luminescent intensities of F2 color centers (peaked at 670 nm) are dominant at all temperatures, while the luminescent intensities of F3+ color centers (peaked at 540 nm) are not obvious at low temperatures and the luminescent intensities of F3-/F2+ color centers (peaked at 880 nm) are weak at high temperatures. The luminescent intensities of these F-type centers reach saturated values at lower fluences at high temperatures. The different evolution behaviors under different temperatures can be due to the influence of temperature on the vacancy migration rate and the non-radiative recombination. In addition, the surface charge accumulation may lead to the luminescent intensities of color centers reaching saturated values at higher fluences, compared with the previous IBIL measurements of LiF. The self-absorption effect would reduce the intensities of F3+ color centers because of the absorption of F-type centers at low temperatures, while the effect is weak at high temperatures due to the degradation of F-type centers.

An improved Feynman-α analysis with a moving–bunching technique

ABSTRACTThe bunching technique has been widely utilized in Feynman-α neutron correlation analysis to synthesize neutron counts within longer gate widths by bunching time-sequence neutron counts stored in multichannel scaler channels. An alternative technique referred to as “moving–bunching technique” was proposed to reduce a statistical scatter of variance-to-mean ratio of neutron counts. The conventional bunching technique has no overlap of adjacent bunches, while the present technique makes adjacent bunches overlap as long as possible similarly to the moving average technique. A Feynman-α experiment was performed in the UTR-KINKI, to confirm the advantage of the proposed bunching technique. When a neutron detector was placed far from the core, a Feynman-α analysis with the conventional bunching technique led to a scattered variance-to-mean ratio from which the prompt-neutron decay constant was never determinable. However, another analysis with the proposed technique remarkably reduced the above scatter and enabled the determination of the decay constant. For a neutron detector close to the core, the proposed technique also reduced statistical error of the decay constant.

Development of a time-of-flight mass spectrometer combined with an ion-attachment method for multicomponent gas analysis

We developed a new mass spectrometer that can analyse multicomponent gases without fragmentation. This is essentially a time-of-flight (TOF) mass analyser in which the ion attachment method is used for ionisation. The method using this new device is referred to as “time-of-flight analysis in combination with ion-attachment” (TOFIA). TOFIA has the capability to analyse breath gas in about 10 min using the radio-frequency (RF) ion-guiding method and a multichannel scaler (MCS). The mass resolution of the trial device was unsatisfactory, but the device can be greatly improved in the future. We successfully analysed exhaled breath gases related to diseases, including ammonia, acetone, and isoprene gases. We expect that the TOFIA device developed in this work will contribute significantly to studies on the relationship between breath gas and health.

Implementation of High Dynamic Raman Lidar System for 3D Map of Particulate Optical Properties and Their Time Evolution

Fast scanning lidar system can provide aerosol volume distribution and time evolution in atmosphere. Usually fast scanning lidar has a relative simple configuration. Multiwavelength depolarization and Raman measurements gave us more information about the particulate shape, type and dimension. The most Raman lidars use high power laser source in order to get enough Raman scattering signal. One of a challenge for Raman lidar system is to have enough dynamic range to satisfy the measurements both for pure molecule Rayleigh scattering and high dene aerosol, such as dust storm, volcano emitted aerosol and high polluted urban aerosol. The estimation of microphysical properties requires independent measurements of both backscatter and extinction coefficient at several wavelengths (multiwavelength Raman lidar). Additional information can be retrieved from simultaneous measurements of the depolarization signal and water vapor mixing ratio, since those measurements are particularly useful to correlate aerosol optical properties with their shape and hygroscopicity. A multi-wavelength depolarization and Raman lidar system has been designed to perform volume scanning of the atmosphere and to retrieve high quality 3D map of particulate optical properties and their time evolution. This system is equipped with a doubled and tripled Nd:YAG diode-pumped laser that is specifically designed for this device, with a repetition rate of 1KHz and average optical power of 0.6W at 355nm, 1.5W at 532nm and 1W at 1064nm. The relative high repetition rate laser source can increase the detectable signal dynamic range. The receiving system is based on a 25cm modified Cassegrain telescope. The spectral selection of the backscatter elastic and Raman signals is made through a system of dichroic beam splitters and narrow band (0.5 nm) interferential filters. Fast single photon counting photomultipliers are used to collect the selected radiation. Each detected signal is acquired by multichannel scalers with a raw spatial resolution varying from 30cm to 30m. Moreover, polarization purity of laser line allows to perform polarization measurements at both 355 and 532nm. This device is installed in the Beijing city area, which is strongly affected from anthropogenic pollution and sand dust from Gobi desert.

Statistical analysis of fragmentation channels of small multicharged molecular ions

Laser-induced multiple ionization and Coulomb explosion of small molecules may lead on average to more than one fragmentation event per laser pulse even when experiments are performed at very low gas pressures in the 10−8–10−9 mbar range. In order to bypass the failure of coincidence techniques in this case, Frasinski et al (1989 Science 246 1029) proposed an alternative technique denoted covariance mapping based on correlated fluctuations of digitized ion signals coming from identical fragmentation channels. A probabilistic approach of the detected signals shows that covariance eliminates false coincidences due to fragments from different fragmentation channels, and false coincidences due to fragments from the same fragmentation channel, but which do not originate from the same unimolecular fragmentation events. The analysis is extended to devices which do not accept more than one count per time-of-flight bin such as multichannel scalers or time-to-digital converters. It is still possible to remove false coincidences using covariance but with a formulation which is noticeably different from the initial proposal for digitized signals.

Discriminator threshold selection logic to improve signal to noise ratio in photon counting

The discriminator threshold plays a vital role in photon counting technique used with low level light detection in lidars and bio-medical instruments. A low discriminator threshold gives high counts due to secondary emitted electrons and ground level (electrical) noise, while high threshold skips the photon pulses having lower amplitude. In both the cases the signal to noise ratio of photon counting system deteriorates. In this article the impact of improper selection of discriminator threshold on photon counting has been described. Here we introduce a simple technique by which the system (micro pulse lidar) selects the discriminator threshold at the set PMT voltage and assigns this value to the multi-channel scaler. The technique is applicable in diverse fields employing photon counting system.

Subunit Movements in Single Membrane-bound H+-ATP Synthases from Chloroplasts during ATP Synthesis

Subunit movements within the H(+)-ATP synthase from chloroplasts (CF(0)F(1)) are investigated during ATP synthesis. The gamma-subunit (gammaCys-322) is covalently labeled with a fluorescence donor (ATTO532). A fluorescence acceptor (adenosine 5'-(beta,gamma-imino)triphosphate (AMPPNP)-ATTO665) is noncovalently bound to a noncatalytic site at one alpha-subunit. The labeled CF(0)F(1) is integrated into liposomes, and a transmembrane pH difference is generated by an acid base transition. Single-pair fluorescence resonance energy transfer is measured in freely diffusing proteoliposomes with a confocal two-channel microscope. The fluorescence time traces reveal a repetitive three-step rotation of the gamma-subunit relative to the alpha-subunit during ATP synthesis. Some traces show splitting into sublevels with fluctuations between the sublevels. During catalysis the central stalk interacts, with equal probability, with each alphabeta-pair. Without catalysis the central stalk interacts with only one specific alphabeta-pair, and no stepping between FRET levels is observed. Two inactive states of the enzyme are identified: one in the presence of AMPPNP and one in the presence of ADP.

A portable high-field pulsed-magnet system for single-crystal x-ray scattering studies

We present a portable pulsed-magnet system for x-ray studies of materials in high magnetic fields (up to 30 T). The apparatus consists of a split-pair of minicoils cooled on a closed-cycle cryostat, which is used for x-ray diffraction studies with applied field normal to the scattering plane. A second independent closed-cycle cryostat is used for cooling the sample to near liquid helium temperatures. Pulsed magnetic fields (approximately 1 ms in total duration) are generated by discharging a configurable capacitor bank into the magnet coils. Time-resolved scattering data are collected using a combination of a fast single-photon counting detector, a multichannel scaler, and a high-resolution digital storage oscilloscope. The capabilities of this instrument are used to study a geometrically frustrated system revealing strong magnetostrictive effects in the spin-liquid state.

On the dead time problem of a GM counter

Characteristics of the dead time of a Geiger–Müller (GM) counter was studied by using a decaying source method and tests were performed for two-parameter dead time models including the general models. Activated 56Mn was used as the decaying source and the counting rates were observed in one minute steps for 20 half-lives using a GM probe and a multichannel scaler. Measured data were compared with predictions of a generalized dead time model, a dead time model of nonextending–extending (NE-E) types, and a model of extending–nonextending (E-NE) types in series. The NE–E series model described the measured counting rates better than the other models. The model rates were consistent with the data within 10% up to a true rate of ∼10 kcps, however, its application in the region of higher counting rates was limited. Possible causes of this limitation are discussed. For practical purposes, a phenomenological model is suggested to describe measured counting rates above ∼10 kcps.

Rossi-alpha experiment in the IPEN/MB-01 research reactor

One major objective of this work is to experimentally estimate the following kinetic parameters on the IPEN/MB-01 research reactor at São Paulo: the effective neutron delayed fraction, betaeff, the prompt neutron generation time, lambda, and the ratio betaeff/ lambda. In order to achieve our goal, we will use a microscopic noise technique called Rossi-alpha method. This method is based on the statistical nature of the fission-chain process. Using a coincidence acquisition system, the rationale is to experimentally determine the probability distribution of detecting neutrons from the same chain. Through a least-squares fit of this distribution we estimate the prompt neutron decay constant alpha = (betaeff-rho)/lambda. The alpha parameter will be measured for three sub-critical levels using three different source configurations, and the ratio betaeff/ lambda is obtained via a extrapolation to rho = 0. A specific acquisition system for Rossi-alpha measurements has been developed in order to achieve our objective. This system is based on a multichannel scaler controlled by virtual instruments that records the timing of all neutron events, allowing data analysis during the acquisition. The first measurements were performed using two BF3 detectors positioned at the center of IPEN/MB-01 reactor core. In the future the same measurements described above will be performed using ³He and photodiode detectors. The photodiode detectors have been developed by the Reactor Physics Division of IPEN. In this work we will present a preliminary set of Rossi-alpha measurements performed on the IPEN/MB-01 research reactor at São Paulo.

Portable active interrogation system

The system consists of a pulsed DT neutron generator (5×107n/s) and a portable but high intrinsic efficiency, custom-designed, polyethylene-moderated 3He neutron detector. A multichannel scaler card in a ruggedized laptop computer acquires the data. A user-friendly LabVIEW program analyzes and displays the data. The program displays a warning message when highly enriched uranium or any other fissionable materials is detected at a specified number of sigmas above background in the delayed region between pulses. This report describes the system and gives examples of the response of the system to highly enriched uranium and some other fissionable materials, at several distances and with various shielding materials.

Multiparameter segmented scan multichannel scaling system

A PC based data acquisition cum control system has been developed using a general purpose interface bus (GPIB/IEEE-488/IEC-625) plug in card and GPIB interfaceable NIM electronics for use in experiments on absorption spectroscopy studies of molecules using laser-induced fluorescence (LIF), resonance multiphoton ionization (REMPI), electron impact ionization and dissociative attachment from the ground state as well as from excited states, to name a few examples. Unlike commercially available multichannel scalers, this system can handle several parameters as the acquisition parameter (e.g., dye laser) is scanned over the desired wavelength in preselected segments saving precious data acquisition time. This system has been tested on laser excited dissociative electron attachment experiments.

An automated fast transfer system at the research reactor Munich

An automated fast sample transfer system for the determination of measurements of short-lived isotopes has been constructed at the Research Reactor Munich FRM. Instrumental neutron activation analysis and analysis of fissile materials by delayed neutron counting are performed on this transfer device. A LabVIEW TM program on a PC with WindowsNT operating system controls the whole pneumatic system via a PCI-1200 interface and four signal conditioning SCXI-modules of National Instruments. Infrared sensors are used to monitor key points in the transfer system. The sample capsule can be automatically removed from the “rabbit” in a special switch prior to spectrum collection. γ-Spectra are acquired by a HPGe detector with the Loss-Free-Counting method of Westphal. The delayed neutrons are measured by five 3He-detectors and a multichannel scaler. The transfer time is about 200 ms . The system and its mode of operation for routine work will be described.

Measurement of subcritical reactivity in unsteady state with Digital Time-Series Data Acquisition System using difference filter technique

The Digital Time-Series Data Acquisition System using first-in-first-out (FIFO) memory module has been developed for the monitoring of subcritical reactivity. The system records arriving time of the signal from a neutron detector, and time-series data are saved in a personal computer (PC). Using this system, the measurement of time-series data is carried out more efficiently than that using a conventional multichannel scaler (MCS) system, and it has been applied for the monitoring of subcritical reactivity of the reactor in a steady state using the conventional Feynman-/spl alpha/ technique. In the present work, this system was applied for the monitoring of subcritical reactivity in an unsteady state using the difference filter technique. The test experiment was carried out with the research reactor of Atomic Energy Institute of Kinki University, Japan. From the experimental results, it was shown that the present system was useful for the continuous monitoring of varying subcritical reactivity by application of the difference filter technique.