Multichannel Plate Detector Research Articles

Absolute calibration of a multichannel plate detector for low energy O, O−, and O+

Absolute detection efficiencies of a commercial multichannel plate detector have been measured for O, O+, and O−, impacting at normal incidence for energies ranging from 30–1000 eV. In addition, the detection efficiencies for O relative to its ions are presented, as they may have a more universal application. The absolute detection efficiencies are strongly energy dependent and significant differences are observed for the various charge states at lower energies. The detection efficiencies for the different charge states appear to converge at higher energies. The strongest energy dependence is for O+; the detection efficiency varies by three orders of magnitude across the energy range studied. The weakest dependence is for O−, which varies less than one order of magnitude.

Mass spectrometer calibration of high velocity impact ionization based cosmic dust analyzer

We are calibrating the time of flight mass spectrometer of the Cosmic Dust Analyzer (CDA) instrument aboard the Cassini spacecraft. The CDA measures the flux of particles in the 10 −15 to 10 −9 g range at intersection velocities of up to 100 km/s. Of special interest are the chemical composition of the particles in orbit about Saturn and/or its satellites that are expected to be captured by CDA during ring plane crossings and upon close encounter with the satellites. Upon impacting a rhodium plate, particles are expected to partially ionize and their chemical composition is expected to be determined from mass analysis of the positive ions. In order to optimize impact ionization calibration experiments using a light gas-gun launched microspheric particles, we have done initial testing with a short duration pulsed laser (4 ns duration nitrogen laser (337 nm)). The beam is focused to deliver the 300μJ energy per laser pulse onto a 33 μm 2. The laser power density (≈10 10 W/cm 2) simulates the impact of particles with various combinations of density and velocities, e.g., 8 g/cm 3 (Fe) projectile at 23 km/s or 1 g/cm 3 projectile at 65 km/s. The CDA spectrometer will operate in the near vacuum of Saturnian zone environment is housed in a laboratory chamber at 10 −6 mbar. The ions and electrons are separated by 680 V between target and grid. The laser ionization produces charge of 4.6pC (mostly Al +1) in aluminum and 2.8pC (Fe +1) in stainless steel. Estimating that each Al +1 and Fe +1 ion requires an energy of 5.98 and 7.90 eV/ion implies that ∼10 −5 % of the laser pulse energy produces ions and the present system has a 10% detection efficiency. Using multi-channel plate detector to detect ions from aluminum alloy and kamacite yields well defined peaks at 24(Mg +1), 27(Al +1) and 64 (Cu +1), and, 56(Fe +1), 58(Ni +1) and 60(Ni +1) amu, respectively. Also contaminant ions at 23 (Na +1) and 39(K +1) amu are detected.

A data-acquisition card without dead time

The knowledge of the ion beam profile in a storage ring is vital and it is measured by a position-sensitive detector. Co-ordinates of hit locations on the anodes of two multi-channel plate (MCP) detectors (one in horizontal and the other in vertical direction) are collected. Task sharing between software and hardware, including dual-buffer memory-management as implemented in the data-acquisition card described here, eliminates acquisition dead time.

Resonance ionization mass spectroscopy for trace determination of plutonium in environmental samples

Resonance ionization mass spectroscopy (RIMS) is a sensitive and isotope selective method and well suited for trace analysis of plutonium in the environment. After the chemical isolation of plutonium from soil, air filters or urine, e.g., it is electrolytically deposited as hydroxide on a tantalum backing and covered with a thin titanium layer. By heating such a sandwich filament in the RIMS-apparatus under vacuum an atomic beam of plutonium is produced. The atoms are ionized by a three-step resonant excitation using pulsed dye lasers, and the ions are mass-selectively detected with a time-of-flight (TOF) spectrometer and a multi channel plate detector. RIMS yields a low detection limit of 106–107 atoms and a high element and isotope selectivity. This technique has been used for the investigation of soil samples from the Chernobyl area, sediments from the Mururoa Atoll and urine samples with respect to the total amount of plutonium and its isotopic composition.

Mass Discrimination in the Analysis of Polydisperse Polymers by MALDI Time-of-Flight Mass Spectrometry. 2. Instrumental Issues

Mass discrimination is generally observed in the analysis of polydisperse polymers by matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry. Using multicomponent blends of polystyrene of narrow polydispersity, instrumental effects on the mass analysis of polydisperse polymers were investigated in a time-lag focusing linear TOF mass spectrometer. It is shown that the lensing action provided by the source electrodes in TOF gives rise to a mass-dependent distribution of ions in the plane of the microchannel plate detector. Therefore, the size of the detector aperture must be sufficient to ensure acceptance of the full ion packet. This distribution is also affected by the choice of push-out pulse delay. For the mass range investigated, ion detection with the use of a multichannel plate detector results from a combination of primary ion to electron conversion, as well as secondary ion to electron conversion. Both processes are shown to give rise to different influences on the measured Mn values of the polystyrene blends. Detector saturation also adds to the observed mass discrimination, due mainly to the saturation caused by matrix species. The issue regarding preservation of the measured polymer distribution function in data presentation is also discussed.

X-ray intensity interferometer for undulator radiation

Abstract Intensity interferometry is well established with visible light but has never been demonstrated with X-radiation. We propose to measure the transverse coherence of an X-ray beam using the method of Hanbury Brown and Twiss. The X-ray interferometer consists of an array of slits, a grazing incidence reflective beam splitter, a pair of fast multichannel plate detectors and a broadband, low-noise correlator circuit. The NSLS X1 or X13 soft X-ray undulator will supply the partially coherent X-rays. We are developing this technique to characterize the coherence properties of X-ray beams from high brilliance insertion devices at third-generation synchrotron light facilities such as the Advanced Photon Source and the Advanced Light Source.

Improving the signal-to-noise ratio of backscattered electron detectors at low beam accelerating voltages

At high beam accelerating voltages, >5kV, backscattered electron (BSE) detectors rely upon the energy of the BSEs to generate the signal. At low beam accelerating voltages, BSEs do not have sufficient energy to generate a strong signal. This is further compounded because the electrons lose energy penetrating through a thin metal film, which is a dead layer on the surface of the detector. Noise bottleneck considerations1show that the bottleneck for the detection of low energy BSEs, is the signal generated when they impinge upon the detector. Consequently, the signal has to be enhanced before it is amplified. One method of achieving this is to use a multi-channel plate detector. Another is to increase the energy of the BSEs, prior to them impinging upon the detector. This can be acheived by accelerating the BSEs. after they emerge from the specimen, through the application of a positive voltage to the surface of the detector.

Droplet emission from a gallium liquid metal ion source as observed with an ion streak camera

Droplets emitted from a gallium liquid metal ion source have been observed using an ion streak camera. The camera records the angle and time of arrival of individual atomic ions at a chevron multichannel plate detector (MCP) with a minimum time resolution of ∼30 ns. The ion hits are recorded with a charge coupled device (CCD) camera observing light from the MCP. Individual droplets are recorded as shadows in the image produced by the broad gallium atomic ion beam. Droplet shadows have large angular widths at times immediately after droplet creation and shrink rapidly in angle with increasing time as the droplets move away from the emitting tip. Associated with each droplet streak is a momentary decrease in atomic ion emission at all angles, as might be anticipated from the perturbation produced by the emission of a droplet. The shape of a droplet streak has been modeled by geometrical shadowing and by Coulomb repulsion shadowing between the droplet and the atomic ions. Through nonlinear fitting methods, both the mass and charge of the droplet may be deduced from this model. Results show that the charge on most large droplets is substantially below the Rayleigh limiting charge. The momentary decreases in atomic ion emission at all angles are roughly periodic under some emission conditions.

Single photon counting imagery.

AbstractAdvent of the multichannel plate and position sensitive detector has made possible true single photon counting imaging tubes. We have investigated the application of these detectors in studies of the ultraweak light emission of biological materials. Initially, we focussed our efforts on two objectives: (1) obtaining single photon counting images of living tissues using only the light (chemiluminescence) emitted by the specimen and (2) developing means of obtaining well‐resolved spectra of weakly emitting sources. We have obtained a variety of images. One striking result of this work is the first observation of tissue specific localization of photon emission in situ. Using this detector we have also obtained the first well‐resolved spectra of some important ultraweak emission processes. These results illustrate the potential use of single photon imaging in bioluminescence and chemiluminescence research.

Fast multichannel time correlator for coincidence experiments in atomic physics

Use of multichannel plate detectors has considerably extended the experimental techniques in atomic physics. In this context, a coincidence circuitry able to determine 64 simultaneous coincidence spectra is described. Use of fast electronic devices and separated amplifiers allows a high counting rate capability (5×105 events per second) with a time resolution of 3.1 ns. UV photon-scattered particle coincidence in He–He collisions is given as an example of the application of the present apparatus.