Search

The mass spectrometer for planetary exploration (MASPEX) is a versatile mass spectrometer with unprecedented mass resolution designed for spaceflight. However, the current version of MASPEX is desi...

In this paper, we examine the history of detection efficiency measurements of photons (soft to hard X-rays and beyond) with microchannel plates (MCPs). We investigate the detection efficiency as a function of photon energy over a wide energy range, from a few hundred eVs up to 20 MeV. We also investigate detection efficiency as a function of incident angle onto the MCP. We interpreted the published efficiency data measured with a variety of MCPs and the use of MCP coatings for enhancement of X-ray quantum detection efficiency, and discuss theoretical expectations based on the main photon interactions with matter: the photoelectric effect, Compton scattering, and pair production. Contributing to the published literature at the highest end of the energy range, we also discuss our photon detection efficiency experiments from 2.5 to 20 MeV and theoretical implications.

Southwest Research Institute investigated the response of a microchannel plate (MCP) detector to isotropic radioactive source emissions at photon energies of 0.662 and approximately 1.25 million electronvolts (MeV) and to a beam of monoenergetic photons (gamma rays) at 2.5, 5, 7, 10, 13, and 20 MeV in the Free Electron Laser Laboratory at Duke University. These measurements were performed to quantify anticipated noise levels of a mass spectrometer instrument for space exploration in a harsh radiation environment and included various incident angles of radiation on the MCP. Measured photon detection efficiencies at 0° incident angle to 0.662 and 1.25 MeV were approximately 0.3%–0.4% and are bracketed by previously published data. In the 2.5- to 20-MeV energy range for which comparable published data are not available, measured detection efficiencies were on the order of 0.02%–0.2%. Radiation transport simulations were compared to the experimental results and showed decent agreement. The measured detection efficiency increased as the incident photon angle was changed from being normal to the MCP surface (0°) to being aligned with the MCP edge (90°). At greater off-axis angles, photons were incident on the side of the detector cartridge and generated secondary radiation from photon interactions in the cartridge materials that subsequently registered MCP counts.

An unshielded microchannel plate detector was irradiated by an electron beam to determine the detection efficiency of electrons to create a detector signal or counts. Tested electron energies spanned a range of 400 kiloelectron volts to 2.6 million electron volts (MeV). Detection efficiency was found to decrease as the electron energy increased and ranged between 0.18 and 0.05 counts per incident electron, at 0.4 and 2.6 MeV, respectively. Simulations of beam losses over the experimental geometry were performed with MCNP6, and found to be similar in magnitude and possess a similar dependence over incident electron energy as the experimentally determined beam loss from beam current measurements. Detection efficiency as a function of incident angle of the electrons was also tested and relatively insignificant changes were observed. For the three beam energies and angles tested, deviation of the measured detection efficiency was 16%–22% (basically within the overlapping error bars of each measurement).

Mass spectrometry is a powerful tool to measure the composition of volatile and semi volatile gases. The necessity to accurately identify and quantify unknown species lead to the requirements of a mass spectrometer as the detector of choice in most separation science and direct sample analysis situations. Advantages of time-of-flight mass spectrometry (TOFMS) are the high mass resolution, high mass range, and the measurement of the entire mass range in each extraction. The multi-bounce time-of-flight mass spectrometer (MBTOF) described in this work, takes advantage of a small footprint without sacrificing mass resolution. To achieve this, the MBTOF prototype uses a linear flight path with dual lens stacks. Ions are bounced in between the mirrors for a specified duration whereby increasing their flight time and resolution. The number of bounces can tune the resolution of the instrument. To show the minimum capabilities of the instrument and further applications of it, MBTOF was operated in linear mode. The instrument is designed for a multibounce passage of the ion optics and the focal point of the ion optics is optimized for this application, therefore the resolution in linear mode is limited. However, even in linear mode of operation, the mass resolution meets or exceeds that of a quadrupole mass spectrometer with limited power supplies required for operations. The measurements presented here are based on lab measurements of the early lab prototype MBTOF operated in a linear flight mode with low ion source extraction fields. A detailed evaluation including filament characterization, dynamic range and resolution are investigated. Further discussion involving applications on planetary missions for rocket science, coupling of MBTOF with laser thermal desorption or gas chromatography for potential organic determination in deep space are included.

The Jovian system is the focus of multiple current and future NASA and ESA missions, but dangerously high radiation levels surrounding the planet make operations of instruments sensitive to high energy electrons or gamma rays problematic. Microchannel plate (MCP) detectors have been the detectors of choice in planetary ultraviolet spectrographs for decades. However, the same properties that give these detectors high response to vacuum ultraviolet photons also make them sensitive to high energy electrons and gamma rays. The success of ultraviolet investigations in the Jovian system depends on effectively shielding these MCP detectors to protect them as much as possible from this withering radiation. The design of such shielding hinges on our understanding of the response of MCP detectors to the high energy electrons and gamma rays found there. To this end, Southwest Research Institute and Massachusetts Institute of Technology collaborated in 2012-13 to measure the response of a flight-spare microchannel plate detector to a beam of high energy electrons. The detector response was measured at multiple beam energies ranging from 0.5-2.5 MeV and multiple currents. This response was then checked with MCNP6, a radiation transport simulation tool, to determine the secondary gamma rays produced by the primary electrons striking the detector window. We report on the measurement approach and the inferred electron and gamma sensitivities.

A compact E × B mass spectrometer is presented. The mass spectrometer presented is termed a "perfect focus" mass spectrometer as the resolution of the device is independent of both the initial direction and energy of the ions (spatial and energy independent). The mass spectrometer is small in size (∼10.7 in.(3)) and weight (∼2 kg), making it an attractive candidate for portability when using small, permanent magnets. A multi-collector Faraday cup design allows for the detection of multiple ion beams in discrete collectors simultaneously; providing the opportunity for isotope ratio monitoring. The mass resolution of the device is around 400 through narrow collector slits and the sensitivity of the device follows expected theoretical calculations of the ion current produced in the electron impact ion source. Example mass spectra obtained from the cycloidal focusing mass spectrometer are presented as well as information on mass discrimination based on instrumental parameters and isotope ratio monitoring of certain ion signals in separate Faraday cups.

A new technique for investigating the surface plasmons by means of a scanning acoustic microscope is proposed. Within this technique, the surface electromagnetic wave (plasmon polariton) is excited by laser radiation on one side of a metal film, while a scanning acoustic microscope excites surface acoustic waves on the other side of the film. Obtained for the first time, the acoustic images of plasmons, propagating on the grating surface, demonstrate the possibility of studying the plasmon wave field distribution by means of a scanning acoustic microscope.