Biomedical subjects

G D Danilatos

Publications and source records attributed to G D Danilatos.

5 recordsLinked to original sources

PubMed2000

Radiofrequency Gaseous Detection Device.

A radiofrequency gaseous detection device is proposed for use with instruments employing charged particle beams, such as electron microscopes and ion beam technologies, as well as for detection of ionizing radiations as in proportional counters. An alternating (oscillating) electromagnetic field in the radiofrequency range is applied in a gaseous environment of the instrument. Both the frequency and amplitude of oscillation are adjustable. The electron or ion beam interacts with a specimen and releases free electrons in the gas. Similarly, an ionizing radiation source releases free electrons in the gas. The free electrons are acted upon by the alternating electromagnetic field and undergo an oscillatory motion resulting in multiple collisions with the gas molecules, or atoms. At sufficiently low pressures, the oscillating electrons also collide with surrounding walls. These processes result in an amplified electron signal and an amplified photon signal in a controlled discharge. The amplified signals, which are proportional to the initial number of free electrons, are collected by suitable means for further processing and analysis.

Journal Article↗

PubMed2000

Reverse Flow Pressure Limiting Aperture.

The reverse flow pressure limiting aperture is a device that creates and sustains a substantial gas pressure difference between two chambers connected via an aperture. The aperture is surrounded by an annular orifice leading to a third chamber. The third chamber is maintained at a relatively high pressure that forces gas to flow through the annular aperture into the first of said two chambers. The ensuing gas flow develops into a supersonic annular gas jet, the core of which is coaxial with the central aperture. A pumping action is created at the core of the jet and any gas molecules leaking through the aperture from the second chamber are entrained and forced into the first chamber, thus creating a substantial pressure difference between the first and second chamber.

Journal Article↗

PubMed1993

Introduction to the ESEM instrument.

An outline is presented of the first commercial environmental scanning electron microscope (ESEM). A concise description of this instrument and its operation, from a user's perspective, is given. More specifically, the description includes the electron optics, pressure stages and control, detection modes, resolution, and ancillary equipment.

Equipment Design↗

PubMed1993

Bibliography of environmental scanning electron microscopy.

Two updated lists of publications on environmental scanning electron microscopy are compiled. One list contains mainly those papers dealing with the development and instrumentation, while the other deals mainly with the applications of the technique. A brief introductory summary of the field is presented.

Microscopy, Electron, Scanning↗

PubMed1982

The environmental scanning electron microscope and its applications.

An environmental scanning electron microscope can be made by incorporating a pressure limiting aperture at some distance below the objective aperture of an SEM, and by providing independent pumping between these two apertures. Tilting of the pressure limiting aperture with respect to the axis of the electron optics column redirects the gas jet which develops above the pressure limiting aperture and which otherwise would inject excessive gas through the objective aperture into the column. The detection of backscattered and multiple-backscattered electrons is achieved below the pressure limiting aperture in the region confined by the sample, the detector and the aperture grid. Wet specimens can be examined in the environmental scanning electron microscope at 7kV and TV rates by placing them at a sufficiently close distance to the pressure limiting aperture. Live seedlings and ants have been observed in this way. Wet (fresh) rat tissues, wool fibers subjected to various treatments, crystallization and rewetting of salts, and some radiation effects have been observed and recorded under the environmental scanning electron microscope. Examination of specimens in the full pressure range, 0-1013 mbar, is possible. A detector-aperture system which will allow the signal originating from the sample to be detected simultaneously both below and above the aperture is under construction. Further development of environmental scanning electron microscopy now depends upon close co-ordination between microscope manufacturers and research groups involved in such fields as biology, fiber technology, radiation and physical chemistry.

Animals↗