Atom Sciences, Inc.

The United States of America As Represented by the United States Energy

Marvin G Payne

George S Hurst

James E Parks

Chung-Hsuan Chen

G Samuel Hurst

Norbert Thonnard

Edward B Wagner

An improved method of operating a time-of-flight mass spectrometer. This method, which involves double pulsing, achieves an increase in the resolution of TOF mass spectrometers by compensating for the energy spread of the species extracted from the source and thus the time spread of ions of a specific mass arriving at a detector. According to this improved method, atoms (or molecules) for analysis are rapidly removed from a surface at a first well defined time. These atoms or molecules are then rapidly ionized at a location or region a distance, R, from the surface at a second well defined time after a selected time delay, T.sub.o. The resultant ions first move through a region of uniform electric field of a distance, S.sub.1, and then into a field-free region having a length, S.sub.2, Lastly, ions leaving the field-free region enter a short high energy accelerating region so as to impinge upon an ion detector. The output signal of the detector, as a function of arrival time, is an indication of the mass distribution of the ions and thus the analysis of the atoms or molecules. A proper choice of the uniform electric field and parameters R, S.sub. 1, S.sub.2 and T.sub.o provide compensation for the energy spread of ionized species and thus a reduction in time spread of ions at the detector. Certain special cases for enhanced resolution are described, as well as operation of the TOF according to the improved method to achieve atom enrichment of a specific mass.

Double pulsed time-of-flight mass spectrometer

Apparatus and methods of operation are described for determining, with isotopic selectivity, the number of noble gas atoms in a sample. The analysis is conducted within an evacuated chamber which can be isolated by a valve from a vacuum pumping system capable of producing a pressure of 10.sup.-8 Torr. Provision is made to pass pulses of laser beams through the chamber, these pulses having wavelengths appropriate for the resonance ionization of atoms of the noble gas under analysis. A mass filter within the chamber selects ions of a specific isotope of the noble gas, and means are provided to accelerate these selected ions sufficiently for implantation into a target. Specific types of targets are discussed. An electron measuring device produces a signal relatable to the number of ions implanted into the target and thus to the number of atoms of the selected isotope of the noble gas removed from the gas sample. The measurement can be continued until a substantial fraction, or all, of the atoms in the sample have been counted. Furthermore, additional embodiments of the apparatus are described for bunching the atoms of a noble gas for more rapid analysis, and for changing the target for repetitive cycling of the gas in the chamber. The number of repetitions of the cyclic steps depend upon the concentration of the isotope of interest, the separative efficiency of the mass filter, etc. The cycles are continued until a desired selectivity is achieved. Also described are components and a method of operation for a pre-enrichment operation for use when an introduction of a total sample would elevate the pressure within the chamber to levels in excess of those for operation of the mass filter, specifically a quadrupole mass filter. Specific examples of three noble gas isotope analyses are described.

Method and apparatus for noble gas atom detection with isotopic

This invention relates to a method for the sensitive and selective analysis of an atomic or molecular component of a gas. According to this method, the desired neutral component is ionized by one or more resonance photon absorptions, and the resultant ions are measured in a sensitive counter. Numerous energy pathways are described for accomplishing the ionization including the use of one or two tunable pulsed dye lasers.

Resonance ionization for analytical spectroscopy

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Harriman, TN, United States of America

Marvin G Payne