Atom Sciences, Inc.

Tom J Whitaker

Thomas B Lucatorto

Charles W Clark

Harold W Schmitt

Norbert Thonnard

G Samuel Hurst

An ultrasensitive mass spectrometry method based on multiphoton sub-Doppler resonance ionization to measure abundance sensitivities. The method preferentially ionizes a selected isotope in a sample by using Doppler-free resonant multiphoton ionization to produce an enhanced ratio of selected isotopes. Background species are separately ionized and rejected. As necessary or desired, selected isotope ions are preferentially ionized by using a second Doppler-free resonant multiphoton ionization to provide an additional isotope enhancement. The ions produced are injected into a mass spectrometer. Isotopic spectrum analysis of the ions is performed by the spectrometer and the ions are then detected by a detector such as a particular photon multiplier capable of observing a single ion. In one embodiment, at least one of the steps of preferentially ionizing the selected isotope is accomplished by two counter propagating laser beams of slightly different frequencies. Further improved sensitivity is achieved by: (1) using a frequency offset of the laser frequency in an amount proportional to the laser intensity to overcome AC Stark shifts, and (2) withdrawing ions for mass separation from only the central portion of the laser interaction volume.

Ultrasensitive method for measuring isotope abundance ratios

A dosimeter which incorporates new methods for determining neutron dose. Less than one millirad of dose due to neutrons of all energies down to approximately 10.sup.3 eV can be measured, and the response can be adjusted by design of the dosimeter. The dosimeter utilizes the sputtering of material from a target due to the action of the neutrons and measuring of the amount of sputtered material to determine the dose. The sputtered material may be, for example, a noble gas or an inert solid. Various radiator materials can be included to interact with the neutrons so that the resulting charged particles control the sputtering process and hereby increase the sensitivity of the dosimeter. The target material can be, for example, noble-gas-impregnated polycrystalline or amorphous metals. The sputtered material is analyzed using resonance ionization spectroscopy, sputter-initiated resonance ionization spectroscopy or other methods to determine its quantity and hence the neutron dose. Applications include, but are not limited to, personnel neutron dosimetry and stationary neutron monitors.

Neutron dosimeter

An ultrasensitive mass spectrometry method based on multiphoton sub-Doppler resonance ionization is used to measure abundance sensitivities. The method preferentially ionizes a selected isotope in a sample by using Doppler-free resonant multiphoton ionization to produce an enhanced ratio of selected isotopes. As necessary or desired, selected isotope ions are preferentially ionized by using a second Doppler-free resonant multiphoton ionization to provide an additional isotope enhancement. The ions produced are injected into a mass spectrometer (24). Isotopic spectrum analysis of the ions is performed by the spectrometer (24) and the ions are then detected by a detector (26) such as a particular photon multiplier capable of observing a single ion. In one embodiment, at least one of the steps of preferentially ionizing the selected isotope is accomplished by two counter propagating laser beams of slightly different frequencies.

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Benton County, WA, United States of America

Tom J Whitaker