Ultrasensitive method for measuring isotope abundance ratios

A method for measuring the isotope abundance ratio between a selected isotope and at least one other isotope having a different atomic mass or atomic number in a sample of a given chemical element, said abundance measuring method being capable of determining ultrasensitive abundance ratios, said method comprising:

• producing a vapor of certain atoms/molecules of said sample of said chemical element;
• preferentially ionizing said at least one other isotope by Doppler-free resonant multiphoton ionization using a first laser beam of at least one selected frequency to achieve said ionization of said at least one other isotope, said frequency of said first laser beam including a frequency offset in proportion to the intensity of said first laser beam, said offset being of a value sufficient to overcome loss in abundance sensitivity due to the AC Stark shift;
• electrostatically removing said ions of said at least one other isotope to achieve a prefiltering removal of a major fraction of said at least one other isotope and thereby enhance an abundance ratio between said selected isotope and said at least one other isotope prior to said ionization of said selected isotope;
• preferentially ionizing said selected isotope within said vapor by Doppler-free resonant multiphoton ionization using a second laser beam of at least one selected frequency to achieve said ionization, said frequency of said second laser beam including a frequency offset in proportion to the intensity of said second laser beam, said offset being of a value sufficient to overcome loss in abundance sensitivity due to AC Stark shifts;
• injecting ions produced by said ionization into a mass spectrometer;
• performing isotopic spectrum analysis of said ions by said mass spectrometer;
• and
• detecting ions analyzed by said mass spectrometer to determine said isotope abundance ratio between said selected isotope and said at least one other isotope.

A method for measuring the isotope abundance ratio between a selected isotope and at least one other isotope having a different atomic mass or atomic number in a sample of a given chemical element, said abundance measuring method being capable of determining ultrasensitive abundance ratios, said method comprising:

• producing a vapor of certain atoms/molecules of said sample of said chemical element;
• preferentially ionizing said at least one other isotope by Doppler-free resonant multiphoton ionization using a first laser beam of at least one selected frequency to achieve said ionization of said at least one other isotope, said frequency of said first laser beam including a frequency offset in proportion to the intensity of said second laser beam, said offset being of a value sufficient to overcome loss in abundance sensitivity due to AC Stark Shifts;
• electrostatically removing said ions of said at least one other isotope to achieve a prefiltering removal of a major fraction of said at least one other isotope and thereby enhance an abundance ratio beween said selected isotope and said at least one other isotope prior to said ionization of said selected isotope;
• preferentially ionizing said selected isotope within said vapor by Doppler-free resonant multiphoton ionization using a second laser beam of at least one selected frequency to achieve said ionization, said frequency of said second laser beam including a frequency offset in proportion to the intensity of said second laser beam, said offset being of a value sufficient to overcome loss in abundance sensitivity due to AC Stark shifts:
• preferentially ionizing said ions of selected isotope by Doppler-free resonant multiphoton ionization using a third lazer beam of at least one selected frequency to achieve said ionization, said frequency of said third laser beam including a frequency offset in proportion to the intensity of said third laser beam, said offset being sufficient to overcome loss in abundance sensitivity caused by AC Stark shifts;
• injecting ions produced by said ionization into a mass spectrometer;
• performing isotopic spectrum analysis of said ions by said mass spectrometer;
• and
• detecting ions analyzed by said mass spectrometer to determine said isotope abundance ratio between said selected isotope and said at least one other isotope.

A method for measuring the isotope abundance ratio between a selected isotope and at least one other isotope having a different atomic mass or atomic number in a sample of a given chemical element, said abundance measuring method being capable of determing ultrasensitive abundance ratios, said method comprising;

• producing a vapor of certain atoms/molecules of said sample of said chemical element;
• preferentially ionizing said at least one other isotope by Doppler-free resonant multiphoton ionization using a first laser beam of at least one selected frequency;
• electrostatically removing at least a portion of said ions of said at least one other isotope to achieve a prefiltering removal of a major fraction of said at least one other isotope and thereby enchance an abundance ratio between said selected isotope and said at least one other isotope;
• preferentially ionizing said selected isotope within said vapor by Doppler-free resonant multiphoton ionization using a second laser beam of at least one selected frequency to achieve said ionization, said second laser frequency including a frequency offset in proportion to the intensity of said second laser beam, said offset being of a value sufficient to overcome loss in abundance sensitivity due to AC Stark shifts caused by time-varying laser intensity;
• injecting ions produced by said ionization of said selected isotope into a mass spectrometer;
• performing isotopic spectrum analysis of said ions by said mass spectrometer;
• and
• detecting ions analyzed by said mass spectrometer to determined said isotope abundance ratio between said selected isotope and said at least one other isotope.