G. S. Hurst

A demonstration of one-atom detection

Resonance ionization spectroscopy, a photoionization method in which all of a given quantum selected species are converted to ion pairs, has been used to develop a detector for a single atom. We have demonstrated the detection of one atom by using a pulsed dye laser to photoionize Cs to saturation and a proportional counter for the detection of single electrons. Some current applications, e.g., the slow transport and chemical reactions of atoms, are briefly discussed. Future applications may include the detection of rare events such as quarks, solar neutrinos, and superheavy elements.

Direct counting of Xe atoms

Abstract Resonance ionization spectroscopy (RIS) is making possible direct counting of inert-gas atoms. Results for Xe are presented along with considerations involved in generalizing to other inert gases. Various applications of counters for inert-gas atoms are described.

Energy transfer from argon resonance states to nitrogen, hydrogen, and nitric oxide

Transfer of electronic energy from the resonance states Ar(1P1) and Ar(3P1) to diatomic nitrogen, hydrogen, and nitric oxide has been studied with a time‐resolved quenching technique. Rate constants for energy transfer were deduced from the changes of the rate of decay of excited states corresponding to known changes of the density of the diatomic molecules. For Ar*–N2 the rate constants were 5.4×10−11 and 0.8×10−11 molecule−1⋅cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively. For Ar*–H2, the measured rate constants were 22×10−11 and 21×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), repectively. The results for nitric oxide were 54×210−11 and 32×10−11 molecule−1 cm3 sec−1 for Ar(1P1) and Ar(3P1), respectively.

A sensitive, absolute, and time-resolved method for the study of reactive atoms

Abstract Laser techniques for the production of free atoms at time t = 0 and their detection at r > 0 have been developed to measure the diffusion of Cs atoms in Ar and the reaction of Cs with O 2 in Ar gas.

One-atom detection in individual ionization tracks.

A major advance in one-atom detection using laser photoionization makes it possible to detect with microsecond time resolution single neutral atoms resulting from the stopping of energetic heavy ions in a buffer gas. This detection at the one-atom level, which gives the first direct evidence of nearly complete charge neutralization of stopped energetic ions, is shown to be possible even under the extremely adverse conditions associated with a densely ionized particle track.

Development of an atom buncher

An ‘‘atom buncher’’ for controlling the concentration of gaseous samples has been conceptualized, evaluated theoretically, fabricated, and tested with excellent results. In effect, the atom buncher greatly increases the probability that a free atom will be in a small detector volume at a desired time. This was accomplished by using cryogenic techniques to condense atoms on a small spot and a pulsed laser to momentarily heat the spot to release the atoms at the desired time. Our work on noble gas atom counting by using resonance ionization spectroscopy is discussed as one example of the applications of the atom buncher.

Saturated photodissociation of CsI

Abstract Every CsI molecule in a small volume was photodissociated with a laser pulse; a second pulsed laser detected each Cs atom through resonance ionization spectroscopy. Besides proving one-molecule detection, we obtained cross sections for photodissociation of CsI as a function of wavelength.

Kinetic studies of N2 and N2–SF6 following proton excitation

Low intensity proton pulses have been used to excite pure N2 and N2–SF6 mixtures. By accumulating time and wavelength resolved information on the fluorescence that arises from a very large number of pulses, we have obtained data that are free from effects due to superelastic collisions with electrons or other nonlinear effects such as the interactions between ions or excited neutral species. For N2 the natural lifetimes of N2(C 3Πu) and N2+(B 2Σu+) were determined by monitoring N2(C 3Πu→B 3Πg) and N2+ (B 2Σu+→X 2Σg+) states, respectively. The quenching rates of N2(C 3Πu) and N2+(B 2Σu+) in different vibrational states by pure N2 and by SF6 were obtained. The addition of small concentrations of SF6 altered the late time behavior of the N2(C 3Πu→B 3Πg) transitions, and the addition of much higher concentrations of SF6 caused a large increase in the intensity of the 3371 A (C→B) transition.

Energy transfer from the resonance states Ar(1P1) and Ar(3P1) to ethylene

A study has been made of the quenching of the 1P1 and 3P1 resonance states of the argon atom by ethylene using a resonance fluorescence technique. Excited atoms were created by a pulsed beam of 2‐MeV protons. The measured values of the rate constants are 10.3×10−10 and 5.6×10−10 cm3 molecule−1 · sec−1 for the 1P1 and 3P1 states, respectively. These compare with the calculated values of 10.3×10−10 and 5.4×10−10 cm3 molecule−1 · sec−1 for the respective states using the theory of Watanabe and Katsuura.

Resonance ionization spectroscopy of lithium

Abstract Saturated three-step resonance ionization of ground state lithium was demonstrated and the first measurement of the photoionization cross section from the excited n = 3 manifold of lithium was made. This demonstration of saturation shows the feasibility of detecting single atoms of lithium using sensitive charge detection methods.