Jeffrey A. Paisner

First ionization potentials of lanthanides by laser spectroscopy

Photoionization and Rydberg spectra of ten lanthanides have been studied using stepwise laser excitation and ionization methods. These spectra were obtained from several different laser populated excited states in each case. Accurate ionization limits were derived from observed photoionization thresholds. Except for praseodymium, the observation of one or more long Rydberg progressions allowed more accurate limits to be determined. The Rydberg convergence values in eV are: Ce, 5.5387(4); Nd, 5.5250(6); Sm, 5.6437(6); Eu, 5.6704(3); Gd, 6.1502(6); Tb, 5.8639(6); Dy, 5.9390(6); Ho, 6.0216(6), and Er 6.1077(10). For praseodymium a threshold value of 5.464(+12-2) was obtained. When plotted against N, the lanthanide ionization limits normalized to correspond to ionization from the lowest level of fNs2 to the lowest level of fNs form two straight lines connected at the half-filled shell.

Radiative lifetimes, absorption cross sections, and the observation of new high-lying odd levels of 238 U using multistep laser photoionization*

We report the observation of over 100 new high-lying odd levels in atomic uranium between 32 600 and 34 200 cm−1 using tunable laser techniques. These augment the 32 odd levels previously determined in this energy regime by conventional atomic spectroscopy. The method used in these studies, multistep photoionization under pulsed dye laser excitation, was also employed to make J assignments, measure radiative lifetimes, and to obtain absorption cross sections of transitions involving these levels.

Determination of absolute atomic transition probabilities using time resolved optical pumping

Abstract We describe a method of determining atomic transition probabilities by independently measuring branching ratios and radiative lifetimes. These quantities are directly determined by time resolved optical pumping. The technique has been applied to the measurement of gA values for particular transitions in 238U I.

The ionization potential of neutral iron, Fe i, by multistep laser spectroscopy

Three-step laser excitation was used to populate and observe members of Rydberg series in neutral iron with high effective quantum numbers. These series converge to the ground and to the first excited state of singly ionized iron. The photoionization threshold was also observed. Analyses of the Rydberg series yield the value 63 737(1) cm−1 or 7.9024(1) eV as the ionization potential of neutral iron.

Conceptual design of the National Ignition Facility

The Secretary of the U.S. Department of Energy (DOE) commissioned a conceptual design report (CDR) for the National Ignition Facility (NIF) in January 1993 as part of a key decision zero (KD0), justification of mission need. Motivated by the progress to date by the inertial confinement fusion (ICF) program in meeting the Nova technical contract goals established by the National Academy of Sciences in 1989, the Secretary requested a design using a solid-state laser driver operating at the third harmonic (0.35 micrometer) of neodymium (Nd) glass. The participating ICF laboratories signed a memorandum of agreement in August 1993, and established a project organization, including a technical team from the Lawrence Livermore National Laboratory (LLNL), Los Alamos National Laboratory (LANL), Sandia National Laboratories (SNL), and the Laboratory for Laser Energetics at the University of Rochester. Since then, we completed the NIF conceptual design, based on standard construction at a generic DOE defense programs site, and issued a 7,000-page, 27-volume CDR in May 1994. Over the course of the conceptual design study, several other key documents were generated, including a facilities requirements document, a conceptual design scope and plan, a target physics design document, a laser design cost basis document, a functional requirements document, an experimental plan for indirect drive ignition, and a preliminary hazards analysis (PHA) document. DOE used the PHA to categorize the NIF as a low-hazard, non-nuclear facility. On October 21, 1994 the Secretary of Energy issued a key decision one (KD1) for the NIF, which approved the project and authorized DOE to request Office of Management and Budget-approval for congressional line-item FY 1996 NIF funding for preliminary engineering design and for National Environmental Policy Act activities. In addition, the Secretary declared Livermore as the preferred site for constructing the NIF. In February 1995, the NIF Project was formally submitted to Congress as part of the Presidents FY 1996 budget. If funded as planned, the Project will cost approximately

Ionization potential of neutral atomic plutonium determined by laser spectroscopy

1.1 billion and will be completed at the end of FY 2002.

Status of the National Ignition Facility Project

The ionization potential of the neutral plutonium atom, Pu i, has been determined by two- and three-step resonance photoionization observation of the threshold of ionization and of Rydberg series. The Rydberg series were observed by field ionization as series that converge to the first ionization limit and as autoionizing series that converge to the second and to several higher convergence limits. The threshold and Rydberg series were obtained through a number of two- and three-step pathways. The photoionization threshold value for the 239Pu i ionization potential is 48582(30) cm−1, and the more accurate value from the Rydberg series is 48604(1) cm−1 or 6.0262(1) eV.

Associative ionization of laser-excited Rydberg states in strontium vapor.

The ultimate goal of worldwide research in inertial confinement fusion (ICF) is to develop fusion as an inexhaustible, economic, environmentally safe source of electric power. Following nearly 30 years of laboratory and underground fusion experiments, the next step toward this goal is to demonstrate ignition and propagating burn of fusion fuel in the laboratory. The National Ignition Facility (NIF) Project is being constructed at the Lawrence Livermore National Laboratory (LLNL) for just this purpose. NIF will use advanced Nd-glass laser technology to deliver 1.8 MJ of 0.35-μm laser light in a shaped pulse, several nanoseconds in duration, achieving a peak power of 500 TW. A national community of US laboratories is participating in this project, now in its final design phase. France and the UK are collaborating on development of required technology under bilateral agreements with the US. This paper presents the status of the laser design and development of its principal components and optical elements.

Selective photoionization of 64Cu in the presence of 63,65 Cu

Using mass spectrometry we have confirmed that Sr(2)(+) ions are produced from laser-populated Rydberg states by the associative ionization process Sr(5snl) + Sr(5s(2)) ? Sr(2)(+) + e(-). Dimer ion signal was detected for the 5s6d(3)D(2) level, indicating that the binding energy of Sr(2)(+) exceeds 0.77 eV. We have observed that under certain conditions the Rydberg states are destroyed by electron-impact ionization before an associative ionization collision can occur.

Gadolinium enrichment technology at Lawrence Livermore National Laboratory

Abstract It has been proposed that a copper crystal enriched in 64Cu relative to 63Cu would provide a source of a low-energy, monoenergetic beam of positrons, with an intensity as much as three orders of magnitude greater than unenriched sources. We have evaluated the use of resonance ionization to selectively photoionize 64Cu in the presence of the stable isotopes 63Cu and 65Cu. It appears that this method may be applied with high selectivity and relatively high efficiency using rather simple laser systems. Various aspects of this technique will be discussed.