John T. Scott

Computer films for research

Lets say you have just completed a computer simulation or numerical modeling of a complex system in your physical or chemical research. The data are likely to be delivered back to you in the form of mountains of Z‐fold computer printout or stacks of Calcomp plots. Rather than picking your way through all this paper, why not turn the material into a short movie that can be projected over and over again, fast or slow, to show you whatever trends, discontinuities and so on your model possesses?

Excitation‐transfer nitrogen lasers

A high‐power, high efficiency laser with a wavelength in the visible or near‐ultraviolet would be very desirable for such proposed applications as laser‐induced fusion and isotope separation. Demonstration models of systems that might lead to this goal have been recently reported from the Naval Research Laboratory, Northrop Corporation, the University of Texas at Dallas and the Lebedev Physics Institute in Moscow. All these systems employ electron‐beam energy deposition; they all use rare‐gas and nitrogen mixtures, and they lase at wavelengths in the 3000–5000 A range with efficiencies around 2%. At Los Alamos work is proceeding on a somewhat different approach that attempts to increase the output pulse length of lasers of this type.

More laser power with electron‐beam control

Our best hope for an ultrahigh‐power laser with good beam quality appears to lie with molecular gas‐discharge devices. The development of these lasers has so far been limited by the difficulty of maintaining stable discharge conditions and by the impossibility of producing a design scalable in all its parameters—size, pressure, and so on. That is, a certain discharge device that runs well cannot in general be rebuilt twice the size for increased power. Now at least three groups in the US and one in Russia are experimenting with devices embodying electron‐beam‐controlled discharges to solve some of these problems.

Pulsed molecular‐beam sources

A new type of fast, pulsed molecular‐beam source for collision studies and molecular spectroscopy appears to have several advantages over the traditional continuous‐flow sources. It improves signal‐to‐noise in the detectors, produces very “cold” beams with little or no rotational or vibrational excitation, and it allows good time‐of‐flight measurements to determine velocity spectra. The source was developed by W. Ronald Gentry and Clayton Giese at the University of Minnesota. Their work employs two such sources to investigate collisions between two molecular beams.

Many models proposed to explain cosmic gamma‐ray bursts

The various wavelength regimes of observational astronomy seem to generate their maximum excitement when rapid time‐varying phenomena are first observed. For example, radioastronomy gave us pulsars; x‐ray astronomy has its flares and pulsating sources. Now it is the turn of gamma‐ray astronomy. Ray Klebesadel, Ian Strong and Roy Olson (Los Alamos) recently reported finding 16 short bursts of cosmic gamma radiation in three‐years‐worth of data from the Vela satellite program.

Two new lasers share short‐wavelength record

The shortest‐wavelength laser light yet obtained has been produced by stimulated emission in the molecular‐hydrogen Werner bands. These 1160–1240‐a transitions in the vacuum ultraviolet correspond to photon energies of about 10 eV, which are suitable for photochemical, photodissociation and photoionization experiments in most molecules. Lasers with output in this frequency range have been reported independently and nearly simultaneously by two different groups—Ronald W. Waynant of the Naval Research Laboratory, and Rod Hodgson and Russell Dreyfus of the IBM Thomas J. Watson Research Center. Both publications are in the 28 February issue of Physical Review Letters (pages 533 and 536 respectively).

Quasars are relatively local. Except those that are not

How far away are the quasars? Either they are at cosmological distances, moving at a substantial fraction of the velocity of light—if you believe that their enormous red‐shifts are of a piece with the general Hubble recession of the galaxies; or they are comparatively local—if you worry about their extraordinary luminosity and short‐term variability. Each viewpoint has its own adherents; each adherent has a persuasive argument.

Hydroxyl Molecules in Space Puzzle Radio Astronomers

Investigations of emission and absorption of radiation by hydroxyl (OH) radicals in interstellar space have turned up many puzzles and anomalies. The newly developed longbaseline interferometers may provide a solution. They may in fact reveal a galactic maser, and further observations may tell us more about the structure of our own planet.

Tandem‐mirror machines promise better efficiency

A major problem with magnetic‐mirror devices for plasma confinement has always been the leakage of particles out of the ends of the machine. An experiment now under construction at Lawrence Livermore Laboratory, known as the Tandem Mirror Experiment (TMX), proposes to turn this failing neatly to advantage by employing two mirror‐pairs, one at each end of a long straight solenoid. Each pair of mirrors confines positive ions by minimum‐B magnetic‐field wells, and the excess positive charge that develops in these “end cells” confines ions within the solenoid. In other words, the two mirror pairs act as plugs for the ends of the solenoid. Calculations for a reactor based on this concept predict that, under appropriate neutral injection conditions, a plasma of a density and temperature sufficient for controlled fusion will build up in the solenoid. The purpose of the TMX experiment is to test the principles of the concept. Other tandem‐mirror experiments are planned or already under construction at Novosibirsk...

New measurement of magnetic‐moment anomaly tests QED

Once again quantum electrodynamics, which has already earned itself the description “the most successful dynamical theory in all of physics,” comes under close scrutiny as further refinements in experimental technique provide data sufficiently precise to test this highly respected theory. Hans Dehmelt (University of Washington) reported at the Chicago meeting of the American Physical Society last month on measurements made in collaboration with Robert Van Dyck Jr and Paul Schwinberg of the magnetic moment anomaly of the electron. Brief notes on the experimental method had appeared earlier in Nature; a more extensive paper on the new measurement is in Physical Review Letters.