Magnetic trapping of cold bromine atoms.

Magnetic trapping of bromine atoms at temperatures in the millikelvin regime is demonstrated for the first time. The atoms are produced by photodissociation of Br2 molecules in a molecular beam. The lab-frame velocity of Br atoms is controlled by the wavelength and polarization of the photodissociation laser. Careful selection of the wavelength results in one of the pair of atoms having sufficient velocity to exactly cancel that of the parent molecule, and it remains stationary in the lab frame. A trap is formed at the null point between two opposing neodymium permanent magnets. Dissociation of molecules at the field minimum results in the slowest fraction of photofragments remaining trapped. After the ballistic escape of the fastest atoms, the trapped slow atoms are lost only by elastic collisions with the chamber background gas. The measured loss rate is consistent with estimates of the total cross section for only those collisions transferring sufficient kinetic energy to overcome the trapping potential.

Production of cold bromine atoms at zero mean velocity by photodissociation.

The production of a translationally cold (T < 1 K) sample of bromine atoms with estimated densities of up to 10(8) cm(-3) using photodissociation is presented. A molecular beam of Br(2) seeded in Kr is photodissociated into Br + Br* fragments, and the velocity distribution of the atomic fragments is determined using (2 + 1) REMPI and velocity map ion imaging. By recording images with varying delay times between the dissociation and probe lasers, we investigate the length of time after dissociation for which atoms remain in the laser focus, and determine the velocity spread of those atoms. By careful selection of the photolysis energy, it is found that a fraction of the atoms can be detected for delay times in excess of 100 µs. These are atoms for which the fragment recoil velocity vector is directly opposed and equal in magnitude to the parent beam velocity leading to a resultant lab frame velocity of approximately zero. The FWHM velocity spreads of detected atoms along the beam axis after 100 µs are less than 5 ms(-1), corresponding to temperatures in the milliKelvin range, opening the possibility that this technique could be utilized as a slow Br atom source.

The potencies of edrophonium and neostigmine as antagonists of pancuronium.

Dose response curves were constructed for edrophonium and neostigmine when used to antagonise pancuronium, 0.07 mg/kg during thiopentone-nitrous oxide-halothane anaesthesia. The antagonist was given when 10% twitch height had been restored and the effect was measured 10 minutes later. Recoveries to 50% and 90% twitch height were achieved with 167 and 828 micrograms/kg of edrophonium, and 10.5 and 51 micrograms/kg of neostigmine. The dose response curves were parallel and neostigmine was 16 times more potent than edrophonium. Combinations of equipotent doses of edrophonium and neostigmine were also administered and produced additive but not synergistic effects. It is concluded that either edrophonium or neostigmine may be used for the reversal of pancuronium neuromuscular blockade, but the combination of the two offers no advantage.

Accelerated onset of pancuronium with divided doses.

To determine the consequences of administering neuromuscular relaxants in divided doses, pancuronium was given either in a single dose, 0.07 mg X kg-1, or in an initial dose of 0.007 mg X kg-1 followed three minutes later with 0.063 mg X kg-1. When the drug was administered in divided dosage the onset time was reduced, the block was more intense and its duration of action was prolonged. It is suggested that such changes may be advantageous in the provision of rapid intense paralysis.