Collisional trap losses of cold magnetically trapped Br atoms

J. Lam, C. J. Rennick, and T. P. Softley
Phys. Rev. A 90, 063419 – Published 11 December 2014

Abstract

Near-threshold photodissociation of Br2 from a supersonic beam produces slow bromine atoms that are trapped in the magnetic-field minimum formed between two opposing permanent magnets. Here we quantify the dominant trap-loss rate due to collisions with two sources of residual gas: the background limited by the vacuum chamber base pressure and the carrier gas during the supersonic gas pulse. The loss rate due to collisions with residual Ar in the background follows pseudo-first-order kinetics and the bimolecular rate coefficient for collisional loss from the trap is determined by measurement of this rate as a function of the background Ar pressure. This rate coefficient is smaller than the total elastic collision rate coefficient, as it only samples those collisions that lead to trap loss, and is determined to be νσ=(1.12±0.09)×109cm3s1. The calculated differential cross section can be used with this value to estimate a trap depth of 293±24mK. Carrier-gas collisions occur only during the tail of the supersonic beam pulse. Using the differential cross section verified by the background-gas collision measurements provides an estimate of the peak molecular-beam density of (3.0±0.3)×1013cm3, in good agreement with the prediction of a simple supersonic expansion model. Finally, we estimate the trap-loss rate due to Majorana transitions to be negligible, owing to the relatively large trapped-atom phase-space volume.

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  • Received 17 September 2014

DOI:https://doi.org/10.1103/PhysRevA.90.063419

©2014 American Physical Society

Authors & Affiliations

J. Lam, C. J. Rennick, and T. P. Softley*

  • Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, United Kingdom

  • *Corresponding author: tim.softley@chem.ox.ac.uk

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Vol. 90, Iss. 6 — December 2014

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