An improved source of spin-polarized electrons based on spin exchange in optically pumped rubidium vapor.

We have improved a polarized electron source in which unpolarized electrons undergo collisions with a mixture of buffer gas molecules and optically spin-polarized Rb atoms. With a nitrogen buffer gas, the source reliably provides spin polarization between 15% and 25% with beam currents >4 μA. Vacuum pump upgrades mitigate problems caused by denatured diffusion pump oil, leading to longer run times.

A search for chiral asymmetry in secondary electron emission from cysteine induced by longitudinally polarized electrons.

We performed experiments searching for chirality-dependent secondary electron emission for a 141 eV longitudinally spin-polarized electron beam incident on a thick solid cysteine target. We determined the secondary electron yield by measuring the positive current produced when the cysteine target was negatively biased. No spin-dependent effects to a level of 10-3 were found for the secondary electron emission yield.

Helmholtz spacing of thin rectangular magnetic field coils.

In this Note, we discuss the Helmholtz spacing for a pair of thin rectangular coils of arbitrary aspect ratio and consider how best to use such coils to compensate for Earth's magnetic field along the coils' Cartesian symmetry axes. Such coils are frequently used in conjunction with charged-particle beam machines. The Helmholtz spacing varies non-monotonically between that for square coils and that for four optimally spaced infinite wires.

Barbiturate dependence and drug preference.

Rats exposed to a daily 3-hr session of intermittent food delivery ingested physical-dependent levels of a 1 mg/ml sodium phenobarbital solution. This chronic, voluntary, high level of session phenobarbital intake had no effect on 21-hr home cage barbiturate preference. Substitution of water for phenobarbital during the session after 7.