Number 146 (Story #1), October 5, 1993 by Phillip F. Schewe and Ben Stein BEAMS OF ULTRA-COLD, SPIN-POLARIZED HYDROGEN ATOMS can be focused with a parabolic copper mirror coated with superfluid helium-4. Hydrogen atoms like to form diatomic molecules but can be kept from doing so by spin-polarizing the electrons in a magnetic field; the Pauli Exclusion principle takes over and keeps the atoms apart. Such atoms are usually confined to a closed vessel, but scientists at the University of Michigan (contact Alan Krisch, 313-936- 1027) have used the recently discovered technique of reflecting hydrogen atoms from a helium- covered surface (the light H's bounce off the He film) to achieve the first externally-extracted beam of spin-polarized hydrogen atoms. The beam delivers 3.7 x 10**15 H's per second. The scientists plan to collide the beam with protons circulating through a high-energy accelerator. For this type of experiment atomic hydrogen (at a temperature of 300 mK) is much preferable to molecular hydrogen, which has internal energy states that complicate the collision process. The hydrogen beam will probably be of use in other areas of physics as well. (V.G. Luppov et al., 11 Oct. Physical Review Letters.)