Dynamic polarization of protons in 2,3-butanediol doped with Cr(V)- complex and in other materials containing adjacent hydroxyl groups

Results are given on 2,3-butanediol doped with Cr(V)-complex as a material for polarized proton targets. It is shown to be an improvement over the presently used 1,2-propanediol since its chemical composition is slightly more favourable and its melting point is near room temperature. Maximum polarization, nuclear relaxation time, reversal time, minimum power requirement, radiation resistance, and annealing temperature are all very similar to 1,2-propanediol. A review of other materials containing adjacent hydroxyl groups is made, and conclusions are drawn as to their possible use as target materials. (17 refs)

ULTRASONIC AND SPECIFIC HEAT MEASUREMENTS IN QUENCHED SUPERCONDUCTING NbZr

In crystalline NbZr the quenching process is known to create a partially amorphous phase containing tunnelling states whose thermal behaviour resembles that of other amorphous materials. In order to study the interaction of the tunnelling states with electrons we have carried out ultra-sonic measurements with longitudinal waves at 30 and at 90 MHz. The absorption does not decrease at the superconducting transition (Tc = 8.6 K) - as expected for crystalline superconductors - but at temperatures well below Tc. Specific heat measurements on the same specimen demonstrate that nevertheless the whole sample becomes superconducting at Tc. In our view the recent theory by Black and Fulde on the interaction between electrons and tunnelling states can account for our observations

Operation and control of a dilution refrigerator for spin conversion measurements with neutrons

We describe the cryogenic and operational aspects of an experiment comprising a dilution refrigerator with a 12-sample container, automatic sample change, automatic refill of cryogenic fluids and a watch-dog alarm system. Thermometry for the range 10 mK to 300 K is described including computer read-out and computerized temperature control.Nous présentons les aspects cryogéniques et opérationnels d'un ensemble expérimental consistant en un cryostat à dilution équipé d'un porte-échantillon multiple, échange-échantillon automatique, alimentation automatisée en cryofluides et un système d'alarme passive. La thermométrie entre 10 mK et 300 K est décrite ainsi que la lecture et le contrôle de la température à l'aide d'un miniordinateur