G. Torzo

The behavior of the4He viscosity near the superfluid transition

Measurements of the shear viscosity at saturated vapor pressure through the lambda transition indicate a singular behavior of the form |1 − (η/ηλ)|=Aεx, (where ε=|1−(T/Tλ)|, with equal values for the critical exponent on both sides of the transition.

Measurements of 4He viscosity near the superfluid transition

The 4He viscosity has been measured with a vibrating wire viscometer on the superfluid side of the λ transition. The results indicate that η should be singular at Tλ, in agreement with the suggestion advanced recently by G. Ahlers.

Simple photoelectronic source for swarm experiments in high‐density gases

A simple photocathode for electron injection into high‐density gas is described. Relatively large electronic current pulses have been obtained by using a commerical low‐power xenon flash lamp. The photocathode efficiency has been studied as a function of the metal film thickness. The device has been used in swarm experiments at pressures up to 10 MPa in the temperature range 40–300u2009K.

Precise temperature controller for resistance thermometers

We describe here a stable and sensitive temperature controller to be used with resistance thermometers. The temperature resolution provided by this instrument was ΔT≂20 μK at room temperature and ΔT≂1 μK at liquid 4He temperature.

Search for Neutron Emission from a Deuterium-Titanium System

Search for neutron emission from a titanium-deuterium system has been performed in a wide temperature range (from 77 K to 1100 K), with a D/Ti atomic percentage up to 165%. The sample was continuously monitored for 40 days, both at constant temperature and in nonequilibrium conditions. No neutron emission above background was observed.

Low-frequency viscocity measurements near the critical point of carbin dioxide☆

Abstract Preliminary CO 2 viscocity measurements have been performed along an isochore near to the critical one. Particular care was taken to avoid gravitational and frequency effects. The results are in agreement with the theoretical prediction of a divergent viscosity critical behaviour.

Method for accurate resonant frequency measurements with a phase‐modulated feedback loop

A new method for accurate measurements of resonant frequency is described here, which uses a phase‐modulated locked loop to avoid errors due to unknown phase shifts or to synchronous pickup noise.

Density dependence of the electronic mobility in high density neon gas

Abstract The low field electron mobility μ in neon gas has been measured as a function of the number density N for temperatures between 48 and 300 K. The low density limit ( μN ) 0 is consistent with the known values of the gas phase scattering cross section. The density dependence is much stronger than predicted by multiple scattering theories, and it is attributed to a density dependence of the scattering cross section.

A simple recirculating pump for high‐pressure high‐purity gas

A bellow‐pump allows to circulate high‐purity gas at high pressure without contaminating the sample. Its main features are low cost, simple design, easy operation, all‐metal construction, and adjustable flow rate.

Simple design for a frequency‐independent voltage‐controlled phase shifter

A very simple general‐purpose phase shifter is described here, that can be linearly voltage controlled in a wide frequency range. This device allows us to implement the standard lock‐in amplifier into a vector tracking lock‐in amplifier.