Effects of Nitrogen contamination in liquid Argon

A dedicated test of the effects of Nitrogen contamination in liquid Argon has been performed at the INFN-Gran Sasso Laboratory (LNGS, Italy) within the WArP R&D program. A detector has been designed and assembled for this specific task and connected to a system for the injection of controlled amounts of gaseous Nitrogen into the liquid Argon. Purpose of the test is to detect the reduction of the Ar scintillation light emission as a function of the amount of the Nitrogen contaminant injected in the Argon volume. A wide concentration range, spanning from about 10^-1 ppm up to about 10^3 ppm, has been explored. Measurements have been done with electrons in the energy range of minimum ionizing particles (gamma-conversion from radioactive sources). Source spectra at different Nitrogen contaminations are analyzed, showing sensitive reduction of the scintillation yield at increasing concentrations. The rate constant of the light quenching process induced by Nitrogen in liquid Ar has been found to be k(N2)=0.11 micros^-1 ppm^-1. Direct PMT signals acquisition at high time resolution by fast Waveform recording allowed to extract with high precision the main characteristics of the scintillation light emission in pure and contaminated LAr. In particular, the decreasing behavior in lifetime and relative amplitude of the slow component is found to be appreciable from O(1 ppm) of Nitrogen concentrations

Kinetic studies following state-selective laser excitation

During the past year, we have made measurements of state-to-state energy transfer cross sections and radiative lifetimes for Xe*(6p,6p{prime},7p) and Kr*(5p) states in xenon and krypton buffer gases. These results are relevant to kinetic models of both excimer lasers and the infrared xenon laser; and they are a significant improvement in the precision of the known radiative lifetimes. 3 refs., 2 figs., 2 tabs

How Useful Are Environmental Safety Standards in Economics - the Example of Safe Minimum Standards for Protection of Species

The use of environmental safety standards is being increasingly advocated, and economists are being increasingly required to adapt their policy models to take account of such standards, e.g. by the use of transferable environmental damage quotas. The use of these standards may be a consequence of a greater desire to achieve more sustainable development and preserve the natural wealth available to future generations. An important means to this goal is to preserve biodiversity and genetic variability. Safe minimum standards for conservation of wildlife have been suggested as a way to achieve this. Sometimes safe minimum standards for conservation of species are defined in terms of their minimum viable populations and their minimum habitat requirements. However, as a review of recent scientific literature indicates, these safe minimum standards are very uncertain