Richard A. Muller

Low background‐rate detector for 40‐keV ions using a conversion dynode and a microchannel‐plate electron multiplier to reject low‐energy ions, electrons, and photons

We have developed and tested an inexpensive ion detector with dark‐count rates below 10−4 s−1 and excellent background rejection. Each 40‐keV ion that strikes a grazing‐incidence Al2O3 conversion dynode ejects a few tens of secondary electrons, which enter separate pores of a microchannel plate and are independently multiplied to saturated pulse height. The pulses are summed to produce an output signal that is proportional to the number of secondary electrons. This permits pulse‐height discrimination against backgrounds of low‐energy ions, electrons, and photons. We have successfully tested the detector with C+, Na+, K+, Rb+, and Cs+ at 5–40 keV, and with 36‐keV C− and CH−. It should detect ions and neutrals of all species, at energies above 5–10 keV, with good efficiency and excellent background discrimination. Counting efficiency and background discrimination improve with higher ion energy. The detector can be operated at pressures up to at least 2×10−7 Torr and be exposed to air repeatedly without requ...

Radiometer System to Map the Cosmic Background Radiation

We have developed a 33-GHz airborne radiometer system to map large angular scale variations in the temperature of the 3 K cosmic background radiation. A ferrite circulator switches a room-temperature mixer between two antennas pointing 60 degrees apart in the sky. In 40 min of observing, the radiometer can measure the anisotropy of the microwave background with an accuracy of +/-1 mK rms, or about 1 part in 3000 of 3 K. The apparatus is flown in a U-2 jet to 20 km altitude where 33-GHz thermal microwave emission from the atmosphere is at a low level. A second radiometer, tuned to 54 GHz near oxygen emission lines, monitors spurious signals from residual atmospheric radiation. The antennas, which have an extremely low side-lobe response of less than -65 dB past 60 degrees , reject anisotropic radiation from the earths surface. Periodic interchange of the antenna positions and reversal of the aircrafts flight direction cancel equipment-based imbalances. The system has been operated successfully in U-2 aircraft flown from NASA-Ames at Moffett Field, CA.

Progress and New Directions for the Berkeley Supernova Search

The Berkeley Automated Supernova Search is a systematic search for supernovae in a known galaxy set. The primary goals of our experiment are to discover close supernovae early in their light curves (before maximum light) and to discover a large number of supernovae which can be used for statistical purposes. To aid in the study of supernova explosions and their classification, we are conducting VRI photometry on supernovae discovered in our data set (including those found by other observers). The supernova discoveries themselves will eventually be used to determine the supernova rates for various supernova types, galaxy types, and positions within the galaxy. With this in mind, we keep an extensive data base of all observations, their results, and characteristics of each galaxy.

Fugitive Methane and the Role of Atmospheric Half-Life

Because methane has an initial GWP (global warming potential) 120x that of carbon dioxide, concern about leaked “fugitive” methane often dominates discussions of natural gas policy. But this high GWP can easily be misinterpreted to conclude that natural gas is a much greater greenhouse danger when used for electric power generation vs. coal. In determining policy, particularly with regard to legacy issues (global warming for future generations) it is essential to take full account of the short 8.6-year lifetime of methane in the atmosphere. Moreover, the Intergovernmental Panel on Climate Change use of time “horizon” must be understood properly; it refers to an average from the present, not a time that lies in the future. The IPCC GWP value cannot be used directly to estimate the effect unless careful account is taken of the lighter weight of the methane molecule compared to that of carbon dioxide. We discusses severalways to take these issues into account, and show that for a wide range of leakages and legacy goals, fugitive methane is typically not a critical issue, and that even with a few percent leakage, natural gas is preferable to coal for legacy global warming considerations.

The Sub-Millisecond Pulsar in SN 1987A: A Review of the Discovery Data After Six Months

Two years ago, when Supernova 1987A was discovered, we were presented with an unusual opportunity to catch a pulsar at its birth. It was of course not known how long it would take before the expanding supernova photosphere would become transparent enough to see into a pulsating center. In collaboration with researchers from the United States, Canada, Chile, and Australia, we began an optical search for pulsations in SN 1987A about a month after the supernova discovery, and this search set upper limits on pulsed light until January, 1989 (PENNYPACKER et al. [1]).