Raymond Davis

Measurement of the solar electron neutrino flux with the Homestake chlorine detector

The Homestake Solar Neutrino Detector, based on the inverse beta-decay reaction νe +37Cl →37Ar + e-, has been measuring the flux of solar neutrinos since 1970. The experiment has operated in a stable manner throughout this time period. All aspects of this detector are reviewed, with particular emphasis on the determination of the extraction and counting efficiencies, the key experimental parameters that are necessary to convert the measured 37Ar count rate to the solar neutrino production rate. A thorough consideration is also given to the systematics of the detector, including the measurement of the extraction and counting efficiencies and the nonsolar production of 37Ar. The combined result of 108 extractions is a solar neutrino-induced 37Ar production rate of 2.56 ± 0.l6 (statistical) ± 0.16 (systematic) SNU.

Measurement of the solar neutrino capture rate with gallium metal

The solar neutrino capture rate measured by the Russian-American Gallium Experiment (SAGE) on metallic gallium during the period January 1990 through December 1997 is 67.2 (+7.2-7.0) (+3.5-3.0) SNU, where the uncertainties are statistical and systematic, respectively. This represents only about half of the predicted Standard Solar Model rate of 129 SNU. All the experimental procedures, including extraction of germanium from gallium, counting of 71Ge, and data analysis are discussed in detail.

Results from SAGE (The Russian-American gallium solar neutrino experiment)

Abstract Fifteen measurements of the solar neutrino flux have been made in a radiochemical 71 Ga- 71 Ge experiment employing initially 30 t and later 57 t of liquid metallic gallium at the Baksan Neutrino Observatory between January 1990 and May 1992. This provides an integral measurement of the flux of solar neutrinos and in particular is sensitive to the dominant, low-energy p-p solar neutrinos. SAGE observed the capture rate to be 73 −16 +18 (stat.) −7 +5 (syst.) SNU. This represents only 56%−60% of the capture rate predicted by different Standard Solar Models.

A review of the Homestake solar neutrino experiment

Abstract The observations from the Homestake radiochemical solar neutrino experiment over the period 1970 to 1992 are given. The observations will be compared to those from the Kamiokande II experiment, the gallium experiments and solar model calculations. A discussion is given of the question of a possible variation of the solar neutrino flux in anticorrelation with the solar activity cycle. The operation of the Homestake experiment, the sensitivity to the solar neutrino spectrum, the background processes and the various tests that have been performed are given in some detail. The Homestake and Kamiokande II experiments are compared on the basis of the standard model and the flux of 8 B neutrinos. There is agreement between these two experiments during the period June 1987 to April 1990 when both experiments were observing. The average 8 B neutrino flux during this period was (2.2 ± 0.2) × 10 6 cm −2 sec −1 . A non-standard solar model of Sienkiewicz, Bahcall, and Paczynski (1990) which presumes that 50% of the core of the Sun is continually mixed on a slow time scale accounts for this reduced 8 B flux and the total neutrino capture rate of the chlorine and gallium experiments.

Effect of PDI overexpression on recombinant protein secretion in CHO cells.

In eukaryotic cells, protein disulfide isomerase (PDI) found in the endoplasmic reticulum (ER) catalyzes disulfide bond exchange and assists in protein folding of newly synthesized proteins. PDI also functions as a molecular chaperone and has been found associated with proteins in the ER. In addition, PDI functions as a subunit of two more complex enzyme systems: the prolyl‐4‐hydroxylase and the triacylglycerol transfer proteins. Increasing PDI activity in bacterial, yeast, and insect cell expression systems can lead to increased secretion of heterologous proteins containing disulfide bridges. Since Chinese hamster ovary (CHO) cells are widely used for the expression of recombinant proteins, we expressed recombinant human PDI (rhu PDI) in CHO cells to increase cellular PDI levels and examined its effect on the secretion of two different recombinant proteins: interleukin 15 (IL‐15) and a tumor necrosis factor receptor:Fc fusion protein (TNFR:Fc). Secretion of TNFR:Fc (a disulfide‐rich protein) is decreased in cells overexpressing PDI; the TNFR:Fc protein is retained inside these cells and colocalizes with the overexpressed rhu PDI protein in the endoplasmic reticulum. PDI overexpression did not result in intracellular retention of IL15. The nature of the interaction between PDI and TNFR:Fc was further investigated by expressing a disulfide isomerase mutant PDI in CHO cells to determine if the functional activity of PDI is involved in the cellular retention of TNFR:Fc protein.

Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a [Formula Presented] source

The neutrino capture rate measured by the Russian-American Gallium Experiment is well below that predicted by solar models. To check the response of this experiment to low energy neutrinos, a 517 kCi source of 51Cr was produced by irradiating 512.7 g of 92.4% enriched 50Cr in a high flux fast neutron reactor. This source, which mainly emits monoenergetic 747 keV neutrinos, was placed at the center of a 13.1 tonne target of liquid gallium and the cross section for the production of 71Ge by the inverse beta decay reaction Ga(νe, e −)71Ge was measured to be (5.55 ± 0.60 (stat.) ± 0.32 (syst.)) × 10−45 cm2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 ± 0.12 (exp.) +0.035 −0.027 (theor.) and to the cross section of Haxton is 0.87 ± 0.11 (exp.) ± 0.09 (theor.). This good agreement between prediction and observation implies that the overall experimental efficiency is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement. PACS codes: 26.65.+t, 13.15.+g, 95.85.Ry Typeset using REVTEX

Chlorine and gallium solar neutrino experiments

The expected capture rates and their uncertainties are reevaluated for the chlorine and gallium solar neutrino experiments using improved laboratory data and new theoretical calculations. Also derived is a minimum value for the flux of solar neutrinos that is expected provided only: (1) that the sun is currently producing energy by fusing light nuclei at the rate that it is emitting energy in the form of photons from its surface, and (2) that nothing happens to solar neutrinos on their way to earth. These results are used, together with Monte Carlo simulations, to determine how much gallium is required for a solar neutrino experiment. 28 references.

A review of measurements of the solar neutrino flux and their variation

The Homestake solar neutrino experiment has observed the solar neutrino flux from 1970 to the present time. During this 24 year period an apparent variation in the neutrino flux that inversely correlates with the solar activity cycle was observed. In the course of these observations two special experiments were performed to search for an enhanced signal from supernova 1987A and from an intense flare-solar mass loss event of 4 June 1991. Neutrinos were not observed from supernova 1987A, but a strong signal was observed from the 4 June 1991 solar event. The data from the Homestake experiment were analyzed by many independent investigators to search for correlations with various solar phenomena. These studies will be summarized and reviewed.

Cosmic Ray Production of Rare Gas Radioactivities and Tritium in Lunar Material

The argon radioactivities 37Ar and 39Ar were obtained by vacuum melting from interior and exterior portions of rock 10057 and from a portion of the fines from the bulk sample container. The release of argon and tritium as a function of the temperature was followed for the fine material. A comparison is made of the activities observed in the lunar samples with those expected from the spallation of iron, titanium, and calcium. From these data and the 38Ar content, the cosmic ray exposure age of rock 10057 is deduced as 110 x 106 years.

Solar neutrinos: a field in transition

Solar-neutrino experiments provide a unique opportunity for studying weak interactions in a realm where new physics may be revealed. At the same time the neutrinos carry important information about the physical processes occurring in the otherwise inaccessible core of a main-sequence star. A variety of experiments, electronic and radiochemical, must be carried out to determine what new physics and astronomy are being uncovered with these underground detectors.