D.L. Wark

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.

Measurement of the response of the Russian-American gallium experiment to neutrinos from a Cr-51 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

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

First results from the Soviet-American gallium experiment

Abstract The Soviet-American Gallium Experiment is the first experiment able to measure the dominant flux of low energy p-p solar neutrinos. Four extractions made during January to May 1990 from 30 tons of gallium have been counted and indicate that the flux is consistent with 0 SNU and is less than 72 SNU (68% CL) and less than 138 SNU (95% CL). This is to be compared with the flux of 132 SNU predicted by the Standard Solar Model.

Recent results from sage

A radiochemical {sup 71}Ga-{sup 71}Ge experiment to determine the primary flux of neutrinos from the Sun began measurements of the solar neutrino flux at the Baksan Neutrino Observatory in 1990. The number of {sup 71}Ge atoms extracted from initially 30 and later 57 tons of metallic gallium was measured in fifteen runs during the period of January 1990 to May 1992. The observed capture rate is 70{plus_minus}19 (stat){plus_minus}10 (syst) SNU. This is to be compared with 132 SNU predicted by the Standard Solar Model.

Status of the Soviet‐American Gallium Experiment

A radiochemical [sup 71]Ga-[sup 71]Ge experiment to determine the primary flux of neutrinos from the Sun began measurements of the solar neutrino flux at the Baksan Neutrino Observatory in 1990. The number of [sup 71]Ge atoms extracted from 30 tons of gallium in 1990 and from 57 tons of gallium in 1991 was measured in twelve runs during the period of January 1990 to December 1991. The combined 1990 and 1991 data sets give a value of 58 [plus] 17/ [minus] 24 (stat.) [plus minus] 14 (syst.) SNU. This is to be compared with 132 SNU predicted by the Standard Solar Model. 2 tabs, 1 fig, 14 refs.

Preliminary results from the Russian-American gallium experiment Cr-neutrino source measurement

The Russian-American Gallium Experiment has been collecting solar neutrino data since early 1990. The flux measurement of solar neutrinos is well below that expected from solar models. We discuss the initial results of a measurement of experimental efficiencies by exposing the gallium target to neutrinos from an artificial source. The capture rate of neutrinos from this source is very close to that which is expected. The result can be expressed as a ratio of the measured capture rate to the anticipated rate from the source activity. This ratio is 0.93 + 0.15, {minus}0.17 where the systematic and statistical errors have been combined. To first order the experimental efficiencies are in agreement with those determined during solar neutrino measurements and in previous auxiliary measurements. One must conclude that the discrepancy between the measured solar neutrino flux and that predicted by the solar models can not arise from an experimental artifact. 17 refs., 3 figs., 1 tab.

Sage: The Soviet-American gallium solar neutrino experiment

Abstract A radiochemical 71Ga-71Ge experiment to determine the primary flux of neutrinos from the Sun has begun operation at the Baksan Neutrino Observatory of the Institute for Nuclear Research of the Academy of Sciences of the USSR. The number of 71Ga atoms extracted from thirty tons of gallium was measured in five runs during the period of from January to July 1990 and in June run og 1991. Assuming that the extraction efficiency for 71Ge atoms produced by solar neutrinos is the same as from natural Ge carrier, we observed for measurements of 1990 the product of the neutrino flux and the cross section for all sources of neutrinos to be 20+15/−20(stat.)± 32(syst) SNU, resulting in a limit of less than 79 SNU (90% CL). The analysis of the combined data sets of 1990 and preliminary data of June run of 1991 results in a limit of less than 63 SNU (90% CL). This is to be compared with 132 SNU predicted by the Standard Solar Model.

Limit on νe mass from observation of the beta decay of molecular tritium

Abstract We report the most sensitive upper limit set on the mass of the electron antineutrino. The upper limit of 9.4 eV (95% confidence level) was obtained from a study of the shape of the beta decay spectrum of free molecular tritium. Achieving such a level of sensitivity required precise determinations of all processes that modify the shape of the observed spectrum. This result is in clear disagreement with a reported value for the mass of 26(5) eV.

The Baksan Gallium Solar Neutrino Experiment

A radiochemical 71Ga-71Ge experiment to determine the integral flux of neutrinos from the sun has been constructed at the Baksan Neutrino Observatory in the USSR. Measurements have begun with 30 tonnes of gallium. The experiment is being expanded with the addition of another 30 tonnes. The motivation, experimental procedures, and present status of this experiment are presented.