K. Lande

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.

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

Measurement of the response of a Ga solar neutrino experiment to neutrinos from an 37Ar source

An intense source of 37Ar was produced by the (n, α) reaction on 40Ca by irradiating calcium oxide in the fast neutron breeder reactor at Zarechny, Russia. The 37Ar was released from the solid target, sealed into a small source, and was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE. The initial source strength was 409 ± 2 kCi. The measured production rate of 71Ge on gallium metal was 11.0+1.0−0.9 (stat) ± 0.6 (syst.) atoms per day, which is 0.79+0.09−0.10 of the theoretically calculated production rate.

Progress and prospects in neutrino astrophysics

Four separate experiments to detect neutrinos from the Sun have now confirmed a deficit in the flux relative to the predictions of standard theories of nuclear physics. Future experiments with new neutrino detectors promise to reveal the explanation for this shortfall. The planned detectors may also engender a new field of astronomy, based on the observation of neutrino emission from distant, energetic astrophysical sources.

Report on the Depth Requirements for a Massive Detector at Homestake

This report provides the technical justification for locating a large detector underground in a US based Deep Underground Science and Engineering Laboratory. A large detector with a fiducial mass greater than 100 kTon will most likely be a multipurpose facility. The main physics justification for such a device is detection of accelerator generated neutrinos, nucleon decay, and natural sources of neutrinos such as solar, atmospheric and supernova neutrinos. The requirement on the depth of this detector will be guided by the rate of signals from these sources and the rate of backgrounds from cosmic rays over a very wide range of energies (from solar neutrino energies of 5 MeV to high energies in the range of hundreds of GeV). For the present report, we have examined the depth requirement for a large water Cherenkov detector and a liquid argon time projection chamber. There has been extensive previous experience with underground water Cherenkov detectors such as IMB, Kamioka, and most recently, Super-Kamiokande which has a fiducial mass of 22 kTon and a total mass of 50 kTon at a depth of 2700 meters-water-equivalent in a mountain. Projections for signal and background capability for a larger and deeper (or shallower) detectors of this type can be scaled from these previous detectors. The liquid argon time projection chamber has the advantage of being a very fine-grained tracking detector, which should provide enhanced capability for background rejection. We have based background rejection on reasonable estimates of track and energy resolution, and in some cases scaled background rates from measurements in water. In the current work we have taken the approach that the depth should be sufficient to suppress the cosmogenic background below predicted signal rates for either of the above two technologies. Nevertheless, it is also clear that the underground facility that we are examining must have a long life and will most likely be used either for future novel uses of the currently planned detectors or new technologies. Therefore the depth requirement also needs to be made on the basis of sound judgment regarding possible future use. In particular, the depth should be sufficient for any possible future use of these cavities or the level which will be developed for these large structures. Along with these physics justifications there are practical issues regarding the existing infrastructure at Homestake and also the stress characteristics of the Homestake rock formations. In this report we will examine the various depth choices at Homestake from the point of view of the particle and nuclear physics signatures of interest. We also have sufficient information about the existing infrastructure and the rock characteristics to narrow the choice of levels for the development of large cavities with long lifetimes. We make general remarks on desirable ground conditions for such large cavities and then make recommendations on how to start examining these levels to make a final choice. In the appendix we have outlined the initial requirements for the detectors. These requirements will undergo refinement during the course of the design. Finally, we strongly recommend that the geotechnical studies be commenced at the 4850 ft level, which we find to be the most suitable, in a timely manner.

The homestake chlorine solar neutrino experiment—past, present and future

The Homestake chlorine solar neutrino detector has measured the total flux of electron neutrinos from the Sun above 0.814 MeV as 2.56±0.16(stat)±0.16(syst) SNU compared to the predicted flux of 7.5 SNU. When combined with the recent SNO measurement of the electron neutrino flux from 8B decays, the Homestake measurement gives 0.55 ± 0.27 SNU for the “1 MeV” electron neutrino flux (7 Be, PeP and CNO) compared to the prediction of 1.83 SNU, assuming no neutrino flavor transitions.

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.