Solar Neutrino Detector Research Articles

Low-background /sup 3/He proportional counters for use in the Sudbury neutrino observatory

Current solar neutrino detectors measure a considerably lower flux of electron-flavor neutrinos than predicted by solar models. This could be an indication of neutrino oscillations, which would provide direct evidence that neutrinos have mass. The Sudbury Neutrino Observatory (SNO) was designed to detect all flavors of neutrinos, and will provide a rigorous test of this theory. The SNO detector's heavy water target gives it the unique ability to detect all non-sterile neutrino flavors via the neutral-current (NC) break-up of the deuteron. This NC interaction liberates a neutron which may be detected with an array of discrete /sup 3/He proportional counters. The strict radioactivity requirements imposed by the need for low backgrounds dictate the use of ultra-pure materials and processes in building these counters. Additionally, they must survive in the heavy water environment for several years. The design, construction, and testing of these unique counters are described.

Solar neutrino experiments: results and implications

The neutrinos that are produced in the solar fusion reaction chains reflect the conditions in the stellar interior. If the model predictions for the expected neutrino fluxes are firm, then the solar neutrino experiments can also test neutrino properties during propagation along the $1.5\ifmmode\times\else\texttimes\fi{}{10}^{8}\mathrm{kilometer}$ ``baseline'' between ``source'' and detector. So far, results have been acquired with five solar neutrino detectors: Homestake, Kamiokande, Superkamiokande, Gallex, and Sage. Taking all of the experimental data together, it appears that the abundant pp neutrinos are present, the moderately abundant ${}^{7}\mathrm{Be}$ neutrinos are strongly or totally suppressed, and the rare ${}^{8}\mathrm{B}$ neutrinos are partially reduced, by a factor of about three. This outcome cannot be explained by modifications of the stellar model but it is consistent with the hypothesis of neutrino flavor oscillations. Such oscillations could occur on the way between the solar core and the detector. In such a scenario, a nonvanishing neutrino rest mass would follow. The evidence is summarized here, and the outlook as regards anticipated future experiments is briefly discussed.

Future solar neutrino projects

In the program to determine the intrinsic properties of the neutrinos and their role in physics and astrophysics, solar neutrino experiments are playing a fundamental part. The “first” and “second” generation detectors in the field have been enormously successful and promise to provide still greater contributions. The challenge to create a “third generation” of solar neutrino detectors arises principally from interest in making detailed investigations of the portion of the neutrino spectrum from a few keV to 1.5 MeV. That portion contains fluxes from the p-p and CNO continuum as well as the 7Be and p-e-p lines. The need to overcome the experimental difficulties presented by working at these low energies have given rise to new ideas for detector technologies. The range of technologies is impressive in its variety and reflects choices of emphasis using real-time and radiochemical methods. In this paper, I present a review of the status of several R & D efforts known to me which are making progress toward providing detectors suitable to meet the various challenges of this low energy region.

Solar neutrino oscillation diagnostics at SuperKamiokande and Sudbury Neutrino Observatory

Results for solar neutrino detection from the SuperKamiokande collaboration have been presented recently while those from the Sudbury Neutrino Observatory are expected in the near future. These experiments are sensitive to the 8B neutrinos from the sun, the shape of whose spectrum is well-known but the normalisation is less certain. We propose several variables, insensitive to the absolute flux of the incident beam, which probe the shape of the observed spectrum and can sensitively signal neutrino oscillations. They provide methods to extract the neutrino mixing angle and mass splitting from the data and also to distinguish oscillation to sequential neutrinos from those to a sterile neutrino.

The relevance of the vertex bremsstrahlung photon detection in the [formula omitted] scattering experiments at low energy

We discuss the size of the ν e ( ν e ) e −→ν e ( ν e ) e − cross section reduction due to the rejection of the events with a vertex bremsstrahlung photon above a certain energy in the final state. In particular we analyze the effect in experiments designed to detect the low energy ν e and ν e from a nuclear reactor and from the Sun. We find that such reduction has to be considered in a relatively high statistic reactor experiment, while it is negligible for pp and 7Be solar neutrino detection.

Partial Houses Built on Common Ground:

Harry Collins and Trevor Pinch, The Golem: What Everyone should know about Science (Cambridge: Cambridge University Press, 1993), Chapter 3, 'The Sun in a Test Tube: The Story of Cold Fusion', 57-78 [hereafter CP T.J. Pinch, Confronting Nature: The Sociology of Solar-Neutrino Detection (Dordrecht: Kluwer, 1986). 3. We note that Lewis' results were delivered in the context of the Baltimore APS meeting where, in conjunction with Koonin's results and the Petrasso results questioning the neutron measurements, they were presented with devastating effect. McKinney has a minor disagreement with us over whether Lewis's talk was indeed the 'knockdown blow', preferring to put most weight upon the results showing problems with the neutron measurements. But this is not the real quarrel between us. We meant that it was a 'knockdown' in the sense that half the physicists present left the meetings after Lewis' talk; that many commentators (for example, Frank Close) point to the importance of these 'back to back' talks in the demise of cold fusion; and that, furthermore, Koonin's claims of incompetence and delusion on the part of Pons and Fleischmann were widely quoted. 4. This is nicely detailed by Greg Myers, Writing Biology: Texts and the Social Construction of Scientific Knowledge (Madison, WI: University of Wisconsin Press, 1990). 5. For more details, see Pinch (1986), op. cit. note 2, 163.

ANALYSIS OF SOLAR NEUTRINO FLUX FROM THE EXISTING SOLAR NEUTRINO DETECTORS

It is suggested that the experimental data on the solar neutrino flux as measured in the existing solar neutrino detectors (e.g. Homestake, Kamiokande II and III, Gallex and Sage) vary with the solar activity cycle to a very high level of statistical significance. We have applied the run test and the change point test to the nine sets of solar neutrino flux that have been generated by the Monte-Carlo simulation with production rate and background parameters that are typical of those in the actual Homestake experiment. Homestake solar neutrino flux data show anticorrelation with sunspot numbers from 1970 to February 1994 at a very high level of statistical significance. However, the Kamiokande solar neutrino flux data show correlation with the sunspot number data at a significant level. Again it is shown that out of nine Monte-Carlo-simulated data only three indicate a variation within the period from 1970 to February 1992, but these three Monte-Carlo-simulated solar neutrino flux data do not show significant anticorrelation with the sunspot number data. The solar neutrino flux data from Gallex and Sage show not only variation within the measurement period, i.e. from January 1990 to October 1995, but are also correlated with the sunspot numbers. The Kamiokande solar neutrino flux data not only show variation from January 1987 to February 1995 but are also correlated with the sunspot number data. The variation of solar neutrino flux data within the solar activity cycle and anticorrelation/correlation indicates that the solar activity cycle is due to the pulsating character of the nuclear energy generation inside the core of the sun.

Measurement of Gamow-Teller strength for127Ias a solar neutrino detector

Gamow-Teller transition strengths obtained in the ${}^{127}\mathrm{I}{(p,n)}^{127}\mathrm{Xe}$ reaction studied at 94, 159, and 197 MeV incident proton energies are presented, and used to evaluate the efficiency of ${}^{127}\mathrm{I}$ as a solar neutrino detector. Excitation of the ${J}^{\ensuremath{\pi}}{=(3/2)}^{+}$ first excited state at ${E}_{x}=0.125 \mathrm{MeV}$ in ${}^{127}\mathrm{Xe},$ sensitive to ${}^{7}\mathrm{Be}$ solar neutrinos, is evaluated. The sum of Gamow-Teller strength up to particle emission threshold and up to 20 MeV excitation energy are also reported. This paper also provides a new measurement of the Coulomb displacement energy $\ensuremath{\Delta}{E}_{c},$ the excitation energy of the isobaric analog state, and the centroid of the Gamow-Teller resonance in ${}^{127}\mathrm{Xe}.$

The HELLAZ solar neutrino detection project

This talk has been given to provide information on the capability of one of the most performing next generation solar neutrino detection experiment. Different phases of the project are very shortly presented.

Verification tests of the GALLEX solar neutrino detector, with 71Ge produced in-situ from the beta-decay of 71As

Previously, it was demonstrated that the GALLEX solar neutrino detector responds properly to low energy neutrinos, by exposing it to two intense 51Cr-neutrino sources; the recovery yield of the product 71Ge was reported to be 93%±8%. New experiments, in which known amounts of radioactive 71As have decayed to 71Ge in the full-scale gallium detector, strongly support this evidence. In several experiments, the gallium detector has been spiked with ∼10 5 71 As atoms, under varying conditions of how the 71As was added (either carrier free, or with Ge carrier), how the gallium solution was mixed, and how long the 71Ge remained in the gallium. 71As decays by electron capture and positron emission to 71Ge, with a half life of 2.72 d. Hot atoms are produced by these decay modes with kinematics that mimic solar neutrino capture, although the 51Cr neutrino source provided a more perfect match. This relative disadvantage is offset by the much better statistics obtainable with the 71As. In all 71As experiments, the recovery of 71Ge from the gallium was 100%, with uncertainties of only ±1%. The combined results from the 51Cr sources and the 71As spikes rule out any loss mechanisms for 71Ge, including hot-atom chemical effects. Chemical processes in the aqueous gallium trichloride - hydrochloric acid solution guarantee that the 71Ge atoms formed in the GALLEX target will be quickly converted to extractable, volatile GeCl 4.

Beta-decay of light nuclei close to the proton drip-line:40Ti and35Ca

The ß-decay of40Ti and35Ca have been studied at the LISE3 spectrometer at GANIL. The decay schemes were deduced from the observed ß-delayed proton and γ emission of40Ti and35Ca into the ground and first excited states of39Ca and34Ar, respectively. The Gamow-Teller strength functionB(GT) of the40Ti ß-decay extracted from the ß-decay branching ratios and the precisely measured40Ti half-life, provides for the first time an experimental calibration of the neutrino detection efficiency for the ICARUS solar neutrino detector.

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.

Cryogenic detection of 7Be with beryllium metal absorber for lithium solar neutrino experiment

A cryogenic micro-calorimeter to detect the 7Be electron capture decay has been developed. The detector absorber is a beryllium metal foil which has been previously irradiated by protons in order to produce the 7Be isotope. The 112 eV spectral line corresponding to the 7Be K-capture decay to the 7Li ground state (Auger-electron plus the nuclear recoil energy) has been successfully detected with an energy resolution of 53 eV FWHM. The observed decrease in the rate of the absorber activity corresponds to the expected 7Be half-life. The obtained results show that the 112 eV 7Be spectral line can be detected by a cryogenic μ-calorimeter with an efficiency close to 100%. This cryogenic method solves the principal problem in the development of a lithium radiochemical solar neutrino detector.

Effects of solar magnetosonic waves in new solar neutrino observations

Abstract Assuming a nonvanishing neutrino magnetic moment, we investigate the consequences of the appearance of solar magnetosonic waves on the solar neutrino spin-flavour conversion. We analyze the resulting distortions of the solar neutrino flux to be measured by new solar neutrino detectors to conclude that, with the time and energy resolution that will be available in these experiments, magnetosonic waves in the Sun can be tested. We discuss how to distinguish this experimental signal coming from magnetosonic waves from other sources of time modulation of neutrino flux like the effect of seasonal variation of the Sun-Earth distance on vacuum oscillations, MSW effect inside the Earth, and solar activity related to the appearance of sunspots on the solar surface.

Can we distinguish Majorana and Dirac neutrinos in solar neutrino experiments?

If neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes then a new opportunity to distinguish Majorana and Dirac neutrinos by measuring the differential v e e scattering cross section in solar neutrino detectors arises. An experiment like HELLAZ would be preferable in testing recoil electron spectra differences initiated by Majorana and Dirac neutrinos since low-energy recoil electrons ( T ⩾ 100 keV) can be detected and the electron energy and direction can be determined with good precision.

β-decay of 40Ti

The β-decay of 40Ti was studied. The Fermi and Gamow-Teller strength function was deduced from the observed β-delayed emission of protons and γ-rays and from the measured half-life of 55(2) ms. The results are compared to shell-model predictions and are used to estimate the neutrino-capture rate of the solar-neutrino detector ICARUS.

DETECTION OF SOLAR NEUTRINOS

The present status of solar neutrino detection is reviewed. Results from the Homestake, Kamiokande, Super-Kamiokande, GALLEX and SAGE detectors all show a deficit when compared to recent standard solar model calculations. Two of these detectors, GALLEX and SAGE, have recently been checked with artificial 51Cr neutrino sources. It is shown that astrophysical scenarios to solve the solar neutrino problems are not favoured by the data. There is hope that the results of Super-Kamiokande and the forthcoming solar neutrino experiments can provide the answers to the open questions.

Results from solar-neutrino experiments

All four operating solar-neutrino detectors (HOMESTAKE, KAMIOKANDE, GALLEX, SAGE) get positive results but below the level expected from solar models. Taking all data together, it appears that the abundant pp-neutrinos are fully present, the intermediate7Be-neutrinos are strongly or totally suppressed and the rare8B-neutrinos are partially reduced (factor 2–3). This cannot be explained by modifications of the stellar model but would be consistent with neutrino flavour oscillations between the solar core and the detector. If this applies, non-zero neutrino mass is required. The evidence is summarized and discussed.

Neutrino astronomy: the Sun and beyond

Astronomers like to build telescopes on the tops of remote mountains where the sky is clear and there is no light pollution from nearby towns and cities. Neutrino astronomers are different. They have to work underground in mines and road tunnels, underwater and, in one experiment, deep in the ice under the South Pole. Despite these obstacles, however, neutrino astronomy has developed as an experimental science over the last three decades. Indeed, this fledgling discipline has already chalked up two of the most remarkable experimental discoveries of the past decade: the conclusive detection of solar neutrinos and the observation of neutrinos from a supernova.

Solar Neutrino Experiments: The Next Generation

In the next few years, three massive new solar neutrino detectors will generate large amounts of precise data that should have a major impact on our understanding of how the Sun shines and how neutrinos behave. They are Super Kamiokande, in the mountains west of Tokyo; the Sudbury Neutrino Observatory (SNO) in a northern Ontario mine and Borexino, in the Apennines east of Rome. Each of these detectors was conceived and is being built by a sizable international collaboration. Each is housed in an underground laboratory shielded from cosmic ray products other than neutrinos and very energetic muons by a mile or so of earth. Super Kamiokande, the most massive of the three, is a 50-kiloton water-Cerenkov detector. (See figure 1 and the cover of this issue.) In all of these new detectors, sophisticated electronics will record and analyze the individual neutrino collision events. Each detector will register more neutrino interactions in two months than all of the previous solar neutrino experiments have detected in a quarter of a century.