Ernst Pernicka

GALLEX solar neutrino observations: Results for GALLEX IV

Abstract We report the GALLEX solar neutrino results for the measuring period GALLEX III, the period from 12 October 1994-4 October 1995. Counting for these runs was completed on 29 March 1996. The GALLEX III result (14 runs) is [53.9 ± 10.6(stat.) ± 3.1 (syst.)] SNU (1σ). This is 15.8 SNU below but statistically compatible with the new combined result for GALLEX (I+II+III) (53 runs), which is [69.7 ± 6.7(stat.) −4.5 +3.9 (syst.)] SNU (1σ) or (69.7 −8.1 +7.8 ) SNU with errors quadratically added. We also give the preliminary result from our second 51 Cr-source experiment: the measured detector response is 83±10% of expectation. The combined result from both GALLEX 51 Cr-source experiments is 92±8% of expectation.

Solar neutrinos observed by GALLEX at Gran Sasso.

We have measured the rate of production of 71Ge from 71Ga by solar neutrinos. The target consists of 30.3 t of gallium in the form of 8.13 M aqueous gallium chloride solution (101 t), shielded by ≈ 3300 m water equivalent of standard rock in the Gran Sasso Underground Laboratory (Italy). In nearly one year of operation, 14 measurements of the production rate of 71Ge were carried out to give, after corrections for side reactions and other backgrounds, an average value of 83 + 19 (stat.) ± 8 (syst.) SNU (1σ) due to solar neutrinos. This conclusion constitutes the first observation of solar pp neutrinos. Our result is consistent with the presence of the full pp neutrino flux expected according to the “standard solar model” together with a reduced flux of 8B + 7Be neutrinos as observed in the Homestake and Kamiokande experiments. Astrophysical reasons remain as a possible explanation of the solar neutrino problem. On the other hand, if the result is to be interpreted in terms of the MSW effect, it would fix neutrino masses and mixing angles within a very restricted range.

First results from the 51Cr neutrino source experiment with the GALLEX detector

Abstract The radiochemical GALLEX experiment, which has been measuring the solar neutrino flux since May 1991, has performed an investigation with an intense man-made 51 Cr neutrino source (61.9 ± 1.2 PBq). The source, produced via neutron irradiation of ≈ 36 kg of chromium enriched in 50 Cr, primarily emits 746 keV neutrinos. It was placed for a period of 3.5 months in the reentrant tube in the GALLEX tank, to expose the gallium chloride target to a known neutrino flux. This experiment provides the ratio, R , of the production rate of Cr-produced 71 Ge measured in these source exposures to the rate expected from the known source activity: R = 1.04 ± 0.12. This result not only constitutes the first observation of low-energy neutrinos from a terrestrial source, but also (a) provides an overall check of GALLEX, indicating that there are no significant experimental artifacts or unknown errors at the 10% level that are comparable to the 40% deficit in observed solar neutrino signal, and (b) directly demonstrates for the first time, using a man-made neutrino source, the validity of the basic principles of radiochemical methods used to detect rare events (at the level of 10 atoms or less). Because of the close similarity in neutrino energy spectra from 51 Cr and from the solar 7 Be branch, this source experiment also shows that the gallium detector is sensitive to 7 Be neutrinos with full efficiency.

Ru, Re, Os, Pt and Au in iron meteorites

The refractory siderophiles Ru, Re, Os and Pt and moderately volatile Au were determined in 41 iron meteorites by neutron activation analysis. For the first time element-Ni trends are defined for groups IID and IIIF; these support a magmatic origin. Concentrations of Re and Os, like that of Ir, are lower in nonmagmatic group IIICD than in IAB at low Ni-concentrations, whereas Ru and Pt concentrations strongly overlap. In groups IAB and IIICD Ru and Pt slopes are slightly steeper than those of Re, Os and Ir on log element-log Ni diagrams; this contrasts with trends observed in magmatic groups, where the Ru and Pt slopes are much less steep. There is no significant change in the ReOs and IrOs ratios with Ni content in nonmagmatic groups, but the ReOs ratio increases by a factor of ∼3 and the OsIr ratio decreases by a factor of ∼6 as one proceeds from low-Ni to moderately high-Ni members of the large magmatic groups IIAB and IIIAB. It should be possible to determine radiometric ages by the 187Re-187Os method for individual iron meteorite groups providing precise isotopic ratios can be determined at low (0.1 μg) Os concentrations. In group IIIAB at Ni concentrations above 90 μg the steep decrease of Re, Os and Ir with Ni levels off and the interelement ratios show appreciable scatter. A plausible explanation of these observations is contamination of the residual molten core with small amounts of late primitive melts draining from the mantle.

GALLEX results from the first 30 solar neutrino runs

Abstract We report new GALLEX solar neutrino results from 15 runs covering 406 days (live time) within the exposure period 19 August 1992–13 October 1993 (“GALLEX II”). With counting data considered until 4 January 1994, the new result is [78±13 (stat.) ±5 (stat.)] SNU (1σ). It confirms our previous result for the 15 initial runs (“GALLEX I”) of [81±17( stat .)±9( syst .)] SNU. After two years of recording the solar neutrino flux with the GALLEX detector the combined result from 30 solar runs (GALLEX I + GALLEX II) is [79±10( stat .)±6( syst .)] SNU (1 σ ). In addition, 19 “blank” runs gave the expected null result. GALLEX neutrino experiments are continuing.

Implications of the GALLEX determination of the solar neutrino flux

Abstract The GALLEX result 83 ± 19 (stat.) ± 8 (syst.) SNU is two standard deviations below the predictions of stellar model calculations (124–132 SNU). To fit this result together with those of the chlorine and Kamiokande experiments requires severe stretching of solar models but does not rule out such a procedure, leaving the possibility of massless neutrinos. It clearly implies that the pp neutrinos have been detected. The Mikheyev-Smirnov-Wolfenstein (MSW) mechanism provides a good fit, and the GALLEX result fixes the Δm 2 and sin 2 2 θ parameters in two very confined ranges (around Δm 2 = 6 × 10 −6 eV 2 and sin 2 2 θ = 7 × 10 −3 and around Δm 2 = 8 × 10 −6 eV 2 and sin 2 2 θ = 0.6). Explanations of the solar neutrino problems based on the decay or magnetic interactions of neutrinos are disfavoured.

GALLEX solar neutrino observations: Complete results for GALLEX II

Abstract We report the solar neutrino results from the complete set of runs in the exposure period, GALLEX II, from 19 August 1992 - 23 June 1994. Counting for these runs was completed on 10 December 1994. The GALLEX II result (24 runs) is [75.2±9.7 (stat) −4.6+4.1 (syst)] SNU (1 σ). After three years of recording the solar neutrino flux with the GALLEX detector, the combined result from the 39 completed solar runs (GALLEX I+II) is [77.1±8.5 (stat) −5.4+4.4 (syst) SNU (1 σ) or 77.1 −10.1+9.6 SNU with errors combined in quadrature. The combined error (± 13%) has now approached a level where the limits on the derived contribution of 7Be neutrinos to the GALLEX signal confront the predictions of solar models.

The Determination of Lead Isotope Ratios by Multiple Collector Icp-Ms: A Case Study of Early Bronze Age Artefacts and their Possible Relation With Ore Deposits of the Erzgebirge*

Lead isotope analyses of Early Bronze Age metal artefacts from the Aunjetitz (Unetice) culture in central Germany and Bohemia were determined in order to find out whether they could be related to ore sources of the Erzgebirge. Historical mining began only in the 12th century AD, but despite the lack of convincing field evidence it has frequently been suspected that this region was already being exploited in prehistoric times. For the determination of the lead isotope ratios, the new technique of multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) was employed, which combines relatively easy sample preparation with highly precise and accurate measurements. The results show that there is still no evidence for prehistoric mining in the Erzgebirge, but the Rammelsberg deposit in the Harz Mountains might have supplied some of the copper. Mining of stream tin in the Erzgebirge remains a possibility, but no positive evidence can be extracted from the data.

GALLEX solar neutrino observations. The results from GALLEX I and early results from GALLEX II

Abstract The first period (GALLEX I) of data taking in the GALLEX solar neutrino experiment has been completed. From 14 May 1991 to 29 April 1992, the experiment observed the solar neutrino flux using neutrino capture by 71 Ga to form 71 Ge. Counting ended on 2 November 1992. The final result from the 15 runs of this periodpis (81±17 [ stat .]±9 [ syst .]) SNU (1 σ ). The first 6 runs of GALLEX II recorded the neutrino signal from 19 August 1992 to 3 February 1993. The preliminary result for this period is (97±23 [ stat .]±7 [ syst .]) SNU (1 σ ). With counting data considered until 29 April 1993, the joint result for all 21 runs is (87±14 [ stat .]±7 [ syst .]) SNU (1 σ ). The present neutrino recording period GALLEX II is continuing with one solar exposure every four weeks.

Precise and accurate determination of boron isotope ratios by multiple collector ICP-MS: origin of boron in the Ngawha geothermal system, New Zealand

Abstract A new technique has been developed for the measurement of boron isotope ratios in fluids using a double focusing multiple collector inductively coupled plasma (ICP) mass spectrometer. Sample introduction using a direct injection nebuliser was found to eliminate memory problems that are common where spray chambers are involved. The 4–9% mass bias can be corrected for by bracketing sample measurements with standards. As matrices were found to affect the mass bias all samples must be purified and that sample and standard solutions must be similar. A new purification technique was developed that yields adequately purified samples. Using this technique, it is possible to make rapid measurements (4 min) from samples containing 250 ng B to a precision of ±0.2‰. This analytical technique has been applied to the Ngawha geothermal system in New Zealand in an attempt to determine the source of B in geothermal fluids where the B concentrations can exceed 100 mmol/l. The δ11B values range between −3.1‰ and −3.9‰ indicating that no seawater sources are involved and that the elevated B concentrations can only be accounted for by low water/rock ratios with the B being derived from basement greywacke/argillite. The similarity of B isotope ratios for hydrothermal fluids that have been diluted and cooled with groundwaters indicates that isotope fractionation due to adsorption is unlikely to occur in cool geothermal fluids (