Measurement of the response of a gallium metal solar neutrino experiment to neutrinos from a 51Cr source

TL;DR

The paper reports a radiochemical calibration of the SAGE gallium solar-neutrino detector using a high-activity ${}^{51}$Cr source. By placing a well-characterized flux of low-energy neutrinos inside a large Ga target and counting the produced ${}^{71}$Ge, the study validates the extraction and counting efficiencies and constrains the total detector efficiency. The measured neutrino capture cross section agrees with Bahcall and Haxton predictions within uncertainties, indicating no large unaccounted systematics in the solar-neutrino measurements. The results bolster confidence that the observed solar neutrino deficit is a physical phenomenon, not an artifact of experimental methodology. By cross-checking with GALLEX, the work strengthens the case for understanding neutrino flavor transformation and solar neutrino fluxes.

Abstract

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 was measured to be (5.55 +/- 0.60 (stat.) +/- 0.32 (syst.)) x 10^(-45) cm^2. The ratio of this cross section to the theoretical cross section of Bahcall for this reaction is 0.95 +/- 0.12 (exp.) +/- 0.03 (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 for the solar neutrino measurements is correctly determined and provides considerable evidence for the reliability of the solar neutrino measurement.

Figures (12)

• Figure 1: Decay scheme of ${}^{51}$Cr to ${}^{51}$V through electron capture.
• Figure 2: Irradiation assembly (IA).
• Figure 3: Cross section of irradiation assembly (IA). The open circles are cooling channels for liquid Na.
• Figure 4: Cut-away drawing of the source. The Cr rods were placed within the inner cylinders.
• Figure 5: Unshielded Ge detector spectrum of the gamma rays emitted by the Cr source taken on 7 January 1995 at 10:40. Gamma lines are labeled by the isotope of origin. Other contaminants whose lines are not labeled include ${}^{59}$Fe, ${}^{182}$Ta, and ${}^{124}$Sb.