[U-02_28PM1] Particle Geophysics

★ [U02-11] Borexino: geo-neutrino results

*SUVOROV Yury¹ (1.Yury Suvorov)

キーワード：neutrinos, geo neutrinos, Earth, crust, mantle

Geo-neutrinos are the electron anti-neutrinos produced by long-lived radioactive isotopes (such as U, Th and K) in the earth crust and mantle. Geo-neutrinos can be detected in kiloton scale organic liquid scintillator detectors located in underground laboratories. The detection reaction is the inverse-beta decay, which has a particular signature given by two correlated in space and time prompt and delayed signals.In spite of the strong signature geo-neutrino can only be detected in massive low background set-ups designed for low energy (1 MeV) neutrinos. Borexino at the GranSasso underground laboratory in Italy has been in operation since 2007 to search for sub-MeV solar neutrinos. At present experimental studies of geo-neutrinos are carried out with Kamland at the Kamioka mine in Japan and with Borexino at GranSasso. The first attempt of a geo-neutrino measurement was done in Kamland in 2005. Only in 2010 and 2011 both Borexino and Kamland observed at more the 4sigma C.L. a signal from geo-neutrinos. The search of geo-neutrinos likewise the one of solar neutrinos for the sun provides a unique tool to probe the interior of the earth. Uranium and thorium from the crust and the mantle make the geo-neutrino flux on surface. The energy spectrum of the detected geo-neutrinos depends on the abundance of uranium and thorium and on the different beta decays in the two radioactive chains. A spectroscopy determination of the geo-neutrino signal can be done. This has been recently shown by Borexino. By means of this analysis the ultimate goal of the geo-neutrino search will be the determination of the uranium and thorium content in the mantle. For this purpose a combined analysis of more than one experiment results will be necessary. In this talk we will review the present status of geo-neutrino research. We elaborate on the recent results from Borexino and Kamland. The experimental difficulties and background sources will be discussed.