Results on 7Li solar axions

2008 - Measurements on LiF samples carried out by using two low background HP Ge detectors. Two LiF powders of different production and a LiF(W) crystal have been used.

The measured spectra have been analyzed, preliminarly, in order to identify the radiactive contaminants. The results show that the LiF(W) crystal is very pure with respect to the powders and only limits on the presence of radioactive contaminants have been obtained for it. Thus further measurements are planned with suitable LiF(W) crystal.
Presently, the spectrum collected with the LiF powder sample of 243 g during 722 h does not show any peak at energy of 478 keV (see Figure). A limit on the axion mass have been derived: ma < 13.9 keV at 90% C.L.

This limit improves the previous available one. Data collected with other two LiF samples were processed in a similar way but the obtained limits were slightly worse. This is related with lower mass of the second LiF sample and with the lower efficiency of the Ge detector used to measure the radiopurity of the LiF(W) crystal.

It has also been investigated in details the reachable sensitivity on 7Li solar axion mass when using pure LiF(W) crystals.