The mass of the neutrino from electron capture in 163Ho

Whether there is mass in neutrinos or not is one of the interesting problems of physics at present. As for electron neutrinos, the direct measurement of the mass of their antiparticles has been carried out many times so far, but the example of the measurement for the normal particles is few. The author's group considers that the direct measurement of the mass of the normal particles is meaningful, and has continued the research using the experimental method which was devised by themselves. This time, the results were able to be put in order, therefore, those are reported. For this measurement, the orbital electron capture and decay process of 163Ho nuclei is used. The course of the researches on the mass of electron neutrinos is outlined. The principle of the measurement is explained. 163Ho was produced by using the AVF cyclotron of Tohoku University CYRIC and utilizing 164Dy(p,Zn)163Ho reaction. The experiments on 163Ho and Dy are reported, and the derivation of the partial decay constants by the electron capture of 163Ho nuclei and the experimental results are described. The examination of the experimental results and the relation with foreign researches are reported. (K.I.)