Uniform large-area (high-radioactivity) LB film radiation source permitting very precise electron spectroscopy

As part of an effort to determine the mass of neutrino from measured beta-ray spectra of tritium, a study is made to identify methods effective for providing spectra with high energy resolution using a high-radioactivity radiation source. To meet the requirements, the Langmuir and Blodgett (LB) method is adopted to develop a radiation source. This method serves to control the thickness of a radiation source at a monomolecular level, permitting the construction of a radiation source that is extremely small in thickness, uniform at a molecular level, and large in area. This ensures a high radioactivity. A shift in the position of the focus is corrected by the non-equivalent potential method, which is intended to apply a varying potential to accelerate or decelerate the beta rays to allow them to converge into a focus at the appropriate position. This ensures a high resolution. A tritium-labeled source and reference source with the same chemical composition are prepared and used to derive a highly reliable response equation. The LB film radiation sources developed have a very small thickness of about 50 angstroms. (N.K.)