We present a reanalysis of the experimental data of electron capture in $^7$Be embedded in Ta which have been published by other authors. Our goal is to set upper limits on a mixture of electron neutrino with a possible right-handed heavy neutrino in the 150--800 keV mass range. In the published experiment a $^7$Li recoil energy spectrum in the 20--200 eV range was measured. In case of electron capture with emission of a heavy neutrino, the recoil spectrum should be shifted to the lower energies. We search for an additional Gauss-shaped structure with the same energy width as the main K-shell transition peak. For this we digitize the published spectrum curve, find the energy resolution, calculate the moving sum of the events along the spectrum in the energy interval of about 3 sigma of energy resolution. Then we use the statistical error of this sum to exclude at some level the appearance of an additional peak. Finally, we present the upper limits at a 95\% confidence level on electron neutrino -- heavy neutrino mixing element, $U^2$, in the mass matrix. New upper limits are at least one order of magnitude lower than the existing data in 300--800 keV mass range.
Magneto-$ν$: Heavy neutral lepton search using $^{241}$Pu $β^-$ decays
Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；University of Zurich（苏黎世大学）；University of New Mexico（新墨西哥大学）；Université Paris-Saclay（巴黎萨克雷大学）；Korea Research Institute of Standard and Science（韩国标准与科学研究所）；University of Michigan（密歇根大学）
Department of Physics E. Pancini, Università di Napoli Federico II（那不勒斯费德里科二世大学E. Pancini物理系）；INFN Sezione di Napoli（意大利国家核物理研究所那不勒斯分部）；Institute for Particle Physics Phenomenology, Durham University（杜伦大学粒子物理现象学研究所）
Comment on the statistical analysis in "A new experimental limit for the stability of the electron" by H.V. Klapdor-Kleingrothaus, I.V. Krivosheina and I.V. Titkova
IRADCAL: A Monolithic Inorganic Scintillator And Thin Scintillators To Measure Low Energy Electron, Proton And Heavy Ion Albedo Spectrums From Lunar Surface
