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[en] The invention concerns a neutron detector adapted for use in the core instrumentation of nuclear reactors. It comprises an emitter electrode which, upon irradiation with neutrons, emits electrons by means of (n,γ) processes, a collector electrode, and a dielectric disposed between the emitter and the collector electrode. Thulium 169 or terbium 159 is used as the emitter substance. With this emitter substance a prompt signal is obtained, the magnitude of which hardly changes for years;any delayed signals that may build up and any interference currents due to them are so small that they can be compensated for by simple, known means. (Official Gazette)
[en] The magnetic dipole (M1) response of the 169Tm nucleus is investigated from a theoretical point of view. The theoretical tool used in this study is the Rotational Invariant Quasiparticle Phonon Nuclear Model (RI-QPNM) which gives a possibility to eliminate spurious contributions in the M1 spectrum. In the framework of this model, both the low-lying and high-lying parts of the M1 excitation spectrum of 169Tm are calculated. The result shows that the low-lying excitations have almost pure orbital character and can be interpreted as scissors mode, whereas the high-lying transitions can be read as spin-flip mode because of its spin nature. The reduced transition probability summed up in the energy range 2–4 MeV is found to be which agrees with the available experimental data. The fragmentation of the low-energy M1 strength is also well reproduced. This is also the first study in which both the low-lying and high-lying M1 spectrum of the 169Tm nucleus is theoretically investigated.
[en] Although neutron capture by stable isotopes has been extensively measured, there are very few measurements on unstable isotopes. The intense neutron flux at the Manual Lujan Jr. Neutron Scattering Center at LANSCE enables us to measure capture on targets with masses of about 1 mg over the energy range from 1 eV to 100 keV. These measurements are important not only for understanding the basic physics, but also for calculations of stellar nucleosynthesis and Science-Based Stockpile Stewardship. Preliminary measurements on 169Tm and 171Tm have been made with deuterated benzene detectors. A new detector array at the Lujan center and a new radioactive isotope separator will combine to give Los Alamos a unique capability for making these measurements