RADIATIVE CAPTURE CROSS SECTIONS OF THE DYSPROSIUM ISOTOPES IN THE 0.023- TO 1-ev RANGE

Use of burnable poisons, such as /sup 164/Dy, are helpful in extending the range of reactor operations and minimizing reactivity changes connected with the burnup of the fuel. Although the radiative cross section of this isotope which is presert in the natural mixture at a concentration of 28.18% is known, the energy dependence of the other isotopes /sup 162/Dy, /sup 162/Dy, and /sup 163/Dy was not previously completely determined. Therefore, the radiative capture cross sections of the Dy isotopes were measured by the time-offlight method, using a pulsed electron accelerator as the source. The prompt gamma radiation emitted by the sample as the result of the (n, gamma ) reaction was recorded by a scintillation detector. Mass spectrographic analysis showed that less than 0.01% of /sup 155/Gd and /sup 157/Gd was contained in the samples. The capture cross section of /sup 162/Dy in the 0.023to 1-ev range was due to resonances at 5.44 and 11.3 ev. The curves obtained indicated that /sup 161/Dy and /sup 163/Dy have levels at a negative'' energy. Tabulations were made also for the capture cross section values for thermal neutrons. (TTT)