Thorium dispenser cathode

Thorium dispenser cathode

NOTES FROM THE BARTOL RESEARCH FOUNDATION NUCLEAR RESONANCE FLIJORESCENCE IN As’6 * BY FRANZ R. METZGER With gaseous sources of Se76 in the form of ...

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NOTES FROM THE BARTOL RESEARCH FOUNDATION NUCLEAR RESONANCE FLIJORESCENCE IN As’6 * BY

FRANZ R. METZGER

With gaseous sources of Se76 in the form of selenium oxide, resonance scattering from the 265 kev leve1 in As’~ has been observed.’ Preliminary measurements indicate an isotopie distribution of the resonance radiation and thus favor assignment of spin 1/2 to the 265 kev leve1 in As’~. Self-absorption experiments indicate a mean life of 10~l1 second for the 265 kev transition. Although this lifetime is one order of magnitude longer than the prediction of the single particle model,2 it is considerably shorter than most Ml lifetimes.3 * Assisted by the joint program of the ONR and AEC. l For the disintegration scheme of S+, see, for example, A. W. SCEARDTAND J. P. WELKER, Phys. Rew., Vol. 99, p. 810 (1955). s V. F. WEINHOPF, Phys. Reu., Vol. 83, p. 1073 (1951). *R. L. GRAHAM AND R. E. BELL, Cm&. Journ. Phys., Vol. 31, p. 377 (1953). THORIUM

DISPENSER CATHODE * BY

D. L. GOLDWATER AND W. E. DANFORTH

Encouraging first results have been obtained in the development of a thorium-dispenser type of cathode for magnetron and other power tube use. The cathode is fabricated in three steps: (a) a porous tungsten matrix is sintered onto the base material, (b) thorium is melted on the surface of the matrix, running in and filling the pores, (c) the thorium-impregnated matrix is ground to final size. Average values of d-c. emission current obtained run from 1 amp.cmd2/ at 1520” C. to 2.5 amp.cmm2 at 1630. Life tests at these current densities as long as 100 hours have been completed without deterioration of the emitting properties. The incorporation of thorium in the form of a thorium-molybdenum alloy is also being studied. It is hoped that the loss of thorium from the cathode by evaporation may thereby be decreased. The use of an alloy, of about 70% Th-30% Mo, rather than the pure element, appears to have no undesirable effects on the thermionic properties of this type of cathode. * This work is supported by the U. S. Navy Bureau of Ships under contract NObsr-72536. 229