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The comparative advantages and drawbacks of some reactor-produced arsenic radioisotopes having favourable characteristics for their use as tracers are discussed. The study comprises their preparation based on: (a) capture reactions on germanium; (b) threshold reactions on germanium, selenium and bromine; (c) secondary reactions on germanium, induced by recoil protons and tritons produced by the action of neutrons on lithium. The recommended options for the production of relatively short half-life radionuclides are 77 As by capture on germanium or 76 As via (n,α) reaction on bromine, while two different ways are applicable for the production of 74 As, longer-lived radioisotope.

Abstract. The problems related with the departures from the ideal behaviour of the epithermal component of the neutron spectrum are discussed, in connection with the measurement of resonance integrals. The characteristics of the methods for the measurement of the α parameter are commented and the bases of a new method for the determination of mean effective resonance energy, developed at the authors' laboratory, are briefly described. On these grounds, the application to the correct measurement of the resonance integrals of 68 Zn(n,γ) 69m Zn, 70 Zn(n,γ) 71 Zn and 70 Zn(n,γ) 71m Zn is presented.

SummaryCross sections, averaged over a