SEARCH FOR THE (n,t) REACTION AT 14 MEV IN SOME MEDIUM WEIGHT NUCLEI

Abstract

The (n,t) reaction a t 14.6 Mev has been observed to occur in SaZ with a cross section of 4 f 1 microbarns. Upper limits for the cross section of this reaction are also given for Ca40, Cr60, Fe64, and Zne4 and the results are discussed qualitatively in the light of recently reported (10) (n,He3) reactions. INTRODUCTIONAmong various types of nuclear reactions which are eilergetically possible with 14-Mev neutrons, the (n,t) reaction has been studied only in very light nuclei (1,2,3,4). In accordance with the reciprocity theorem such reactions should be important in some cases since reactions of the type (t,n) are known to occur a t 2.65 Mev in medium weight nuclei (5, 6).Intuitively the emission of a complex loosely bound structure such as a triton seems much less probable than that of single-particle emission. In early work on (p,t) reactions, however, Cohen and Handley (7) already concluded that the inherent probability for triton emission, in the breakup of a compound nucleus a t least, was little, if any, less than that for protons or neutrons. Reactions of the type (n,t) are in general characterized by large negative Q values and on the statistical theory the cross sections are expected to be generally very small. In lighter elements, however, a strong component of direct interaction is evident in Li6 and Li7 (1) as well as in Be9 (3). More recent work by Cohen and others (8, 9) on the (p,t) reaction a t 23 i\/Iev shows strong evidence for a pickup mechanism for this reaction in heavier elements.Recently Icumabe et al. (10) have reported the occurrence of (n,He3) reactions a t 14.8 Mev in Mns5, Corn, AsT5, and Rh103. The cross sections observed range in value from 1 to 6 millibarns and the authors have suggested several possible direct interaction mechanisms to account for the cross-section magnitudes.In view of the accumulating evidence of significant contributions froill direct interaction in 14-Mev neutron reactions, we have made a cursory search for the (n,t) reaction in medium weight elements. Several isotopes were selected for study by the activation method, from a consideration of reaction Q values and unambiguous identification of the product nucleus with the (n,t) reaction. This has restricted us to stable even-even target nuclei of low neutron number, to avoid interference from (n,p) or (n,d) reactions on other isotopes. EXPERIMENTALThe various targets were bombarded with neutrons of average energy 14.6 Mev (11) from the T(d,n)He4 reaction using about 1 ma of 120-kev deuterons incident on a thick tritium-loaded titanium target.* Cross sections were measured by comparison of the positron activity induced in the sample with t h a t induced in a fluorine "flux monitor"

Observation and cross-section of the reaction Zn64(n, t)Cu62

“…For this purpose, we investigated the cross-section of Zn64(n, t)Cu 62. The existence of this reaction could not be confirmed by previous investigations anda 100 p,b upper limit was given for the cross-section [2].…”