Proton Decay of Analog States Formed in the (d,n) Reaction

Abstract

Cross sections were measured for proton decay from isobaric analog states (IAS; r=7Vf-l) formed in the (d,n) reactions on the following targets: O 16 , AF, Ni 64 , Zn 68 , Y 89 , Zr 90 -91 -92 ' 94 , Mo 92,94 -98 , Sn 114 ' 116 ' 118 -120 , and Pb 206 . A AE-E detector telescope having a combined energy resolution of about 34 keV was used. Excitation functions (0iab= 170°) were obtained with the deuteron energies ranging from the (d,n) threshold of the IAS to about 16 MeV. Angular distributions were also obtained at the various incident energies for a few of the strong transitions. The cross sections are large only for reactions leading back to the target ground state when, in addition, the neutron decay channels are closed to the IAS. Particular attention is paid to the large variations in the cross sections for reactions proceeding through the analogs of 2d 5 /2, Ssi/2, and 2dz/2 states in Zr, Mo, and Sn isotopes. At incident energies several hundred keV above the (d,n) threshold, these variations are shown to be consistent with a sequential process in which the (d,n) formation mechanism is direct, when the decay through the spreading width is explicitly taken into account in the branching ratios. However, the over-all energy dependence of the (d,n) cross sections, particularly near threshold, deviate sharply from that predicted by a simple direct process in the stripping model. From the study of the angular distributions of the decay to the 0 + ground state from the d 5 /2 (g.s.) IAS in Nb 91 * and Tc 98 *, the w-substate populations of the IAS are extracted. The values at energies near threshold suggest the importance of spinorbit interactions in the (d,n) formation mechanism. Phys. Rev. Letters 17, 926 (1966).

The88Sr(d, n∼p)88Sr reaction

“…The similarity of the present (d, np) data to the 9~ n/~) data of Cue and Richard [13] is very striking, as is its lack of similarity to the 92Mo(d, np) data also obtained by Cue and Richard. An explanation of these differences must mainly lie in the proton partial width of the IAS in each instance: for 89yA, Fp,-~6 keV; for 91NbA, Fp,,-3 keV; for 93Tca, Fp,~l.5 keV [25].…”

“…As is seen from our data (Fig. 2b) the 88Sr(d, n/~) total cross section rises from threshold to maximum in less than 0.25 MeV, as compared to 0.5 MeV for 9~ and about 4 MeV for 92Mo [13,15].…”

“…Optical potentials are as given in the text cedure to compute or estimate Rp is evident in the literature concerning the (p, np) reactions. For (d, n/~) the interpretation of Rp is further complicated by the high probability of branching [13] in the IAS decay.…”

“…When the f,, are known, they can be used to convert the measured differential cross section at a given angle directly to the angle-integrated cross section. Cue and Richard [13] have previously extracted the experimental m-substate populations for the d~/z IAS in 91Nb, and 93Tc by least-squares fits to the i0 angular distributions, from threshold to 10 MeV above. Alexander and Watson [19] have performed a similar analysis for 9~ We have used these results to angle-integrate our 170 ~ 88Sr(d, np) cross sections, with results shown in Fig.…”

“…The direct population of isobaric analog states (IAS) by (d, n), (p, d), and (3He, d) has also been of considerable recent experimental interest [11,12]. However, the measurement of decay protons (/3) from the residual IAS, after population via (d, n) or (3He, d) has very seldom been carried out [1,13,14]. This is surprising, because the (d, np) cross section provides data directly complementary to the (d,p)-excitation-function studies of the charge-exchange coupling [15].…”