Bare Potential DWBA for (d, p) Reactions

Abstract

Applicability of potential (BPDWBA), recently applied for heavy ion inelastic reactions with success, to light ion induced transfer reactions is investigated. The reaction 160(d, p) 17 0 and 4°Ca(d, p) 41 Ca at Ed=10.5MeV are studied, for which coupled channel (CC) calculations exist. Search is made of the potential which fit the CC results of (d, d) and (p, p) scatterings. The potentials and/ or the potentials (the distorting potentials in the CC equations) are used in DWBA calculations of (d, p) cross sections. Results of the various types of DWBA distinguished by the choice of the distorting potentials are compared with the CC results. It is found that none of such DWBA's reproduces the CC cross sections. Physical implications of these types of DWBA are discussed in detail. Justification of DWBA has been a long standing problem in the theory of direct nuclear reactions. In a pioneering work on the subject, Perey and Satchlerl) analyzed a (p, p') process with one-phonon excitation. These authors compared DWBA with the method of coupled channels (CC) and concluded that first order perturbation theory in the channel coupling potential was unwarranted when the coupling was strong, but DWBA was still valid even in such a case if the optical potentials, UoPt, were used as the distorting potentials. They argued that the higher order effect of the coupling was taken into account effectively by the Uopt since they correctly described the elastic scattering in the initial and final chan­ nels. Hereafter we shall call this type of DWBA DWBA. Later, however, Satchler 2 ) questioned the theoretical basis of conventional DWBA. As a theoretically more transparent alternative to it he introduced asymmetric DWBA (ADWA) in which the distorting potential was the optical potential for the entrance channel while for the exit channel it was the bare potential, the distorting potential, U, of the CC calculation. The two methods were compared with CC for the case of 56Fe(p, p') with a 2+-phonon excitation. It was found that ADWA agreed with CC better, though only slightly, than conventional DWBA. Also other cases of inelastic scattering were mentioned for which ADW A gave better agreement with experimental data. DWBA with the potential both for the entrance and exit channels was also tested for 56Fe(P, p') and found to be inadequate.