Role of breakup and direct processes in deuteron-induced reactions at low energies

Background: Recent studies of deuteron-induced reactions around the Coulomb barrier $B$ pointed out that numerical calculations for deuteron-induced reactions are beyond current capabilities. The statistical model of nuclear reactions was used in this respect since the compound-nucleus (CN) mechanism was considered to be responsible for most of the total-reaction cross section ${\sigma }_R$ in this energy range. However, specific noncompound processes such as the breakup (BU) and direct reactions (DR) should be also considered for the deuteron-induced reactions, making them different from reactions with other incident particles.

Purpose: The unitary and consistent BU and DR consideration in deuteron-induced reactions is proved to yield results at variance with the assumption of negligible noncompound components.

Method: The CN fractions of ${\sigma }_R$ obtained by analysis of measured neutron angular distributions in deuteron-induced reactions on ${}^{27}\mathrm{Al}$, ${}^{56}\mathrm{Fe}$, ${}^{63,65}\mathrm{Cu}$, and ${}^{89}\mathrm{Y}$ target nuclei, around $B$, are compared with the results of an unitary analysis of every reaction mechanism. The latter values have been supported by the previously established agreement with all available deuteron data for ${}^{27}\mathrm{Al}$, ${}^{54,56-58,\mathrm{nat}}\mathrm{Fe}$, ${}^{63,65,\mathrm{nat}}\mathrm{Cu}$, and ${}^{93}\mathrm{Nb}$.

Results: There is a significant difference between the larger CN contributions obtained from measured neutron angular distributions and calculated results of an unitary analysis of every deuteron-interaction mechanism. The decrease of the latter values is mainly due to the BU component.

Conclusions: The above-mentioned differences underline the key role of the breakup and direct reactions that should be considered explicitly in the case of deuteron-induced reactions.

Figure 1

(a,c) Comparison of the CN fraction of the total-reaction cross section ${\sigma }_R$, obtained by analysis of measured neutron angular distributions in deuteron-induced reactions on (a) ${}^{27}\mathrm{Al}$ and (c) ${}^{56}\mathrm{Fe}$ target nuclei [6] around the Coulomb barrier, and the calculated values [9, 10] of this fraction (solid curves) as well as for the BU+DR (dashed curves) and PE (dotted curves) processes. (b,d) The corresponding calculated cross sections [9, 10] of either the BU+DR components sum (dashed curves) or the distinct BU (dash-dotted curves), where $(d,p)$ and $(d,n)$ are stripping direct reactions (dash-dot-dotted and short dash-dotted curves, respectively), while ${\sigma }_R$ values are also shown (short-dotted curves).

Figure 2

Same as Fig. 1 but for the target nuclei ${}^{63,65}\mathrm{Cu}$, with the measured neutron angular distributions of Ref. [1], and calculations of Ref. [11].

Figure 3

Same as Fig. 1 but for ${}^{89}\mathrm{Y}$ nucleus, with measured neutron angular distributions of Ref. [2], and DR calculations [12] for the similar odd-even neighboring nucleus ${}^{93}\mathrm{Nb}$.