Summary
Starting from an exact three-body formulation of nuclear rearrangement, inclastic and break-up processes, we develop an operator reduction procedure of the three-body equations, by which the components from implicit channels—channels different from the initial and final ones—are formally eliminated. This procedure allows us to introduce in a simple way a distorted-wave approximation scheme involving generalized transition potentials, which take account also of contributions from the implicit channels. In order to facilitate the comparison between this approximation scheme and the DWBA, we recast the former one in an alternative form, in which the DWBA contributions appear explicitly separated from the additional ones. The importance of these latter contributions is discussed. As far as rearrangement processes are concerned, it is shown that the polar- and triangular-diagram mechanism contributions—contained in the generalized transition potential—sum up to give, in interesting practical cases, the DWBA.
Riassunto
Si parte da una formulazione esatta a tre corpi per le reazioni nucleari con riarrangiamento, inelastiche e di break-up e — tenendo conto di suggerimenti che provengono da metodi fenomenologici — si introduce una tecnica di riduzione operatoriale che permette di eliminare formalmente le componenti degli operatori di transizione relative ai canali impliciti, cioè a canali diversi da quelli iniziale e finale. In questo contesto si ottiene facilmente un’approssimazione generalizzata con onde distorte in cui il potenziale che causa la transizione ha una struttura più generale di quelle usuali e contiene anche contributi provenienti dai canali impliciti. Al fine di facilitare il confronto fra la DWBA e l’approssimazione generalizzata, l’ampiezza di transizione di quest’ultima viene trasformata in modo tale da isolare i contributi della DWBA. Si dimostra, con riferimento ai processi di riarrangiamento, che, in alcuni casi specifici, i contributi che provengono dai meccanismi descritti dai grafici polare e triangolare e che sono contenuti nel potenziale generalizzato di transizione si sommano in modo da dare, nella rappresentazione delle onde distorte, la DWBA.
Реэюме
Исходя иэ точной трехчастичной формулировки процессов ядерной перегруппировки, неупругих процессов и процессов распада, мы раэвиваем процедуру приведения операторов для трехчастичных уравнений, благодаря которой компоненты иэ неявных каналов — каналов, отличных от начального и конечного каналов — формально исключаются. Эта процедура поэволяет нам ввести простым обраэом приближение искаженных волн, включаюшее обобшенные потенциалы переходов, которые также учитывают вклады от неявных каналов. Чтобы облегчить сравнение между зтой схемой приближения и DWВА, мы представляем рассматриваемую схему приближения в альтернативной форме, в которой вклады DWВА, по-видимому, явно отделяются от дополнительных вкладов. Обсуждается важность зтих добавочных вкладов. Поскольку рассматриваются процессы перегруппировки, то покаэывается, что вклады механиэмов полярных и треугольных диаграмм — которые содержатся в обобшенных потенциалах переходов — в интересных практических случаях суммируются и дают DWВА.
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Anni, R., Taffara, L. & Vanzani, V. Three-body dynamics and channel distortions in direct nuclear reactions. Nuov Cim A 23, 431–446 (1974). https://doi.org/10.1007/BF02821228
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DOI: https://doi.org/10.1007/BF02821228