-analysis of recent experimental data of elastic scattering and fusion cross sections. From this, energy dependent forms for W F (E) and W DR (E) can be determined and by the dispersion relation the corresponding real polarization potentials V F (E) and V DR (E) are also found. The appearance or absence of the threshold anomaly can therefore be extracted from these energy dependent forms. By turning on and off the potentials responsible for breakup reactions (V DR and W DR) the effect of breakup on fusion can be studied. So, regions of suppresion and of enhancement around the barrier energy can be determined for the nuclear systems under study.]]>
A. Gómez Camacho, E.F. Aguilera, and E.M. Quiroz
Departamento del Acelerador, Instituto Nacional de Investigaciones Nucleares, Apartado Postal 18–1027, 11801, México, D.F. e–mail: agc@nuclear.inin.mx
Recibido el 13 de febrero de 2006
Aceptado el 8 de agosto de 2006
Abstract
]]> A simultaneous Distorted Wave Born Approximation calculation of elastic scattering, fusion and breakup cross sections for energies above and below the Coulomb barrier energy is presented for reactions involving weakly bound projectiles on heavy targets. In the approach, a Woods–Saxon optical potential U is used where its imaginary part W is split into a volume part WF which is only responsible for fusion absorption and a surface part Wdr which accounts for direct reactions. The fusion and direct reaction cross sections are calculated in terms of WF and WDR respectively. The optical potential parameters are determined from a simultaneous
–analysis of recent experimental data of elastic scattering and fusion cross sections. From this, energy dependent forms for WF (E) and WDR (E) can be determined and by the dispersion relation the corresponding real polarization potentials VF (E) and VDR (E) are also found. The appearance or absence of the threshold anomaly can therefore be extracted from these energy dependent forms. By turning on and off the potentials responsible for breakup reactions (VDR and WDR) the effect of breakup on fusion can be studied. So, regions of suppresion and of enhancement around the barrier energy can be determined for the nuclear systems under study. Keywords: Nuclear reactions; exotic nuclei; threshold anomaly.
Resumen
Dentro de la aproximación de ondas distorsionadas de Born, se hace un estudio simultáneo de reacciones de dispersión elástica, fusión y de rompimiento del projectil conocido como breakup para reacciones nucleares que involucran projectiles debilmente ligados con blancos pesados. Se utilizan potenciales de Woods–Saxon U en los que la parte imaginaria W que es responsable de todos los procesos de absorción es dividida en dos partes, una WF responsable solo de los procesos de fusión y otra WDR de los demás procesos, es decir de las reacciones directas. Los parámetros de tales potenciales serán determinados através de un ajuste simultáneo de los datos experimentales de fusión y de dispersion elástica. Se formulan entonces formas dependientes de la energía para WF y WDR através de las cuales de pueden determinar las partes reales de los potenciales de polarización VF y VDR usando la relación de dispersión. Del comportamiento con la energía de estas cuatro formas puede entonces determinarse la presencia o ausencia de la anomalía de umbral para el potencial de fusión y de reacciones directas respectivamente y en consecuencia del potencial total de absorción W. Finalmente considerando o anulando los potenciales VDR y WDR se realiza un estudio de la influencia que el proceso de rompimiento del projectil (breakup) tiene sobre el de fusión.
Descriptores: Reacciones nucleares; núcleos exóticos; anomalía de umbral.
PACS: 24.10.–i; 25.70.Jj; 23.23.+x; 56.65.Dy
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]]>Acknowledgments
This work has been supported in part by CONACYT under project 44251.
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