Cross section measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>Sm</mml:mi><mml:mprescripts/><mml:none/><mml:mn>144</mml:mn></mml:mmultiscripts><mml:mo>(</mml:mo><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi>n</mml:mi><mml:mo>)</mml:mo><mml:mmultiscripts><mml:mi>Gd</mml:mi><mml:mprescripts/><mml:none/><mml:mn>147</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> reaction for studying the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math>-nucleus optical potential at astrophysical energies

Abstract

Background: Nuclear reactions involving $\ensuremath{\alpha}$ particles play an important role in various astrophysical processes such as the $\ensuremath{\gamma}$ process of heavy element nucleosynthesis. The poorly known low-energy $\ensuremath{\alpha}$-nucleus optical potential is a key parameter to estimate the rates of these reactions.Purpose: The $\ensuremath{\alpha}$-nucleus optical potential can be tested by measuring the cross section of $\ensuremath{\alpha}$ scattering as well as $\ensuremath{\alpha}$-induced reactions. Low energy elastic $\ensuremath{\alpha}$ scattering on $^{144}\mathrm{Sm}$ has recently been measured with high precision. The aim of the present work was to complement that work by measuring the $(\ensuremath{\alpha},n)$ cross sections on $^{144}\mathrm{Sm}$ at low energies. The experimental data shall be used to constrain the $\ensuremath{\alpha}$-nucleus optical model potential. From this potential the $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$ reaction rate can be derived with reduced uncertainties.Method: The $^{144}\mathrm{Sm}(\ensuremath{\alpha},n)^{147}\mathrm{Gd}$ reaction was studied by bombarding Sm targets with $\ensuremath{\alpha}$ beams provided by the cyclotron accelerator of Atomki. The cross section was determined using the activation method. The $\ensuremath{\gamma}$ radiation following the decay of the $^{147}\mathrm{Gd}$ reaction product was measured with a high-purity germanium (HPGe) detector. The experimental data are analyzed within the statistical model.Results: The cross section was measured in the $\ensuremath{\alpha}$-energy range between 13 and 20 MeV in 1 MeV steps, i.e., from close above the $(\ensuremath{\alpha},n)$ threshold. The results were compared with statistical model calculations using various approaches and parametrizations for the $\ensuremath{\alpha}$-nucleus optical potential, and excellent agreement was obtained for two recent potentials. However, these potentials cannot reproduce literature data for the $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$ reaction with the same accuracy.Conclusions: Constraints for the $\ensuremath{\alpha}$-nucleus potential were derived from an analysis of the new $^{144}\mathrm{Sm}(\ensuremath{\alpha},n)^{147}\mathrm{Gd}$ data and literature data for $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$. These constraints enable a determination of the reaction rate of the $^{144}\mathrm{Sm}(\ensuremath{\alpha},\ensuremath{\gamma})^{148}\mathrm{Gd}$ reaction with significantly reduced uncertainties of less than a factor of 2.

Topics & Concepts