Accessing tens-to-hundreds femtoseconds nuclear state lifetimes with low-energy binary heavy-ion reactions
Annotatsiya
Abstract A novel Monte Carlo technique has been developed to determine lifetimes of excited states in the tens-to-hundreds femtoseconds range in products of low-energy heavy-ion binary reactions, with complex velocity distributions. The method is based on a detailed study of Doppler-broadened $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -ray lineshapes. Its relevance is demonstrated in connection with the $$^{18}\text {O}(7.0\, \text {MeV/u})+\,^{181}\text {Ta}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>18</mml:mn> </mml:msup> <mml:mtext>O</mml:mtext> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>7.0</mml:mn> <mml:mspace/> <mml:mtext>MeV/u</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> <mml:mo>+</mml:mo> <mml:msup> <mml:mspace/> <mml:mn>181</mml:mn> </mml:msup> <mml:mtext>Ta</mml:mtext> </mml:mrow> </mml:math> experiment, performed at GANIL with the AGATA+VAMOS+PARIS setup, to study neutron-rich O, C, N, ... nuclei. Excited states in $$^{17}\text {O}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>17</mml:mn> </mml:msup> <mml:mtext>O</mml:mtext> </mml:mrow> </mml:math> and $$^{19}\text {O}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>19</mml:mn> </mml:msup> <mml:mtext>O</mml:mtext> </mml:mrow> </mml:math> , with known lifetimes, are used to validate the method over the $$\sim 20{-}400\,\text {fs}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>∼</mml:mo> <mml:mn>20</mml:mn> <mml:mo>-</mml:mo> <mml:mn>400</mml:mn> <mml:mspace/> <mml:mtext>fs</mml:mtext> </mml:mrow> </mml:math> lifetime-sensitivity range. Emphasis is given to the unprecedented position resolution provided by $$\gamma $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>γ</mml:mi> </mml:math> -tracking arrays, which turns out to be essential for reaching the required accuracy in Doppler-shift correction. The technique is anticipated to be an important tool for lifetime investigations in exotic neutron-rich nuclei, produced with intense ISOL-type beams.