First <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>β</mml:mi></mml:mrow></mml:math> -Delayed Two-Neutron Spectroscopy of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>r</mml:mi></mml:mrow></mml:math> -Process Nucleus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>In</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>134</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> and Observation of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>i</mml:mi></mml:mrow><mml:mrow><mml:mn>13</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> Single-Particle Neutron State in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Sn</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>133</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math>

Abstract

This manuscript reports on the direct observation of a β-delayed two-neutron emission in a study of 134In at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in β-decay of the long-sought 13/2+ excited state in 133Sn, attributed to be the neutron single-particle i13/2 orbital. The observation of sequential neutron emission is used to extract the relative population of the i13/2 state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the r-process path. Understanding β-delayed two-neutron emission probabilities is essential to validate models used in astrophysical r-process nucleosynthesis calculations. Observing two-neutron emissions in β-decay paves the way for new experiments to study energy and angular correlations for β-delayed multineutron emitters.