New nuclear experiment challenges decades of physics theory
Scientists using a new $730 million U.S. facility have measured the behavior of a heavy nucleus in ways that contradict long-standing models of how atomic nuclei behave. The finding could reshape nuclear physics research priorities and influence how the Department of Energy allocates funding for fundamental science infrastructure.
Originaltitel: Collapse of Nuclear Collectivity along the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mi>N</mml:mi> <mml:mo>=</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> Line
The lifetime of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msup> <a:mrow> <a:mi>J</a:mi> </a:mrow> <a:mrow> <a:mi>π</a:mi> </a:mrow> </a:msup> <a:mo>=</a:mo> <a:msup> <a:mrow> <a:mn>2</a:mn> </a:mrow> <a:mrow> <a:mo>+</a:mo> </a:mrow> </a:msup> </a:mrow> </a:math> state in the self-conjugate <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mmultiscripts> <c:mrow> <c:mi>Ru</c:mi> </c:mrow> <c:mprescripts/> <c:none/> <c:mrow> <c:mn>88</c:mn> </c:mrow> </c:mmultiscripts> </c:mrow> </c:math> nucleus has been determined in an experiment performed using rare-isotope beams provided by the new Facility for Rare Isotope Beams. This is the heaviest <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mi>N</e:mi> <e:mo>=</e:mo> <e:mi>Z</e:mi> </e:mrow> </e:math> nucleus for which such a measurement has been achieved. <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mrow> <g:mmultiscripts> <g:mrow> <g:mi>Ru</g:mi> </g:mrow> <g:mprescripts/> <g:none/> <g:mrow> <g:mn>88</g:mn> </g:mrow> </g:mmultiscripts> </g:mrow> </g:math> was populated by both one-neutron knockout and charge-exchange reactions, and the lifetime of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mrow> <i:msubsup> <i:mrow> <i:mn>14.3</i:mn> </i:mrow> <i:mrow> <i:mo>−</i:mo> <i:mn>3.4</i:mn> </i:mrow> <i:mrow> <i:mo>+</i:mo> <i:mn>2.5</i:mn> </i:mrow> </i:msubsup> <i:mtext> </i:mtext> <i:mtext> </i:mtext> <i:mi>ps</i:mi> </i:mrow> </i:math> was determined using the triple-foil plunger technique. The extracted electromagnetic transition strength shows that the quadrupole collectivity has dropped significantly compared with the highly deformed <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:mrow> <k:mi>N</k:mi> <k:mo>=</k:mo> <k:mi>Z</k:mi> </k:mrow> </k:math> region around <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mrow> <m:mi>A</m:mi> <m:mo>∼</m:mo> <m:mn>80</m:mn> </m:mrow> </m:math> . These results are compared with state-of-the-art large-scale shell-model and discrete nonorthogonal shell-model calculations. The theoretical calculations indicate a moderate triaxial deformation and suggest that low-lying states in this nucleus are no longer dominated by strong many-particle many-hole excitations, unlike the lighter, highly deformed <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:mrow> <o:mi>N</o:mi> <o:mo>=</o:mo> <o:mi>Z</o:mi> </o:mrow> </o:math> nuclei nearby.