Collapse of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>28</mml:mn></mml:math>Shell Closure in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">S</mml:mi><mml:mprescripts/><mml:none/><mml:mn>42</mml:mn></mml:mmultiscripts><mml:mi mathvariant="normal">i</mml:mi></mml:math>

The energies of the excited states in very neutron-rich $^{42}\mathrm{S}\mathrm{i}$ and $^{41,43}\mathrm{P}$ have been measured using in-beam $\ensuremath{\gamma}$-ray spectroscopy from the fragmentation of secondary beams of $^{42,44}\mathrm{S}$ at $39A\text{ }\text{ }\mathrm{MeV}$. The low ${2}^{+}$ energy of $^{42}\mathrm{S}\mathrm{i}$, 770(19) keV, together with the level schemes of $^{41,43}\mathrm{P}$, provides evidence for the disappearance of the $Z=14$ and $N=28$ spherical shell closures, which is ascribed mainly to the action of proton-neutron tensor forces. New shell model calculations indicate that $^{42}\mathrm{S}\mathrm{i}$ is best described as a well-deformed oblate rotor.

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