= Randolf Pohl
{c}
{tag=Physicist}
<Randolf Pohl> led a precision measurement of the <Lamb shift> in muonic <hydrogen>, an exotic <chemical atom> in which a <muon> replaces the <electron>. The heavier orbiting particle is localized much closer to the <proton>, making its <energy levels> especially sensitive to the proton's finite charge distribution.
Measuring the transition and subtracting the other calculated contributions therefore constrains the proton's charge <radius>. The 2010 result disagreed with then-standard determinations, turning nuclear-size extraction into a consistency test across different experimental and theoretical methods.<The size of the proton by Randolf Pohl and others>[Abstract and spectroscopy method: muonic-hydrogen transition, finite-size sensitivity and comparison with other determinations]{ref}
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