hans geiger
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Hans Geiger demonstrated that energy and mass are conserved in atomic processes. Hans became an assistant to Ernest Rutherford at the University of Manchester after schooling at Munich and Erlangen Gieger. After the University, he devised equipment to count alpha particles. In 1928, he co-invented the Geiger Counter, a very portable machine that counted alpha particles, with Walther Muller, a fellow physicist. During World War II, he participated in the German attempt to build an atomic bomb.