Semi-empirical mass formula

<p>In <a href="/facts/Nuclear_physics/fzQbt1aF">nuclear physics</a>, the semi-empirical mass formula (SEMF; sometimes also called the Weizsäcker formula, Bethe–Weizsäcker formula, or Bethe–Weizsäcker mass formula to distinguish it from the <a href="/facts/Bethe%25E2%2580%2593Weizs%25C3%25A4cker_process/ClM5eAGc">Bethe–Weizsäcker process</a>) is used to approximate the <a href="/facts/Mass/HHdc8XmF">mass</a> of an <a href="/facts/Atomic_nucleus/orpIm5Xl">atomic nucleus</a> from its number of <a href="/facts/Proton/clCjepXP">protons</a> and <a href="/facts/Neutron/oRCM1geb">neutrons</a>. As the name suggests, it is based partly on <a href="/facts/Scientific_theory/moMsLrUn">theory</a> and partly on <a href="/facts/Empirical_evidence/JUaYSGJc">empirical measurements</a>. The formula represents the liquid-drop model proposed by <a href="/facts/George_Gamow/n79Pqk8R">George Gamow</a>, which can account for most of the terms in the formula and gives rough estimates for the values of the coefficients. It was first formulated in 1935 by German physicist <a href="/facts/Carl_Friedrich_von_Weizs%25C3%25A4cker/HJFv48U0">Carl Friedrich von Weizsäcker</a>, and although refinements have been made to the coefficients over the years, the structure of the formula remains the same today.
</p><p>The formula gives a good approximation for atomic masses and thereby other effects. However, it fails to explain the existence of lines of greater <a href="/facts/Binding_energy/2Q3poXgg">binding energy</a> at certain numbers of protons and neutrons. These numbers, known as <a href="/facts/Magic_number_(physics)/v9PwXFzQ">magic numbers</a>, are the foundation of the <a href="/facts/Nuclear_shell_model/1Qgep495">nuclear shell model</a>.
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Semi-empirical mass formula open-in-new

Semi-empirical mass formula