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Victor Weisskopf developed a statistical treatment of particle emission from highly excited heavy atomic nuclei. His 1937 paper compares the process with evaporation: the excitation energy is shared among many internal quantum states, and the available final states constrain which particles can escape with which energies. This connects nuclear level density with emission probabilities and approximately thermal-looking outgoing spectra. Nuclear evaporation supplies a way to predict the aggregate outcome of a complicated nuclear reaction without following every individual internal trajectory.^[ref]

Named for Victor Weisskopf, a Weisskopf estimate is a benchmark electromagnetic nuclear transition strength based on a simple single-particle size model. It supplies a scale against which enhancement or hindrance is measured, rather than a universal rate. The partial rate contains both the photon-energy power $E_{\gamma }^{2L+1}$ and the actual reduced nuclear strength. Electric and magnetic multipoles at different energies cannot be universally ranked by order alone.^[ref]