# Spontaneous emission and neutron decay
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## https://en.wikipedia.org/wiki/Spontaneous_emission
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- https://en.wikipedia.org/wiki/Stimulated_emission
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- 2016 - Sidney Nagel, Burton [Echoes from Anharmonic Normal Modes in Model Glasses](https://arxiv.org/pdf/1601.05157.pdf)
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*We show that these echoes are due to anharmonic, weakly-coupled vibrational modes*, and perhaps **provide an alternative explanation** for the phonon echoes observed in glasses at low temperatures
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We offer **an 
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2016 [Random Nonlinear Infinite-Level-System Model for **Amorphous Solid Phonon Echo and Saturation Phenomena**](https://arxiv.org/abs/1510.05538)
Di Zhou, Anthony J. Leggett
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## https://en.wikipedia.org/wiki/Free_neutron_decay
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in free space
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# Parents
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* QSNS universality - Leggett et al⏎