# In the Pound Rebka Experiment, how were the gamma rays generated?

Lest my question be dismissed as poorly-worded, let me first say that I do understand the concept of how a gamma ray is emitted when an electron in an excited (higher energy) state transitions to a lower state. Also, I'm aware that they used $^{57}\text{Fe}$ as its photon energy (and thus gamma ray frequency) were/are well-known to an accurate value.

# How did they get the $^{57}\text{Fe}$ electrons all excited to begin with?

Certainly the electrons in the iron samples don't maintain their excited state unless one keeps adding some external energy, correct?

Related side question: How difficult was it to get "enriched" $^{57}\text{Fe}$? And, just how well-enriched were the samples?

Facetious side-question: How loud could one hear the rumbling bass notes across the Harvard Campus while Dr. Pound and his student were running the experiment? :)