Final answer:
The emission of a gamma particle from an astatine atom does not change the number of neutrons; the atom would have the same number of neutrons before and after the gamma emission.
Step-by-step explanation:
The emission of a gamma particle from an astatine atom does not affect the number of neutrons in the nucleus. Gamma decay involves the release of a gamma-ray photon from an excited nucleus, but there is no change in the number of protons or neutrons. Therefore, to answer how many neutrons would an astatine atom have after emitting a gamma particle, we first need to know the isotope of astatine we are considering because astatine has multiple isotopes with different numbers of neutrons. However, since a gamma emission does not change the number of neutrons, the number of neutrons will be the same as it was before the emission.