If Eu-174 loses an alpha particle, what is left?
An alpha particle is the same as a He-4 nucleus.
Eu-174 has atomic number 63, Helium has atomic number 2.
Losing a He-nucleus will drop the atomic number to 61, which is Pm.
It will also drop the mass number by 4 to 170.
Answer : Pm-170 , or Promethium-170
Note : I could not find any reference to a Eu-isotope this heavy, and I doubt if it exists. But if it does, and lost an alpha particle, this is what would happen.