Beta decay changes the atomic number by +1 (the nucleus gains a proton) but the mass number remains unchanged (it gains a proton but loses a neutron by ejecting an electron, so a beta particle is an electron).
Gamma is pure energy and will not change the structure of the nucleus in any way.
Uranium 238, , emits an alpha particle to become what nucleus?
Alpha decay (two protons and two neutrons) changes the mass number of the element by -4 and the atomic number by -2 so the remaining nucleus will be .
A periodic table shows that element number 90 is thorium, .