plutonium (238 pu,z94) has been used as power source in space flights. 238 pu has an o-decay half-life of 90 years (2.7 x 109 sec). (a) what are the z and n of the nucleus which remains after a-decay?

In an alpha decay, the atomic number (Z) decreases by 2 and the mass number (A) decreases by 4.

For plutonium-238 (238Pu, Z=94), after alpha decay, the new nucleus will have:
Z = 94 - 2 = 92
A = 238 - 4 = 234

Therefore, the nucleus that remains after alpha decay of plutonium-238 is Uranium-234 (234U, Z=92).

a-decay:

- The atomic number (Z) decreases by 2.
- The mass number (A) decreases by 4.

Given:

- Initial nucleus: 238Pu (Z = 94, n = 144)
- a-decay half-life: 90 years (2.7 x 10^9 seconds)

After a-decay:

- Z decreases by 2: Z = 94 - 2 = 92
- n decreases by 4: n = 144 - 4 = 140

Therefore, the nucleus which remains after the a-decay of 238Pu is 92U (Uranium-234).