Question

For alpha decay to cause a loss in mass, such as that in the uranium 238 conversion to thorium 234, what must the atomic weight of the alpha particle be?

Answer 1

Explanation:

Reaction equation showing alpha decay in Uranium-238 is as follows.

    $^{238}_{92}U \rightarrow ^{234}_{90}Th + ^{4}_{2}He$

It is known that an alpha particle is basically a helium nucleus and it contains 2 protons and 2 neutrons.  

Symbol of an alpha particle is $^{4}_{2}\alpha$.

As atomic mass or weight is the sum of total number of protons and neutrons present in an atom.

Hence, the atomic weight of the alpha particle is (2 + 2) = 4.