Question

The radioactive decay of thorium-232 occurs in multiple steps, called a radioactive decay chain. The second product produced in this chain is actinium-228. Which of the following processes could lead to this product starting with thorium-232? A. Alpha decay followed by emission

B. Electron capture followed by positron emission

C. Beta emission followed by electron capture

D. Positron emission followed by alpha decay

E. More than one of the above is consistent with the observed transormation

Answer 1

A. Alpha decay followed by emission

Step-by-step explanation:

The given nuclide is thorium-232

The product formed in the decay of thorium-232 is actinium -228

`^(232)_(90)Th\Rightarrow ^(228)_(89)Ac`

the difference between the atomic number is 1 (90-89)

the difference between the mass number is 1 (232-228)

A decrease in mass number by 4 and atomic number by 2 indicates an alpha decay.

`^(232)_(90)Th\Rightarrow ^(228)_(88)Ra+ ^(4)_(2)He`

now to get ^{228}_{89}Ac from ^{228}_{88}Ra, Radium undergoes beta emission to increase the atomic number by 1 and no change in the mass number.

`^(228)_(88)Ra\Rightarrow ^(228)_(89)Ac+ ^(0)_(-1)e`

Thus alpha decay followed by beta emission gives Ac-228

hence option A is correct