Hi, since the concept cannot be changed with the subject, the root and the pattern is the same in both of the subjects. Although, the question presentation type may vary with the subject so I'd suggest to give atleast a reading to both the subjects separately. Try to solve some questions too.

All the best! 

Hello aspirant

The basic concepts remain the same for topics like radioactivity, be it physics or chemistry. Understanding the basic concepts will help you grasp the topic and answer questions from both the subjects. Only a few new concepts may arise in either subject which you would have to study seperately. 

Hope this helps.