Question

• What is radioactive decay?
• Spliting of heavy nucleus Ra with centre of mass at rest.why it is convenient to work with centre of mass rather than in laboratory frame of reference?(ncert)

Answer 1

Radioactive decay is the spontaneous breakdown of an atomic nucleus resulting in the release of energy and matter from the nucleus. Remember that a radioisotope has unstable nuclei that does not have enough binding energy to hold the nucleus together. Radioisotopes would like to be stable isotopes so they are constantly changing to try and stabilize. In the process, they will release energy and matter from their nucleus and often transform into a new element. This process, called transmutation, is the change of one element into another as a result of changes within the nucleus. The radioactive decay and transmutation process will continue until a new element is formed that has a stable nucleus and is not radioactive. Transmutation can occur naturally or by artificial means.

The lab frame is obvious: it’s the measurement frame in which the laboratory and the measurement apparatus are stationary.

The center of mass is the average, weighted by mass, of the positions of the objects or particles involved in the collision. If the objects are just interacting among themselves, with no external forces, then you can prove from Newton’s Laws that the COM has to move in a straight line at constant speed. That is, there’s some inertial measurement frame in which it’s stationary, and that’s the COM frame.

The COM frame is of interest when studying collisions because it turns out that the motion of the COM is of little importance to the way the collision unfolds, and so is best abstracted away.