IB Physics Exam Preparation – Energy and Momentum in a Nuclear Decay

This video is aimed at IB and A-Level students studying Physics. It can also help students preparing other diplomas that include Nuclear Physics in their cursus.

In this episode, we will be working on an exercise typical of a past exam: The first question is about a decay series transforming Thorium 232 into another isotope of Thorium by alpha decay followed by two beta minus decays.

The second question focuses on the initial alpha decay. The student has to figure out the energy released by this decay and the speed at which the alpha particle is ejected. This involves the concepts of mass defect, mass-energy equivalence and conservation of momentum.

Pause the video and work the problem by yourself. Then, resume the video and we review the exercise together. When relevant, I remind the viewer on concepts required to solve the exercise.

This video is produced and presented by Edouard Reny, Ph.D. in materials sciences and private tutor in Physics.

_ Introduction and Outro music are composed and produced by Edouard Reny (www.synaptic-machines.com). _ Calm background music attributed to “Huma-Huma” (Track names: Hydra and Nevaday-City, both available in Youtube’s Free Audio Library)

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Website: http://www.physics-tutor.nl/

***************** Text of the exercise ****************** Thorium 232 (232 ; 90) decays into Radium (Ra) by alpha decay. The isotope of Radium formed decays into Actinium (Ac) by beta minus decay. Then, the Actinium nucleus becomes Thorium again after another beta minus decay.

1/ Write down the 3 successive decay reactions. (3 Marks)

2/ The masse of a thorium 232 nucleus is 232.0380553u. The Radium isotope formed after the beta decay has a mass of 228.0310703u. An alpha particle has a mass of 4.0026603u.

a/ Calculate how much energy is released in the decay from Thorium to Radium (2 Marks)

b/ State what the energy released has become? (1 Mark)

c/ A Thorium nucleus was at rest before decaying, determine the speed of the alpha particle after reaction. (4 Marks) ... https://www.youtube.com/watch?v=6qZJHfAvCKY