Chapter 24.2, Problem 7PP

Interpretation Introduction

Interpretation:

The type of decay to be determined due to which thorium 229 decays to form radium -225.

Concept introduction:

Isotopes are atoms of same element whose number of neutrons is different. Isotopes having unstable nuclei are termed as radioisotopes. These unstable nuclei emit radiation to attain more stable atomic configuration is termed as radioactive decay.

Answer to Problem 7PP

The type of decay is alpha decay due to which thorium-229 decays to form radium -225.

Explanation of Solution

Depending on the relative number of neutrons and protons, atoms can undergo different type of decay-beta decay, alpha decay, positron emission or electron capture to gain stability. In alpha decay, decrease of mass number and atomic number takes place by 4 and 2 respectively. In decay of thorium 229 to form radium -225, the decrease of mass number by 4 and decrease of atomic number by 2 takes place. So, it will be an alpha decay.

The nuclear equation is,

$\text{T}\text{h}\to \text{H}\text{e}\text{+}\text{R}\text{a}$

Conclusion

In alpha decay, atomic number decrease by 2 and mass number decreases by 4.