The radioactive decay of a strontium (Sr) nucleus is represented in Fig. 7.1.

Question 3

The radioactive decay of a strontium (Sr) nucleus is represented in Fig. 7.1.

Fig. 7.1

(a) State whether Fig. 7.1 represents α-decay, β-decay or γ-decay. [1]

(b) One type of radioactive decay cannot be represented on Fig. 7.1.

Identify this decay and explain why it cannot be represented. [2]

Reference: Past Exam Paper – June 2007 Paper 2 Q7

Solution:

(a) β(-decay)

{Let the new element formed be X.

As the strontium (Sr) nucleus changes into X, its proton number increases to 39 while its nucleon number remains the same.

⁹⁰₃₈Sr - - > ⁹⁰₃₉X + ???

For the equation to hold, the ‘proton number’ of the radiation should be -1 such that 39 + (-1) = 38

Its nucleon number should be zero.

This corresponds to a β-particle.}

(b)

γ-decay. This is because the nucleon number and proton number of the nucleus do not change during this decay. (γ-radiation is only a loss of energy)