Question

A student investigates the penetrating abilities of ionising radiation.
Fig. 12.1 shows the equipment used by the student.

(a) The student places different shielding materials between the source and the detector and uses the counter to record the number of counts in 1 minute.
Table 12.1 shows the student’s results.

(i) Use Table 12.1 to state and explain which type of ionising radiation is emitted by the source.
type of ionising radiation …………………………………………………..
explanation …………………………………………………………………………

(ii) The source used in Fig. 12.1 has a half‐life of 29 years.
Calculate the time it will take for the activity of the source to drop to 12.5% of the original value.

                                  time = ……………………………………….. years [2]

(b) The lead used in the student’s investigation is a solid.
The melting point of lead is 327°C. When lead melts, it turns from a solid into a liquid.
Describe the changes in the forces between particles when a solid melts.

(c) The density of liquid lead is 10.6g/cm3.
A sample of liquid lead has a mass of 37.1g.
Calculate the volume of the sample of liquid lead.

                                   volume = ……………………………. cm3 [2]

▶️Answer/Explanation

Ans : 12(a)(i) beta ;

(beta) can penetrate (air and) paper ;
(beta) can’t penetrate thin aluminium (and thicker materials) ;

12(a)(ii) 3 half lives ;
(t = 3 × 29 =) 87 (years) ;

12(b) (forces between particles) decrease ; 
12(c) d = m / v or v = m / d or v = 37.1 / 10.6 ;
= 3.5 (cm³) ;