The diagram shows a spark chamber used by a technician to identify particles emitted from a nuclear source. The source is inside an evacuated box between tw...
Question 1 Report
The diagram shows a spark chamber used by a technician to identify particles emitted from a nuclear source. The source is inside an evacuated box between two charged metal plates. The curved track is made by an alpha particle. The electric force on the particle changes its direction.
The alpha particle has kinetic energy 8.0 x 10-13 J and mass 6.64 x 10-27 kg.
(a) State the particles inside an alpha particle. [2]
(b) Which plate attracts the alpha particle in Fig. 1? [1]
(c) Explain the curved path shown in the diagram. [3]
(d) Calculate the speed of the alpha particle as it leaves the source. Use kinetic energy = ½mv2. [4]
(e) Describe one safety precaution the technician should use when handling the source. [3]
Answer Details
(a) An alpha particle contains two protons [1] and two neutrons. [1]
(b) The alpha particle is attracted to the negative plate. [1]
(c) An alpha particle has positive charge. [1] It experiences an electric force towards the negative plate. [1] This force changes the direction of its motion, producing the curved track. [1]
(d) Start with \(E_k=\frac{1}{2}mv^2\), then rearrange:
\[v=\sqrt{\frac{2E_k}{m}}\]
\[v=\sqrt{\frac{2\times8.0\times10^{-13}}{6.64\times10^{-27}}}\]
\[v=\sqrt{2.41\times10^{14}}=1.55\times10^7\text{ m/s}\]
The alpha-particle speed is \(1.55\times10^7\text{ m/s}\), or \(1.5\times10^7\text{ m/s}\). [4]
(e) Suitable precautions include keeping the source in a lead-lined container when not in use, using tongs or remote handling to increase distance, minimising handling time, placing shielding between the source and technician, and wearing a radiation monitor or dosimeter. Any three are credited. [3]
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