IGCSE Physics (0625) 5.2.1 Detection of radioactivity Paper 4

Question

(a) The isotope hydrogen-1 has a proton number of 1 and a nucleon number of 1.
Two isotopes of helium are helium-3 and helium-4.
Helium-3 has a proton number of 2 and a nucleon number of 3.
Helium-4 has a nucleon number of 4.
Complete Table 11.1 for neutral atoms of these isotopes of helium.

                                                                      Table 11.1

 

helium-3

helium-4

number of neutrons

   

number of electrons

   

mass compared to a neutral atom of hydrogen-1

   

(b) An experiment takes place in a laboratory shielded from all background radiation. A sample of radioactive material is wrapped in aluminium foil of thickness 0.1 mm. A detector of ionising radiation placed 1 cm from the foil records a reading.

A piece of aluminium of thickness 5 mm is placed between the detector and the foil. The detector reading drops to zero.
State and explain any type of radiation passing through the aluminium foil.

Answer/Explanation

Answer:

(a) neutrons 1 2
electrons 2 2
mass 3 4 OR 2 more 3 more

(b) β
β – (would be) stopped by 5 mm / thick Al
α – (would be) stopped by 0.1 mm Al / Al foil
AND γ – (would) not (be) stopped by 5 mm / thick Al

Question

 (a) Fig. 9.1 shows a beam of α-particles moving towards a thin sheet of gold in a vacuum.

Detectors in the region surrounding the thin gold sheet detect the α-particles and determine the number of particles that travel in various directions.
State and explain what can be deduced from the following observations.
(i) The majority of the α-particles pass through the gold sheet undeflected and are detected on the far side.
deduction
explanation
(ii) A small number of α-particles are deflected as they pass through the gold sheet.
deduction 
explanation
(iii) A very small number of α-particles are deflected through very large angles or return back the way they came.
deduction
explanation

(b) A beam that consists of both α-particles and β-particles is passed through a region of space where there is a magnetic field perpendicular to the direction of the beam.
State two ways in which the deflection of the α-particles differs from that of the β-particles.
1.
2.

▶️Answer/Explanation

Answer:

(a)(i) mark both explanation and deduction together
nucleus is very small
very few α-particles hit or pass near to a nucleus

(a)(ii) mark both explanation and deduction together
nucleus is charged
(charged) α-particles experience a force

(a)(iii) mark both explanation and deduction together
centre / (small) part of atom OR nucleus includes most of the mass of the atom / is (very) dense
(α-particles move and) nucleus stays still

(b) any two from:
opposite direction
(much) smaller deflection
undergo deflections of similar magnitude

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