The Nuclear Atom (OCR A Level Physics)

In the 1800s, the atom was considered to be a fundamental particle. It was an indivisible particle of matter. Modern physics shows that this idea is not correct.

Describe the fundamental particles within an atom of carbon-14 ().

In your answer state the composition of the hadrons.

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The half-life of the isotope carbon-14 is 5700 years (y).

i) Show that the decay constant λ for this isotope is about 1.2 × 10⁻⁴ y⁻¹.

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ii) Carbon-dating is a technique used to date an ancient wooden axe.

The ratio of carbon-14 to carbon-12 in the axe material is 78% of the current ratio of carbon-14 to carbon-12 in a living tree.

Calculate the age in years of the wooden axe.

age = ...................................... y [3]

iii) State one assumption made in the calculation in (ii).

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A graph of the density ρ of a nucleus against distance d from the centre of the nucleus is shown below.

The radius of the nucleus r is taken as the distance d where the density is half the maximum density.

Fig. 21.1 shows the density ρ variation for three different nuclei and Table 21.1 shows the nucleon number A of each nucleus.

Fig. 21.1

  Table 21.1

Use the information provided opposite to

• describe how the density of a nucleus depends on its nucleon number A

• show numerically that 

• estimate the mean density of the nuclei.

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