Atomic Structure & Decay Equations (AQA A Level Physics)

State what is meant by the specific charge of a nucleus and give an appropriate unit for this quantity.

The nucleus of a particular atom has a nucleon number of 15 and a proton number of 7.

Calculate the specific charge of the nucleus.

Use values on the data sheet to help you.  

Another nucleus P has the same nucleon number as nucleus Q. The specific charge of P is 1.5 times greater than that of Q.

Explain, in terms of proton number and nucleon number, why the specific charge of P is greater than that of Q.

Nucleus P is .

Deduce the number of proton and the number of neutrons in nucleus Q. 

Under certain circumstances, it is possible for a pair of gamma ray photons to be created from a collision of an electron and positron.

State what this process is called and give one example of its application.

Compare the mass, charge and rest mass energy of an electron and a positron. 

Calculate the minimum energy of each gamma ray photon in joules.

Calculate the wavelength of the gamma ray photons.

Describe the role of the strong nuclear force in keeping the nucleus stable.  

Describe how the strong nuclear force between a pair of nucleons varies with the separation of the nucleons, quoting appropriate values for separation.  

An unstable nucleus plutonium 239 () decays into an isotope of Uranium, U, by emitting an alpha particle.

Write an equation for the decay of the nucleus and determine the proton and nucleon number of U.

The α particle is emitted from a stationary   nucleus at a speed of 4.5 × 10⁶ m s^–1.

Calculate the recoil speed of the daughter nucleus.

Give your answer to an appropriate number of significant figures.

Explain the process of pair production.

Muons and antimuons are heavier versions of the electron and positron.

Calculate the minimum energy of the gamma-ray photon required to create a muon-antimuon pair in joules.

Give your answer to an appropriate number of significant figures.

Calculate the frequency and wavelength of the gamma ray photon required to create a muon-antimuon pair.  

A photon of a slightly lower frequency than that calculated in part (c) does not convert into a muon-antimuon pair.

Explain why the production of a muon-antimuon pair does not occur if the frequency of the photon is below a certain value.

An unstable isotope of neodymium–144 () decays by emitting an α particle.

Calculate the specific charge of an alpha particle, state an appropriate unit.       

Determine the ratio  

An atom of  is instead ionised by the addition of three orbiting electrons.

State the constituents of the ion that have           

• A zero charge per unit mass ratio

• The smallest charge per unit mass ratio

• The largest charge per unit mass ratio

Calculate the percentage of the total mass of the ion that is accounted for by the mass of its electrons.    

A radioactive nucleus  undergoes a beta–minus decay followed by an alpha decay to form a daughter nucleus .

Write a decay equation for this interaction and hence, determine the values of A and Z.

Thorium decays to an isotope of Radium  through a series of transformations.

The particles emitted in successive transformations are:

Determine the resulting nuclide after these successive transformations.

Clearly show how you arrive at your final answer.

Through a combination of successive alpha and beta decays, the isotope of any original nucleus can be formed.

Determine the simplest sequence of alpha and beta decays required to do this and explain your reasoning.

A nucleus of bohrium decays to mendelevium by a sequence of three alpha particle emissions.

Determine the number of neutrons in a nucleus of bohrium.

A muon and an anti–muon annihilate leading to the emission of two photons.

Calculate the wavelength of the photons. 

Using your answer to part (a): 

(i) Deduce the type of electromagnetic radiation emitted after the annihilation. 

(ii) Explain why this is the longest possible wavelength of the photons produced.

Recombining the photons can produce a muon and an anti–muon in a process called pair production. Alternatively, one of the photons could spontaneously convert into an electron and positron.

Show that the energy required to produce a positron is about 200 times less than the energy required to produce an anti–muon and hence deduce the mass of a muon in kg.

In 1995, scientists at CERN created atoms of anti-hydrogen for the first time. An atom of anti-hydrogen consists of a positron in orbit around an antiproton. Each atom of anti-hydrogen survived for only around forty nanoseconds.

Describe the properties of an atom of anti-hydrogen and explain why they only survived for around forty nanoseconds.

Despite the electrostatic repulsion acting between protons, nuclei with low nucleon numbers tend to be most stable when they contain equal amounts of protons and neutrons.

Explain why.

Figure 1 shows a graph of neutron number N against proton number Z for stable nuclei.

Figure 1

The solid line indicates where N = Z.

In terms of nuclear forces, suggest why N = Z for lighter nuclei but not for heavier nuclei.

All nuclei have approximately the same density.

Suggest, with reasons, what this implies about the nature of the strong nuclear force. 

A proton travelling at a moderate velocity is fired at a stationary proton. It stops momentarily at a very short distance from the stationary proton and then deflects in the opposite direction.

A proton travelling at a high velocity is then fired at the stationary proton. It also stops momentarily at a very short distance from the stationary proton but does not deflect.

In terms of fundamental forces, describe what happens to the proton travelling at a high velocity and explain why this happens.

Table 1 shows some of the isotopes of phosphorus and, where they are unstable, the type of decay.

Table 1

 Predict whether the isotope   is stable or not. If not, determine, with a reason, the type of decay it experiences.

The isotope of phosphorus decays into an isotope of silicon.

Complete the decay equation for this phosphorus isotope and explain the need for the third emission product.

In one instance, one of the unstable isotopes of phosphorus decays and is then immediately bombarded by electrons. This leads to the ionisation of the decay product. 

The specific charge of the ionised decay product is found to be 5.835 × 10⁶ C kg^–1 and it has a negative charge of 3.2 × 10^–19 C.

Determine the original isotope of phosphorus that decayed.

Calculate the percentage of the total mass of the ion in part (c) that is accounted for by the mass of its neutrons.