Nuclear Flashcards
(26 cards)
What was the aim of Rutherford’s experiment?
To investigate the different angles of deflection of the alpha particles and the number of alpha particles that were deflected at each angle
Draw and explain the set-up of Rutherford’s experiment
Look in booklet for answer
What are the 4 conclusions made from Rutherford’s experiment?
1) The atom must be mostly empty space because most of the alpha particles just pass straight through
2) The nucleus must have a large positive charge, as the alpha particles are repelled and deflected
3) The nucleus must be very ting as very few particles are deflected by an angle that is greater than 90°
4) Most of the mass must be in the nucleus, since the alpha particles with a high momentum are deflected by it
What would happen if the alpha particles in Rutherford’s experiment had a higher energy?
They would be able to approach the positively charged nucleus more closely before being deflected, because they have more kinetic energy
Describe the history of the atom
Democritus- All matter is made of indivisible particles called atomos
Dalton- Atoms of each element are identical to eachother but different to other elements
Plum pudding model - Atoms are positvely charged spheres with electrons embedded inside
Rutherford- Atoms are mostly empty space but contain a small positively charged nucleus at the centre
Bohr- Electrons orbit the nucleus in discrete energy levels/shells
Schrodinger- Electrons exist in probability regions or orbitals rather than in fixed orbits
Chadwick- The neutron was discovered
How can you identify whether a radioactive source is alpha, beta or gamma?
If it is blocked by paper it is alpha radiation, if it passes through paper but is blocked by aluminium it is beta and if it passes through paper and aluminium but is reduced by lead then it is gamma radiation
Explain how beta radiation is used to keep the thickness of paper constant when it is produced
A beta source is placed above the material and a detector is positioned below, as the material moves through, the detector measures the amount of beta radiation that passes through if the count rate drops, the material is too thick — if it increases, it’s too thin. The system automatically adjusts the rollers to maintain a constant count rate, ensuring uniform thickness
Why is beta radiation used to help keep the thickness of paper constant during production?
Beta radiation is ideal because it is partially absorbed — alpha is stopped completely and gamma is barely affected
How does the intensity of gamma radiation change with distance?
It follows an inverse square law so as the distance away from the source increases the intensity increases by a larger amount
What are the benefits of using gamma emitters to treat cancer?
- The gamma rays can reach tumours deep inside the body without invasive surgery
- It reduces recovery time and risk of infection compared to alternative procedures
- The radiation dose can be precisely calculated to maximise tumour damage
What are the drawbacks of using gamma emitters to treat cancer?
- They could damage healthy cells that surround the tumour
- Extended or repeated exposure can increase the risk of secondary cancers developing
- It can be difficult to focus the ray precisely on the area of the body without affecting the surrounding area
Explain what happens when ionising radiation enters a Geiger-Muller tube and how this leads to a ‘count’
When the radiation enters the tube it causes the low-pressure gas inside to become ionised, resulting in positive ions and free electrons. The free electrons are attracted to the positively charged rod inside the tube and the positive ions are repelled away from it causing them to attract to the walls of the tube. This creates a pulse of charge (current), which leads to a ‘count’
What is background radiation?
The level of radiation that is always present
List the main contributors to background radiation
1) Radon gas
2) Cosmic rays
3) Food and drink (C-14)
4) Medical purposed (e.g. X-rays)
5) Rocks/ the ground/ buildings
6) Nuclear weapons, air travel and nuclear power
How can you determine the background count rate?
By using in Geiger-Muller counter and letting it run for 30 minutes (without any radioactive sources present) and then divide the recorded value by 30x60 to get the count rate (per second)
What is meant by ‘corrected count rate’?
The recorded count rate with the background radiation count rate deducted from it
Draw the two graphs to show how count rate changes with distance from the source
Look in booklet for answer
How can you show that gamma radiation follows an inverse square law?
By placing a Geiger-Muller counter at a recorded distance away from a source, then vary the distance in regular intervals, noting down the count rate at each distance. Then you can calculate the constant of proportionality (k) for each distance and compare them to show they are similar/ the same
Why does the line of stability on a graph of N against Z curve upwards?
The strong nuclear force acts between all nucleons but it has a short range and the electromagnetic force of repulsion acts between protons and has an infinite range meaning it becomes stronger as more protons are added. So to maintain stability more neutrons are needed to increase the strong nuclear attraction (in order to keep the nucleus together) but without increasing the electromagnetic force of repulsion. This results in an imbalance between the number of protons and neutrons which causes the graph to curve up
What are 2 sources of gamma ray photons?
From the de-excitation of electrons or the de-excitation of a nucleus
What is meant by the ‘random nature of decay’?
The decay process is completely random and it is impossible to predict when a nucleus will decay or which will decay next
What is meant by the ‘decay constant’ of a radioactive isotope?
It is a measure of the probability that a single nucleus will decay per unit of time
What is meant by the ‘activity’ of a radioactive isotope?
The number of nuclear decays occuring per second in a sample of a radioactive isotope
What is meant by the ‘half-life’ of a radioactive isotope?
The time that it takes for half of the radioactive nuclei in a sample of a radioactive isotope to decay
