TOPIC 4 - ATOMIC STRUCTURE

Compare the structure of an atom of carbon-14 with the structure of an atom of carbon-12

• same number of protons/ same atomic number

• same number of electrons

• different number of neutrons

What does a half-life mean?

the time it takes for the number of nuclei in a radioactive sample to halve; the time it takes for the activity to halve

Why does a source with the greatest half-life have the greatest risk to health?

greatest activity; greatest dose of radiation absorbed

What is irradiation?

the exposure of an object/ person to radiation
What is contaimination?

Give one health risk to a person working close to a source of nuclear radiation

• cancer/ tumours
• DNA/ genetic mutation
• damages/ kills cells
• radiation poisoning/ sickness/ burns

Explain why the worker needs to stand close to the radiation detector

some radioactive materials emit alpha radiation; which has a very short range in air

In what order was the electron,, neutron, nucleus and proton discovered?

electron; nucleus; proton; neutron

Why are an alpha particle deflect from the gold foil?

both the alpha particles and the gold nucleus have a positive charge; so the alpha particle + gold nucleus repel each other

Why would some alpha particles deflect more than others?

if the particle passes closer to the nucleus; it experiences a stronger repulsive force/ electric field

Why did most alpha particles pass straight through?

the atom is mostly empty space

How is the Bohr model of the atom different from the nuclear model of the atom?

in Bohr model the electrons orbits the nucleus; at specific distances; but in the nuclear model, they can orbit at a continuous range of distances

Explain how an electron can move up and down between energy levels in an atom

• to move to a higher energy level, an electron absorbed energy from EM radiation
• to move to a lower energy level - it emits energy in the form of EM radiation

Explain how an absorbing material could be used to show which type of radiation (beta/gamma) is emitted by Source B;
use an aluminium sheet; beta won't penetrate but only gamma will

Suggest one safety precaution the teacher would have taken to reduce the radiation dose the teacher received

• increase distance between source + teacher
• limit exposure time
• use tongs/ foreceps
• wear lead apron
• keep source in box unless in use
• stand behind safety screen

Suggest one safety precaution that the teacher would have taken to avoid becoming contaminated

• wear gloves/ apron, lab coat, handle source with tongs/ foreceps

What does an alpha particle consist of?

two protons; two neutrons

Explain how the risk from internal contamination is different to the risk from external irradiation by a source of alpha radiation

• alpha has a low penetrating ability; so is stopped by skin; so low risk
• interally; alpha radiation is absorbed by lviving tissue; alpha is highly ionising; so contaimination will cause greater harm to cells

Suggest one precaution taken to reduce the hazard caused by radioactive waste from power stations

• bury the radioactive waste
• put the radioactive waste in cooling ponds
• trasnport the radioactive waste in secure vessels
• store the radiaoctive waste in metal containers
• cover the radioactive waste in concrete

What is the fuel for nuclear fission + fusion? Uranium; Hydrogen

What is meant by the ‘random nature of radioactive decay’?

it is unpredictable which nucleus will decay next and when it will decay

Give some other man-made sources of background radiation

radioactive waste; medical x-rays; radiotherapy; nuclear weapons

Explain how the process of nuclear fusion leads to the release of energy

lighter nuclei join to form heavier nuclei; some of the mass of the nuclei is converted to energy

Explain the advantage of the radioactive waste having a shorter half-life

activity decreases quickly; risk of harm decreases quickly

Explain why contamination of the inside of the human body by a radioactive material that emits alpha radiation is highly dangerous

• highly ionising
• causes increased risk of cancer; organ failure; radiation sickness/ poisoning; mutation of DNA; damage to cells
• until the radioactive material is removed/ excreted or the activity reaches background radiation levels

Why does the alarm switch on when smoke particles enter the plastic casing?

smoke absorbs alpha radiation

Why is it safe to use a source of alpha radiation in a house?

it has a low penetrating ability; wouldn't penetrate skin

The smoke alarm would not work with a radiation source that emits beta or gamma radiation - why?

beta + gamma will penetrate smoke; so no change in count rate would be detected

Explain the ideal properties of a radioactive source for use in medical diagnosis

• short half life of a few hours -> less damage to cells
• low ionising power -> less damage to cells
• highly penetrating -> can be detected outside the body
• emits gamma radiation

Explain how the paths of the alpha particles were used to develop the nuclear model of the atom

• most alpha particles pass straight through the atom
• which shows that the atom is mostly empty space
• very few alpha particles are deflected through a large angle
• which shows the atom contains a nucleus where the mass/ charge of the atom is concentrated

Explain how the distance at which an electron orbits the nucleus may be changed

• it may absorb EM radiation; and move further move the nucleus; to a higher energy level

Explain how the energy released by the chain reaction is affected by moving the control rods

lowering the control rods increases the number of neutrons absorbed; so energy released decrease