The nuclear atom

1) Atoms consist of:
  • Nucleus: central part of atom made of protons (positively charged) and neutrons. These two types of particles are called nucleons. They are bound together by the strong nuclear force.
  • Electrons: almost mass-less particles which orbit nucleus in shells
  • This is proved by Rutherford’s Gold Foil Experiment.
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  • Proton/Atomic number: number of protons in an atom
  • Nucleon/Mass number: the number of nucleons (protons + neutrons) in an atom​.
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  • Nuclear Fission: process of splitting a nucleus.
  • Nuclear Fusion: process of fusing two nuclei.
Nuclide Notation

Radioactivity

2) Describe an Isotope:
  •  Atoms of the same element that have different numbers of neutrons e.g. Carbon 12 and Carbon 14.  
  • There are non-radioactive isotopes and radio-isotopes.
  • Radio isotopes are unstable atoms, which break down giving radiation.
 
Uses:
  • Medical use: cancer treatment (radiotherapy).
  • Industrial use: to check for leaks, radioisotopes (tracers) added to oil/gas, leaks is detected as radiation using a Geiger counter.
  • Archaeological use: used for carbon dating.
3) Characteristics of the three kinds of emission
Nature
Alpha (α)
Helium nucleus (2 protons and 2 electrons)
Beta (β)
One high speed electron
Gamma (γ)
​Electro-magnetic radiation
Charge
+2
-1
-
Penetration
Very weak.
​Stopped by paper
Moderately weak.
​Stopped by aluminum
Very strong.
​Only reduced by lead
Ionising Effect
Very strong
Moderately
Very weak
4) Describe the deflection of α-particles, β-particles and γ-rays in electric fields and in magnetic fields
Electric Field:
  • Alpha and beta particles deflected in opposite direction due to their charges.
  • Beta particles deflected more due to smaller mass.
Magnetic Field:
  • Dots represent magnetic field coming out of page.
  • Use Flemings Left Hand Rule.
5) What is Ionising Radiation
  • Is the radiation emitted from unstable nuclei.
  • 3 main types of ionising radiation - alpha, beta and gamma radiation.​
6) Describe and explain examples of practical applications of α, β and γ-emissions
Uses of Alpha Radiation:
  • Ionisation is useful for smoke detectors. If smoke enters the detector, some of the alpha particles are absorbed and the current drops, triggering the alarm.

​Uses of Beta Radiation:
  • Beta radiation is used for tracers and monitoring the thickness of materials. The thicker the material, the more radiation is absorbed and the less radiation reaches the detector.

​Uses of Gamma Radiation:
  • Gamma radiation is used in the treatment of cancer, sterilising medical instruments.
7) Detection of Radioactivity
  • Photographic film: The more radiation absorbed by the film, the darker it gets (the film is initially white). They are worn as badges by people who work with radiation, to check how much exposure they have had.
  • Geiger-Muller tube: A Geiger-Muller tube is a tube which can detect radiation. Each time it absorbs radiation, it transmits an electrical pulse to the machine, which produces a clicking sound. The greater the frequency of clicks, the more radiation present.

radioactive decay

8) State the meaning of Radioactive Decay
  • A radioisotope (unstable arrangement of neutrons and protons) is altered to make a more stable arrangement.
  • The parent nucleus becomes a daughter nucleus and a particle (decay products).
Alpha decay:
  • A heavy nucleus emits an alpha particle (helium nucleus).
Beta decay:
  • A neutron changes into a proton, and emits a beta particle (electron).
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Gamma Emission:
  • Gamma emission by itself causes no change in mass number or atomic number
  • They just emit energy.
  • A form of electromagnetic radiation.
9) Half Life
  • Half-life of a radioisotope is the time taken for half the nuclei present in any given sample to decay, time taken for the activity to halve.
  • Some nuclei are more stable than others.​
 10) Safety precautions
  • Shielding: radioactive material is stored in a lead container.
  • Minimize contact: picked up radioactive material with tongs, not bare hands.
  • Keeping a big distance: keep as big a distance from radioactive source.​
  • Minimize time of exposure: use radioactive tracers with short half life.