radioactivity basics / P6.1

• alpha - 2 protons, 2 neutrons, positive charge
• when an atom absorbs EM radiation, its electrons will move further away from the nucleus and move to a higher energy level
• when an atom EMITS EM radiation, the electrons will move closer to the nucleus and move to a lower energy level
• 4 types of nuclear radiation

  1. alpha particles
  2. beta particles
  3. gamma rays
  4. neutrons
• unstable nuclei undergo decay to become more stable by releasing their radiation.
• alpha particle equation

  A) a

  B) 4

  C) 2

  
• what will stop beta radiation from passing through a point?

  a thin sheet of aluminium or several metres of air
• beta particle equation

  A) 0

  B) -1

  
• what will stop gamma radiation from passing through a point?

  a few metres of concrete or several centimetres of lead.
• gamma radiation equation

  A) Y

  B) 0

  C) 0

  
• which type of radiation is the most ionising?

  alpha radiation
• which type of radiation is the LEAST ionising?

  gamma radiation
• describe the nature of radioative decay?

  random, which nuclei decays and when it happens is by chance. it is impossible to predict what happens and when.
• define the half life of a radioactive isotope.

  the time it takes for the number of unstable nuclei in a substance to halve. the time it takes for the count rate of a sample to fall to half from its initial level.
• isotopes - atoms of the same element with different numbers of neutrons
• how to calculate the half life from a graph?

  half the number of days and find out the value on the x-axis
• unstable nuclei emit radiation, which is made up of particles or waves. materials that emit radiation are radioactive
• how do you detect radiation?

  you use a Geiger counter, which 'clicks' when radiation enters the device. each click is a tiny current produced when radiation ionises the atoms of the gas inside the tube.
• alpha - stopped by skin or a few sheets of paper

  beta - a few mm of aluminium

  gamma - a few cm of lead or conrete
• types of radiation

  A) high

  B) medium

  C) low

  D) alpha

  E) none

  
• atomic number - number of protons
• mass number - number of protons and neutrons
• alpha is the most ionising, while gamma is the least ionising
• in alpha decay, 2 protons and 2 neutrons are emitted
• in beta decay, a neutron turns into a proton and an electron
• A Geiger counter can measure the radiation emitted per second, which is called the count rate or the activity of the sample, measured in becquerels, Bq. one Bq is one count (wave or particle) per minute
• the time it takes for the activity to halve is the half life, this is the same time it takes for the number of nuclei of half of the atoms to decay. after each half life, the number of radioactive atoms halves.
• half lives of some radioactive isotopes

  A) seconds

  B) 3.8

  C) 14

  D) uranium

  E) billion

  
• practice question:

  A) 11.4 days

  B) 3

  C) 2

  D) 8

  E) 100

  F) Bq

  
• electron arrangements

  electrons can occupy certain energy levels; different atoms have different energy levels. electrons usually occupy the lowest possible energy level, at the smallest possible distance from the nucleus.
• 'excited' electrons

  the electron absorbs the energy carried by the EM radiation IN and is excited to the next energy level. it moves up if it absorb the EM radiation with the right amount of energy. the electron then falls back down an energy level and the EM radiation carries the excess energy AWAY.
• geiger counter

  when the count rate is low, there is a range of count rates.
• electromagnetic radiation

  electromagnetic radiation is absorbed by electrons. alpha particles are emitted from the nucleus --> electrons are not present in the nucleus
• half life is the time it takes for the number of radioactive nuclei to halve
• beta particles will partially pass through aluminium foil