7) Radioactivity & particles Flashcards
Units: frequency of decay, distance, time
frequency of decay : becquerel (Bq), 1 (Bq) for 1 decay / sec
distance : centimetres (cm), normally (m)
time : hour (h), minute (min), normally (s)
Isotope
Atoms of the same element with the same number of protons but different numbers of neutrons
-emit radiation as the atoms are unstable and undergo radioactive decay
–unstable due to large size, or because they have too many or too few neutrons
Atomic/ proton number
The number of protons in an atom
Mass/ nucleon number
The total number of particles in the nucleus of an atom is called its mass number
-number of protons and neutrons in the atom
Radiation
-Unstable nuclei can emit radiation to become more stable
-Radiation can be in the form of a high energy particle or wave
-as it moves away from the nucleus, takes some energy with it - reduces overall energy of the nucleus/ makes the nucleus more stable
-emitting radiation: radioactive decay - a random process
Types of radiation that can be emitted
When an unstable nucleus decays, it emits radiation
-Alpha (α)
-Beta (β-)
-Gamma (γ)
Alpha particle - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-two neutrons and two protons - same as a helium nucleus
+2 charge
-can be affected by an electric field
-relatively large mass
-slow speed
-strong ionizing effect
-most dangerous inside the body
-low penetration - can be stopped by a piece of paper or skin
Beta Particles - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-fast moving electrons
-produced in nucleu when a neutron changes into a proton and an electron
-1 charge
-can be affected by an electric field
-very small mass
-fast speed
-weak ionizing effect
-most dangerous outside the body
-medium penetration - can be stopped by 2-3mm of aluminium
Gamma rays - nature, charge, electric field, mass, speed, ionizing, most dangerous, penetration
-electromagnetic waves
-highest energy
-no charge
-not affected by an electric field
-no mass
-speed of light
-very weak ionizing effect
-most dangerous outside the body
-high penetration - partially stopped by thick lead/ concrete
Investigating radiation
- use Geiger-Müller tube to measure background radiation over a one minute period
- Repeat this three times, and take an average
- Place a radioactive source a fixed distance (3 cm) away from the tube and take another reading over a one minute interval
- Now take a set of absorbers: some paper, several different thicknesses of aluminium (increasing in 0.5mm intervals) and different thickness of lead
- One at a time, place these absorbers between the source and the tube and take another reading over a one minute interval
- Repeat the above experiment for other radioactive sources
Investigating radiation - safety conditions
-when not using a source - keep in a lead lined container
-when in use: keep a metre between you and the source
-when handling: use tweezers/ tongs and point the source away from you
Alpha decay equation
The mass number decreases by 4
The atomic number decreases by 2
Charge on the nucleus decreases by 2
Beta decay equation
The mass number remains the same
Atomic number increases by 1
Gamma decay equation
Mass number and atomic number remain the same
Detecting radiation
-photographic film
-geiger-muller tube
Detecting radiation - photographic film
Photographic films detect radiation by becoming darker when it absorbs radiation, just like it does when it absorbs visible light
-The more radiation the film absorbs, the darker it is when it is developed
Detecting radiation - geiger-muller tube
-Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
-This makes a clicking sound or displays the count rate
-measured in becquerels (bq)
Background radiation
-rocks
-cosmic rays
-food and drink (bananas, brazil nuts)
-nuclear weapons testing
-nuclear accidents
-medical equipment
Radioactivity
Rate at which the unstable nuclei from a source of radiation decays
-measured in becquerels (Bq)
-1 Bq = 1 nucleus in the source decaying in 1 second
-activity of a source decreases with time
Half life definition
The time it takes for the number of nuclei of a sample of radioactive isotopes to decrease by half
Uses of radioactivity
-monitoring thickness of aluminum foil/ paper in factories
-detecting leaks in underground pipes
-smoke alarms
-sterilizing food/ medical equipment
-medical tracers
-gamma radiography
Use of radioactivity - smoke detector
- Household smoke alarms measure the movement of alpha particles across a small gap
- if smoke enters a detector, it will absorb the alpha particles and the detector will measure a drop in the number of particles across the gap
- This will trigger an alarm
Use of radioactivity - detecting leaks in underground pipes
- Water supplies can be contaminated with a gamma-emitting isotope
- When there is a leak, contaminated water seeps the ground
- Build up of gamma emissions in that area can be detected with a Gieger Muller tube
Use of radioactivity - monitoring thickness of aluminum foil/ paper in factories
- Rollers roll out sheets of aluminum foil and beta particles are passed through the foil and detected
- The detector monitors width of foil and expects particle activity to remain the same
- If it changes, the detector sends signals to the roller to change the width accordingly
