Radioactivity Flashcards
Explain why the count rate shown at graph A is not due to alpha particles, no matter what kinds of radiation are emitted by the source [1]
Alpha particles have very short range in air
State and explain what type of radiation(s) is/are emitted by the source based on graphs B and C. [3]
Beta and gamma rays
Gamma rays are present and they travel undeflected and are picked up by he GM tube at position P.
Graph shows a drop in value from 1000cpm to 450cpm at Q.
Beta particles are present as they have been deflected downwards by the magnetic field and are picked up by the GM tube at Q.
Explain why the sum of the average count rate obtained at B and C is greater than that at A. [1]
Sum does not add up as background radiation is recorded at both positions P and Q
half life
Time taken for half the number of radioactive atoms in a sample to decay
Proton or atomic number
Number of protons in an atom
Nucleon or mass number
Total number of neutrons and protons in the nucleus of an atom
Nuclides
Atoms whose nuclei contain a particular number of protons and neutrons
Isotopes
Atoms of the same element that have the same number of protons but different numbers of neutrons
Radioactivity/nuclear decay/radioactive decay
Process by which an unstable atomic nucleus loses its energy by emission of electromagnetic radiation or particles in order to form a more stable nuclei of the same element or other elements
Spontaneous
Happens by itself without any external influence
Random
Impossible to predict exactly where and when an emission, the disintegration of a nucleus occurs
Ionisation
Ability to eject electrons from atoms to form ions
Ionising radiation
Radiation with high energy that can knock off electrons from atoms to form ions
Background radiation
Nuclear radiation in an environment where no radioactive source has been deliberately introduced
Nuclear fission
Process in which the nucleus of an atom splits and releases a huge amount of energy
Nuclear fusion
Process in which 2 light atomic nuclei combine to form one heavier atomic nucleus and releases a huge amount of energy
1 becquerel
1 disintegration per second
Alpha particle radiation and their properties
Nature: An alpha particle is actually the nucleus of a helium atom.
Mass: heavy
Charge: positive
Speed: Up to 10 –20 % speed of light
Ionising power: strong
Penetrating power: have a range of about 5cm in air and are easily stopped by paper
Effect of electric field: slight deflection towards the negative plate
Beta particles and their properties
Nature: A beta particle is actually a fast moving electron ejected from a radioactive nucleus
Mass: light
Charge: negative
Speed: Up to 80 % speed of light
Ionising power: moderate
Penetrating power: have a range of about few metres in air and are stopped by aluminium
Effect of electric field: strong deflection towards the positive plate
Gamma rays and their properties
Nature: high energy electromagnetic waves emitted by a radioactive nucleus
Mass: zero
Charge: no
Speed: speed of light
Ionising power: very weak
Penetrating power: have a range of about few hundred metres in air and are stopped by lead
Effect of electric field: not deflected
Radioactive detectors
- Photographic plates
- GM tube (Geiger-mueller tube)
How to measure background radiation
- Remove all known radioactive sources.
- Start the counter and the stopwatch.
- Stop the counter after 10 minutes and record the number of counts.
Number of counts per minute = (number of counts in 10 minutes)/10 - Repeat your measurement at least once and calculate an average value.
Uses of radioactivity
- Radiotherapy (Cobalt-60 emits strong gamma radiation to kill cancerous cells)
- Sterilisation (gamma rays are
used to sterilise food and hospital equipment.) - Radioactive Tracers
- Thickness Gauge**
- Carbon dating
Safety aspects of radiation
(I) All radioactive sources should be kept in thick lead boxes.
(ii) Special clothing such as lead-lined suits should be worn by persons doing
radioactive experiments. Dosimeters should be worn also.
(iii) Food and drinks are strictly prohibited when a person is doing radioactive
experiments.
(iv) The international radiation symbol should be displayed in risk areas.
