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Notes for Candidates - Class 1/Class 7
THESE NOTES MUST NOT BE TAKEN INTO THE EXAMINATION
Explosives Terms
- Detonation
An extremely fast explosive decomposition, in which an exothermic reaction wave follows and also maintains a shock front in an explosive - Deflagration
A rapid burning assisted by convection. - High Explosive
An explosive which is capable of detonation under normal conditions of use. - Low Explosive
An explosive which burns very rapidly, rather than detonates. - Initiation
Explosives can be ignited or initiated by a prescribed stimulus. The stimulus can be thermal or mechanical. Accidental ignition of explosives can be caused by exposure to heat, flame, spark and impact and friction.
Notes for candidates in Class 7
These notes/definitions are intended to be a guideline for Class 7 candidates. It is believed that candidates should have knowledge of these areas to have a firm understanding of the regulations.
- Activity
A measure of radioactive material by the number of nuclear disintegrations per second. (number of atomic nuclei that decay in one second). Unit becquerel. 1 bq = 1 transformation per second.
Radiation Dose
- Absorbed Dose
Measure of energy that is deposited in a material - for a fixed amount of mass (normally 1 Kg) from any interaction with radiation. - Dose equivalent
Because some radiations are more damaging than others they are given a Q factor to take into account the different biological effects that comes from irradiation with different types of radiation. The Dose equivalent is the Absorbed Dose modified by a quality factor.
Radiation Types
- Alpha particles - (helium nuclei)
These behave like a single particle and are easily absorbed by matter eg A thin sheet of paper is enough to stop most Alpha particles. - Beta particles - High speed single electrons
These have a range of about 4 metres in air and can be stopped by light materials like perspex or aluminium. Light materials are a better choice because heavier materials such as lead or steel can cause Bremsstrahlung radiation (X-rays) when they absorb beta particles. - Gamma - Electromagnetic Radiation
Short wave (high energy) electromagnetic radiations are more penetrating than beta radiation. Heavy shielding such as concrete, lead or steel may be used to reduce the intensity but in theory it cannot be stopped completely. - X-Radiation
A form of electromagnetic radiation but with generally lower energy than gamma rays.
Units
- Activity = becquerel (Bq)
- Absorbed dose = gray (Gy)
- Dose equivalent = sievert (Sv)
Half Life
The time taken for the activity of a radionuclide to lose half of its value by decay. The following estimated examples give an idea of the time and types of radiation half-lifes and can be very important when transporting medical items.
| Radionuclide | Radiation | Half-life |
|---|---|---|
| nitrogen 16 | gamma | 7 seconds |
| technicium - 99 | beta | 6 hours |
| sodium - 24 | gamma | 15 hours |
| phosphorous - 32 | beta | 14 days |
| uranium 238 | alpha | 4,500,000,000 years |
Biological Effects
There are many biological effects which can develop from ionising radiation.
When energy (radiation) passes through a material some of this energy may be absorbed, with biological material the majority of energy transferred is heat energy. The important effect is that chemical changes can occur. There may be effects on molecules and cells within the body.
There are three main levels of damage which may occur to cells. Massive, Intermediate and Minor damage.
Radiation can be taken into the body in three ways:
- Absorption: Through the skin
- Inhalation: Through the lungs
- Ingest: Through the mouth
The damage will depend on the type of radiation, exposure and method of intake.
The four basic principles to protect against damage are:
- Time: The shorter the time spent near the source the smaller the dose.
- Distance: The further away you are the smaller the dose.
- Shielding: The correct type of shielding and thickness for source.
- Source Activity: Smallest activity actually necessary for work / transport is used.
THESE NOTES MUST NOT BE TAKEN INTO THE EXAMINATION
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