Topic 6 Flashcards
Name three places that background radiation comes from
1) Radioactivity of naturally accruing unstable isotopes (air, food, building material, rocks)
2) Radiation from space (cosmic rays-sun) earths magnetic field deflects cosmic rays away from us
3) Tiny proportion from radiation due to human activity (fallout form nuclear explosions, dumped nuclear waste)
What cN certain underground rocks cause
(E.g granite) high levels of background radiation at surface
Especially if release radioactive radon gas which gets trapped in people’s houses
What does the radon concentrations depend on
Type of rock your house is built on therefore also region you live in.
Why is it that the older a radioactive source becomes the activity decreases so less radiation is emitted
Each time the radioactive nucleus decays a radiation is emitted
One more radioactive nucleus disappears causing activity to decrease
Why do we have to measure half life of a radioactive source
Because the activity never reaches zero
What is half-life
The half-life of a radioactive isotope is the time taken for half of the un decayed nuclei to decay.
What does a short half-life mean
Activity it’s falls quickly as lots of nuclei decay quickly.
What is the radioactivity of an isotope measured in and by
In becquerels (Bq) 1=1 decay per second By Geiger-Muller (G-M) tube
What kind of radiation do household fire alarms use and how
Weak source of Alpha radiation placed close to two electrodes
Source causes ionisation and a current flows
If a fire then smoke will absorb the radiation
The current stops and alarm sounds
What are gamma rays used for
Sterilising food and equipment
Food irradiated with high dose which kills microbes
Medical equipment instead of being boiled so doesn’t involve high temps so both are not damaged
What must the gamma rays be for sterilising
Source a very strong emitter of gamma rays with reasonably long half-life (several months) so doesn’t need replacing often
What can certain radioactive isotopes be used as
Tracers
Medical tracer injected into patient (or swallowed) progress around body followed using external detector
Computer uses readings to produce an image following the flow of injected isotope
Can detects and diagnose medial conditions
What kinds do isotopes must they be to be taken into the body
BETA OR GAMMA so that radiation passes out of body
Only last a few hours so radioactivity quickly disappears (short half-life)
What can gamma rays be used for in industry
Detecting leaks in underground pipes
How is beta radiation used in thickness control
Direct radiation through what is being made (paper) put detector on other side connected to control unit
When amount of detected radiation changes means the paper is coming out too thick or thin
Control unit adjusts rollers to give correct thickness
