Chapter 25: Radioactivity Flashcards
What are the defining features of radioactive decay?
Spontaneous and random - cannot predict when an individual nucleus will decay
What features of a nucleus may cause radioactive decay?
- Too many or too few neutrons
- Too heavy overall
- Too much energy
Name 4 types of radiation
- Alpha
- Beta (plus and minus)
- Gamma
What is the ionising order from most to least
Alpha
Beta
Gamma
What is an alpha particle
A particle which contains two protons and two neutrons, the same as a helium nucleus
What type of radiation can be stopped by lead or concrete
Gamma
How far does a beta particle typically penetrate the air?
50cm to 1m
What is the activity of a source?
The number of radioactive decays per second (Becquerels)
What is the half-life of an isotope?
The average time taken for the activity of the sample to half
What occurs when a particle and antiparticle meet?
- Annihilation
Release two gamma rays, in order to conserve momentum
Mass will transform into the energy equivalent
What is pair production
When a gamma ray has enough energy to produce a particle and its antiparticle
Why does beta plus decay have a very low penetration
Because it will annihilate with matter almost immediately
What isotope is commonly used to find the age of artifacts
Carbon-14 (radiocarbon dating)
Techniques and Procedures used to investigate the absorption of alpha, beta and gamma
- Use GM tube to record background count rate
- Place radioactive source into room and measure count rate after 5 mins
- Place few sheets of paper in front of the source and repeat, if count rate drops to 0, emit alpha only
- Repeat with aluminium foil and cm of lead to detect beta
How do you find the activity of a source?
activity = decay constant x number of particles
