P4 Atomic Structure Flashcards
What are the 3 types of radiation?
Alpha, beta, gamma
What does an alpha particle consist of?
2 protons, 2 neutrons
What does a beta particle consist of?
An electron
What does gamma radiation consist of?
Waves
What is the charge of alpha radiation?
+2
What is the charge of beta radiation?
-1
What is the charge of gamma radiation?
0
What is the range in air of alpha radiation?
A few cm
What is the range in air of beta radiation?
A few m
What is the range in air of gamma radiation?
Kilometres
What is alpha radiation absorbed by?
Paper
What is beta radiation absorbed by?
A few cm Aluminium
What is gamma radiation absorbed by?
A few cm Lead OR metres of concrete
What is the ionising power of alpha radiation?
High
What is the ionising power of beta radiation?
Medium
What is the ionising power of gamma radiation?
Low
Name 3 safety precautions to take when handling radioactive sources:
- Keep tool in a lead box to stop gamma spreading
- Sources handled at arm’s length and pointed at ground
- Audience stands back - greater distance, less exposure
What is ionising radiation?
Radiation which can ‘knock’ electrons off of atoms which is what makes it dangerous
Give 3 uses of radiation?
- Target cells to treat tumours
- Radioactive tracer
- Automatic thickness monitoring (beta particles)
What are gamma rays?
Very high frequency electromagnetic waves
When are gamma rays produced?
When an unstable nucleus loses energy
What is the greek letter for gamma radiation?
ɣ
What is a beta particle?
A high speed electron
Where do beta particles come from?
A nucleus where a neutron has decayed into an electron and a proton
What is the greek letter for beta radiation?
β
What is an alpha parrticle?
The same as a Helium nucleus - 2 protons, 2 neutrons
What is the greek letter for alpha radiation?
α
What is radioactivity?
Radioactive atoms with unstable nuclei
Why do unstable nuclei decay?
To become more stable - emits radiation
How do you predict radioactive decay?
You can’t - it is a random event
What is the count rate?
The number of decays recorded each second by a detector (eg.a Geiger-Muller Tube)
What is the activity?
The rate at which a stable nuclei decays
What are activity and count rate measured in?
Becquerels
What is the equation for count rate?
No. of emissions / Time (s) - background radiation
What is the half-life?
The time it takes for the number of nuclei in a sample to halve OR for the count rate for an isotope in a sample to fall to 1/2 its initial value
Who first talked about atoms in 440 BC?
Democritus
What does ‘atom’ mean in Greek?
No cut
What did John Dalton say in 1800s?
Different elements have different atoms. Imagined these as indivisible spheres
What did J.J. Thompson say in 1898?
Discovered electrons. Developed Plum Pudding Model - electrons randomly embedded in a ball of positive charge
Who developed the Plum Pudding Model?
J.J. Thompson
What did Rutherford say in 1908?
Alpha scattering - fired alpha particles at gold foil to discover nucleus.
Who developed the nuclear model?
Earnest Rutherford
What did Neils Bohr say in 1913?
Electrons found in shells and charge concentrated in centre of atom
What did James Chadwick say in 1939?
Discovered the neutron and added to the nucleus
What is nuclear fission?
Splitting a nucleus (often Uranium) into 2 or more daughter nuclei and 2 - 3 neutrons moving at high speeds - energy released as gamma waves
What is nuclear fusion?
Forming of 2 smaller atomic nuclei to form a larger one. Some mass converted into energy.
Give an example of alpha decay:
238 92 U –> 234 90 Th + 4 2 α
How is alpha decay calculated:
4 from mass number, 2 from atomic number (4 from top, 2 from base)
Give an example of beta decay:
14 6 C –> 14 7 N + 0 -1 β
How is beta decay calculated:
Mass number stays same, add 1 to atomic number (Add one to base, top stays same)
What happens in beta decay?
A neutron turns into a proton (too many neutrons in a nucleus). Proton comes with a +1 charge. Also forms a -1 electron to balance charge. Electron booted out of the nucleus as can’t stay there (electrons orbit in shells)
