8) Nuclear Physics Flashcards
Properties of alpha radiation
Two protons, two neutrons
Weakly penetrating
Easily absorbed
Positively charged
What nuclei can emit alpha particles
Nuclei with atomic number greater than 60
What stops each type of radiation
Alpha - sheet of paper
Beta - 5mm of aluminium, 30cm air
Gamma -
Alpha radiation applications
Fire alarms - alpha particles cannot pass through smoke so sets of alarms
Properties of beta radiation
Electrons (or positrons) emitted from unstable nucleus
Moderately penetrative
Either positively or negatively charged
Which nuclei emit what type of beta radiation
Beta+ emitted by proton rich nuclei
Beta- emitted by neutron rich nuclei
Applications of beta particles
Gauging thickness of aluminium sheeting or foil
Beta+ emitter used in medical PET scans
Radioactivity protective measures
Stay at arms length
Protective clothing (goggles, gloves)
Reduce exposure time
Point sources away from you
Store in lead-lined box
What was Rutherford’s experiment and what happened
Fired alpha particles at very thin pieces of gold leaf
Particles mostly passed through the gold lead but some were deflected at large angles
What model did Rutherford disprove
Plum pudding model
Explain Rutherford’s results of strong deflections
Caused by electrostatic repulsion between positive nucleus and positive alpha particles
Most alpha particles travelled through free space
What model did Rutherford find
Current atomic model
When and what did Democritus suggest
5th century BC
Matter made of lumps called atomos
All atomos identical
Atomos smallest unit of matter
When and what did Dalton suggest
1800s
Different atoms corresponded to different elements
What did Thomson discover
Electrons could be removed from atoms
Atoms were not the smallest unit of matter
Atoms were clouds of positive charge with negative electrons suspended inside
Plum pudding model
From latest to earliest name the leaders in atomic discovery
Democritus
Dalton
Thomson
Rutherford
How does gamma radiation affect a nucleus
Does not change proton or nucleon number
Properties of gamma radiation
Makes nucleus more stable
Highly penetrative
What absorbs gamma radiation
Several centimetres of lead
Travels indefinitely through a vacuum
Part of EM spectrum
What law does gamma radiation follow
Inverse square law
intensity at distance x from the source = constant / x^2
Applications of gamma radiation
Medical imaging, curing cancer by destroying tumour cells
Sterilisation
Food irradiation
Explain experiment for inverse square law
1) Find background radiation (Geiger-Muller tube) (repeat for average)
2) Position source into holder, position GM tube at different distances from source, measure count rate at each distance several times and find average
3) Calculate corrected count rate per minute = average count rate at each distance - average background count
4) Plot graph of count rate against 1 / x^2 where x is distance between source and GM tube. Straight line through origin proves inverse square law
Sources of background radiation
Radon gas (from the ground)
Buildings (brick)
Cosmic rays (sun and space)
Medical procedures
Food and drink
What experimental error is there in radiation experiments
Not deducting background radiation
How do we measure decay and why
Decay is random and spontaneous so we look at the count rate over a long time to see if it decreases
What is the probability that a nucleus will decay in a given time proportional to
The number of nuclei
Equation for calculating rate of decay
Rate of nuclei decay = decay constant x number of nuclei
λ is the decay constant
N is the number of nuclei
NOT DONE 2ND SLIDESHOW OF 8.1.4
X
What is a half life
Time taken for number of radioactive nuclei (activity) in a sample to halve
What is the activity of a sample directly proportional to
The number of nuclei remaining
Equation for decay activity
Activity = decay constant x number of nuclei remaining
Benefits of nuclear power
No CO2 released
Responds well to demand changes
Output per unit mass of fuel is far higher than hydrocarbon sources such as oil, coal or gas
Negative of nuclear power
Some waste materials need storage for hundreds or thousands of years in a secure geographically stable location in steel containers
What can be done with low level radioactive waste
