3.8 - Nuclear Physics Flashcards
Who discovered radioactivity?
Marie Curie and Henri Becquerel
What are some ways you can safely handle radioactive sources
use long handled tongs to move it around
keep it as far away as possible
don’t point the source towards people
store in a lead-lined container when not using
How do you figure out the distance of closest approach for a particle?
The electrical potential when the particle is at its closest approach is equal to the initial kinetic energy so equate these two [PE= (Q1Q2)/4(pi)r] and rearrange to make r (distance) the subject
Why is the closest approach not the most accurate calculation of nuclear radius?
it is the distance between the atoms’ centres, so will always be an overestimate
If a gold nucleus was changed for an atom with fewer protons, what would change about the alpha particles distance of closest approach?
it would travel closer to the atom as there is less of an electrostatic repulsive force so needs to travel further to lose the same initial KE
what are the a, b, g radiation ranges in air
alpha: a few cm (2-10)
beta: 1m
gamma: infinite
How ionising are a, b, g radiation and how dangerous does this make them to the human body
alpha: highly/ very dangerous if ingested or inhaled
beta: weakly/ damage more spread out than alpha but more penetrating
gamma: very weakly/ not dangerous, small chance of interaction with body cells
which radiation are/ not deflected in an electric field
alpha: yes
beta: yes
gamma: no
What are a, b, g radiation absorbed by?
alpha: paper
beta: 3mm aluminium foil
gamma: several m of concrete OR several inches of lead
How does gamma radiation spread out?
as a sphere, intensity follows inverse square law
What are some natural sources of background radiation?
radon gas from rocks, cosmic rays
What are some man-made sources of background radiation?
medical x-rays, fallout from nuclear weapons testing
What is a better estimate of nuclear radius? How does it work?
High-energy electron diffraction.
A beam of high-energy electrons are accelerated to make their De Broglie wavelength in order of 10^-15, around same as diameter of nucleus. They’re fired at thin film of a material in front of a screen where they produce a diffraction pattern of concentric circles; bright centre and getting dimmer as you move away.
What are the benefits of using electrons instead of alpha particles in e- diffraction?
no electrostatic repulsion with e- so it can get closer
alpha particles give an overestimate (closest approach)
e- are easier to produce
What should a tracer isotope have?
half life stable enough for necessary measurements to be made but also short enough to decay quickly after use
What factors should you consider when using radioactive isotopes?
the half-life and type of radiation needed
toxicity
whether or not a stable product is needed
What are uses of radioactive isotopes?
carbon dating
alpha particles for smoke detectors
What is an isotopes activity proportional to?
its mass
Why could it be difficult to obtain a reliable age of an ancient boat by comparing the wood with living wood
There is uncertainty in the ratio of carbon-14 in the atmosphere thousands of years ago
The boat may have been made with the wood some time after the tree was cut down
When can it be unreliable to use carbon dating? Why?
When a sample is less than 500 years old since the change in activity is too small to be accurately measured.
When a sample is more than 50,000 years old since the activity of remaining C-14 isotopes would be too small compared to background radiation to be accurately measured.
What are the equations relating intensity and distance
I=k/r^2 where k=nhf/4pi
I1/I2=(r1/r2)^2
When does gamma radiation happen?
following alpha or beta decay
What is activity dependent on?
The number of atoms of the isotope present in the sample (N)
The probability that an atom will decay in the next second
What does the decay constant always need to be between?
0 and 1(its a probability)
