radioactivity unit 5 Flashcards
Why does rutherford scattering tell us that the nucleus is small and positive in charge?
Most of the alpha particles go straight through, so most miss.
Must be positive to repel the positive alpha particles.
How do you find the closest point an alpha particle can get to a nucleus?
It is the point where the electric potential of the particle is equal to the original KE.
This is the upper limit of the diameter of nucleus
Why is electron diffraction the most accurate way to find out about a crystals atomic structure?
They are leptons meaning that they don’t interact with the strong nuclear force that would interferer with them.
How can electron diffraction get used to examine a crystal.
An electron beam is shone through and this will diffract through the thin layer of crystal. This will produce a diffraction pattern which is like several rings inside each other.
How can the first minimum of a electron diffraction pattern get used to find the nuclear diameter?
The first minimum is the first and smallest ring. This will be produced by electrons that are diffracted by a certain angle from the line of no diffraction.
Use sinϴ=(1.22λ)/d and the equation for de broglie wavelength to find λ to then solve for d which is the nuclear diameter.
What is the typical diameter of the atom?
1 X 10^-10m
What is the typical diameter of the nucleus?
2 X 10^-15m
What relationship does the nuclear radius increase by?
By the cube root the the nucleon number
what is r0 in the equation for nuclear radius?
the value of r when A is 1. it is 1.4 fm. (1.4 X 10^-15m)
Find the radius of a nucleus with 16 nucleons
1.4 X 10^-15 X 16^(1/3)= 3.5 X 10^-15 m
Why is nuclear density much the same for nucleses?
Protons and neutrons have similar mass and volume.
What, approximately, is nuclear density?
1.46 X 10^17 Kg m^-3
Nuclear density is significantly larger than atomic density. What does this suggest?
Most of the mass of an atom is in the nucleus.
The nucleus is small compared to the atom.
An atom must contain a lot of empty space.
What can cause a nucleus to be unstable?
Having too many or too few neutrons and having too much energy.
What is a gamma particle?
Short wavelength, high frequency, electromagnetic wave.
What is a beta plus particle?
A positron.
Why is radiative emissions also known as ionising radiation?
A radioactive particle can hit an atom and remove an electron, creating an ion.
How fast is the alpha particle
slow
How fast is the beta particle
fast
what is the alpha particle stopped by?
a few cm of air or paper.
what is the beta particle stopped by?
5 mm of aluminium
What is the beta plus particle stopped by?
It annihilates with an electron so virtually zero range.
What is the gamma particle stopped by?
Many cm of lead or several m of concrete.
Why is the alpha particle highly ionising ?
They are strongly positive.
Why does the alpha particle have a small range?
They are highly ionising and each time they ionise something they give some energy to the ion. They quickly lose their energy and so stop.
Why are alpha particles used in smoke alarms?
They allow current to flow and have a small range.
Why is gamma radiation used in medicine?
It does the less damage to the body.
What is intensity?
radiation per unit area.
what is the unit for radioactivity?
the becquerel. One count per second.
what are the sources of background radiation?
The air. It contains radon gas that comes from rocks and emits alpha particles.
The ground.
Cosmic radiation. It collides with the atmosphere, making radiation.
Living things as they all contain carbon, meaning they all contain carbon 14.
Man made radiation from industry or hospitals.
what are the units of the decay constant?
s^-1
what is the decay constant a measure of?
The probability that an individual nucleus will decay in one second.
In the activity equation, what does the N mean?
The no. of atoms.
What is the half life?
The average time it takes for the number of undecayed atoms is halve.
How do you find the decay constant?
ln2 / half life.
How does carbon dating work?
Living things take in carbon meaning they take in carbon 14. When they die, the amount of carbon 14 starts to fall as it decays with a half life of 5730 years.
What are the qualities needed for a medical tracer?
Needs to have a half life long enough to detect it but short enough to limit the radiation exposer)
Emits gamma radiation.
Decays to a more stable isotope.
When does alpha emission happen?
In atoms that are too heavy (82 + protons)
When does beta emission happen?
Too many neutrons.
What happens in beta plus emission?
neutron becomes a proton, and electron and electron anti neutrino are emitted.
What is the symbol of the electron anti neutrino?
a curly v with a bar onto next to an e
What happens in beta plus emission?
A proton becomes a neutron, and and electron neutrino emitted.