RADIOACTIVITY Flashcards
How are Electrons held in the atom?
By the electrostatic force of attraction between them and the nucleus
Charge of Proton and Electron
1.6x10^-19C and -that for electron
What are Isotopes?
Atoms of the same element with a different number of neutrons and same number of protons
What is the specific charge of a particle
Charge/Mass.Measured in Ckg^-1
What determines the stability of a nucleus?
Number of neutrons relative to the number of protons
How does the strong nuclear force hold a nucleus together?
It overcomes the force of electrostatic repulsion between the protons and neutrons to hold the nucleus together.It is repulsive at separations below 0.5fm to prevent the nucleons from crashing into each other.It is attractive at separations greater than this to prevent the nucleus from flying apart.
Features of the strong nuclear force?
Range of 4fm
Repulsive below separations of 0.5fm to stop nucleons crushing each other
Attractive from 0.5fm-4fm
Has same affect on all nucleons
Much smaller range than electrostatic force.
Max attractive value then falls to minimum.
Range of electrostatic force between particles?
Infinite range but decreases with distance between particles.
What type of atoms undergo alpha decay?Name some features of this radiation.
Very large atoms with more than 82 protons.Very ionising, range of few cm in the air.Described as a helium nucleus.Cause A number to decrease by 4 and Z number to decrease by 2.
What type of atoms undergo Beta- decay?Name some features of this radiation.
It occurs in neutron rich nuclei.It is the ejection of an electron from the nucleus along with an anti-electron neutrino.This is to carry away some energy and momentum.It causes a neutron in the nucleus to change into a proton.This increases the proton number by 1. Mildly ionising and range of a few metres.
Features of Gamma Radiation?
Has no mass or charge and is emitted by a nucleus with too much energy after alpha or beta decay.
Discovery of the neutrino?
Energy in beta decay was previously not conserved until the discovery of the neutrino.The neutrino was responsible for carrying away the missing energy.The particle has to be neutral to conserve charge and have almost 0 mass as it was never detected.In order to fit with the conservation of energy.
What are Em Waves?
They are oscillating electric and magnetic fields which travel and vibrate at 90’ to each other and the direction they are travelling in.The waves are in phase so peaks form.
When are EM Waves Emitted?
They are emitted by a charged particle when it loses energy.For example when a fast moving electron slows down, changes direction or stops completely.Or when an electron in a shell of an atom moves to a different shell of lower energy.
What are Photons and what is the formula for energy of a photon?
EM waves are emitted as short bursts of waves.Each burst is a packet of em waves.Photons are packets of em radiation waves.Photon energy=hf
What type of photons do laser beams consist of and whats the formula for power of laser?
Laser beams consist of photons with the same frequency.The power of a laser beam is the energy per second transferred by the photons.The power of the beam=nhf.N=the number of photons passing through a fixed point per second.
When does positron emission take place?
When matter and antimatter meet they annihilate each other radiation is released.
Positron emission takes place when a proton changes into a neutron in a proton rich unstable nucleus.AKA Beta plus decay where a electron neutrino is also released
How are positron emitting isotopes produced?
They do not occur naturally and are produced when a stable nucleus in solid or liquid form is put in the path of a beam of protons which the nucleus absorbs and becomes unstable.
Describe energy with regard to annihilation and pair production?
Rest energy is the energy equivalent of a particles mass.Energy into mass occurs in pair production.Mass into energy occurs in annihilation.
What happens to a particle antiparticle pair in annihilation?
All the mass of the particles get converted into energy which is carried away by 2 gamma photons.Antiparticles only exist for a fraction of a second before they are annihilated.
What happens in pair production?
A photon(usually gamma photons) with sufficient energy passing near a NUCLEUS or electron could turn into a particle antiparticle pair which would separate from each other.
What happens in pair annihilation?
Annihilation occurs when a particle and anti-particle meet and their mass is turned into radiation energy.Two gamma photons are produced in the process to ensure the total momentum is zero(conserved).
What is an electron-volt?How many joules are in an electron volt?
An electron volt is the energy transferred when an electron is moved through 1volt of pd. 1ev=1.60x10^-19J
1Mev=1.60x10^-13J
What happens when objects interact?
When a force acts on an object it changes the momentum of the object.When objects interact they exert an equal and opposite force on each other.Momentum is transferred between these objects by these forces.When proton meets another proton they repel.
Describe the exchange particle of the EM force?
The EM force between two objects is due to the exchange of virtual photons.Virtual photons cant be detected directly, if we intercepted them we would stop the force acting.
