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Summary AQA: Particles and Radiation key notes
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for the AQA specification - topic 1 = Particles and Radiation. It covers specific charge, particle interaction, Feynman diagrams and more..
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1. Particles and RadiationParticles
Constituents of the atom
Spe
cific
charge = charge / mass
Proton has charge of + 1.6 x 10-19 C and mass of 1.67 x 10-27kg
Therefore of + 1.6 x 10-19 C ÷ 1.67 x 10-27kg = 9.58 x 107 Ckg-1
Electron has the largest specific charge of any particle = 1.76 x 10 11
Isotopes are atoms with the same number of protons but different numbers of neutrons
e.g. carbon -14
Isotopic data = relative amount of different isotopes of an element in a substance
o Carbon 14 is radioactive, used to find how old and organic material is known as carbon dating
o Carbon dating calculates the percentage or carbon 14 remaining in the objects and using the starting
value and its half life to calculate age.
What is the specific charge for carbon (14- 6 protons):
C = 6 x + 1.6 x 10-19 C = 9.60 x 10-19C
m = 14 x 1.67 x 10 -27 = 2.34 x 10-26 kg
SC = C/M = 4.10 x 107 Ckg-1
Stable and unstable nuclei
Electrostatic force = attractive or repulsive forces between particles due to their electric charges
Strong nuclear force (SNF) = keep nuclei stable by
counteracting the electrostatic force of repulsion - less than 0.5 = repulsive
between protons in the nucleus. - 0.5 > 3.0 = attractive
o It overcomes proton – proton repulsion at - >3.0 = no force
short distances
o Short range = 3 femtometres (3 x 10 -15m)
scale of small nucleus
o Attractive to down to 0.5fm and the
repulsive for separations less than this.
o Neutrons also help keep nucleus together,
therefore for big atoms more neutrons are
needed to overcome repulsion protons are feeling.
Unstable nuclei = too many protons, neutrons or both meaning the SNF is not enough to keep them stable.
These nuclei will decay to become stable.
Decay Basics
, Alpha decay: 2 protons + 2 neutrons = 4 nucleons (short range few cm)
Beta decay: neutron turns into proton as an electron, antiparticle, and antineutrino. (neutron rich) (range of
several meters)
o Antineutrino/neutrino carries away some energy and momentum. Needed for conservation rules
Gamma radiation: no mass, no charge. Emitted after alpha or beta. Emitted by a nucleus with too much
energy too become stable.
Too many
neutrons Too many protons and
neutron (too large)
Too many
Atoms with 83+ protons
protons
+ strong force cannot
counter-balance
electromagnetic force of
repulsion.
Photons
Electromagnetic wave consits of an electric wave and a magnetic
wave which travel together and vibrate.
They are:
o At right angles to each other and direction they are
travelling
o in phase with each other(peak at the same time, therefore
in step)
Electromagnetic waves are emitted when a charged particle loses
energy.
o A fast-moving electron is stopped, e.g. in an X-Ray tube, or slows down or changes direction
o Orbital electron de-excites and moves to a lower energy shell
EM waves are emitted in short bursts of waves, each bursts leaving the source
in a different direction.
Each burst = packet of EM wave = photon
Photons transfer energy and have no mass.
h=
Laser beam = photons of the same frequency.
Power of a laser beam = nhf where n = number of photons each second
c
Etotal = nhf = nh λ
P=
nhf
t
= ()
n
t
hf
Particles and antiparticles
, Antimatter = antiparticles which have the same rest mass, equal and opposite charge to the corresponding
particle
For every type of particle there is an antiparticle. (positron is antiparticle for the electron)
Annihilation
Particle and its antiparticle collide, their masses are converted into energy:
∆E = ∆mc2
This energy, along with kinetic energy of the two particles is released
in the form of 2 photons moving in opposite directions to conserve
momentum
o In a PET scanner (3D images of inside body for medical
diagnosis) annihilation occurs
o a positron emitting radioisotope (Beta- plus decay) are
released they annihilate with electrons in patient’s system,
emitting gamma photons which can be easily detected
Pair- production
Where a photon is converted into an equal amount of matter and
antimatter.
Only occurs when photon has a greater energy than total rest energy
of both particles, any excess energy is converted into kinetic energy
of the particles
Emin =2 E0 where Emin is minimum energy required in MeV, and E0 is the rest energy of particles
o For and electron positron pair production: 2 x (0.510999) = 1.021998Mev. 0.510999 is the rest energy
of the electron and positron
In cloud chamber, and electron and positron will curve away from each other, due to applied magnetic field
and Fleming left hand rule
In hadron collider, two protons collide and produce 2 protons, and 1 proton and antiproton pair (if extra
proton formed, there will always be and antiproton with it)
Beta- minus decay/ beta emission
Happens in neutron rich isotopes
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