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the strong nuclear force
binds nucleons together
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there are several different forces acting on the nucleons in the nucleus . the two you already know about are electrostatic forces from the protons' electric charges , and gravitational forces due to the masses of the particles . if you do the calculations you find the repulsion from the electrostatic force is much .... than the gravitational attraction . if these were the only forces acting in the nucleus , the nucleons would ..........
- bigger
- fly apart . So there must be a another attractive force that holds the nucleus together - called the strong nuclear force
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the strong nuclear force is quite complicated
- 1) to hold the nucleus together , the strong nuclear force must be an attractive force thats stronger than the electrostatic force
- 2) experiments have shown that the strong nuclear force has a very short range . it can only hold nucleons together when they're separated by up to a few fentometers - the size of a nucleus
- 3) the strength of the strong nuclear force
- rapidly falls beyond this distance
- 4) experiments have shown the nuclear force works equally between all nucleons . this means that the size of the force is the same whether it's a proton-proton , neutron-neutron or proton-neutron
- 5) at very small separations , the strong nuclear force must be repulsive - otherwise there would be nothing to stop it crushing the nucleus to a point
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1 femtometer = .... meters
1x10^-15m
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strong nuclear force on a graph
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alpha decay
- release alpha particles (positively charged helium ions)
 - reduces mass number of nucleus by 4 and atomic number by 2
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beta deacy
- there are two types of beta radiation
- beta +
- and
- beta -
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beta - deacy
- beta - decay is the emission of an electron from the nucleus along with an anti-neutron
- beta decay happens in isotopes that neutron rich (i.e. have too many more neutrons than protons in their nucleus)
- when a nucleus ejects a beta particle , one of the neutrons in the nucleus is changed into a proton an electron and anti-neutrino are emitted
- the proton number increases by 1 and the nucleon number stays the same
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beta + decay
- neutron deacys into a proton emitting an electron and an electron anti neutrino
- the proton number decreases by one and the nucleon number stays the same
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gamma radiation
when alpha or beta decay occurs the nucleus is usually left in an excited state it subsequently releases a high energy photon (gamma particle) to reduce this energy
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photons have ... mass and ... charge
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the speed of the wave is given by
- c = f*
 - c = speed of light = 3x10^-8 ms^-1
- f = frequency = Hz
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photons are emitted when
- fast moving electron stopped
- electron jumps from higher quantum level (shell) in an atom to a lower one
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energy of an electron can be given by
- E=hf
- where h = planck's constant = 6.63x10^-34
- as c = f this can also be written as E=hc/
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when a particle and its corresponding anti particle meet they
annihilate and are converted completely into energy (found by E=mc^2)
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it is also possible for a photon of high enough energy to spontabeously change to
a particle and its antiparticle counterpart ; this is known as pair production
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energy of a particle is usually measured in
Mev and is defined as the energy required to accelerate an electron through the potential difference of 1 volt
-
1Mev = ......J
1.60x10^-13
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antiparticle
- same rest mass as corresponding particle
- same rest energy as corresponding particles
- opposite charge
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rest energy of a particle can be found by
E=mc^2
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pair production occurs when
a photon with a high enough energy changes into a particle and its corresponding anti-particle
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as one photon turns into two particles , using E=mc^2 , the photon must have at least the rest energy of the 2 particles that it turns into hence
- E~0=mc^2
- (kinetic energy must be added in if given)
- as 2 particles are produced
- 2E~0 = 2(mc^2)
- therefor the energy of the photon must be
- E~gamma=2E~0
- as E=hf
- hf= 2E~0
-
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annihilation occurs
when a particle and its corresponding antiparticle meet and convert themselves to energy in the form of two photons
-
as two photons are produced in annihilation it can be shown :
- 2E~gamma = 2E~0
- E=mc^2
- hf=E~0
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electromagnetic particle interaction
- occurs only between charged particles
- opposite charges attract
- same charges repel
- the mediators of the force are virtual photons
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