Slides in this set
Recap from AS:
Einstein's theory of special 1.When a particle and its
relativity: corresponding antiparticle meet,
Mass of an object increase
or decreases when it gains
Energy and mass they annihilate each other and 2
gamma photons are produced,
each of energy mc^2 (m is the
or loses energy. mass of particle/antiparticle.
APPLIES TO ALL ENERGY Energy changes in reactions: 2.A single photon of energy in
CHANGES OF ANY Reactions on a sub-nuclear excess of 2mc^2 can produce a
OBJECT particle and antiparticle, each of
level involve significant mass m( pair production)
changes of mass.
Energy released Q=delta mc^2
A DECAY: the nucleus recoils when the a
particle is emitted-so the energy released is When energy is released the
shared between the a particle and nucleus. mass after the change is
use conservation of momentum to show always less than the total mass
energy released is shared.
before the change some of the
B DECAY: the energy released is shared mass is changed into energy)
in variable proportions between the B
NEUTRINO/ANTINEUTRINO. If the b
particle has maximum kinetic energy the 1u=1.661*10^-27kg.
neutrino has negligible kinetic energy. The b
particle will always have less kinetic energy E=1.661*10^-27kg * C(3*10^-8ms)
than the energy released because of the
recoil of the nucleus.
ELECTRON CAPTURE: nucleus
emits a neutrino which carries away all =931.3MeV
energy released. Also emits a X-ray photon-
when de-excitation.…read more
STRONG NUCLEAR FORCE-attractive force
When calculating Q in beta decay assume
between any 2 nucleons in the nucleus. neutrino has negligible mass.
Strength?: estimate the force of repulsion If mass of each atom is given instead of mass
between 2 protons at distances of 1fm apart of its nucleus calculate mass of each nucleus
(=10^-15). Between 2 protons= 200 N, so strong by subtracting mass of the electrons from
nuclear must be at least 200 N. mass of each atom.
Range?: no more than 3-4*10^-15m. The
diameter of nucleus can be found by electron
scattering-shows even spacing so strong nuclear
must act between nearest neighbouring
Energy to remove?: in MeV; force is about 200
N, over about 2-3*10^-15 m. SO work
= 200N * 3.5*106-15M.
Repulsion?: become repulsive at 0.5fm or less. If
not the nucleons would pull closer and closer
and the nucleus wouldn't be the same size.…read more
Binding energy of a nucleus: work that must be done to separate a nucleus into its constituent
neutrons and protons.
To separate a nucleus into
its separate nucleons
work must be done to
overcome the strong
nuclear force. The
potential energy of
each nucleons Is
When a nucleus forms energy
when removed from is released, as the strong
its nucleus. nuclear force does work pulling
nucleons together, ENERGY
Because energy is released
when nucleus forms, the
nucleuses mass is less than
the mass of its separated
MASS DEFECT: difference between mass of the separated nucleons with the mass of
MASS DEFECT for =Zmp+(A-Z)mn-Mnuc.
mp-mass of proton, mn-mass of nuetron, Z-protons,A-Z-neutrons, Mnuc-mass of
The mass defect is due to energy released when the nuclues is formed from separate
neutrons and protons.
Binding energy=mc^2…read more
A particle tunnelling
1. If 2 protons and 2 2. Why?: A particles binding 3. The potential energy of
neutrons bind energy is very large the particle varies with the
together in a big (7MeV per nucleon) distance it is to the outside
enough nucleus, So the particle gains enough the nucleus from inside.
then they emitted kinetic energy to give it
as a A particle enough probability of
4. The gain of kinetic energy when
the A particle forms is not enough
to over come the coulomb barrier
but due to the WAVE NATURE of
A particle it has the probability of
tunnelling through the barrier.
The coulomb barrier is due to the electrostatic
force on the A particle.
The `well' is due to the strong nuclear force.…read more
Binding energy PER NUCELON:
average work done per nucleon
= MORE BINDING
to remove all nucleons from a
FUSION?: process of making
small nuclei fuse together to form
a larger nucleus.
Product has more energy than
smaller nuclei. so binding energy
of each nucleon INCREASES
FISSION?: process in which a
large unstable nucleus splits into 2
fragments which are more stable-
Binding energy per nucleon