13.2.3: Describe one piece of evidence for the existence of nuclear energy levels.
We know that ELECTRONS have different energy levels- but the NUCLEUS itself has different energies too.
Unlike beta emission, which forms a continuous spectrum of energies, when an alpha particle or gamma photon is released from the nucleus, only discrete (quantized) energies are absorbed- as these particles are emitted from the NUCLEUS, it means that the nuclei have discrete energies.
When the kinetic energy of different alpha particles released during emission (using a stopping voltage circuit) is measured, it is seen that there are a range of kinetic energies- these energies correspond to the difference between 2 nuclear energy levels. If a lower energy alpha particle is emitted, the nucleus is left in an ‘excited’ state, as it still has surplus energy- it will then release this energy in the form of gamma photons. However, if a high energy alpha particle is released, bringing the nucleus to a ‘ground’ state, then no gamma photons are emitted.
13.2.4 Describe β+ decay, including the existence of the neutrino.
Experiments have shown that beta decay is CONTINUOUS- there are a range of energies.
However, calculations showed that the Beta particle had less kinetic energy than expected, and some energy was mission- this appeared to contradict the law of energy conversation. But, in 1930, Wolfgang Pauli postulated that there was another particle that was carrying away the missing KE and momentum- known as NEUTRINO.
Neutrinos (and anti-neutrinos) have no charge, VERY small mass (cannot be measured empirically) and travels at close to the speed of light.
Neutrinos (and anti-neutrinos) have no charge, VERY small mass (cannot be measured empirically) and travels at close to the speed of light.
The equation above shows the decay of a tritium nucleus- A beta particle is emitted, as well as an ANTI-NEUTRINO (opposite of neutrino- when they collide, they annihilate each other).
A positron decay occurs when a proton in a nucleus decays into a neutron and the anti-matter particle of an electron- a POSITRON.
In this case, a NEUTRINO is released.
These particles account for the fact that beta emission forms a continuous spectrum.
