Unit 5 - Radioactivity Flashcards
Describe how Rutherford’s gold leaf scattering experiment was acheived.
- A narrow beam of alpha particles, all of the same KE are fired in a vacuum towards a thin sheet of gold foil.
- Alpha particles scattered by the metal foil were detected by a detector which could move round the metal foil at a constant distance from the impact point
Describe what Rutherford found in his scattering experiment.
Describe what can be interpreted from his results.
He found:
Most alpha particles passed straight through the foil with little or no deflection but a small percentage were deflected through angles of more than 90 degrees.
He interpreted that:
Most of the atoms mass is concentrated in a small region at the centre of the atom and that this concentration of mass is positively charged as it repelled the alpha particles.
Explain how Rutherford’s experiment can be used to determine the radius of a nucleus.
Alpha particles are repelled by the nucleus when the kinetic energy of the alpha particles equals the electrical potential energy of the nucleus at a certain radius. As the velocity of the alpha particles can easily be found this radius can be found by calculation and this maximum radius for the nucleus found.
How can the radius of a nucleus be determined from electron diffraction?
Electron beams have a de broglie wavelength and when this wavelength is similar to the diameter of a nucleus it is diffracted and its first order minimum can be used to determine the diameter of the nucleus using:
Write an equation for beta minus emission.
Write an equation for Beta positive emission.
Write an equation for electron capture
When and how does gamma emission occur?
When a nucleus has excess energy after alpha or beta decay a gamma photon is emitted.
When does beta minus decay occur?
When a nucleus is neutron rich.
When does beta positive decay occur?
When a nucleus is proton rich
When does electron capture occur and how?
When a nucleus is proton rich.
Inner electrons captured by proton.
Gap filled by outer electrons emitting an X-Ray photon.
How does ionising radiation affect living cells?
It can destroy cell membranes causing cells to die.
OR
It can damage DNA which may affect cell division and cause cancer.
List sources of background radiation.
Rocks, Soil, air, food
Define half life
The half life of a radioactive isotope is the time taken for the mass of the isotope to decrease to half the initial mass.
Define the Activity of a radioactive isotope
The activity A of a radioactive isotope is the number of nuclei of the isotope that distintergrate per second.
The rate of change of the number of nuclei of the isotope.
Measured in becquerels (Bq)
