Radioactivity (6) Flashcards
What is an atom?
A positively charged nucleus containing protons and neutrons surrounded by electrons. Most of the mass is in the nucleus despite it’s small radius compared to the atom.
What is an isotope?
Atoms of the same element with the same number of protons but a different number of neutrons.
How do electrons change energy level?
Electrons can move up an energy level when they absorb EM radiation. The electron will then fall back down and lose the excess energy via EM radiation.
What is ionisation?
When an outer electron absorbs enough energy to escape the atom. Radiation that causes this is called ionising radiation.
What is an alpha particle?
Alpha particles are helium nuclei (2 protons 2 neutrons). They can be stopped by a few cm of air, skin or a sheet of paper but are very ionising. When a nucleus emits an alpha particle, its mass # decreases by 4 and atomic # by 2.
What are beta minus and beta plus particles?
Beta minus particles are fast moving electrons released by the nucleus. Beta plus particles are fast moving positrons. They will travel a few metres in air, can be stopped by a few mm thick aluminium and are moderately ionising. A neutron changes to a proton and an electron is emitted meaning the atomic # increases by 1. During beta plus decay, the opposite occurs.
What are gamma rays?
Gamma rays are EM waves with short wavelengths. They travel a few km in air, are absorbed by several metres of concrete or thick lead and are weakly ionising. When an atom undergoes gamma decay, it just becomes more stable.
What is background radiation?
Low level radiation that is around us at all times. It comes from food, some rocks (that produce radon gas) and building materials. Some background radiation comes from cosmic rays mostly produced by the sun.
How can you measure and detect radiation?
Photographic film:
Becomes darker and darker as more radiation reaches it.
Geiger-muller tube:
When radiation passes through the tube, it ionises a gas inside it and allows a short pulse of current to flow. It can be connected to a counter and a count rate can be measured.
What was the gold foil experiment and what did it show?
Rutherford shot alpha particles through gold foil and observed how most particles passed through the foil and some bounced back. Therefore, he suggested that atoms are mostly made of empty space with a tiny central nucleus with positive charge and electrons surrounding it.
What is the difference between irradiation and contamination?
Irradiation is being exposed to a radioactive substance while contamination is when radioactive particles get onto an object.
What is half-life?
The average time taken for the # of radioactive nuclei in an isotope to halve. It’s the average because it cannot be predicted when a nucleus is going to decay.
What are some uses of radioactivity?
Fire systems:
There is a constant current of ionised air particles (due to alpha radiation) between two electrodes. Smoke absorbs the particles stopping the current and ringing the alarm.
Irradiating food and equipment:
High doses of gamma rays kill all microbes,. Sources of the gamma rays need long half lives so that they don’t need replacing often.
Tracing and gauging thickness:
Beta particles are passed through paper to a detector. If too many beta particles reach the detector, the paper is too thin and the rollers apply less force and vice versa.
How can you diagnose with gamma rays?
Tracers which contain a radioactive isotope are injected or swallowed into the body (cannot emit alpha rays and has to have a short half life). The tracer emits gamma rays which are picked up by gamma cameras. They can find sources of internal bleeding and tumours using radioactive glucose molecules which are absorbed by the cancer cells quicker than normal cells.
How can you diagnose with positrons?
The tracer emits a positron which meets an electron and both get destroyed emitting gamma rays which get detected by PET scanners.
