6: Radiation + Radioactivity - YK Flashcards
(15 cards)
What are the three main models of the atom?
Atoms as spheres:
Plum Pudding Model: positively charged sphere with negative electrons scattered throughout the sphere
Rutherford Model: small, dense, positively charged nucleus surrounded by negatively charged electrons
How did the Rutherford experiment suggest the Rutherford model?
Very thin gold foil bombarded by alpha particles, surrounded by a scintillation screen (so alpha particles could be detected)
Most particles passed straight through: atoms must be mostly empty
Some particles deflected at small angles: a positively charged area must have repelled the particles
Some particles deflected at large angles: a large mass must have been collided into
What is an atom?
The smallest independent particle of an element that still maintains the properties of that element, consisting of a positively charged nucleus (containing almost all of the mass of the atom) orbited by negatively charged electrons
What are the atomic and mass numbers?
Atomic number is the number of protons in an atom, mass number is the number of protons and neutrons in the nucleus of an atom
What are isotopes and ions?
Isotopes are atoms of the same element with a different number of neutrons, an ion is an atom or molecule that has lost or gained to become electrically charged
How are energy levels and light related?
Electrons orbit the nucleus in specific energy levels. When an atom absorbs a photon (particle of light), an electron jumps from a lower energy level to a higher energy level if the photon energy is equal to the difference between energy levels. When an electron falls from a higher energy level to a lower energy level it emits a photon with a specific energy (difference between levels)
What is radioactive decay?
The emission of radiation from an unstable nucleus (unstable because it has too many protons or neutrons), it is random and unpredictable
What is ionisation?
The removal of an electron from an atom to create a positive ion
What is background radiation and what are some sources of it?
Background radiation is the low-level ionising radiation that is always present throughout Earth; the sun and space, radioactive minerals in the ground (or transferred into concrete), nuclear waste, medical equipment, radon gas
What are two methods of detecting radiation?
Photographic film (develops, changes colour, when exposed to radiation), Geiger-Müller Tube (detects ionising radiation)
How does a Geiger-Müller Tube work?
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What are the four types of radiation and their composition, ionising power, and penetrating power?
Alpha radiation - 2 protons + 2 neutrons (helium nucleus) - very high ionising power - low penetrating power (5cm in air, stopped by paper)
Beta radiation - 1 electron/positron - moderate - moderate (1-2cm in air, stopped by aluminium foil)
Gamma radiation - 1 photon - very low - very high (infinite in air, stopped by lead)
Neutron radiation - 1 neutron - very low - very high
What are alpha and beta (plus and minus) decay?
Alpha decay is the emission of an alpha particle from a nucleus, beta minus decay is the emission of an electron and a neutron turning into a proton, beta plus decay is the emission of a positron and a proton turning into a neutron
What are gamma rays?
High energy electromagnetic waves
What is the half-life of a material?
The time it takes for half of the radioactive nuclei in a sample to decay
