Radioactivity Flashcards
Describe the basic structure of an atom and give the relative masses and charges of each
Small (10000 x smaller than the whole atom) nucleus made of protons (mass 1, charge +1) and neutrons (mass 1, charge 0) orbited by electrons (mass negligibe, charge -1)
How did modern theories about atomic structure (the nuclear model) come about?
Rutherford and Marsden fired alpha particles at gold foil and observed that MOST passed through but a few were deflected. This showed that atoms are mostly empty space. It proved that the ‘plum pudding’ model was inaccurate. It showed that all positive charge is in the nucleus
Define a radioactive substance
An unstable material which gives out radiation from the nucleus in the form of alpha particles, beta particles or gamma rays all the time, no matter what conditions they are under
What are the origins of background radiation?
Rocks (such as uranium ore), cosmic rays from space, fallout from nuclear weapons and nuclear accidents
Define an alpha particle, a beta particle and gamma radiation
Alpha particles are two neutrons and two protons, the same as a helium nucleus
Beta particles are electrons from the nucleus
Gamma radiation is electromagnetic gamma waves of very high frequencies
What happens to the nucleus when an ALPHA particle is ejected? Give the nuclear equation, using uranium-238 (92 protons) as an example
Nucleus loses 2 protons and 2 neutrons therefore atomic number goes down by two, mass number goes down by 4
Equation: 23892U – 42 a → 23490 Th + (ENERGY)
What happens to the nucleus when an BETA particle is ejected? Give the nuclear equation, using carbon-14 (6 protons) as an example
Nucleus loses one electron therefore atomic number goes down by one, mass number stays the same
Equation: 146C – 0-1ß → 147N + (ENERGY)
Compare properties of alpha beta and gamma radiations in terms of relative ionising power, their penetration through materials and their range in air
Alpha: causes very strong ionisation, can be stopped by a piece of paper, few centimetres in air
Beta: weak ionisation, can be stopped by a few mm of aluminium, few metres in air
Gamma: very weak ionisation, can be reduced by several metres of lead and concrete, infinite range in air
Define half-life
The half-life of a radioactive isotope is the average time it takes for the number of nucliei of the isotope in a sample to halve, OR the activity to halve, OR the mass of the isotope remaining to halve
How are alpha, beta and gamma radiation each used?
Alpha: in paper mills, to alert a computer if the thickness of the paper is not ideal (it cannot pass through if too thick, and its energy is increased if too thin). This needs long half-lifes
Beta: the same, except in foil manufacture (alpha particles would not be able to pass through foil)
Gamma: in radioactive tracers for medical purposes because gamma rays can pass through the body without difficulty, allowing us to detect them. They are also the least damaging of the three types. They need half-lifes long enough that they can be monitored but not too long
How does radioactive dating work?
An isotope in the sample with a similar half life to the age of the sample is needed
What makes radioactive particles and waves dangerous?
They knock electrons out of atoms and the atoms become charged (ionised). In a living cell, this ionisation can damage or kill the cell. It damages DNA and also turns water into highly reactive H and OH radicals
Describe what happens when each type of radiation enters a magnetic field?
Alpha: radiation is deflected by the magnetic field in one direction. They are difficult to deflect because they have a large mass.
Beta: radiation is deflected in the opposite direction to alpha radiation. They have a smaller mass than alpha particles.
Gamma: rays pass through undeflected because they have no mass.
Explain what happens when each type of radiation enters an electric field
Alpha particles are attracted to the -ve plate as they are +vely charged (opposites attract). They have a charge twice that of beta particles but a much greater mass so deflection is less
Beta particles are attracted to the +ve plate as they are -vely charged. They deflect more than alpha particles because their mass is so much smaller
Gamma rays do not deflect because they are electromagnetic and so have no charge