Flashcards
P7 Radioactivity
Cards in this deck (27)
- 1What does a radioactive substance contain?Unstable nuclei that become stable by emitting radiation.
- 2What are the three main types of radiation?alpha, beta, gamma
- 3What is a random event?Radioactive decay- you cannot predict or influence when it will happen.
- 4What did Ernest Rutherford discover about radiation?That alpha and beta radiation is made up of different types of particles.
- 5What was the plum pudding model?In this model, the atom was imagined to be a sphere of positive charge with negatively charged electrons dotted around inside it like plums in a pudding.
- 6What did Rutherford's experiment show?-that most of the alpha particles passed straight through the metal foil
-the number of alpha particles deflected per minute decreased as the angle of deflection increased - 7Why was Rutherford astonished by the results?It was like firing naval shells at tissue paper and discovering that a small number of shells rebound.
- 8What was deduced from the results?That there is a positively charged nucleus at the centre of every atom that is:
-Much smaller than the atom because most 'a' particles pass through the atom without deflection
-where most of the mass of the atom is located. - 9Why was Rutherford's model quickly accepted?-It agreed with measurements Geiger and Marsden made in their experiments.
-It explained radioactivity in terms of changes that happen to an unstable nucleus when it emits radiation.
-It predicted the existence of the neutron - 10What did Neil's Bohr put forward?The theory that electrons in an atom orbit the nucleus at specific distances and specific energy values or energy levels.
His models showed that the electrons in an atom can to another orbit by absorbing radiation to move away from the nucleus or by emitting em radiation to move closer to the nucleus. - 11What are isotopes?Atoms of the same element with different numbers of neutrons.
- 12What is the atomic number?The number of protons (and electrons)
Atoms of the same element each have the same number of protons. - 13Alpha emissionAlpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises two protons and two neutrons.
Its relative mass is 4 and its relative charge is +2. - 14What happens when an unstable nucleus emits an alpha particle?Its atomic number goes down by 2 and its mass number goes down by 4.
the mass and the charge of the nucleus are both reduced. - 15Beta emissionBeta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus. Instead, they form when a neutron splits into a proton and an electron. The electron then shoots out of the nucleus at high speed.
The relative mass of a 'b' particle is effectively 0 , and its relative charge is -1 - 16What happens when a beta particle is emitted<the atomic number goes up by 1, and its mass number is unchanged (because a neutron changes to a proton )
-the charge of the nucleus, and the mass of the nucleus is uncharged. - 17gamma radiationa gamma ray is em radiation from the nucleus of an atom. It is uncharged and has no mass. So its emission does not change the number of protons or neutrons in a nucleus.
- 18A particles and abilitiesAlpha radiation is stopped by paper. It consists of particles, each composed by 2 protons and 2 neutrons. It has the greatest power.
- 19B particles and abilitiesB radiation is stopped by a thin sheet of metal. It consists of fast-moving electrons emitted from the nucleus. It is less ionsing than alpha rad. but ionisng that gamma.
- 20Gamma radiation and its abilitiesIt is stopped by thick lead and has an unlimited range in air. It consists of electromagnetic rad.
- 21What do all types of radiation do?Ionise substances they pass through. Ionisation in a living cell can damage or kill the cell.
- 22What is the activity of a radioactive source?The number of unstable atoms in the source that decay per second. The unit if Bq, which is one decay per second.
- 23What is radioactive decay?The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom.
For example, carbon-14 decays to nitrogen-14 when it emits beta radiation. - 24Circumstances of a radioactive isotopeIt is not possible to predict when an individual atom might decay. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay
- 25Define half-life1 The time it takes for the number of nuclei of the isotope in a sample to halve
2 the time it takes for the count rate from a sample containing the isotope to fall to half its starting level - 26What is resolution?This is the smallest change is quantity being measured 0.001
- 27measuring half-lifeWe know that after one half life, one half of the original radioactive nuclei remain. After two half lives, one half of this half remains or one quarter of the original radioactive nuclei remain.
We can therefore say:
1 half life = ½ of the original radioactive nuclei remain
2 half lives = ¼ of the original radioactive nuclei remain
This can be written as an equation as:
The amount remaining=1/2n x the original amount
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- Physics Flashcards on P7 Radioactivity , created by Annie Loizides on 20/04/2017.
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- Annie Loizides
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