# Decay

• Created by: syaqub18
• Created on: 20-04-15 18:40
Why cant you predict the decay of an atom?
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what is the decay constant of a radioactive isotope?
the probability of an atom decaying per unit time
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what is an isotope?
an element which has the same number of protons but a different number of neutrons
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what is the meant by the activity of a radioactive isotope?
the number of atoms that decay per unit time
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what is the half life of an isotope?
the time it takes for the number of unstable nuclei in a sample of an isotope (or the samples activity or count rate) to halve
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what is the symbol of the decay constant?
lambda
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what does a big value of the decay constant mean?
the faster the rate of decay
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what is the unit of the decay constant?
s^-1
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what is activity measured in?
becquerels (1Bq = 1 decay per second)
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how else can activity be written?
A= -dN/dt (dN is the change of unstable nuclei, dt is the change in time, the minus sign is there because dN is always a decrease)
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In practice, how is the half-life measured?
by measuring the time it takes for the activity to halve
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what is the relationship between the half-life and the radioactivity level?
the longer the half-life, the longer it takes for the radioactivity level to fall
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how does the number of unstable nuclei decrease over time?
exponetially
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how can you calculate the half-life of an isotope from a graph?
read off the value of count rate, particles or activity at t=0, go to half the original number of unstable nuclei on the y axis, draw a horizontal line to the curve and then a line down, read the half life where it crosses the x axis
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what are the applications of radioactive isotopes?
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by using carbon-14, living matter is made up of carbon some of it being carbon-14, the activity of this starts to fall when the living organism dies, acitivity of the archeological find and the stable carbon-14 is compared
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why is it difficult to get a reliable age from radiocarbon dating?
object may have been contaminated, can only find the age of the materials used for man-made objects made from natural materials, there may have been a high background radiation count, uncertainty in the amount of carbon-14 that existed before
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how are radioactive isotopes used in medicine?
technetium-99m used as medical tracer to show tissue or organ function, tracer injected and moves through the body to point of interest, radiation is emitted and recorded to produce image, technetium emits gamma radiation and has short half-life
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what are the two forces acting on the nucleus?
strong nuclear force keeping it together and electromagnetic pushing protons apart
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under what conditions will a nucleus become unstable?
too many or too few neutrons, too many nucleons/too heavy, too much energy
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In which isotopes does alpha emission occur?
very heavy ones (more than 82 protons) such as uranium and radium, nuclei is too massive so alpha particle is released to make it more stable, proton number decreases by 2 and nucleon number by 4
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in which isotopes does beta-minus emission occur?
Neutron rich ones (more neutrons than protons), when a nucleus ejects a beta minus particle/electron and an antineutrino, a neutron changes to a proton, proton number increases by one, nucleon number remains the same
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in which isotopes does beta-plus emission occur?
Proton rich (high proton to neutron ratio), when a nucleus ejects a beta plus particle/positron and a neutrino, a proton changes to a neutron, proton number decreases by one and nucleon number stays the same
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in which isotopes does gamma emission occur?
after alpha or beta decay, nucleus has excess energy if in an excited stated, energy is lost by emitting a gamma ray, it is also produced by electron capture (nucleus absorbs an orbiting electron) so proton changes to a neutron
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what must be conserved in nuclear reactions?
energy, momentum, charge, nucleon number and lepton number
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## Other cards in this set

### Card 2

#### Front

what is the decay constant of a radioactive isotope?

#### Back

the probability of an atom decaying per unit time

### Card 3

#### Front

what is an isotope?

### Card 4

#### Front

what is the meant by the activity of a radioactive isotope?

### Card 5

#### Front

what is the half life of an isotope?