Chapter 25 Radioactivity Flashcards
What is the charge of an alpha particle?
2+
What is a beta particle?
A fast moving electron
What is gamma radiation?
High frequency photons
What and how are different types of radiation affected by charge?
Gamma is unaffected
Beta - is attracted by a positive charge
Beta + is attracted by a negative charge
Alpha is affected by a negative charge
What absorbs alpha (what is its range) and why?
It has a short range because it easily ionises surrounding particles. Paper or air absorbs them fine.
It is a large particle so it collides with other particles easily
What absorbs beta particles and what is its range?
It is less ionising than the alpha particle. They have a much longer range in air and a few mm of aluminium stops it
How ionising is gamma, what is its range and why?
It is not very ionising at all. A few cm of lead will absorb it but an infinite amount of lead could also still allow it through. The graph of absorption per thickness is exponential.
What can ionising radiation do to the body?
It can cause damage to living cells and dna mutation
How must radiation sources be handles?
With tongs
Describe the equation for alpha decay
A particle with a mass of A and proton number of Z decays into a particle with a mass of A-4 and a proton number of Z-2
What causes beta decay?
The weak nuclear force
What is the equation for gamma decay?
X ==> X + γ
What does random mean when it comes to decay?
It means that we cannot predict when a nucleus is about to decay
Each nucleus within the sample has an equal chance of decaying
What does spontaneous mean when it comes to decay?
The decay is not affected by the presence of other nuclei
The decay is not affected by external factors such as pressure
Even through decay is random and spontaneouse we can…
still predict the way that the overall substance decays
What is the half life?
This is the time it takes for half the nuclei in a sample to decay
What affects the half life?
The activity of the nuclei
What is the activity?
This is the amount of decays in a sample per second
What is the activity affected by?
The number of nuclei
The decay constant
What is the equation for activity?
A = λ x N A = Activity λ = Decay constant N = Number of nuclei
What is the unit for activity?
bq (becquerel)
The decays per second
What is the decay constant?
It is the probability that a nucleus will decay
What is the unit for the decay constant?
S^-1
What is the decay equation?
N = N0e^(-λt)
What is an alternative to the decay equation that also involves activity?
A = A0e^(-λt)
What is the simplified decay equation at the half life? and when is it used?
e^(λ t-half) = 2
How does carbon dating work?
When an organism dies, It stops consuming carbon-14. The ratio of carbon-12 to carbon-14 from a sample of a living material is used and and compared to a dead sample. The amount of carbon-14 is calculated by analysing the activity of a sample of carbon. Activity is proportional to the number of undecided carbon-14 nuclei
Describe the process for atmospheric carbon
High speed protons from cosmic rays collide with atom in the upper atmosphere to produce neutrons which collide with nitrogen-14 nuclei and form carbon-14 which emit beta-minus particles and become nitrogen 14 again so the amount of nitrogen-14 in the atmosphere is repleished
What are the limitation of carbon dating and why?
Assumptions are made that the ratio of carbon-14 to carbon-12 has remained constant. This ratio is also affected by CO2 levels and solar flairs
Because the amount of carbon-12 to carbon-14 is low, the count from a sample is very low
Why cant carbon dating be used on rocks?
Because the rocks were never living and the half life is too short. Other elements are used to date rocks
What is the process of rock dating?
Rubidium-87 emits a beta- particle and transform into a strontium-87. The half life is about 49 billion years.
What is the maximum time that carbon dating is affective to?
50,000 years
