Radioactivity Flashcards
How does ionising radiation work?
ionise atoms by removing electrons
What is an alpha particle?
a helium nucleus
What is the charge of an alpha particle?
+2e
What is the range of alpha in air?
1-2cm
What can alpha be stopped by?
sheet of paper
What is beta minus?
an electron
What is the charge of beta minus?
-e
What is the range of beta minus in air?
1-2m
What can beta minus be stopped by?
1-3mm of aluminium
What is beta plus?
a positron
What is the charge of beta plus?
+e
How far can beta plus travel in air?
not very as positrons get annihilated by electrons
What is gamma radiation?
EM wave
What is the range of gamma in air?
kilometers
What can gamma photons be stopped by?
few cm of lead
Which form of radiation is the most ionising?
alpha
Which type of radiation is the least ionising?
gamma
How does an unstable nucleus with more than 82 protons decay?
alpha- emitting a helium nucleus
What is emitted in beta minus decay?
an electron
What is emitted in beta plus decay?
a positron
What is emitted in gamma decay?
surplus energy- gamma photon
Define radioactivity:
random decay of an unstable nuclei
Define half life:
time taken for half the number of active nuclei in a sample to decay
Define activity:
rate of nuclei decay
What is decay constant?
probability of decay of an individual nucleus per unit time
What is āNā representative of in the nuclear decay equation?
number of undecayed nuclei left in the source at time t
What is the relationship between decay constant and half life?
inversely proportional
What is carbon dating used for?
determining the age of organic materials
Which isotopes have a constant ratio?
carbon 12 and carbon 14
What happens to a living thing once it dies?
stops taking in carbon so the carbon 14 nuclei within the dead material decreases exponentially with time
How can the age of a dead material be determined?
by comparing the carbon 12 to carbon 14 ratio of the dead thing with the same type of living thing
Why can the C12 to C14 ratio not be assumed to remain constant?
it is affected by natural events such as volcanic eruptions as well as increased emissions from cars and burning fossil fuels
Why is there large uncertainty when aging a relic? eg rocks
the value of the ratio in the past is not known
