Radioactivity. Atoms and Radioactivity. Introduction. Types of Radiation. Using Radioactive Decay. Carbon Dating. Other methods. Example. Glossary. By Mark Varley 11SY. Proton. Neutron. Atoms and Radioactivity. Isotopes of some elements have unstable nuclei
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Atoms and Radioactivity
Types of Radiation
Using Radioactive Decay
By Mark Varley 11SY
Atoms and Radioactivity
Isotopes of some elements have unstable nuclei
In order to become stable the make break apart or decay
This decay causes the nucleus to emit ionising radiation, and an atom of a different element is formed
These isotopes are called radioisotopes or radionuclides
Example – using Carbon
A normal carbon nucleus looks like this, it has 6 protons and 6 neutrons. This is perfectly stable.
This forms a nitrogen nucleus with 7 protons and 7 neutrons, that is a stable nucleus.
However, another isotope of carbon, (carbon 14) has 6 protons and 8 neutrons, causing the nucleus to be unstable.
The carbon 14 decays by beta radiation, a neutron turns into a proton emitting a beta particle.
Different types of radiation
It is actually the nucleus of a helium atom consisting of 2 protons and 2 neutrons, held tightly together.
It comes directly from the nucleus, so only big atoms tend to emit it.
This is a massive particle, with 2 positive charge.
It strongly interacts with matter around it, smashing past atoms and ionising them.
This quickly absorbs their energy so they can only penetrate short distances through air.
Beta radiation, (a high speed electron) neutrons).
Gamma Radiation, (a short electromagnetic wave)
Is a high speedelectron, given off when a neutron turns into a proton
They are many times smaller than alpha radiation
They only carry 1 single negative charge
They interact much less strongly with matter
So the radiation is much less quickly absorbed, so they can travel through thin sheets of aluminium.
Sometimes a nucleus that is still unstable after a beta or alpha decay is still unstable so may emit gamma radiation to become more stable.
This is an electromagnetic wave with a very short wavelength
It does not change the number of protons or neutrons in the nucleus
It is not strongly absorbed by matter at all
It is most penetrating and needs thick lead 10cm plus to absorb most of it.
Using Radioactive Decay neutrons).
As radioactive substances decay, the amount of radiation they emit decreases, this means it can be used to date things.
High in the earths atmosphere, carbon atoms are bombarded by radiation from space, this converts some stable carbon atoms into radioactive carbon atoms.
Many of these molecules are taken up by plants in photosynthesis (CO2) and incorporated into matter. That can then end up in animals due to them eating plants.
When a plant or creature dies, the amount of radioactive carbon in it decreases through radioactive decay.
The age of the remains of the plant or animal can be calculated from the amount of radioactive carbon in it.
Two other ways to remember: neutrons).
This uses the fact that uranium decays through several short lived radioisotopes to produce a stable isotope of lead.
By measuring the relative proportion of uranium to lead in a rock, an age can be calculated.
Potassium-40 – Argon
Potassium-40 decays to argon and no further
This decay can date many rocks as many rocks have potassium atoms in them.
The age is determined by measuring the relative amounts or argon gas trapped and potassium atoms.
This relies on the gas being trapped therefore meaning it only works for igneous rocks that are impermeable to gas.
A sample of rock is examined. Inside the rock, argon gas is found, formed through the radioactive decay of potassium-40 ions. For every 3 atoms of argon there is is 1 atom of potassium. Estimate the age of the rock, with the half life of potassium being 1300 million years.
When the rocks formed
There are no argon atoms present so for every 4 potassium atoms there are 0 argon atoms
Ratio 4 : 0
After 1 half life
Half the potassium atoms have decayed to form argon atoms, so for every 4 potassium atoms in the rock when it was formed, 2 will have decayed to produce argon atoms.
Ratio 2 : 2 (= 1 : 1)
After 2 half lives
A further half the potassium atoms have decayed to form argon atoms, so for every 2 potassium atoms after 1 half life, one will have decayed to form an argon atom. This means 3 out of the 4 potassium atoms have decayed to argon.
Ratio 1 : 3
This means the age of the rock is 2 half lives old. As each half life is 1300 million years
Age = 2 X 1300 million
= 2600 million years old
Isotopes The same element (same number of protons) but with different numbers of neutrons
Nuclei The centre of an atom where almost all the mass is held, (protons and neutrons)
Decay The process of the atom changing into something else by releasing radiation
Ionising Radiation Radiation that can ionise another atom, if it hits
Proton A positive particle with a mass of 1, a charge of +1 and found in the nucleus
Neutron A neutral particle with a mass of 1, no charge and found in the nucleus.
Electron A negative particle with a mass of 1/1840, a charge of –1 and found orbiting the nucleus
Half Life The time it takes for half the atoms in a substance to decay.