Physics tracker test revision
11/08/22
Atomic and nuclear radioactivity.
Nuclear equations
Alpha and beta decay
The mass number remains unchanged (it gains a proton by loses a neutron by ejecting an electron).
Beta decay - changes the atomic number by +1 (the nucleus gains a proton)
An alpha particle is the same as a helium-4 nucleus.
Alpha decay - (two protons and two neutrons) changes the mass number of the element by -4 and the atomic number by -2.
A nucleus changes into a new element by emitting alpha or beta particles. These changes are described using nuclear equations.
Half life
Half life is the time it takes for half of the unstable nuclei in a sample to decay of for the activity of the sample to halve or for the count rate to double.
But they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed.
This is called half life
Scientists cannot tell when a particular nucleus will decay
Types of radioactive decay
Gamma decay causes the atomic nuclei to dissipate excess energy by a random electromagnetic process. This occurs after alpha and beta decay.
Beta decay causes the atomic number of the nucleus to increase by one and the mass number remains the same.
Alpha decay causes the mass number of the nucleus to decrease by four and the atomic number of the nucleus to decrease by two
An unstable nucleus can decay by emiting an alpha particle, a beta particle, a gamma ray or in some cases a single neutron.
There are three types of ionising radiation.
Gamma ray - is a high-energy electromagnetic wave. Gamma rays are caused by changes within the nucleus. They have no mass or charge.
It requires severel centimetres of lead or about 1 metre of concrete to absorb it
It can easily penetrate body tissue
Gamma radiation is the most penetrating of the three radiations.
Beta particle - is a fast moving electron. It has a very small mass and a negative charge
It can pass through the skin, but it is absorbed by a few centimeters of body tissue or a few milimeters of aluminium
Beta radiation is more penetrating than alpha radiation
Alpha particle - is a helium nucleus. It has two protons and two neutrons. It has a large mass, compared to other ionising radiations, and a strong positive charge.
Alpha radiation is absorbed by the thickness of the skin by a few centimeters of air.
The alpha radiation transfers more energy to an absorber than beta or gamma radiation.
The range of the alpha radiation is absorbed by the material through which the radiation passes