Atoms and radiation
Atoms can gain energy when a substance is heated, when an electric current is passed through it, or when it absorbs electromagnetic radiation.
An atom emits (or absorbs) electromagnetic radiation when electrons jump from one energy level to a lower or higher energy level.
The energy of the radiation emmited by an atom is equal to the energy difference between the energy levels the electron moves to and from.
The frequency of the radiation given out by an atom is proportional to the energy of the radiation given out by an atom.
Marie Curie and her husband Pierre discovered radioactivity.
Gieger counters detect radioactivity.
Ernest rutherford discovered 2 types of radiation;
. Alpha- doesn't penetrate paper, made up of positively charged particles, fired alpha particles at a piece of foil and discovered that atoms nuclei contain both protons and neutrons
. Beta- penetrates paper
Scientists later discovered Gamma which is more penatrative than Beta.
A radioactive substance has an unstable nuclei that becomes stable by emmiting radiation.
Isotopes of an element are atoms with the same number of protons but different numbers of neutrons. So they have the same atomic number but different mass numbers.
. Alpha Decay;
. Nucleus loses 2 protons and 2 neutrons
. 2 protons and 2 neutrons emitted as an Alpha particle
. Equation -
. Beta Decay;
. A neutron in the nucleus changes into a proton
. An electron is created in the nucleus and instantly emitted
. Equation -
The half-life of a radioactive substance is the average time it takes;
. For the number of nuclei of the isotope in a sample (and so the mass of parent atoms) to halve
. For the count rate from the isotope in a sample to fall half its intial value
Radioactive decay is a random process, this means no-one can predict exactly when an individual atom will suddenly decay.
. The half-life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
. The count rate of a Geiger counter caused by a radioactive source decreases as the activity of the source decreases.
. The number of atoms of a radioactive isotope and the count rate both decrease by half every half-life.
. The count rate after n half-lives = the initial count rate/ 2n
Properties of radiation
. Alpha radiation- is stopped by paper and has a range of a few centimeters in air. It consists of particles, each composed of two protons and two neutrons.
. Beta radiation- is stopped by a thin sheet of metal and has a range of about 1 metre in air. It consists of fast-moving electrons emitted from the nucleus.
. Gamma radiation- is stopped by thick lead and has an unlimited range in air. It consists of electromagnetic radiation.
. Ionisation is the process of creating ions by knocking electrons out of atoms.
. Irradiation occurs when an object is exposed to ionising radiation. Radioactive contamination is the presence of unwanted radioactive atoms on or in other materials or living organisms.
. Alpha radiation is more ionising than Beta radiation, which is more ionising than Gamma radiation.
. Radon gas is an Alpha emitting isotope that seeps into houses in some area through the ground.
Benign and malignant tumors result from abnormal, uncontrolled cell division.
Benign tumors form in one place and do not spread to other tissues.
Malignant tumor cells are cancers. They invade neighbouring tissues and may spread in the blood to different parts of the body, where they form secondary tumors.
Lifestyle risk factors for various types of cancer include smoking, obesity, common viruses and exposure to ultraviolet light. There are also genetic risk factors for some cancers.
Ionising radiation can also cause cancer.