3.7 Nuclear Physics Flashcards
Size of an atom?
Atoms are very small, having a radius of about 10-1 metres.
Simple model of an atom?
The simple model of an atom is a small central positively charged nucleus composed of protons and neutrons, surrounded by electrons. The radius of the nucleus is much smaller than that of the atom with almost all of the mass in the nucleus.
What provides evidence for the distribution of mass in the atom?
The scattering of alpha particles by thin metal foil provides evidence of the distribution of mass in the atom
The relative masses and electric charges of protons, neutrons and electrons are..
Relative mass. Relative charge
proton. 1 1
neutron. 1. 0
electron Very small. -1
In an atom the number of electrons is equal to the number of…
In an atom the number of electrons is equal to the number of protons in the nucleus.
What charge does an atom have?
The atom has no overall electrical charge.
How are electrons arranged?How do atoms form ions?
In each atom its electrons are arranged at various distances from the nucleus. Atoms may lose or gain outer electrons to form charged particles called ions.
Isotopes?
The atoms of a particular element always have the same number of protons, but have a different number of neutrons for each isotope.
Proton/atomic number?
The total number of protons in an atom is called its proton number or atomic number.
Mass number?
The total number of protons and neutrons in an atom is called its mass number.
Radioactive decay?
Some atomic nuclei are unstable. The nucleus emits particles or radiation and the nucleus changes to that of a different element and becomes more stable. This is a random process called radioactive decay.
How is energy emmited?
Energy is emitted by changes in the nucleus.
What do unstable nuclei emit?
Unstable nuclei emit alpha particles, beta particles, or neutrons, and electromagnetic radiation as gamma waves.
What affects the behavior of unstable nuclei emitting these products? Is it possible to predict when a random atom may decay?
Neither chemical nor physical processes affect this behaviour. These substances are said to be radioactive and although the general process follows a pattern this radioactive decay is a random process. It is impossible to predict when a particular atom might decay.
Background radiation?
Background radiation is around us all of the time. It comes from a range of sources, such as radioactive substances in the environment, from space or from devices such as X-ray machines in hospitals.
What does an alpha particle consist of?
An alpha particle consists of two neutrons and two protons (ie a Helium nucleus).
What is a beta particle?
A beta particle is a high speed electron ejected from the nucleus as a neutron turns into a proton.
Gamma radiation?
Gamma radiation is electromagnetic radiation from the nucleus.
What is used to represent radioactive decay?
Nuclear equations are used to represent radioactive decay.
What conditions are needed for predicting radioactive decay?
Radioactive decay is random, but with a large enough number of nuclei it is possible to predict how many will decay in a certain amount of time.
Half life of a radioactive isotope is?
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 time it takes for the count rate from a sample containing the isotope to fall to half its initial level.
What is radioactive contamination?
Radioactive contamination is the unwanted presence of radioactive atoms on other materials.
Hazards from contamination?
The hazard from contamination is due to the decay of the contaminating atoms. The type of radiation emitted affects the level of hazard.
Irradiation?
Irradiation is the process of exposing an object to ionizing radiation. The irradiated object does not become radioactive. Suitable precautions must be taken to protect against the hazards of the radioactive source used in irradiation.
