9848 Lecture Notes - Lecture 7: Niels Bohr, Mass Number, Bohr Model
19 Jun 2018
School
Department
Course
Professor
Introduction to radiation safety - Read bushongt to get intodction of physics
Learning objectives
•be able to correctly use the medical physics units and terminology introduced in this
module
• be able to discuss atomic structure
• be able to discuss the various types of electromagnetic radiation
• be able to discuss the basic principles of radiation safety
Some Physics Fundamental Properties
There are 2 fundamental properties of nature.
These are:
matter – anything that occupies space◦
energy – this is more difficult to define as there are many types of energy, energy is nevr lost ◦
it gets converted
matter – anything that occupies space.
•fundamental building blocks of matter are atoms
•atoms were once thought to be the smallest particle with the word “atom” meaning
undividable
• atoms are composed of sub-atomic particles
• the 2 main parts of an atom are = the nucleus (inner) made up of protons and neutrons ◦
orbital electrons (outer)
• diameter of atoms are 1 to 5 x 10^-10m and the diameter of the nuclei are 1.6 to 15 x 10-
^15m
most common model of atom
The Bohr model (named after Niels Bohr) is the simplest accepted model of an atom
•this model has:
- a central nucleus consisting of protons and neutrons
-an outer area of orbiting electrons
•protons have a positive (+ive) electrical charge
• neutrons have no electrical charge
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• electrons have a negative (-ive) charge
structure of matter
atoms consist of subatomic particles such as:
•quarks and gluons which make up protons and neutrons (collectively called nucleons when
in the nucleus of the atom)
• leptons with electrons being one type
•and other subatomic particles
•Leptons – main interest in MRS are electrons. Some other are positrons and neutrinos
- electrons form the outer shells of the atom
•Hadrons - main interest in MRS are protons and neutrons
- protons and neutrons are main sub-atomic particles of the nucleus (centre or core) of the
atom
•matter’s primary characteristic is its mass (do not get confused with weight)
- note: weight is a measure of mass under a gravitational force such as the earth’s gravity.
The mass of an object on the earth and another planet will not change, but the weight may.
•mass is measured in kilogram (kg) or subunits of kilograms such grams being 1 x 10-3kg or
0.001kg
differences
Compare the atomic mass units of things to the amu of carbon – another way to measure
Atomic Mass Unit (AMU)
an alternative measure of mass
• 1 AMU = 1/12 of a Carbon 12 (12C) atom
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find more resources at oneclass.com
• mass of an electron (e-) ≈ 5.49 x 10-4 AMU
Chemistry review -
•Atomic Number (Z) - Z of an element is determined by the number of protons in the nucleus
•Atomic Mass Number (A) - A, also called the nucleon number, is the total number of protons
and neutrons in the nucleus
•Nomenclature (how it is written) - where X is the element
•an isotope of an element will chemically react the same as all isotopes of that element
•some isotopes are stable, ie they never change and other isotopes are unstable.
• unstable isotopes may decay to other elements or may give off subatomic particles and/or
EM radiation note: the EM radiation energy given up from such a decay is gama( ◦) rays
differebt types ofnucleas configuration – a = atomic mass number , z = atomic number
•isotope: same z; different A; different no. of neutrons ie. the same element
• isobar: different z; same A; different no. of protons ie. different elements
• isotone: different z; different A; same no. of neutrons ie. different elements
• isomer: same z; same A; same no. of neutrons ie. same elements always but may have
decayed with a loss of energy
Radioactivity
•Is breakdown if atom and undergoes disintegration radionuclides are atoms that
undergo radioactive disintegration
main types of radiation
•particular – main 3 types of particles given off
- beta (β) being β- or β+ (or electrons / positrons) - can cause damage to tissue , but
very easy to stop
- alpha (α) (2 protons and 2 neutrons, ie identical to a helium (He) nucleus nucleus) –
don’t have charge so are more difficult to stop, will travel throuf matter easily
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find more resources at oneclass.com
Document Summary
Introduction to radiation safety - read bushongt to get intodction of physics. The bohr model (named after niels bohr) is the simplest accepted model of an atom this model has: A central nucleus consisting of protons and neutrons. Leptons main interest in mrs are electrons. Electrons form the outer shells of the atom. Hadrons - main interest in mrs are protons and neutrons. Protons and neutrons are main sub-atomic particles of the nucleus (centre or core) of the atom: matter"s primary characteristic is its mass (do not get confused with weight) Note: weight is a measure of mass under a gravitational force such as the earth"s gravity. The mass of an object on the earth and another planet will not change, but the weight may: mass is measured in kilogram (kg) or subunits of kilograms such grams being 1 x 10-3kg or. Compare the atomic mass units of things to the amu of carbon another way to measure.
