Lecture 2-4

• Matter is anything that occupies space and has mass.
• The half life of 60 Co is 5.26 years.
• All matter is made up of substances called elements, which have specific chemical and physical properties and cannot be broken down into other substances.
• Oxygen and Hydrogen are elements.
• There are 118 elements, but only 92 occur naturally.
• The remaining elements have only been made in laboratories and are unstable.
• Physical changes in matter are changes in matter that do not change the composition of a substance such as changes of state, temperature, volume, etc.
• Chemical changes in matter are changes that result in new substances.
• Solids are substances which have definite volume and definite shape, with molecules held together by strong forces.
• Liquids are substances which do not have definite shape, with molecules held by relatively weak forces.
• Gases are substances where the molecules move randomly and there is space between them.
• Each element is specified by its chemical symbol, which is a single capital letter or, when the first letter is already “taken” by another element, a combination of two letters.
• Some elements follow the English term for the element, such as C for carbon and Ca for calcium.
• The four elements common to all living beings are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N), which together make up about 96% of the human body.
• An atom is the smallest unit of matter that retains all of the chemical properties of an element.
• A gold coin is simply a very large number of gold atoms molded into the shape of a coin.
• Gold atoms cannot be broken down into anything smaller while still retaining the properties of gold.
• Radioactivity is the process by which atoms that are unstable change and eventually become stable through the emission of particles or electromagnetic radiation or both.
• The binding energy of electron is the quantity of the energy required to remove an electron from the shell.
• Isotopes are different forms of an element that have the same number of protons but different numbers of neutrons.
• The binding energy of electron depends on two factors: Type of shell and Number of protons (atomic number) in the nucleus.
• The SI unit for activity is one decay per second and is given the name becquerel (Bq), so: 1 Bq = 1 decay/s.
• Many elements—such as carbon, potassium, and uranium— have multiple naturally occurring isotopes.
• Electrons are distributed in different shells or orbits, these are called K, L, M, and N shells.
• Some isotopes are stable, but others can emit, or kick out, subatomic particles to be more stable.
• If the initial activity of 60 Co is disintegration per year, calculate the activity of this radionuclide after 5 years.
• One of the most common units for activity is the curie (Ci), 1 Ci = 3.70 Bq.
• An unstable nucleus tries to achieve a balanced state by giving off a neutron or proton and this is done via radioactive decay.
• Activity is often expressed in other units, such as decays per minute or decays per year.
• The strength of a radioactive source is called its activity, which is defined as the rate at which the isotope decays.
• Such isotopes are called radioisotopes or radioactive atom, and the process in which they release particles and energy is known as decay.
• Half-life (T1/2) is the time in which half of the original number of nuclei decay.
• An atom consists of two regions: the atomic nucleus, which is in the center of the atom and contains positively charged particles called protons and neutral, uncharged, particles called neutrons, and the electron cloud, a “cloud” of electrons, negatively charged particles that orbit around the nucleus.
• Radiation interactions, both formation and absorption, occur within individual atoms.
• The nucleus contains 2 of the 3 subatomic particles: Protons, which are positively charged subatomic particles, Neutrons, which are neutrally charged subatomic particles, and Electrons, located outside of the nucleus in the electron cloud.
• Atoms consist of two major regions: the nucleus and the electron shells.
• Each region has a role in radiation interactions.
• Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom.
• The nucleus is the source of energy for the radiations used in nuclear medicine procedures.
• The electrons transitions between the shells produce x-ray radiation.