Radioactive Decay PDF

Section 19.1 Radioactivity Objectives 1. To learn the types of radioactive decay 2. To learn to write nuclear equations for radioactive decay 3. To learn how one element may be changed to another by particle bombardment 4. To understand half-life Section 19.1 Radioactivity A Review of...

Section 19.1 Radioactivity Objectives 1. To learn the types of radioactive decay 2. To learn to write nuclear equations for radioactive decay 3. To learn how one element may be changed to another by particle bombardment 4. To understand half-life Section 19.1 Radioactivity A Review of Atomic Terms Nucleons – particles found in the nucleus of an atom – neutrons – protons Atomic Number (Z) – number of protons in the nucleus Mass Number (A) – sum of the number of protons and neutrons Isotopes – atoms with identical atomic numbers but different mass numbers Nuclide – each unique atom or are the nuclei of a specific isotope Section 19.1 Radioactivity Why do you need to study nuclear reaction? 1. Nuclear chemistry is central to development of nuclear energy 2. Nuclear chemistry is used in medicine to treat cancer and to produce images of organs inside human body ( PET) 3. Nuclear chemistry is used in chemistry to investigate reaction mechanisms 4. In archeology is used to date ancien object 5. Is part of military strategy of many nations ( Russia, USA, North Korea, Iran etc) Section 19.1 Radioactivity A. Radioactive Decay Radioactive nucleus - A nucleus that spontaneously changes and emits (releases) energy. This occurs spontaneously: by itself and with no outside energy required. You don't always have to "split an atom." Many isotopes do it naturally. A radioactive nucleus spontaneously changes into a different nucleus, releasing other particles and energy in the process. This occurs randomly and without any outside source of energy. Section 19.1 Radioactivity A. Radioactive Decay Radioactivity – the spontaneous decomposition of a nucleus forming a different nucleus and producing one or more additional particles Nuclear Equation – shows the radioactive decomposition of an element 14 6 C → 147N + 0 -1 e Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus (counters electromagnetic repulsion). Weak nuclear force operates within individual nucleons and gives rise to some kinds of radioactivity Strong and Weak Nuclear Forces Section 19.1 Radioactivity Discovery of Radioactivity Antoine Henri Becquerel (1852-1908) – Noticed the fogging of photographic plate by uranium crystals Section 19.1 Radioactivity Discovery of Radioactivity Pierre Curie (1859-1906), Marie Curie (1867-1934) – Further studies of uranium and discovery of polonium and radium. Marie received two Nobel prizes. She died from the effects of radiation doses received during her experiments. Section 19.1 Radioactivity Discovery of Radioactivity Ernest Rutherford (1871-1937) – His understanding of atomic structure helped us understand the role of the nucleus. He defined many of the terms used to discuss radioactivity today Section 19.1 Radioactivity A. Radioactive Decay Types of Radioactive Decay Alpha-particle production or alpha decay Alpha particle – helium-4 nucleus. These particles are blocked by paper. deflected by elec & magnetic field. – Examples Net effect is loss of 4 in mass number and loss of 2 in atomic number. Section 19.1 Radioactivity A. Radioactive Decay Alpha decay A nuclear reaction is written to conform to two rules: 1. The sum of mass number should be the same on both side. 2. The sum of atomic number should be the same on each side. Section 19.1 Radioactivity A. Radioactive Decay Types of Radioactive Decay Beta-particle production or beta decay Beta particle – electron. 1. Beta particles can go through paper but cannot penetrate Al 2. Deflected by the electrical & magnetic field but in the opposite direction 3. Less massive than an alpha particle 4. travel with speed less than 90% c 5. produced by a decay of a free neutron Section 19.1 Radioactivity A. Radioactive Decay Beta-particle production or beta decay – Examples Net effect is to change a neutron to a proton. Section 19.1 Radioactivity A. Radioactive Decay Types of Radioactive Decay Gamma ray release or gamma decay Gamma ray – high energy photon. 1. They travel @ speed of light. Can penetrate almost everything but are blocked by Pb 2. Undeflected by electromagnetic field 3. Present at almost all nuclear reaction Section 19.1 Radioactivity A. Radioactive Decay Gamma ray release or gamma decay – Examples This reaction can be written as two stage reaction Section 19.1 Radioactivity A. Radioactive Decay Types of Radioactive Decay Positron production Positron – particle with same mass as an electron but with a positive charge (antimatter version of an electron) – produced when nuclei has more protons than neutrons Net effect is to change a proton to a neutron.  Section 19.1 Radioactivity A. Radioactive Decay Conservation of Mass Number and Charge Number − both are retained in a nuclear reaction − sum of both from the “reactants and products” are constant Section 19.1 Radioactivity A. Decay Series Section 19.1 Radioactivity B. Nuclear Transformations or transmutation Nuclear Transformation – forced change of one element to another Bombard elements with particles Section 19.1 Radioactivity Practice question Write and balanced the following equation 131 0 I → + e 53 -1 Section 19.1 Radioactivity Practice question Write and balanced the following equation 59 1 Co + n → 27 0 Section 19.1 Radioactivity C. Detection of Radioactivity and the Concept of Half- life Geiger-Muller counter – instrument which measures radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas-filled chamber Section 19.1 Radioactivity C. Detection of Radioactivity and the Concept of Half- life Half-life – time required for half of the original sample of radioactive nuclides to decay Section 19.1 Radioactivity Decay of a Radioactive Element Half of the radioactive parent atoms decay after one half-life. Half of the remainder decay after another half-life and so on……..