Energy Unit Learning Goal 4: Examine how changes in the nucleus of an atom result in emissions of radioactivity.

Nucleus  Very Small The typical nucleus is about cm.  Very Large Density The typical density is about 1.6 x g/cm 3.  Large amounts of Energy The typical nuclear process is millions of times larger than those associated with normal chemical processes.

Nuclear Symbols Element symbol Mass number (p + + n o ) Atomic number (number of p + )

Radioactive Decay  Radioactive is when the nuclei spontaneously decompose, forming a different nucleus and producing one or more particles.  Nuclear Equation Both the atomic number and the mass number must be conserved.  That is the sums of both on each side must be equal.

Types of Radioactive Decay  alpha production (  ): (helium nucleus)  beta production (  ): (Electron) 2 4 He  1 0 e 2+

Types of Radioactive Decay  Alpha-particle Production Alpha particle is a helium nucleus  Atomic number of helium is 2; mass number is 4.

Alpha Radiation Limited to VERY large nucleii.

Types of Radioactive Decay  Beta-particle production A beta-particle is an electron.  The value of Z= -1.  The net effect of beta-particle production is to change a neutron to a proton. No change in mass number, but an increase in one in atomic number.

Beta Radiation Converts a neutron into a proton.

Types of Radioactive Decay  gamma ray production (  ):   positron production :  electron capture: (inner-orbital electron is captured by the nucleus) 1 0 e

Types of Radioactive Decay  Gamma Ray A high-energy photon of light. A nuclide in an excited nuclear energy state can release excess energy by producing gamma rays. Gamma rays are photons of light so they have zero charge and zero mass number.

Types of Radioactive Decay  Positron Production The positron is a particle with the same mass as an electron but opposite charge. Results in no change of mass, but a decrease of 1 in atomic number.

Types of Radioactive Decay  Electron Capture A process in which one of the inner-orbital electrons is captured by the nucleus. Does not occur often enough to make it practical to change mercury to gold. Atomic number increases by one. Mass remains the same.

Types of Radiation

Half-life  The time required for half of the original sample of nuclei to decay.

Half-life Concept

Sample Half-Lives

Decay Series  Often radioactive nucleus cannot achieve stable state through a single decay process.  A decay series will occur until a stable nuclide is formed.

Copyright © Houghton Mifflin Company19-19 Figure 19.1: The decay series.

A Decay Series A radioactive nucleus reaches a stable state by a series of steps

Nuclear Fission and Fusion Fusion: Combining two light nuclei to form a heavier, more stable nucleus. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.

Nuclear Fission   The process of splitting an atom.  Releases an enormous amount of energy. 1 mol of uranium-238 can produce about 26 million times as much energy as 1 mol of methane.

Fission Copyright © Houghton Mifflin Company19-23 Figure 19.4: Unstable nucleus.

Copyright © Houghton Mifflin Company19-24 Figure 19.5: Representation of a fission process.

Copyright © Houghton Mifflin Company19-25 Figure 19.6: Diagram of a nuclear power plant.

Copyright © Houghton Mifflin Company19-26 Figure 19.7: Schematic of the reactor core.

Nuclear Fusion  The process of combing two light nuclei. Produces more energy than fission.