Nuclear Chemistry Text Chapter 18 Tomotherapy machine for radiation treatment of cancer at Johns Hopkins Glow in the Dark Stars Nuclear Submarine

Nuclear Chemistry What does nuclear refer to? Nucleus Protons & neutrons (nucleons). Overall positive charge.*** Strong force holds nucleons together. Neutrons space positive charges and add stability. Who discovered the very dense, positive nucleus?

Same atm #(protons) but diff # of neutrons (diff atomic mass). Most isotopes are stable but many are unstable. If unstable, the neutrons can’t balance all protons and the nucleus spontaneously decays, emitting radiation and/or particles (radioactivity). Radioactive isotopes are called radioisotopes. Isotopes

Predicting Nuclear Stability Stability of isotopes is based on the ratio of neutrons and protons in its nucleus. Low atomic #’s(<20) stable atoms have a ratio of neutrons/protons=1. High atomic #’s stable atoms have ratio of neutrons/protons=1.5. Above atomic #83, no atoms are stable. How shown on Ref Tables? Predicting Nuclear Stability

Radioactivity or Radioactive Decay Process by which an unstable nucleus emits particles and/or radiant energy. If emitted particles are protons, what will happen? The atomic # is altered and one element is changed to another due to the nuclear change (transmutation).

Emanations: emission of particles and/or energy from nucleus Types of Emanations differ from each other in mass, charge, penetrating power and ionizing power. Reference Table O.

Alpha particle (helium nucleus) is given off as a result of nuclear disintegration. High energy, relative velocity. Shielding: stopped by thickness of a sheet of paper, skin Alpha decay ()

A neutron is converted to a proton by emitting an electron. Beta decay (-) Beta particle (high speed electron) is given off as the result of nuclear disintegration. High velocity, low energy. Beta particles have virtually no mass. Shielding: stopped by 1cm of aluminum, average thickness of book. A neutron is converted to a proton by emitting an electron.

Gamma Radiation () Gamma rays are similar to high energy x-rays. Travel @ speed of light like all other forms of electromagnetic energy. Do not have charge or mass. Type of radiation (photons) , not particles. Shielding: 13cm of lead

Positrons are given off as result of nuclear disintegration. Positrons are antiparticles of electrons. When a positron hits an e-, they annihilate each other, forming 2 gamma rays (high penetration and high ionizing power). Positron decay(+) A proton is converted to a neutron.

Separating , , and  emissions Geiger Counters are used to measure radioactivity. Gamma rays and alpha and beta particles can be separated using an electric or magnetic field. Review

Radioactivity Equations Notice that the sum of the mass numbers (superscripts) on both sides of equation are equal (226=222+4). Why? Law of Conservation of Mass The sum of the atomic numbers (subscripts) on both sides of equation are also equal (88=86+2). Why? Law of Conservation of Charge

Balancing Radioactivity Equations Use both Reference Table O & (PT). If the atomic number changes, remember the identity of the element changes. What 2 quantities must be balanced? #1 #2 The breakdown of Co60 in cancer radiation therapy.

More Balancing of Radioactivity Equations First use Reference Table N to determine the decay mode. Continue and finish similar to other problems. Radioactive Orchestra

Artificial Radioactivity Elements can be made radioactive by bombarding their nuclei with high energy particles. Use particle accelerators. Most elements from 93 and up (transuranium elements) were created with the use of particle accelerators. Artificial Radioactivity CERN Particle Accelerator in France & Switzerland + ___

Nuclear Reactions Mass is converted to energy. Think E=mc2. Produce tremendous amounts of energy!!! 2 Types: Fission and Fusion Nuclear Reactions Nuclear explosion at sea

Nuclear Fission Type of nuclear rxn. Splitting of nucleus of a large atom into two or more fragments. Produces additional neutrons and a lot of energy. *Think binary fission or fissure. (splitting) Nuclear Fission

Each nucleus emits 3 neutrons that can cause the fission of another radioactive nucleus and so on. Continues until a stable compound forms. Ex: Atomic Bomb. Nuclear reactors can control fission chain reactions and convert released energy into electric power. Chain Reactions

Parts of a Nuclear Reactor Fuel (U235 & Pu239) Moderator (slow down speed of neutrons, H2O, Be or graphite) Control Rods (absorb neutrons, B & Cd) Coolants (lowers temp,H2O) Shielding (protects the reactor and people from radiation, steel or concrete) Parts of a Nuclear Reactor

Two nuclei unite to form a heavier nucleus with release of enormous amounts of energy. High temps and High pressures are necessary. Occurs in the Sun and stars and the Hydrogen Bomb. Think Unite, Fusion. Nuclear Fusion 1st aerial test of H-bomb makes Bikini Atoll unlivable

Compare & Contrast Fission and Fusion Similarities Both release a lot of energy. Both convert mass into energy. Differences Fission:splitting Fusion: uniting Fusion releases much more energy than fission. Fission produces radioactive waste, fusion only produces He.

Half-lives Each radioisotope has a specific mode and rate of decay (half-life). Ref Table N Half-life is the time required for one-half of the nuclei of a given sample of an isotope to disintegrate.

Half-life Problems can be used to find the following 4: Fraction of radioisotope remaining (left) Half-life Initial amount (original amount) of radioisotope Age of sample containing radioisotope (Radioactive Dating) Decay animation

Benefits of Radioisotopes Tracers Medical Diagnosis or Treatment Radiation of food Radioactive Dating Nuclear Power Industrial Measurement Industrial Applications

Radioisotopes can be used to follow the course (trace/track) of a chemical or biological reaction. This is one way scientists learn about the many steps involved in reactions. For example, C-14 has been used as a tracer to learn the steps of respiration (Kreb’s cycle) Tracers

Medical Diagnosis & Treatment Isotopes with very short half-lives and which will be quickly eliminated from the body are used in detecting and treating diseases. Has created field of medicine called “Nuclear Medicine.” A PET scan using radiotracers to identify heart disease

Medical Diagnosis & Treatment Examples Tc-99 is used for pinpointing brain tumors and bone scans. Radium and Cobalt-60 are used to attack cancer. I-131 is used for diagnosis and treatment of thyroid disorders. A CT scan of the brain using Tc-99

Irradiation of Food Radiation kills bacteria, molds and yeast. It permits food to be stored for a longer time. Symbol for Irradiated Food

Radioactive Dating Comparing the ratio of radioactive to stable isotopes in a rock sample can give the age of the rock or geologic formation (mountains, etc.) (ie: U-238 to Pb-206 Ratio of C-14:C-12 can be used to find age of organic materials.

Nuclear Power Nuclear reactors are used to produce electrical energy or electricity.

Industrial Measurement A beam of subatomic particles (α,β, or γ) is blocked by a certain thickness of metal. Measuring the fraction of the beam that is blocked gives a precise measurement of the thickness of the metal.

Industrial Applications A variety of radioisotopes are used in everyday applications. Am-251 is used in smoke detectors. The neutron activation analysis method can be used to detect artwork forgeries. Industrial Applications

Risks of Radioisotopes Biological Damage Long Term Storage Accidents Pollution Uranium Implosion Little Boy and Plutonium Implosion Fat Man

Radiation exposure can damage or destroy cells of organisms Radiation exposure can damage or destroy cells of organisms. Examples are burns, cataracts, cancer, etc. When reproductive cells are damaged, the damage is passed on to offspring. Biological Damage Radiation burns from A-bomb in Hiroshima

Long Term Storage Yucca Mtn. Storage Project Fission products from nuclear reactors are very radioactive and dangerous. These products must be stored in special containers underground for hundreds of thousands of years until radioactively decayed.

Accidents Nuclear reactor accidents can cause fuel and wastes to escape and harm the environment and biosphere. Example: Chernobyl, Ukraine (1986) in the former USSR. Uncontrolled chain reaction and fire allowed winds to spread radioactivity across Europe. Chernobyl Meltdown Solidified

Pollution Traces of radioactive materials are present in air, water, food and soil either naturally or released by human activities. People can be harmed if there is too much radioactive material.