Something to be aware of… lest you be irradiated! Nuclear Chemistry Something to be aware of… lest you be irradiated!
Radioactivity: what is it? 1896: Becquerel discovered that some uranium salts were able to fog photographic plates…the first recorded exposure to radioactivity! Radioisotopes: unstable isotopes, which undergo nuclear decay. Nuclear decay cannot be sped up, slowed down, or turned off.
Types of Radiation Alpha: the emission of an alpha particle, which is a Helium-4 nucleus, 2 protons and 2 neutrons, which is positively charged Alpha particles are slow, low penetrating, and are readily stopped by a sheet of paper or your skin.
Types of radiation, continued Beta: 10n ->11H + 0-1e Less charge than an alpha particle, much less mass, but are more penetrating…will pass through paper, but are usually stopped by thin metal or wood
Types of radiation, continued Gamma: a high energy photon, with no mass! Extremely penetrating! Very dangerous! Needs several meters of cement or centimeters of lead to stop to any degree. May be a by-product of either alpha or beta decay.
Nuclear Stability Band of stability: see separate slide. Ratio of stability gradually increases as mass of nucleus increases, from 1:1 to 1: 1.5…there is a greater need for more neutrons to serve as “spacers” for the protons as the size of the nucleus increases. When the ratio is smaller, the nucleus is less stable, which we usually call radioactive. Positron: positively charged electron (antimatter)
Half lives A half life is the amount of time for half a given amount of a radioisotope to decay into a new element. Half lives can vary from a tiny part of a second to billions of years. Useful for determining age of compounds…has allowed for dating of various Earth structures
Transmutation Transmutation is the conversion of one element into another, either by decay or nuclear bombardment Transuranic elements: those above U on periodic table, all of which undergo transmutation.
Nuclear Reactions: fission Fission: splitting of a nucleus into more stable daughter nuclei, also usually liberating neutrons (to enable further reactions), and energy! Can be moderated by materials that absorb these liberated neutrons…water, carbon are examples of common moderators. Neutrons can also be absorbed, by materials such as Cadmium…these control rods act similarly to an adjustable throttle on the fission reactor. Issue: nuclear waste: radioactive a long time!
Nuclear reactions: fusion Fusion: the combination of small nuclei into larger nuclei, liberating some positrons and lots of energy Think stars as the prime example of this. Problem: containing the reaction: millions °C
Radiation in your life Detection Medical Geiger counters: gas filled tube, ionizes when exposed to radiation Scintillation counter: photoelectric effect detector, more sensitive than Geiger counters Film badges: shows cumulative effect Medical Xrays Radiotherapy: radioisotopes