Nuclear Chem Class #5

1. Nuclear Chem Class #5 X. Nuclear Chemistry – From NYS Curriculum X.1 Stability of isotopes is based on the ratio of neutrons and protons in its nucleus. Although most nuclei are stable, some are unstable and spontaneously decay, emitting radiation. X.2 Each radioactive isotope has a specific mode and rate of decay (half-life). X.3 A change in the nucleus of an atom that converts it from one element to another is called transmutation. This can occur naturally or can be induced by the bombardment of the nucleus by high-energy particles. X.4 Spontaneous decay can involve the release of alpha particles, beta particles, positrons and/or gamma radiation from the nucleus of an unstable isotope. These emissions differ in mass, charge, and ionizing power, and penetrating power. X.5 Nuclear reactions include natural and artificial transmutation, fission, and fusion. X.6 There are benefits and risks associated with fission and fusion reactions. X.7 Nuclear reactions can be represented by equations that include symbols which represent atomic nuclei (with the mass number and atomic number), subatomic particles (with mass number and charge), and/or emissions such as gamma radiation. X.8 Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of mass converted into energy. Nuclear changes convert matter into energy. X.9 Energy released during nuclear reactions is much greater than the energy released during chemical reactions. X.10 There are inherent risks associated with radioactivity and the use of radioactive isotopes. Risks can include biological exposure, long-term storage and disposal, and nuclear accidents. X.11 Radioactive isotopes have many beneficial uses. Radioactive isotopes are used in medicine and industrial chemistry, e.g., radioactive dating, tracing chemical and biological processes, industrial measurement, nuclear power, and detection and treatment of disease.

2. How does radioactive carbon dating work? On Earth there is a certain amount of radioactive carbon by percent. It’s measurable if you’re college level smart and you have some fancy tools. I can’t do it, but I am sure I could learn how. Many college students can do this, all over the world. There is a “normal” level of radioactive carbon in our environment, and it’s been stable a long time. The ratio of radioactive carbon to stable carbon is a constant. Although some is always transmuting, there is always more being made, by a variety of means, all involving the bombardment of carbon with high energy particles (from the Sun, from inside the Earth, etc. The ratio is known and measurable. If this ratio were to be different, that would be measurable too. This radioactive carbon is everywhere in small quantities. In plants and in the animals that eat the plants, and in animals that eat both plants and animals. Even though it’s always decaying, it’s also being replaced constantly too. There in lies the catch. High energy neutrons + Nitrogen C-14 + protons

3. If an animal eats regularly, and all animals do (except for one kind), they all have a constant ratio of radioactive to stable carbon. Only when they stop eating (when they die) does the ratio begin to change. It changes because the decaying doesn’t stop but the replacing does. Casually, the radioactive carbon is 1 part per trillion, or, 600 billion atoms per mole. (moles are really big). It has been more or less constant with some fluxuations that are explained by radioactive bomb testing, the industrial revolution adding so much carbon to the atmosphere, etc. Once animals die, this ratio changes. Since the ratio is not great to start (1 part per trillion), the measuring is only going to be accurate to about 60,000 – 80,000 years. After that there is so little C-14 left, that the measurements become very much less accurate. Using this method scientists can definitively determine the ages of biological materials that died up to about 80,000 years ago.

4. Saber tooth cats lived until about 11,000 years ago. Some lived millions of years ago. Some cats that died in the more recent era can be accurately dated with carbon dating. Dinosaurs died out too long ago to use carbon dating, but you can measure the other isotopes in the rocks that they have been found in to determine how old they are(many millions of years).

5. Nuclear Medicine There are only 2 uses for nuclear radiation that are discussed in our class. 1, use of Iodine-131 for the diagnosis of thyroid disorders. This radioactive isotope is injected into a person, then after a given period of time a special “picture” is taken, a radiograph, which measures the amount of radiation in someone’s throat (that’s where the thryoid gland is). Since it’s chemically identical, just different mass (that’s why it’s radioactive), the thryoid gland picks it up (or doesn’t) and doctors can assess your glandular activity. 2. Use of cobalt-60. This isotope produces excess beta radiation, which can be aimed as a sort of invisible beam of killer rays, which gets pointed at tumors inside people. The beta particles kill most all cells they pass though, but they also can kill some cancers. The plan is to zap the tumors precisely, and kill as few of the good cells at possible. Pain and sickness followed by (hopefully) smaller or no tumors.

6. Let’s practice three easy problems, and be done. Choose 2 table N isotopes that you have not worked out the decay reactions for, and do them. Describe the difference between natural and artificial transmutation. Give one example reaction for each as well. Describe the difference between fusion and fission. Where is one place that fusion can occur? What is a place that fission can occur? Finally, you win the boobie prize at a party, it’s 39.0 grams of Cs-137. How long until you have just one thirtysecond of that amount? (oooh, tricky, tricky!)