Nuclear Instability & Radioactive Decay Homework Unit 13 - Topic 3 Sources of Nuclear Radiation To date, 114 (now more than that) have been observed (atomic numbers 1-112, 114, 116, and 117). Of those, only the first 92 elements occur in nature. The rest are the result of nuclear reactions in power plants or bombs, or from experiments in particle smashers. 1. Look at the Periodic Table on the back cover of your textbook. What is true about the elements with a green symbol, according to the key? 2. Besides the elements with an atomic number higher than 92, which other two elements fall into this category? 3. For all of these elements, what do you notice about the way the atomic mass is written? This is because these elements have NO NATURALLY OCCURRING ISOTOPES. Therefore, the mass number shown is an approximation to the nearest whole number. 4. Turn to p. 115-116 in your textbook. On p. 115, atomic mass is defined. Write out that definition. 5. Turn to the first paragraph on p. 800 and also p. 803. How many different isotopes have been discovered to date? 6. How many of those isotopes are stable? 7. Do stable nuclei emit radiation? 8. Unstable nuclei emit radiation and are therefore called radioisotopes. What is it about a nucleus that determines whether or not it will be stable?!
What is Radioactivity?
1. Determine whether each of the isotopes below is stable or unstable by first determining the N/Z ratio. N/Z Stable/Unstable 3 H 14 N 14 O 97 K 206 Pb 2. Calculate the N/Z ratio for elements with atomic numbers 104 through 109. Are they in the belt of stability? Are they stable? How do you know? What does this show about the belt of stability? 3. Why are all elements with atomic numbers above 82 unstable? 4. What is radioactivity? 5. What are three common types of radioactivity given off by unstable atoms? How are they similar? How are they different?
The Band of Stability The plot below represents the number of protons vs. the number of neutrons for the 264 stable isotopes. It is often referred to as the band of stability. Some Observations: 1. Stable isotopes, when plotted on a graph of number of protons vs. number of neutrons, would all fall in an area enclosed by two curved lines known as the band of stability. In the band of stability, atoms are stable. 2. The band of stability stops at element 83 because there are no known stable isotopes above it. 3. Atoms that have a p/n ratio that falls outside the band of stability are unstable, or radioactive, and will spontaneously decay. 4. Another thing that is noticed about the band of stability is that as the number of protons increases, the ratio of neutrons to protons increases. This is because more neutrons are needed to compensate (adjust) for the increasing proton-proton repulsions.! Questions: Figure out the number of protons and neutrons in each isotope below, and then find its position on the band of stability graph. Identify each as radioactive or stable: 1. Cesium-137: 2. Calcium-42: 3. Gold-198: 4. Chlorine-35: 5. Radium-226: 6. Uranium-238:
Assignment: Making a Radioisotope become Stable refer to your text p. 800-802 Nature s solution for an unstable nucleus is for it to radioactively decay. This means that the nucleus will change into a different isotope (often of a different element) by emitting an alpha particle, a beta particle, or a positron. As this happens, the proton-to-neutron ratio of the nucleus changes, perhaps causing it to lie within the band of stability. Some wild things happen in the nucleus as this happens! Use Table O to help you with this page!! Beta: 1. a) Beta particles are formed when a (proton or neutron?) changes into a (proton or neutron?)!!! (More on this in Physics! ) b) As a result the atomic mass will (go up by one, go down by one, stay the same). c) As a result the atomic number will (go up by one, go down by one, stay the same). Positron: 2. a) Positrons are formed when a (proton or neutron?) changes into a (proton or neutron?)!!! YIKES!!? (Yup, quark flipping ) b) As a result the atomic mass will (go up by one, go down by one, stay the same). c) As a result the atomic number will (go up by one, go down by one, stay the same). Alpha: 3. a) Alpha particles are formed when the nucleus ejects (how many?) protons and also (how many?) neutrons. b) As a result the atomic mass decreases by and the atomic number decreases by. Gamma: 4. What causes gamma rays? 5. How is gamma radiation different from the other 3 forms?
Fill in the following Table. The objective of this exercise is to learn the material. Use the information from the text, p. 800-802 and/or the ChemComm book, p. 438-440. Greek Symbol (Table O) Mass Number Alpha Beta Positron Gamma Atomic Number Chemical Symbol (Table O) Electrical Charge Energy (realitiely high or low?) Ability to Damage Human Tissue Penetrating Ability Can be blocked by: Study the diagram on p. 800 of your textbook The type of radiation can be determined by the response of the radiation when it is passed through an electrical field. 1. Positive electrical charge is (attracted or repelled?) by negative charge. 2. Sketch the picture from p. 800 below. You need to really know this diagram!! 3. On your sketch, draw the path that a positron would take. Would it be deflected more than or less than an alpha particle? Why?