Chapter 28. Radioactivity. Types of Radiation. Beta Radiation. Alpha Radiation. Section 28.1 Nuclear Radiation. Objectives: Nuclear Radiation

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1 Section 28.1 Nuclear Radiation Chapter 28 Nuclear Radiation Objectives: Discuss the processes of radioactivity and radioactive decay Characterize alpha, beta, and gamma radiation in terms of composition and penetrating power Adapted from notes by Stephen L. Cotton Radioactivity Radioisotopes nuclei of isotopes that go through nuclear reactions in an attempt to gain. Radioactivity process by which materials give off or mass and/or energy when the nucleus spits stuff out. Radiation penetrating and/or emitted by the. of a radioisotope. Radioactive decay process by which a radioisotope emits energy and/or particles in an attempt to stabilize its. Radioactive decay is totally Name Types of Radiation Relative Penetration Symbol Comp. mass Blockage Alpha Radiation Beta Radiation The nucleus of an unstable radioisotope throws out or an. Loss of and Write the nuclear equation for the alpha decay of U-238. The nucleus of an unstable radioisotope throws out or a. A neutron decays into a (which stays in the nucleus) and a that is ejected from the nucleus. This is WHY the atomic #, the number of n ø, and the mass #. Write the nuclear equation for the beta decay of Th

2 Gamma Radiation Gamma is the high-energy radiation or by a radioisotope. γ-rays are often (but not always) emitted along with α or β radiation from nuclei of.. X-rays are like γ-rays, but X-rays can be produced by energizing the electrons of certain metals when the metals relax they emit X-rays. Write the nuclear equation for the beta decay of Th-230. Electron Capture Too few relative to p + a p + is converted to a. HOW?... an is captured by the nucleus and combined with a Write the nuclear equation for the electron capture by a Ni-59 nucleus. Positron Emission The nucleus of an unstable radioisotope throws out or a positron particle. Similar to a beta particle, but with an atomic# of. A proton changes to a neutron, throwing out or its positive charge. Write the nuclear equation for the positron emission of O-15. Section 28.2 PART I. Nuclear Transformations Objectives: Understand how and why radioisotopes go through radioactive decay. Use half-life information to determine the amount of radioisotope remaining at a given time. Give examples of equations for the synthesis of transuranium elements by transmutation. What Holds the Nucleus Together? Ex: Li-6 Has p + and n ø p + and n ø attract due to a force similar to gravity known as. Neutrons are the of the nucleus. p + and p + due to like charges. Why Does Radiation Occur? Begins with an of some. Unstable because of too few or too many. relative to the number of Too many p + leads to too many. Too many n ø leads to too many particles and not enough space in the, nucleus. 2

3 Nuclear Stability and Decay Nuclear stability depends on its ratio. Determine the n ø /p + ratio for the following: He-4 N-14 O-16 Pb-206 U-235 Radiation generally occurs in all elements after element # WHY? Too many Mass Defect Is the difference between the sums of the mass of individual. in an atom compared to the of the same atom reported in the periodic table. The actual mass is always than the experimental mass whenever the nucleus contains more than one particle. This difference in mass is converted into that holds the nucleus together and can be released in reactions. Energy is when the nucleus throws out or radiates Is why matter is in nuclear reactions. Mass Energy equivalence: the concept that any has an associated and vice versa, where Band of Stability F.28.6 pg.845. nuclei are stable with n ø /p + ratio of Up to atomic, a ratio of 1 : 1 works. For larger atoms (atomic# ), a ratio of 1 : 1.5 is needed need more n ø glue to hold nucleus together. n ø /p + ratio > 1.5 results in. Determine the n ø /p + ratio for the following: C-12 C-14 Tc-101 Where is C-14 relative to C-12 on the band of stability? HINT: Is C-14 located above, within, or below the B.O.S.? Example 1 3

4 The band of stability is above the line on the graph that has a slope of 1. What does this indicate about the number of protons and neutrons in the majority of elements? HINT: Compare the B.O.S. to the line with slope = 1 Example 2 What type of decay would stabilize an atom of U-238? HINT: Need to get rid of some of the 92 p + s in the Uranium nucleus to get to atomic #82 (STABLE). Example 3 A nuclide has 90 neutrons and 60 protons. What type of decay will this nuclide undergo? HINT: What is the proton/neutron ratio? Example 4 Some radioisotope X has 60 protons and 60 neutrons. What type of radioactive decay would it most likely undergo? HINT: 60/60 = 1.0 Big atom above atomic #20!!! Example 5 Example 6 Identify the region of the graph associated with beta emission. HINT: Too many neutron to proton ratio = high n ø /p + ratio. Identify the region of the graph associated with the emission of alpha particles. HINT: Need to get rid of p +. Example 7 4

5 Example 8 Identify the region of the graph associated with electron capture OR positron emission. HINT: Electron capture AND positron emission both happen to make more n ø s Section 28.2 PART II. Half-Life (t 1/2 ) & Transmutation There is a characteristic rate of the nucleus in every radioisotope. t 1/2 is the time required for of the nuclei of a radioisotope sample to decay to products. 1 st t 1/2 = 2 nd t 1/2 = 3 rd t 1/2 = 4 th t 1/2 = 5 th t 1/2 = of Example 1 C-14 has a t 1/2 of 5730 years. If a medical anthropologist determines that a sample of human bone has only 25% of its original C-14 remaining, how old would the human bone be (approximately)? Example 2 Tc-104 has a t 1/2 of 18 minutes. If a sample originally contained 1.00g of Tc- 104, how many grams would remain after 1 ½ hours? t 1/2 Used for Transmutation Reactions C-14 t 1/2 = Tc-104 t 1/2 = U-238 t 1/2 =. the and/or of the nucleus of one element into the nucleus of another element. By nuclear OR forced of the nucleus such as Fermi National Accelerator Lab or the Hadron Collider!!! Rutherford transmutated N-14 into F-18 by bombarding it with an, which quickly decomposed into the more stable O-17 and a proton. Write the nuclear equation for the above! 5

6 Transuranium Elements Means Uranium and man-made. Most use as the building block. Example: U-238 is bombarded with a neutron; the product is unstable and goes through beta decay; this product is unstable and goes through beta decay as well; finally a somewhat stable element results what element is it? Section 28.3 Fission and Fusion of Atomic Nuclei Objectives: Compare nuclear fission and nuclear fusion, and comment on their potential as sources of energy. Describe the methods used in nuclear power plants to produce and control fission reactions Nuclear Fission The of the nuclei of radioisotopes into smaller fragments when bombarded with neutrons. U-235 and Pu-239 are two most common. radioisotopes. F pg.853 Neutron gun (fires n ø s ) fissionable U-235 unstable U-238, Kr-91, Ba-142, more neutrons U-235 CHAIN RXN!!! Nuclear Powerplants F.28.12, pg.854 KNOW & UNDERSTAND THE DIAGRAM!!! Neutron Moderation down the neutrons so that they may be absorbed by the nucleus of a radioisotope H 2 O or C. Neutron Absorption neutrons control rods of Cd. Nuclear Regulatory Commission (NRC) Nuclear Regulatory Commission (NRC) 6

7 Nuclear Fusion The of the nuclei of two light isotopes to produce a nucleus of greater mass + ENERGY. Requires tremendous and. H-2 (Deuterium) + H-3 (Tritium) + FORCE + HEAT He-5 (Unstable Intermediate) He-4 + neutron + Thermonuclear fusion occurs in the provides energy to the Earth. Fusion not yet possible on Earth If used, 1 gal. of sea water contains enough H-isotopes to equal the energy released by the combustion of gal. of gasoline. Section 28.4 Radiation in Your Life Objectives: Describe three methods of detecting radiation. List some applications of radioisotopes in research and medicine. Detecting Radiation Ionizing Radiation has enough energy to knock electrons off atoms to produce (β) Geiger Counter F.28.15, pg Scintillation Counter phosphor screen produces flashes of when hit by radiation (β) Film Badge uses camera film that turns dark upon exposure to (detects all types and strength) Other Implications of Radiation Neutron Activation Analysis firing n ø s at samples activates radioactive elements present used in. Tracers study reactions, biological processes/food ingestion,, water seepage. Medical Diagnosis Cancer Treatment Nuclear Weapons Radon Poisoning result of decaying Positron Emission Tomography (PET) using fluorodeoxyglucose (FDG) tracer PET brain image using FDG Scintillation Material & Photomultipliers Wikipedia Wikipedia 7

8 First nuclear test, Trinity in New Mexico, 16 July 1945 First nuclear weapon used by the U.S. on Hiroshima, 6 August ~140,000 dead Second nuclear weapon used by the U.S. on Nagasaki, 9 August ~74,000 dead At least 4 major false alarms of nuclear weapon release since then, most recent ~29,000 nuclear weapons held by 8 countries. Wikipedia Wikipedia - Figure 4. One major means by which fallout and nuclear debris are transferred through the atmosphere to people is via the production and consumption of dairy products. Fallout descends onto vegetation, which is eaten by dairy animals. The fallout passes into the animals' milk, which is prepared for human consumption. This pathway is the single largest means by which people in the U.S. were exposed to iodine-131 from fallout generated by nuclear weapons testing. Figure adapted from the National Cancer Institute; illustration by Barbara Aulicino American Scientist Online - 8