Nuclear Radiation Natural Radioactivity A person working with radioisotopes wears protective clothing and gloves and stands behind a shield. 1 Radioactive Isotopes A radioactive isotope • has an unstable nucleus • emits radiation to become more stable • can be one or more isotopes of an element • is written with a mass number and an atomic number • includes the mass number in its name Example: iodine-131 2 Examples of Radioactive Isotopes 3 Learning Check Thallium-201 is used for heart scans to determine cardiac function. A. How many protons are in thallium-201? B. How many neutrons are in thallium-201? C. What is the atomic symbol of thallium-201? 4 Solution Thallium-201 is used for heart scans to determine cardiac function. A. How many protons are in thallium-201? Thallium, symbol Tl, has 81 protons. B. How many neutrons are in thallium-201? mass number 201 atomic number 81 = 120 neutrons C. What is the atomic symbol of thallium-201? mass number 201 Tl atomic number 81 5 Nuclear Radiation Nuclear radiation • is the radiation emitted by an unstable atom • takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays 6 Alpha Particle An alpha () particle has • a helium nucleus • 2 protons and 2 neutrons • a mass number of 4 • a charge of 2+ • a low energy compared to other radiation particles 7 Beta Particle A beta () particle • is a high-energy electron • has a mass number of 0 • has a charge of 1- • forms in an unstable nucleus when a neutron changes into a proton and an electron 8 Positron A positron ( +) • has a mass number of 0 • has a charge of 1+ • forms in an unstable nucleus when a proton changes into a neutron and a positron 9 Gamma () Ray A gamma () ray • is high-energy radiation • has a mass number of 0 • has a charge of 0 • is emitted from an unstable nucleus to give a more stable, lower energy nucleus 10 Summary of Common Forms of Nuclear Radiation 11 Learning Check Give the mass number and charge of each type of radiation. 1. alpha particle 2. positron 3. beta particle 4. neutron 5. gamma ray 12 Solution Mass Number Charge 1. alpha particle 4 2+ 2. positron 0 1+ 3. beta particle 0 1- 4. neutron 1 0 5. gamma ray 0 0 13 Radiation Protection Radiation protection requires • paper and clothing for alpha particles • a lab coat or gloves for beta particles • a lead shield or a thick concrete wall for gamma rays • limiting the amount of time spent near a radioactive source • increasing the distance from the source 14 Radiation and Shielding Required 15 Radiation Protection Different types of shielding are needed for different radiation particles. 16 Learning Check Indicate the type of radiation (alpha, beta, and/or gamma) protection for each type of shielding. 1) heavy clothing 2) paper 3) lead A person working with radioisotopes wears protective clothing and gloves 4) lab coat and stands behind a shield. 5) thick concrete 17 Solution Indicate the type of radiation (alpha, beta, and/or gamma) protection for each type of shielding. 1) heavy clothing alpha, beta 2) paper alpha 3) lead alpha, beta, gamma 4) lab coat alpha, beta 5) thick concrete alpha, beta, gamma 18 Nuclear Radiation Nuclear Equations A radon gas detector is used to determine radon levels in buildings with inadequate ventilation. 19 Radioactive Decay In radioactive decay, • a nucleus spontaneously emits radiation • a nuclear equation is written for the radioactive nucleus, the new nucleus, and the radiation emitted Radioactive nucleus new nucleus + radiation (, , , +) 20 Nuclear Equations In a nuclear equation, the type of radiation emitted causes • changes in the mass numbers • changes in the atomic numbers for the nuclei of the unstable and stable nuclei 21 Balancing Nuclear Equations In a balanced nuclear equation, • the sum of the atomic numbers for the nuclei of the reactant and the products must be equal Mass Numbers Total = 238 = 238 238 234 4 92U 90Th + 2 He Total = 92 = 92 Atomic Numbers 22 Guide to Completing a Nuclear Equation 23 Alpha Decay In alpha decay, a radioactive nucleus emits an alpha particle to form a new nucleus that has • a mass number 4 less than that of the initial nucleus • an atomic number that has decreased by 2 from that of the initial nucleus 24 Example of Writing an Equation for Alpha Decay 222 Write an equation for the alpha decay of 86 Rn STEP 1 Write the incomplete nuclear equation. 222 4 86Rn ? + 2 He STEP 2 Determine the missing mass number. 222 = ? + 4 222 – 4 = 218 218 = ? (mass number of new nucleus) 25 Equation for Alpha Decay (continued) STEP 3 Determine the missing atomic number. 86 = ? + 2 86 – 2 = ? 84 = ? (atomic number of new nucleus STEP 4 Determine the symbol of the new nucleus. Symbol of element 84 = Po 218 84 Po STEP 5 Complete the nuclear equation. 222 218 4 86Rn 84Po + 2 He 26 Beta Decay Beta decay occurs when • an electron (beta particle) is emitted from the nucleus • a neutron in the nucleus breaks down 1 0 1 0ne -1 + 1H 27 Writing an Equation for a Beta Emitter Write an equation for the beta decay of potassium-42. STEP 1 Write the incomplete nuclear equation. 42 0 19K ? + -1e STEP 2 Determine the missing mass number. 42 = ? + 0 42 0 = 42 = ? (mass number of new nucleus) STEP 3 Determine the missing atomic number. 19 = ? 1 19 + 1 = ? 20 = ? (atomic number of new nucleus) 28 Writing an Equation for a Beta Emitter (continued) STEP 4 Determine the symbol of the new nucleus. Symbol of element 20 = Ca 42 20Ca STEP 5 Complete the nuclear equation. 42 42 0 19K 20Ca + -1e 29 Learning Check Write the nuclear equation for the beta decay of Xe-133. 30 Solution STEP 1 Write the incomplete nuclear equation. 133 0 54Xe ? + -1e STEP 2 Determine the missing mass number. 133 = ? + 0 133 0 = 133 = ? (mass number of new nucleus) STEP 3 Determine the missing atomic number. 54 = ? 1 54 + 1 = ? 55 = ? (atomic number of new nucleus) 31 Solution (continued) STEP 4 Determine the symbol of the new nucleus. Symbol of element 55 = Cs 133 55 Cs STEP 5 Complete the nuclear equation. 133 133 0 54Xe 55Cs + -1e 32 Positron Emission In positron emission, • a proton is converted to a neutron and a positron 1 1 0 1H 0ne +1 • the mass number of the new nucleus is the same, but the atomic number decreases by 1 49 49 0 25Mn 24Cr + +1e 33 Learning Check Write the nuclear equation for the positron emission by Rb-82. 34 Solution STEP 1 Write the incomplete nuclear equation. 82 0 37Rb ? + +1e STEP 2 Determine the missing mass number. 82 = ? + 0 82 = 82 = ? (mass number of new nucleus) STEP 3 Determine the missing atomic number. 37 = ? + 1 37 1 = ? 36 = ? (atomic number of new nucleus) 35 Solution (continued) STEP 4 Determine the symbol of the new nucleus. Symbol of element 36 = Kr 82 36 Kr STEP 5 Complete the nuclear equation. 82 82 0 37Rb 36Kr + +1e 36 Gamma ( ) Radiation In gamma radiation, • energy is emitted from an unstable nucleus, indicated by m following the mass number • the mass number and the atomic number of the new nucleus are the same 99m 99 0 43Tc 43Tc + 0 37 Summary of Types of Radiation 38 Producing Radioactive Isotopes Radioactive isotopes are produced • when a stable nucleus is converted to a radioactive nucleus by bombarding it with a small particle • in a process called transmutation 39 Learning Check What radioactive isotope is produced when a neutron bombards cobalt-59 and an alpha particle is emitted? 59 1 4 27Co + 0n ? + 2 He 40 Solution STEP 1 Write the incomplete nuclear equation. 59 1 4 27Co + 0n ? + 2 He STEP 2 Determine the missing mass number. 59 +1 = ? + 4 59 + 1 4 = 56 (mass number of new nucleus) STEP 3 Determine the missing atomic number. 27 = ? + 2 27 2 = ? 25 = ? (atomic number of new nucleus) 41 Solution (continued) STEP 4 Determine the symbol of the new nucleus. Symbol of element 25 = Mn 56 25 Mn STEP 5 Complete the nuclear equation. 59 1 56 4 27Co + 0n 25Mn + 2 He 42 Nuclear Radiation Radiation Measurement A radiation technician uses a Geiger Counter to check radiation levels. 43 Radiation Detection A Geiger counter • detects beta and gamma radiation • uses ions produced by radiation to create an electrical current 44 Radiation Measurement Radiation units of activity include • curie (Ci) SI unit = becquerel (Bq) number of atoms that decay in one second 1 Ci = 3.7 x 1010 disintegrations/s 1 Ci = 3.7 x 1010 Bq • rad (radiation absorbed dose) SI unit = gray(Gy) radiation absorbed by the tissues of the body 1 Gy = 100 rad • rem (radiation equivalent) SI unit = sievert (Sv) biological damage caused by different types of radiation = absorbed dose (rad) x factor 1 Sv = 100 rem 45 Units of Radiation Measurement 46 Exposure to Radiation Exposure to radiation occurs from • naturally occurring radioisotopes • medical and dental procedures • air travel, radon, and smoking cigarettes 47 Radiation Sickness Radiation sickness • depends on the dose of radiation received at one time • is not detected under 25 rem • involves a decrease in white blood cells at 100 rem • includes nausea and fatigue over 100 rem • reduces white-cell count to zero over 300 rem • leads to death in 50% of people at 500 rem 48 Nuclear Radiation Half-Life of a Radioisotope The age of the Dead Sea scrolls was determined using carbon-14. 49 Half-Life The half-life of a radioisotope is the time for the radiation level (activity) to decrease (decay) to one-half of its original value.