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 4) lab coat 5) thick concrete A person working with radioisotopes wears protective clothing and gloves and stands behind a shield. 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 U Th + He 238 234 4 92 90 2 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 STEP 1 Write the incomplete nuclear equation. Rn? + He 222 4 86 2 86 Rn 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. STEP 5 Symbol of element 84 218 Po 84 = Po Complete the nuclear equation. Rn Po + He 222 218 4 86 84 2 26
Beta Decay Beta decay occurs when an electron (beta particle) is emitted from the nucleus a neutron in the nucleus breaks down n e + H 1 0 1 0-1 1 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. K? + e 42 0 19-1 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 42 20 Ca = Ca STEP 5 Complete the nuclear equation. K Ca + e 42 42 0 19 20-1 29
Learning Check Write the nuclear equation for the beta decay of Xe-133. 30
Solution STEP 1 Write the incomplete nuclear equation. Xe? + e 133 0 54-1 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 55 133 55 Cs = Cs STEP 5 Complete the nuclear equation. Xe Cs + 133 133 0 54 55-1 e 32
Positron Emission In positron emission, a proton is converted to a neutron and a positron H n e 1 1 0 1 0 +1 the mass number of the new nucleus is the same, but the atomic number decreases by 1 Mn Cr + e 49 49 0 25 24 +1 33
Learning Check Write the nuclear equation for the positron emission by Rb-82. 34
Solution STEP 1 Write the incomplete nuclear equation. Rb? + e 82 0 37 +1 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 82 Kr 36 = Kr STEP 5 Complete the nuclear equation. Rb Kr + e 82 82 0 37 36 +1 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 Tc Tc + 99m 99 0 43 43 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? Co + n? + He 59 1 4 27 0 2 40
Solution STEP 1 Write the incomplete nuclear equation. Co + n? + He 59 1 4 27 0 2 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 56 Mn 25 = Mn STEP 5 Complete the nuclear equation. Co + n Mn + He 59 1 56 4 27 0 25 2 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 10 10 disintegrations/s 1 Ci = 3.7 x 10 10 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. 50
Decay Curve A decay curve shows the decay of radioactive atoms the remaining radioactive sample 51
Half-lives of Some Radioisotopes Half-lives of radioisotopes that are naturally occurring tend to be long used in nuclear medicine tend to be short 52
Half-Life Calculations In one half-life, 40 mg of a radioisotope decays to 20 mg. After two half-lives, 10 mg of radioisotope remain. 40 mg x 1 x 1 = 10 mg 2 2 Initial 40 mg 1 half-life 2 half-lives 20 mg 10 mg 53
Examples of Half-Lives 54
Using Half-lives 55
Learning Check The half-life of iodine-123 is 13 h. How much of a 64-mg sample of I-23 is left after 26 h? 1) 32 mg 2) 16 mg 3) 8 mg 56
Solution STEP 1 State the given and needed amounts of radioisotope. Given 64 mg of I-123; 13 h/half-life Need mg of I-123 remaining after 26 h STEP 2 Write a plan to calculate amount of active radioisotope. number of hours mg of I-123 Half-life Number of half-lives number of half-lives mg of I-123 remaining 57
Solution (continued) STEP 3 Write the half-life equality and conversion factors. 1 half-life = 13 h 1 half-life and 13 h 13 h 1 half-life STEP 4 Set up problem to calculate amount of active radioisotope. number of half-lives = 26 h x 1 half-life = 2 half-lives 13 h 13 h 13 h 64 mg 32 mg 16 mg 64 mg x ½ 32 mg x ½ = 16 mg (2) 58
Nuclear Radiation Medical Applications Using Radioactivity 59
Medical Applications Radioisotopes with short half-lives are used in nuclear medicine because they have the same chemistry in the body as the nonradioactive atoms give off radiation that exposes a photographic plate (scan), giving an image of an organ 60
Using a Scanner to Detect Radiation (a) A scanner is used to detect radiation from a radioisotope that has accumulated in an organ. (b) A scan of the thyroid show the accumulation of radioactive iodine-131 in the thyroid. 61
Radioisotopes in Nuclear Medicine 62
Learning Check Which of the following radioisotopes are most likely to be used in nuclear medicine? 1) K-40 half-life 1.3 x 10 9 years 2) K-42 half-life 12 hours 3) I-131 half-life 8 days 63
Solution Which of the following radioisotopes are most likely to be used in nuclear medicine? Radioisotopes with short half-lives are used in nuclear medicine. 2) K-42 with a half-life of 12 h. 3) I-131 with a half-life 8 days. 64
Positron Emission Tomography (PET) In positron Emission Tomography (PET), positrons are emitted from positron emitters such as carbon -11, oxygen-15, and fluorine-18 F O + e 18 18 0 9 8 1 positrons are used to study brain function and metabolism positrons combine with electrons to produce gamma ray that can be detected, giving a threedimensional image 0 0 0 1 + 1 0 e e 65
Positron Emission Tomography (PET) These PET scans of the brain show a normal brain on the left and a brain affected by Alzheimer s disease on the right. 66
Computed Tomography (CT) In computed tomography (CT), 30 000 X-rays are directed at the brain in layers are absorbed at different rates due to differences in densities of body tissues and fluids create three-dimensional images of the brain and any tumors or hemorrhages 67
Computed Tomography (CT) A CT scan shows a brain tumor (yellow) on the right side of the brain. 68
Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI) protons in the presence of a strong magnetic field align with the magnetic field protons release energy when magnetic field is removed protons in different environments emit energies of different frequencies to provide images of soft tissue 69
Magnetic Resonance Imaging (MRI) An MRI scan provides images of the heart and lungs. 70
Nuclear Radiation Nuclear Fission and Fusion 71
Nuclear Fission In nuclear fission, a large nucleus is bombarded with a small particle the nucleus splits into smaller nuclei and several neutrons large amounts of energy are released 72
Nuclear Fission When a neutron bombards U-235, an unstable nucleus of U-236 forms and undergoes fission (splits) smaller nuclei are produced such as Kr-91 and Ba-142 neutrons are released to bombard more U-235 nuclei 73
Nuclear Fission n + U U Kr + Ba + 3 n + energy 1 235 236 91 142 1 0 92 92 36 56 0 74
Chain Reaction A chain reaction occurs when a critical mass of uranium undergoes fission releasing a large amount of heat and energy that produce an atomic explosion 75
Chain Reaction 76
Learning Check Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction. 1 n + 235 U 137 Te +? + 2 1 n + energy 0 92 52 0 77
Solution 1 n 235 137 97 Zr 1 0 92 52 40 0 + U Te + + 2 n + energy 78
Nuclear Power Plants In nuclear power plants, fission is used to produce energy control rods in the reactor absorb neutrons to slow the fission process Nuclear power plants supply about 10% of the electricity in the United States. 79
Nuclear Power Plants 80
Nuclear Fusion Nuclear fusion occurs at extremely high temperatures (100 000 000 C) combines small nuclei into larger nuclei releases large amounts of energy occurs continuously in the sun and stars 81
Nuclear Fusion 82
Learning Check Indicate if each of the following is 1) nuclear fission or 2) nuclear fusion A. a nucleus splits B. large amounts of energy are released C. small nuclei form larger nuclei D. hydrogen nuclei react E. several neutrons are released 83
Solution Indicate if each of the following is 1) nuclear fission or 2) nuclear fusion 1 A. a nucleus splits 1, 2 B. large amounts of energy are released 2 C. small nuclei form larger nuclei 2 D. hydrogen nuclei react 1 E. several neutrons are released 84
Concept Map 85