Chapter 9 Nuclear Radiation 9.1 Natural Radioactivity

Stable and Radioactive Isotopes A radioactive isotope has an unstable nucleus emits radiation to become more stable, changing the composition of the nucleus is identified by the mass number of the isotope

Nuclear Radiation Nuclear radiation is the radiation emitted by an unstable atom and takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays.

Types of Radiation Alpha () particle is two protons and two neutrons. Beta () particle is a high-energy electron. Positron (+) is a positive electron. Gamma rays are the high-energy radiation released from a nucleus when it decays.

Learning Check Give the name and symbol for the following types of radiation. A. alpha radiation B. radiation with a mass number of 0 and atomic number of +1 C. radiation that represents high-energy radiation released from the nucleus

Solution Give the name and symbol for the following types of radiation. A. alpha radiation B. radiation with a mass number of 0 and atomic number of +1 C. radiation that represents high-energy radiation released from the nucleus

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 distance from the source

Shielding for Radiation Protection

Learning Check What type of radiation will be blocked by A. lead shield B. paper, clothing

Solution What type of radiation will be blocked by A. lead shield gamma radiation B. paper, clothing alpha radiation

Chapter 9 Nuclear Radiation 9.2 Nuclear Equations

Balancing Nuclear Equations In a balanced nuclear equation, particles are emitted from the nucleus, and the mass number and atomic number may change the sum of the mass numbers and the sum of the atomic numbers are equal for the reactants and the products Mass number sum: 251 = 251 251Cf  247Cm + 4He 98 96 2 Atomic number sum: 98 = 98

Guide to Balancing Nuclear Equations

Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus forms with a mass number that is decreased by 4 and an atomic number that is decreased by 2.

Equation for Alpha Emission Write an equation for the alpha decay of Rn-222. Step 1 Write the incomplete nuclear equation. Step 2 Determine the missing mass number. 222 – 4 = 218 Step 3 Determine the missing atomic number. 86 – 2 = 84

Equation for Alpha Emission Write an equation for the alpha decay of Rn-222. Step 4 Determine the symbol of the new nucleus. 84 = Po Step 5 Complete the nuclear equation.

Beta Emission A beta particle is an electron emitted from the nucleus when a neutron in the nucleus breaks down, increasing the atomic number by 1.

Equation for Beta Emission Write an equation for the decay of 42K, a beta emitter. Step 1 Write the incomplete nuclear equation. Step 2 Determine the missing mass number. 42 – 0 = 42 Step 3 Determine the missing atomic number. 19  (1) = 20

Equation for Beta Emission Write an equation for the decay of 42K, a beta emitter. Step 4 Determine the symbol of the new nucleus. 20 = Ca Step 5 Complete the nuclear equation.

Learning Check Write the nuclear equation for the beta decay of 60Co.

Solution Write the nuclear equation for the beta decay of 60Co. Step 1 Write the incomplete nuclear equation. Step 2 Determine the missing mass number. 60 – 0 = 60 Step 3 Determine the missing atomic number. 27  (1) = 28

Solution Write the nuclear equation for the beta decay of 60Co. Step 4 Determine the symbol of the new nucleus. 28 = Ni Step 5 Complete the nuclear equation.

Positron Emission In positron emission, a proton is converted to a neutron and a positron. the mass number of the new nucleus is the same, but the atomic number decreases by 1.

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

Summary of Types of Radiation

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 When nonradioactive B-10 is bombarded by an alpha particle, the products are radioactive N-13 and a neutron.

Learning Check What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle?

Solution What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle? Step 1 Write the incomplete nuclear equation. Step 2 Determine the missing mass number. 98 + 1  4 = 95 Step 3 Determine the missing atomic number. 27  2 = 25

Solution What radioactive isotope is produced when a neutron bombards 98Tc, releasing an alpha particle? Step 4 Determine the symbol of the new nucleus. 25 = Mn Step 5 Complete the nuclear equation.

Chapter 9 Nuclear Radiation 9.3 Radiation Measurement

Geiger Counter A Geiger counter detects beta and gamma radiation uses ions produced by radiation to create an electrical current

Units for Measuring Radiation Units for measuring radiation activity include Curie – measures activity as the number of atoms that decay in 1 second rad (radiation absorbed dose) – measures the radiation absorbed by the tissues of the body rem (radiation equivalent) – measures the biological damage caused by different types of radiation

Measuring Radiation Activity Often the measurement for an equivalent dose is in millirems (mrem). One rem is equal to 1000 mrem. The SI unit is the sievert (Sv). One sievert is equal to 100 rem.

Radiation Exposure Exposure to radiation occurs from naturally occurring radioisotopes medical and dental procedures air travel, radon, and smoking cigarettes cosmic rays

Radiation Sickness LD50 is the amount of radiation to the whole body that is the lethal dose for one-half the population varies for different life-forms, as Table 9.6 shows

Learning Check A typical intravenous dose of I-125 for a thyroid diagnostic test is 100 Ci. What is this dosage in megabecquerels (MBq) (3.7  1010 Bq = 1 Ci)? A. 3.7 MBq B. 3.7  106 MBq C. 2.7  102 MBq

Solution A typical intravenous dose of I-125 for a thyroid diagnostic test is 100 Ci. What is this dosage in megabecquerels (MBq) (3.7  1010 Bq = 1 Ci)? 100 Ci  1 Ci  3.7  1010 Bq  1 MBq x 1 x 106 Ci 1 Ci 1  106 Bq = 3.7 MBq The answer is A.

Chapter 9 Nuclear Radiation 9.4 Half-Life of a Radioisotope

Half-Life and Decay Curves The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one-half of the original value. The decay curve for I-131 shows that one-half the sample decays every 8 days.

Half-Lives of Some Radioisotopes

Guide to Using Half-Lives

Half-Life Calculations The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years? Step 1 State the given and needed quantities. Given: 36 mg, 152.4 years, half-life of 38.1 years Needed: mg Sr-90 remaining Step 2 Write a plan to calculate unknown quantity. Half-life 152.4 years number of half-lives Number of half-lives 36 mg Sr-90 mg Sr-90 remaining

Half-Life Calculations The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years? Step 3 Write the half-life equality and conversion factors. 1 half-life = 38.1 years 38.1 years and 1 half-life 1 half-life 38.1 years

Half-Life Calculations The radioisotope strontium-90 has a half-life of 38.1 years. If a sample contains 36 mg of Sr-90, how many milligrams will remain after 152.4 years? Step 4 Set up the problem to calculate amount of active radioisotope. Number of half-lives 4 years x 1 half-life = 4 half-lives 38.1 years 1 half-life 2 half-lives 3 half-lives 4 half-lives 36 mg  18 mg  9 mg  4.5 mg  2.3 mg Sr-90

Learning Check Carbon-14 was used to determine the age of the Dead Sea Scrolls. If the Dead Sea Scrolls were determined to be 2000 years old and the half-life of carbon-14 is 5730 years, what fraction of this half-life has passed?

Solution Carbon-14 was used to determine the age of the Dead Sea Scrolls. If the Dead Sea Scrolls were determined to be 2000 years old and the half-life of carbon-14 is 5730 years, what fraction of this half-life has passed? 2000 years x 1 half-life = 0.35 half-life 5730 years

Learning Check The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours? A. 32 mg B. 16 mg C. 8 mg

Solution The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours? Step 1 State the given and needed quantities. Given: 64 mg, 26 hours, half-life of 13 hours Needed: mg I-123 remaining Step 2 Write a plan to calculate unknown quantity. Half-life 26 hours number of half-lives Number of half-lives 64 mg I-123 mg I-123 remaining

Solution The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours? Step 3 Write the half-life equality and conversion factors. 1 half-life = 13 hours 13 hours and 1 half-life 1 half-life 13 hours

Solution The half-life of I-123 is 13 h. How much of a 64-mg sample of I-123 is left after 26 hours? Step 4 Set up the problem to calculate amount of active radioisotope. Number of half-lives 26 hours x 1 half-life = 2 half-lives 13 hours 1 half-life 2 half-lives 64 mg  32 mg  16 mg I-123 The answer is B, 16 mg of I-123 remain.

Chapter 9 Nuclear Radiation 9.5 Medical Applications Using Radioactivity

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 in the organs of the body, they give off radiation that exposes a photographic plate (scan), giving an image of an organ

Medical Applications of Radioisotopes

Scans with Radioisotopes After a radioisotope is ingested by the patient, the radiologist determines the level and location of the radioactivity emitted by the radioisotope the scanner moves slowly over the organ where the radioisotope is absorbed the gamma rays emitted from the radioisotope can be used to expose a photographic plate, giving a scan of the organ

Scans with Radioisotopes (a) A scanner is used to detect radiation from a radioisotope that has accumulated in an organ. (b) A scan of the thyroid shows the accumulation of radioactive iodine-131 in the thyroid.

Positron Emission Tomography (PET) Positron emitters with short half-lives can be used to study brain function, metabolism, and blood flow include carbon-11, oxygen-15, nitrogen-13, and fluorine-18 combine with electrons after emission to produce gamma rays, which are then detected by computers, creating a 3-D image of the organ

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.

Computed Tomography (CT) A computer monitors the absorption of 30 000 X-ray beams directed at the brain in successive layers. Differences in absorption based on tissue densities and fluids provide images of the brain.

Magnetic Resonance Imaging (MRI) is an imaging technique that does not involve X-ray radiation is the least invasive imaging method available is based on absorption of energy when protons in hydrogen atoms are excited by a strong magnetic field works because the energy absorbed is converted to color images of the body

Magnetic Resonance Imaging An MRI scan of the heart and lungs, with the left ventricle shown in red.

Learning Check Which of the following radioisotopes are most likely to be used in nuclear medicine? A. 40K half-life 1.3 x 109 years B. 42K half-life 12 hours C. 131I half-life 8 days

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. A. 40K half-life 1.3  109 years Not likely: half-life is too long. B. 42K half-life 12 hours Short half-life, likely used. C. 131I half-life 8 days Short half-life, likely used.

Chapter 9 Nuclear Radiation 9.6 Nuclear Fission and Fusion

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

Nuclear Fission When a neutron bombards 235U, an unstable nucleus of 236U undergoes fission (splits) the nucleus splits to release large amounts of energy smaller nuclei are produced, such as Kr-91 and Ba-142 neutrons are also released to bombard more 235U nuclei

Nuclear Fission Diagram 1n + 235U 236U 91Kr + 142Ba + 3 1n + energy 0 92 92 36 56 0

Nuclear Fission Chain Reaction In a nuclear chain reaction, the fission of each U-235 atom produces three neutrons that cause the nuclear fission of more and more uranium-235 atoms.

Energy and Nuclear Fission The total mass of the products in this reaction is slightly less than the mass of the starting materials. The missing mass has been converted into energy, consistent with the famous equation derived by Albert Einstein, E = mc2. E is the energy released, m is the mass lost, and c is the speed of light, 3.0  108 m/s. Using this equation, a small amount of mass is multiplied by the speed of light squared, resulting in a large amount of energy. Fission of 1 g U-235 produces same energy as 3 tons of coal.

Learning Check 1n + 235U 137Te + ?X + 2 1n + energy 0 92 52 ? 0 Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction. 1n + 235U 137Te + ?X + 2 1n + energy 0 92 52 ? 0

Solution 1n + 235U 137Te + 97Zr + 2 1n + energy 0 92 52 40 0 Supply the missing atomic symbol to complete the equation for the following nuclear fission reaction. 1n + 235U 137Te + 97Zr + 2 1n + energy 0 92 52 40 0

Nuclear Power Plants In nuclear power plants, fission is used to produce energy control rods in the reactor absorb neutrons to slow and control the chain reactions of fission

Nuclear Fusion 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 Hydrogen atoms combine in a fusion reactor at very high temperatures.

Learning Check Indicate whether each of the following describes nuclear fission or 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.

Solution Indicate whether each of the following is nuclear fission or nuclear fusion. nuclear fission A. A nucleus splits. nuclear fission and fusion B. Large amounts of energy are released. nuclear fusion C. Small nuclei form larger nuclei. nuclear fusion D. Hydrogen nuclei react. nuclear fission E. Several neutrons are released.

Nuclear Radiation – Concept Map