1 Chapter 11 Nuclear Chemistry Use of 131 I in detecting Hyper- or hypo- thyroidism

2 Brain images with 123 I-labeled compound

3 Nuclear Reactions

4 © 2003 John Wiley and Sons Publishers

The Discovery of Nature of Radioactivity Radioactivity: The spontaneous emission of radiation from a nucleus. Henry Becquerel, a French physicist, discovered radioactivity in Henry Becquerel placed a sample of uranium-containing mineral on top of a photographic plate wrapped in black paper. On developing the plate, Becquerel found a silhouette of the mineral on the plate. He concluded some kind of radiation emitted by the mineral passed through the paper and exposed the photographic plate.

Stable and Unstable Isotopes A radioactive isotope has an unstable nucleus and emits radiation to become more stable. Isotopes of elements may be stable or unstable.

7 Alpha Decay When a radioactive nucleus emits an alpha particle, a new nucleus results. The mass number of the new nucleus is 4 less than that of the initial nucleus. The atomic number is decreased by Nuclear Decay Animation

8 Equation for Alpha Decay Write an equation for the alpha decay of Rn Rn new nucleus + 4 He 86 2  Determine the mass and atomic numbers of the new nucleus. Mass number: 222 – 4 = 218 Atomic number:86 – 2 = 84 Symbol of element 84 = Po  Complete the equation with the new symbol: 222 Rn 218 Po + 4 He

9 Beta Decay  A beta particle  Is an electron emitted from the nucleus.  Forms when a neutron in the nucleus breaks down. 1 n 0 e + 1 H

10  Potassium - 42 is a beta emitter. 42 K new nucleus + 0 e  The atomic number of the new nucleus increases by 1. Mass number : (same) = 42 Atomic number: = 20 Symbol of element 20= Ca  The nuclear equation is 42 K 42 Ca + 0 e

11 Write the nuclear equation for the beta decay of Co Co 27 Learning Check

12 Write the nuclear equation for the beta decay of Co Co 60 Ni + 0 e 2728  1 beta particle Solution

13 Gamma radiation is energy emitted from an unstable nucleus indicated by m. In a nuclear equation for gamma emission, the mass number and the atomic number are the same. 99m Tc 99 Tc +  Gamma  Radiation

14 Summary of Radiation

Radioactive Decay Series Decay series: A sequential series of nuclear disintigrations (decay) leading from a heavy radioisotope to a nonradioactive product, Fig 11.5.

16 Producing Radioactive Isotopes A nucleus is converted to a radioactive nucleus by bombarding it with a small particle.

17 What radioactive isotope is produced when a neutron bombards cobalt-59? 59 Co + 1 n ???? + 4 He Learning Check

18 What radioactive isotope is produced when a neutron bombards cobalt-59? mass numbers = 60 = Co + 1 n 56 Mn + 4 H e = 27 = 27 atomic numbers Solution

Detecting Radiation A Geiger counter detects radioactive radiations. Ions produced by radiation create an electrical current.

20 Geiger counter

21 Chapter 22Slide 21 A Geiger counter determines the amount of ionization by detecting an electric current. A thin window is penetrated by the radiation and causes the ionization of Ar gas. The ionized gas carried a charge and so current is produced. The current pulse generated when the radiation enters is amplified and counted.

22 Chapter 22Slide 22 Biological Effects of Radiation The penetrating power of radiation is a function of its mass:  -rays >  -particles >>  -particles. When ionizing radiation passes through tissue it removes an electron from water to form H 2 O + ions. The H 2 O + ions react with another water molecule to produce H 3 O + and a highly reactive OH radical. Free radicals generally undergo chain reactions, producing many radicals in the biomolecules.

23 Radiation Measurement Curie: 1 Ci = 3.7 x disintegrations The Curie measures the number of atoms that decay in one second. Curie: 1 Ci = 3.7 x disintegrations The rad (radiation absorbed dose) measures the radiation absorbed by the tissues of the body. The rem (Roentgen equivalent for man (rem) ) measures the biological damage.

24 Calibration of film dosimeters In calibrating film badges the object is to obtain a series of curves relating radiation exposure to the blackening of the film. Different typesof film and holder require different conditions of calibration. Exposure-absorbance curves should be produced for each new batch of films manufactured, and in addition, for each set of films processed, a few badges should be exposed to known doses to check that there has been no change in the exposure-absorbance curve

25 Biological Effects of Radiation Radiation absorbed dose (rad) 1 rad = 1 x J/g of material Roentgen equivalent for man (rem) 1 rem = 1 rad x QQuality Factor  -ray = 1  = 1  = 20 Curie: 1 Ci = 3.7 x disintegrations/s SI unit is the becquerel: Bq = 1 disintegrations/s

26 Units of Radiation Measurement

27 Background Radiation A person is exposed to radiation from naturally occurring radioisotopes and medical X rays.

28 Effects of Radiation

29 Radioactive Decay Rates

30 Half-life is the time for the radiation level to decrease (decay) to one-half of the original value Radioactive Half-Life decay curve

31 The decay of a radioactive nucleus over time is shown in the following fig 11.4decay of a radioactive nucleus

32 Half-Lives of Some Radioisotopes

33 After one half-life, 40 mg of a radioisotope will decay to 20 mg. After two half-lives, 10 mg of radioisotope remain. 40 mg x 1 x 1 = 10 mg half-life 2 half-lives Initial 40 mg 20 mg 10 mg Half-Life Calculations

34 The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours? 1) 32 mg 2) 16 mg 3) 8 mg Learning Check

35 2) 16 mg Half life = 13 hrs Number of half lives = 2 Amount remaining = 64 mg x 1 x 1 = 16 mg hrs 13 hrs 64 mg 32 mg 16 mg Solution

36 Medical Applications Radioisotopes with short half-lives Are used in nuclear medicine. Have the same chemistry in the body as the nonradioactive atoms. In the body give off radiation that exposes a photographic plate (scan), which gives an image of an organ.

Radioisotopes in Medicine 1 out of every 3 hospital patients will undergo a nuclear medicine procedure 24 Na, t ½ = 14.8 hr,  emitter, blood-flow tracer 131 I, t ½ = 14.8 hr,  emitter, thyroid gland activity 123 I, t ½ = 13.3 hr,  ray emitter, brain imaging 18 F, t ½ = 1.8 hr,   emitter, positron emission tomography 99m Tc, t ½ = 6 hr,  ray emitter, imaging agent Brain images with 123 I-labeled compound

38 Some Radioisotopes Used in Nuclear Medicine

39 Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

40 Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs.Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.

41 Learning Check Which of the following radioisotopes are most likely to be used in nuclear medicine? 1) 40 K half-life 1.3 x 10 9 years 2) 42 K half-life 12 hours 3) 131 I half-life 8 days

42 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) 42 K half-life 12 hours 3) 131 I half-life 8 days

43  In nuclear fission, a large nucleus is bombarded with a small particle.  The nucleus splits into smaller nuclei, several neutrons and a great amount of energy Nuclear Fission and Nuclear Fusion

44 Nuclear Fission When a neutron bombards U-235, an unstable nucleus of U-236 undergoes fission (splits) to form smaller nuclei such as Kr-91 and Ba-142.

45 Chain Reaction  A chain reaction occurs when a critical mass of uranium undergoes fission so rapidly that the release of a large amount of heat and energy results in an atomic explosion.

46 Fusion involves the combination of small nuclei to form a larger nucleus. Nuclear Fusion

47 Indicate if each of the following is 1) nuclear fissionor 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. Learning Check

48 Indicate if each of the following is 1) nuclear fissionor 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. Solution

49 Chapter Summary Nuclear reaction: reaction that changes an atomic nucleus, causing the change of one element into another. Radioactivity: Spontaneous emission of radiation from nucleus of unstable atom.  radiation,  radiation, and  radiation are the three major types of radiation. The rate of nuclear reaction is expressed in units of half life (t 1/2 ). High energy radiation of all type is known as ionizing radiation.

50 Chapter Summary Contd. Radiation intensity is expressed in various ways depending on the radiation properties measured. - The curie (Ci) measures the number of radioactive disintigrations per second in a sample. - The Roentgen (R) measures the ionizing ability of radiation; - The rad measures the amount of radiation energy absorbed per gram of tissue; - The rem measures the amount of tissue damage caused by radiation.

51 Chapter Summary Contd. Nuclear fission: Splitting of nucleus apart by the bombardment of neutrons to give smaller fragments. Enormous amount of energy is released in the fission process. Nuclear fusion: Combination of two lighter nuclei to produce a heavier one. Like fusion, fission also releases enormous amount of energy.

52 End of Chapter 11