Types of Radioactive Decay

Types of Radioactive Decay

Chapter Eighteen: THE NUCLEUS: A CHEMISTS VIEW How Often Does Nuclear Decay Appear On The Exam? 3 Out Of 75 On Mc Occasionally On FR Terminology Nucleon refers to both Nuclides = individual neutron & proton atom particles Isotope is a group of Z = atomic number nuclides Example 126C, 136C, 146C

A = atomic mass represent the nuclides in Isotopes = atoms with the isotopes of Carbon different number of neutrons, hence different A Copyright Houghton Mifflin Company. All rights reserved. 182 Nuclear Stability and Radioactive Decay emissionemission The Zone of Stability

Red dots indicate the nuclides that do not undergo radioactive decay. + emissionor emissionElec. emissionCapt. Trends in Nucleus Stability Number of Stable Isotopes Protons Neutrons 157 53 50

5 Copyright Houghton Mifflin Company. All rights reserved. Even Even odd Odd even odd even odd 184 Types of Radioactive Decay

A. Involving a change in mass (2 types) 1.alpha production (): 4 2 He 2.Spontaneous fission Splitting of heavy nuclides into lighter ones. 1 n + 235 U 141 Ba + 92 Kr + 31 n 0 92 56 36 0 B. Involve NO change in mass (4 types) 1.beta production (): Copyright Houghton Mifflin Company. All rights reserved.

185 Types of Radioactive Decay 3. gamma ray production (): 4. positron 0 production: 1e 5. electron capture: Copyright Houghton Mifflin Company. All rights reserved. 186

Practice Write balanced equations for each of the following 11 C produces a positron 6 241 Bi produces a particle 83 237 Np produces an particle 93 Copyright Houghton Mifflin Company. All rights reserved.

187 Decay Series The decay series from 238U to 206Pb. Each nuclide except 206Pb is unstable and transformations continue until it reaches the stable form. Copyright Houghton Mifflin Company. All rights reserved. 188

Rate of Decay N Radioactive Decay Rate = t The rate of decay is the change in number of nuclides (N) over change in time (t). This represents a first-order process and its rate is proportional to the number of nuclides radioactive (N) in the sample times k, the decay constant. Copyright Houghton Mifflin Company. All rights reserved. 189 Half-Life (t) Defined as the time required for the number of nuclides of a sample to reach half the

original value. t1/2 ln(2) 0.693 k k t1/2 is half-life k is the rate constant for decay Copyright Houghton Mifflin Company. All rights reserved. 1810

Nuclear Decay Problem Technetium 99m is used to form pictures of internal organs in the body and is often used to assess heart damage. The m for this nuclide indicates an excited nuclear state that decays to the ground state by gamma emission. The rate constant for decay of 99m Tc is known to be 1.16 x 10-1 /h./ What 43 is the half-life of this nuclide? Copyright Houghton Mifflin Company. All rights reserved. 1811 Calculate k Nuclear Material

t1/2 U 14 C 230 Rn 4.51 x 109 years decaydecay 5730 years decaydecay 55.6 seconds decaydecay 238 0.693 0.693 10

1 U k= = 1.54 x 10 yr t1/2 4.51x109 yr 238 Copyright Houghton Mifflin Company. All rights reserved. 1812

Nuclear Transformation The change of one element into another. Done by bombarding nuclides with particles. Use particle accelerators (aka cyclotron) to achieve high velocities to the particles. Examples: 27 4 30 1 13 Al + 2 He 15 P + 0 n 249 98 18 8

Cf + O Copyright Houghton Mifflin Company. All rights reserved. 263 106 1 0 Sg + 4 n 1813 A Schematic Diagram of a Cyclotron Copyright Houghton Mifflin Company. All rights reserved.

1814 A Schematic Diagram of a Linear Accelerator The accelerator uses a changing electric field to accelerate a positive ion along a linear path. The polarity of the tubes is reversed propelling the ion along, eventually reaching high velocity. Copyright Houghton Mifflin Company. All rights reserved. 1815 Fermilab in Batavia, Illinois Largest

particle accelerator in the U.S. It has 3 linear and 2 circular accelerators. Copyright Houghton Mifflin Company. All rights reserved. 1816 Detection and Uses of Radioactivity Geiger counters make use of high energy particles from radioactive

decay producing ions. Ar(g) Particles Ar+(g) + e The ions produce an electrical current. Copyright Houghton Mifflin Company. All rights reserved. 1817 Dating by Radioactivity Radiocarbon Dating 14 C 0 e + 14 N 6 -1 7 Based on 146C : 126C

Copyright Houghton Mifflin Company. All rights reserved. 1818 Radiotracers Copyright Houghton Mifflin Company. All rights reserved. 1819 Thermodynamic Stability of the Nucleus You can determine the thermodynamic stability of the nucleus by calculating the change in potential energy (PE) if that nucleus where formed from constituent P + N, (n = neutrons, H=protons) Ex.: Making 16O 1

1 16 8 n + 8 H O 0 1 8 1 1 24 8 n(1.67493x10 g ) 8 H (1.67262 x10 24 g ) 2.67804 x10 23 g 0 1 Mass of 16O nucleus = 2.65535x10-23g Difference in mass for one nucleus is -2.269x10-25g Copyright Houghton Mifflin Company. All rights reserved.

1820 Energy and Mass When a system gains or loses energy it also gains or loses a quantity of mass. Einsteins theory of relativity showed that energy could be considered as a form of matter. E = mc2 m = change in mass E = change in energy If E is negative (exothermic), mass is lost from the system. Copyright Houghton Mifflin Company. All rights reserved. 1821

Binding Energy Def. The energy required to decompose a nucleus into its components. Iron-56 is the most stable nucleus known and has a binding energy of 8.97 MeV fig 18.9 p.858 Copyright Houghton Mifflin Company. All rights reserved. 1822

Binding Energy per Nucleon vs. Mass Number Copyright Houghton Mifflin Company. All rights reserved. 1823 Nuclear Fission and Fusion Fusion: Combining two light nuclei to form a heavier, more stable nucleus. 1 1 2 0 H H H e 1

1 1 1 Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers. 1 0 n+ 235 92 U Copyright Houghton Mifflin Company. All rights reserved.

142 56 Ba + 91 36 1 0 Kr + 3 n 1824 Fission Processes A self-sustaining fission process is called a chain reaction.

Critical Mass is the mass of fissionable material necessary to achieve a sustained reaction Neutrons Causing Event Fission subcritical <1 critical =1 supercritical >1 Copyright Houghton Mifflin Company. All rights reserved. Result reaction stops

sustained reaction violent explosion 1825 Schematic Diagram of a Nuclear Power Plant Copyright Houghton Mifflin Company. All rights reserved. 1826 Schematic Diagram of a Reactor Core Copyright Houghton Mifflin Company. All rights reserved.

1827 Biological Effects of Radiation depend on: 1. Energy of the radiation rads = radiation absorbed dose 1 rad = 10-2J / kg tissue 2. Penetration ability of the radiation highest penetration penetration about 1cm Copyright Houghton Mifflin Company. All rights reserved. 1828 Biological Effects of Radiation

3. Ionizing ability of the radiation radiation has ability to remove e- from molecules in cells creating big problems 4. Chemical properties of the radiation source where it ends up in the body and how long it stays (relative effectiveness of the radiation = RBE) Copyright Houghton Mifflin Company. All rights reserved. 1829 Effects of Short-Term Exposures on Radiation roentgen equivalent for man = rem rem = number of rads X RBE

Copyright Houghton Mifflin Company. All rights reserved. 1830

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