* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Photo chapter opener 21 Subatomic particle tracks in a bubble
Survey
Document related concepts
Nuclear and radiation accidents and incidents wikipedia , lookup
Ionizing radiation wikipedia , lookup
Nuclear fission wikipedia , lookup
Nuclear fusion–fission hybrid wikipedia , lookup
Radioactive waste wikipedia , lookup
Background radiation wikipedia , lookup
Nuclear fission product wikipedia , lookup
Technetium-99m wikipedia , lookup
Isotopic labeling wikipedia , lookup
Nuclear binding energy wikipedia , lookup
Radioactive decay wikipedia , lookup
Atomic nucleus wikipedia , lookup
Nuclear transmutation wikipedia , lookup
Transcript
The Nucleus: A Chemist’s View Nuclear Stability and Radioactive Chapter 19 Lesson 1 Nuclide • A nuclide is a type of atom characterized by its proton number, neutron number and its energy condition. • Nuclides with identical proton number but differing neutron number are called isotopes. • Conditions with a life of less than 10-10s are called excited conditions of a nuclide. • At present, more than 2,770 different nuclides are known, distributed over the 113 currently known elements, only 279 are stable with respect to radioactive decay. 2 A Z X A : the sum of the neutrons and protons Z : atomic numbers 3 Radioactive Stability • Nuclides with 84 or more protons are unstable. • Light nuclides are stable when Z equals A – Z (neutron/proton ratio is 1). • For heavier elements the neutron/proton ratio required for stability is greater than 1 and increases with Z. 4 Radioactive Stability • Certain combinations of protons and neutrons seem to confer special stability. Even numbers of protons and neutrons are more often stable than those with odd numbers. 5 Known nuclides • Light nuclides are stable when (A-Z)/Z ratio is 1. • For heavier elements for stability, (A-Z)/Z ratio is greater than 1 and increases with Z. 6 • Magic numbers: 2, 8, 20, 28, 50, 82, 126 • Specific numbers of protons or neutrons produce especially stable nuclides. 7 Types of Radioactive Decay a-particle production The common modes of decay 238 92 U He(a ) Th 4 2 234 90 Th He(a ) Ra 230 90 4 2 226 88 Spontaneous fission (a)The splitting of a heavy nuclide into two lighter nuclides with similar mass numbers. (b)Slow rate for most nuclides 8 Types of Radioactive Decay b-particle production The common modes of decay Th Pa e(b ) 234 90 131 53 234 91 0 1 I Xe e(b ) 131 54 0 1 (a)The net effect of b-particle production is to change a neutron to a proton. (b)The nuclides lie above the zone of stability. (c)The ratios of neutron/proton are too high. 9 Types of Radioactive Decay gray production 238 92 U He 4 2 Th 2 γ 234 90 0 0 (a) high-energy photon (b) g-ray production accompanies unclear decays and particle reaction. (c)The emission of g rays is one way a nucleus with excess energy can relax to its ground state. 10 Types of Radioactive Decay positron production 22 11 Na Ne e 22 10 0 1 (a)The net effect of this process is to change a e a proton to a neutron. (b)Higher neutron/proton ratio (c)Nuclides lie below the zone of stability. 11 Antiparticle 0 1 e e 2 γ 0 1 0 0 Matter-antimatter collisions, is called annihilation. 12 13 Types of Radioactive Decay • Electron capture: Inner-orbital electron Concept Check Which of the following produces a b particle? a) 68 31 b) 62 29 c) 212 87 d) 129 51 Ga + 0 1 Cu Fr Sb e 0 1 4 2 e+ He + 0 1 e+ 68 30 62 28 Zn electron capture Ni positron 208 85 At alpha particle Te beta particle 129 52 15 Decay series • Often a radioactive nucleus cannot reach a stable state through a single decay process. 16 The Kinetic of Radioactive Decay • First order reaction dN N Rate kN ln( ) kt N N 0 e kt dt N0 17 Half-Life • Time required for the number of nuclides to reach half the original value. t1/ 2 ln 2 0.693 = = k k Nuclear Particles Half-Life of Nuclear Decay Exercise A first order reaction is 35% complete at the end of 55 minutes. What is the value of k? k = 7.8 x 10-3 min-1 Nuclear Transformation • The change of one element into another. 27 13 249 98 Al + He 4 2 30 15 1 0 P+ n 263 Cf + 188 O 106 Sg + 4 01 n The decay of a 10 g sample of Sr-90 23 Change in the amount of Mo with time 24 Nuclear Transformations • The conversion of one element into another Observatio n from Rutherford 14 7 N He O H 4 2 17 8 1 1 Observatio n from Irene Curie 27 13 Al He P n 4 2 30 15 1 0 26 Experiments for Nuclear Transformations cyclotron Particle accelerators 27 Diagram of a linear accelerator 29 Detection of Radioactivity Geiger-Muller counter Ar(g) Ar (g) e high energy particle 30