Unit 2-6 Nuclear reaction and radioactivity

1. Unit 2-6 Nuclear reaction and radioactivity Chap 19

2. Nuclear reaction • Nuclear reaction involves in a change in nucleus of radioactive atom. • Types of nuclear reaction: • Fission: splitting of large, heavy nucleus • Fussion: combining of light nuclei.

3. Fission Fission - Splitting a heavy nucleus into two nuclei with smaller mass numbers.

4. A Fission Reactor

5. Deuterium – Tritium Fusion Reaction Fusion - Combining two light nuclei to form a heavier, more stable nucleus.

6. Radioactivity • Radioactivity – the ability of substance spontaneously emit high-energy radiation. • Radiation – rays and particles emitted by the radioactive material. • By emitting radiation atoms of one element change into atoms of another element. • A lot of isotopes of elements, the unstable ones, are radioactive-Radioisotope

7. History • Radiation was discovered in 1896 by French scientist Henri Becquerel. He discovered that uranium gave off a type of ray he called “nuclear radiation”. He also called this type of element “radioactive”. • Marie and Pierre Curie later discovered that other elements could also be radioactive, such as polonium and radium.

8. What causes radioactivity? • Radioactivity comes from the unstable nucleus of an atom. • Why? Repulsion between protons. When the “strong force” that holds the nuclear particles together is not strong enough, the nucleus disintegrates. • Unstable nucleus • Very large nucleus • Proton v.s. neutron ratio is not the magic number • the magic number: • For elements of Z≤20, p/n= 1

9. What are the three types of radiation? • Alpha (α) • Beta (β) • Gamma (γ)

10. Alpha (α) • Has a positive charge; no electrons • Same as a helium nucleus • 4 2 He2+ • 4 = mass # • 2 = 2 p+ • Charge is 2+ • Particles are blocked by paper

11. Beta (β) • Radiation deflected toward the positively charged plate • 0-1β = e- • Mass = 0 • Charge = -1 • no is converted to a p+ & an e- (gaining a 1+ charge) • Particles are blocked by foil & glass

12. Gamma (γ) • High energy radiation that has no mass or charge (light-like) • 00γ • Not completely blocked by lead or concrete • Not affected by electric or magnetic fields • Usually accompany alpha or beta radiation

13. Radioactive Decay • This is the process in which atomic nuclei emit particles or rays for the purpose of becoming more stable. • Parent nuclide: the atomic nuclide before decay • Daughter nuclide: the atomic nuclide after decay • Let’s look at the three types in more depth.

14. Alpha decay is limited to VERY large nuclei such as those in heavy metals.

17. Nuclear equation of Radioactive Decay • alpha production (a, He2+): helium nucleus • beta production (b, e): • gamma ray production (g):

18. Nuclear Equations for alpha particle Ex: 226 Ra 4He + 222 Rn 88 286 Mass # 226 – 4 = 222 Atomic # 88 – 2 = 86

19. Nuclear Equations for beta particle Ex: 14 C 0β + 14 N 6 -17 Mass # 14 – 0 = 14 Atomic # 6 – (-)1 = 7

20. Practice 1. 174 Lu  4 He + 71 2 2. 259 No  + 255 Fm 102 100 3. 208 Po  4 He + 84 2 4. 205 Hg  + 201 Pt 80 78 5. 267 Hs  4 He + 108 2 6. 183 Ta  + 179 Lu 73 2 71

21. Practice 1. 159 Tb  + 159 Dy 65 66 2. 244 Pu  0 β + 94 -1 3. 231 Pa  + 231 U 91 92 4. 193 Os  0 β + 76 -1 5. 265 Sg  + 265 Bh 106 107 6. 193 Ir  0 β + 77 -1

23. Homework • Please finish the practices in previous slides. • Page 898, question 33 a, b, c; 34 a, b, c; 35, 36