Physics 2 - Lecture 11: Nuclear Physics - Huynh Quang Linh

Nội dung text: Physics 2 - Lecture 11: Nuclear Physics - Huynh Quang Linh

1. NUCLEAR PHYSICS Tran Thi Ngoc Dung – Huynh Quang Linh – Physics A2 HCMUT 2016
2. NUCLEAR COMPONENTS Nucleus contains nucleons: protons and neutrons • Atomic number Z = number of protons • Neutron number N = number of neutrons • Mass number A = number of nucleons = Z + N • Each element has unique Z value • Isotopes of element have same Z, but different N and A values 1 2 3 1H, 1H,1H A Notion: Isotopes 16 17 18 Z X 8 O, 8 O, 8 O
3. NUCLEAR DENSITY • All nuclei have approximately the same density 2.3 1017 kg / m3 Volume of the nucleus: : 4 4 4 V R 3 (R A1/3 )3 R 3A. 3 3 o 3 o Mass density 27 M mpA 1.67 10 nucleus 2.3.1017 kg / m3 4 4 4 R3 R3 .A (1.2 10 15 )3 3 3 o 3
4. NUCLEAR SPINS • Protons and neutrons are also spin ½ particle. • The magnitude of Spin angular momentum S of a nucleon: 3 S  s(s 1)  1 (1 1)  2 2 4 1 S  • The z component is z 2 In addition to the spin angular momentum, there may be orbital angular momentum associated with their motions within the nucleus. The total angular momentum 퐽 of the nucleus is the vector sum of the individual spin and orbital angular momenta of all the nucleons.
5. Total angular momentum j=nuclear spin • When A is even, j is an integer; 0,1,2,3 • When A is odd, j is a half interger. ½, 3/2 • All nuclides for which both Z and N are even have J=0, which suggests that pairing of particles with opposite spin components may be an important consideration in nuclear structure. • The total nuclear angular momentum number j is usually called the nuclear spin
6. Spin magnetic moment  • The proton has a positive charge; its spin magnetic moment  and spin angular momentum 푆 are parallel. • The neutron has no charge, its spin magnetic moment  and spin angular momentum 푆 are opposite ( as for a negative charge distribution) • The magnetic moment of an entire nucleus is typically a few nuclear magnetons. • When a nucleus is placed in an external magnetic field , there is an interaction energy : 푈 = −. = −
7. Binding Energy • The mass of nucleus is less than the mass of total nucleons. • The mass defect: M=Zmp+(A-Z)mn-M Where : M: Mass of the nucleus Or A M ZMH Nmn Z M • Where MH: mass of Z protons and Z electrons combines as Z neutral of atoms 1 to balance 1H A with Z electrons included in Z M neutral atom.
8. Atomic mass, u No Element Symbol Z 1u=1.660.10-27 kg (1 u)c2 = 931.5 MeV 1. Neutron n 0 1.008 665 2. Hydrogen 1H 1 1.007 825 M 28 1.007825 34*1.008665 61.928349 0.585361u 2 EB M.c 0.585361u 931.5 MeV / u 545.3MeV E 545.3MeV  B 8.795MeV / nucleon A 62
9. The NUCLEAR FORCE The force that binds protons and neutrons together in the nucleus, despite the electrical repulsion of the protons is call nuclear force. It is an example of strong interaction. Some characteristics a) Nuclear force has short range, within 10^-15m. b) Nuclear force does not depend on charge: the binding n-n, p-p, p-n is the same. c) The nuclear force has saturation property. A nucleon cannot interact with all the other nucleon in the nucleus, but only with those few in its immediate vicinity d) The nuclear force depends on the spins of the nucleons. The nuclear force favors binding of pair of protons or neutrons with opposite spins and of pairs of pairs - pair of protons and a pair of neutrons, each pair having opposite spins.
10. Radioactivity • Unstable nuclei decay to more stable nuclei • Can emit 3 types of radiation in the process 4 particles: 2He nuclei  particles: e ore  rays: highenergy photons A positron (e+) is the antiparticle of the electron (e−) Fig. 29.5, p. 962
11. 2. ACTIVITY dN H N e t N H e t dt o o • ACTIVITY is the number of decay per unit time • Ho activity at time t=0. • The SI unit of activity is Bq (becquerel). 1Bq=1decay/s • Curi (Ci) : 1 Ci is equal to the activity of 1gram of radium 1Ci 3.7 1010 Bq
12. 1 a) T mean  ln 2 0.693  2.95 10 8 s 1 T1/ 2 272day 24h / day 3600s / h 1 7 Tmean 3.39 10 s 392days 2.95 10 8 b)H N H 2 10 6 3.7 1010 N 2.51 1012 nuclei  2.95 10 8 t 6 2.95 10 8 365 24 3600 c)H Hoe 2 10 e 0.788Ci
13. Beta()Decay • Involves conversion of proton to neutron or vice-versa • Involves the weak nuclear force • KE carried away by electron/antineutrino or positron/neutrino pair • Neutrinos: q = 0, m < 1 eV/c2, spin ½, very weak interaction with matter 1 1 A A 0 n 1p + e + ν Z X Z+1Y + e + ν 1 1 + A A + 1p 0 n + e + ν Z X Z 1Y + e + ν
14. Radioactive Carbon Dating 14 • Cosmic rays create14 12C Constant ratio of –12 C/ C (1.3×10 ) in atmosphere • Living organisms have same ratio • Dead organisms do not (no longer absorb C) 14 • T½ of C = 5730 yr • Measure decay rates, R ln RR) R Re t t 0 0 
15. Natural Radioactivity • Many radioactive elements occur in nature. For example, you are very slightly radioactive because of unstable nuclides such as carbon(C14) and potassium (K40) that are present throughout your body. • The decaying nucleus is usually called the parent nucleus; the resulting nucleus is the daughter nucleus. When a radioactive nucleus decays, the daughter nucleus may also be unstable. In this case a series of successive decays occurs until a stable configuration is reached. • Several such series are found in nature. The most abundant radioactive nuclide found on earth is the uranium isotope which undergoes a series of 14 decays, including eight emissions and six - emissions, terminating at a stable isotope of lead, 206 Pb.
16. Natural Radioactivity • Four radioactive series of naturally occurring radioactivity • Nuclear power plants use enriched uranium • Other series artificially produced
17. Beta Decay 228 0 228 88 Ra 1e 89Ac
18. Gamma Decay 240 240 0 94 Pu 94Pu 0
19. Reaction energy A B C D 2 Q (MA MB MC MD )c When Q is positive, the total mass decreases and the total kinetic energy increases. Such a reaction is called an exothermic reaction. When Qis negative, the mass increases and the kinetic energy decreases, and the reaction is called an endothermic. In an endothermic reaction the reaction cannot occur unless the initial kinetic energy in the center-of-mass reference frame is at least as great as |Q|. That is, there is a threshold energy, the minimum kinetic energy to make an endothermic reaction go. m KEmin = 1+ Q M
20. Fusion 2 3 4 1 1 H 1H 2 He 0n nuclear fusion is the process by which multiple like-charged atomic nuclei join together to form a heavier nucleus. It is accompanied by the release or absorption of energy.
21. Fission Bomb One class of nuclear weapon, a fission bomb is a fission reactor designed to liberate as much energy as possible as rapidly as possible A nuclear reactor is a device in which nuclear chain fission reactions are initiated, controlled, and sustained at a steady rate. Nuclear power plant