NUCLEAR ENERGY LEVELS CHAPTER-V

POINTS TO BE STUDY 5.1 Alpha decay- α disintegration energy 5.2 α particle spectra 5.3 Nuclear energy levels 5.4 Beta decay –Experimental study of β decay 5 .5 Continuous β ray spectrum 5.6 Pauli’s neutrino hypothesis 5.7 Nuclear energy levels from β decay

RADIOACTIVITY The phenomenon of spontaneous emission of highly penetrating radiations from radioactive substance is called “Radioactivity” The emitted radiations are α, β and γ rays

α- Decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or 'decays' into an atom with a mass number that is reduced by four and an atomic number that is reduced by two.

β- Decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta ray(fast energetic electron ), and a neutrino are emitted from an atomic nucleus.

α- Ray Spectra X X X X X X X X X X X X X X X X X X X X X X X X X X X X Magnetic Field Evacuated Chamber (C) To Pump X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X Photographic Plate (P) S

FINE STRUCTURE OF α- LINE 6.09 α5= 5.586 MeV 0.621 α4= 5.715 MeV α3=5.734 MeV γ α2= 5.879 MeV Energy in eV α1= 6.167 MeV 0.493 α0= 6.207 MeV γ 0.473 γ 0.328 γ 0.04 γ Ground State

LONG RANGE α- PARTICLE SPECTRUM ThC ( 83Bi212) β β ThC1 ( 84Po212) β β 1.793 MeV γ 1.772 M.eV γ 0.726 MeV γ 0 MeV Ground State α4 ( 10.738MeV) α3 ( 10.617MeV) α2 ( 9.671MeV) α1 ( 8.945 MeV) ThD ( 82Pb208) Ground State

β-Decay

1)β-Decay by emission of electron 0n1 1H1 + -1e0 + γ Neutron proton electron antineutrino 2) β-Decay by emission of positive electron. 1H1 0n1 + +1e0 + γ proton neutron positron neutrino K- electron capture P+ + e- + 0n1 zXA + -1e0 + z-1YA

β- Ray Spectra D A X X X X X X X X X X X X X X X X X X X X X Magnetic Field Evacuated Chamber (C) To Pump X X X X X X X X X X X X X X X X X X X X X D X X X X X X X X X X X X X X A X X X X X X X Photographic Plate (P) S

CONTINEOUS β- RAY SPECTRUM Tav = 1/3Tm Nmax = No N End Point Energy Tm T0 K.E

Pauli’s Neutrino Hypothesis According to Pauli, In each β-disintegration an additional particle is emitted along with β particle. It was assumed to be neutral to maintain conservation of charge. It has zero rest mass to maintain law of conservation of energy and linear momentum. It has given the name “neutrino”. This postulate is called Pauli’s neutrino hypothesis. Neutrinos are ‘fermions’ Spin equal to ½. They moves with velocity of light. n p+ + e- +γ i.e 0n1 1H1 + -1e0 + γ