1. Nuclear Physics An Introduction

2. What does it mean when something is “Radioactive”? Atomic nuclei that emit particles and energy are said to be radioactive As this material emits particles, it is “Decaying” Atomic nuclei decay to become more stable

3. History of Radioactivity 1896 - First observed by Henri Becquerel while he was working with Uranium 1909 – Ernest Rutherford identified this radiation as Helium-4 nuclei.

4. Applications of Nuclear Radiation Medical – Radiation treatments – Diagnostic Imaging Military – Nuclear powered submarines – Nuclear weapons Industrial – Nuclear Power Plants

5. TYPES OF RADIATION

6. Alpha Decay (α) Alpha decay happens when an atom emits an “alpha particle” from their nucleus Alpha particles are helium nuclei ( ) α particles are made up of 2 protons and two neutrons. mass number = 4 atomic number = 2 Only occurs in nuclei with at least 106 nucleons

7. Alpha Decay (α) Upon emission of an alpha particle, mass # is reduced by 4 and atomic # reduced by 2, so new element formed. For Example: Uranium-238 emits α particles and as a result decays into Thorium-234 since atoms are identified by their atomic number (number of protons) and an alpha particle carries 2 of those protons away from the nucleus.

8. Beta Decay (β) Beta decay is considered to be an electron ejected from the nucleus. – WAIT!! Only Protons & Neutrons are in the nucleus! So how can a nucleus emit an electron??? Apparently… a neutron can change to a proton (and must lose a negative charge to go from “neutral” to “positive”) In other words the mass number is remains constant while the atomic number is increased by 1.

9. When a neutron “decays” it breaks into a … β particle (mass# = 0, atomic# = -1) which is ejected from the nucleus, a proton (mass#=1, atomic#=1) which stays in the nucleus and an antineutrino.

10. Beta Decay (β) Example: Thorium-234 undergoes a beta decay (neutron decay) to transmutate into Protactinium. An electron and an antineutrino are emitted in the process.

11. Positron Emission Another kind of β decay A proton changes to a neutron A positively charged electron (positron) is emitted PET scans are used in diagnostic imaging – Positron Emission Tomography

12. Gamma Decay (γ) Gamma rays are high-energy photons emitted by the nucleus – Photons are “particles” of electromagnetic energy A redistribution of energy with the nucleus occurs and gamma rays are emitted from the nucleus Mass # and Atomic # remain the same after gamma decay.

13. NUCLEAR REACTIONS

14. Fission The process of splitting the nucleus of an atom into two separate atoms. Energy is released during this reaction if the starting atom is larger than lead. The total mass decreases during the reaction leading to the idea that mass has been converted into energy.

15. A Fission Reaction

16. Fission in a Nuclear Reactor Uranium fuel rods are put into a reactor core, where they undergo a chain reaction. The energy released during the fission process is in the form of heat that is used to heat water to create steam which can then be used to turn a turbine and create electricity.

17. A Chain Reaction

18. Fusion The process of combining 2 atomic nuclei into 1 new larger element. Process that fuels our sun and all of the stars Energy is released during the process in the form of light and heat. Mass is not conserved during the Nuclear Fusion leading to the belief that mass is converted to energy during the process.

19. A Fusion Reaction

20. Fusion in our Sun The Sun converts approximately 700 million tons of Hydrogen into approximately 695 million tons of Helium each second through Nuclear Fusion. The missing 5 million tons per second is converted into energy.