Nuclear Physics 243 NMT Dr. Abdo Mansour Assistant Professor of radiology E-mail : a_mansour@inaya.edu.sa

بسم الله الرحمن الرحيم Lecture No. 1 Introduction to Nuclear Physics

The Atom The word “atom” derives from the Greek word “atom” which means indivisible particle; an atom was the smallest component of matter. However, we now know that atoms are actually composed of subatomic particles: Protons and neutrons in the nucleus of the atom, and electrons orbiting that nucleus.

Atom

Atomic Structure

Inside atom

The Atom Nucleus

The total number of Protons and Neutrons in a nucleus p + n is the mass number , symbolized by A. The total number of Protons is called the atomic number and is symbolized by Z. The atomic number and the mass number of an element X are usually presented in the form

9.1 Natural Radioactivity Example Mass Number number of protons and neutrons 9.1 Natural Radioactivity atomic symbol boron Atomic Number number of protons

Radiation The transmission of energy can take the form of electromagnetic radiation (i.e., electromagnetic waves, non-ionizing). X-rays and γ-rays, are grouped together under the terms “electromagnetic radiation, ionizing” .

Radiation Structure If the smallest unit of an element is considered to be its atom, the photon is the smallest unit of electromagnetic radiation. Photon properties: It have no mass. It propagates in a straight line. It travels at the speed of light (300,000 km/s). It transfers energy to the medium via it passes through the medium.

The energy of the radiation decreases as it passes through a material, due to absorption and scattering .

Radioactivity

Radioactivity Process Radioactivity process means, the nucleus emit energetic particles or rays (α and β particles as well as γ ray).

Types of radioactivity 1- Natural radioactivity: Nuclear reactions occur spontaneously 2- Artificial radioactivity: The artificial radioactivity produced by particle bombardment the nucleus.

Isotopes of an atom have the same number of protons, but a different number of neutrons. Example: Carbon atom means, number of protons = number of neutrons (6 = 6) is carbon-12. * But carbon isotope means number of protons ≠ number of neutrons (6 ≠ 8) is carbon-14.

Three Isotopes of Carbon Each nucleus contains the same number of protons. Only the number of neutrons is different. With different numbers of neutrons the mass of each isotope is different. 9.1 Natural Radioactivity

Properties of emission radiations Radiation refers to particles or waves coming from the nucleus of the atom (radioisotope or radionuclide).

Alpha Particles Alpha particle (a) is 2 protons and 2 neutrons. Same as He nucleus (He2+) Slow moving, and stopped by small barriers, such as paper. 9.1 Natural Radioactivity

Alpha Decay 238 = 234 + 4 Mass number 92 = 90 + 2 Atomic number

Beta Particles Beta particles (b) is fast-moving electron, Emitted from the nucleus as a neutron is converted to a proton. Higher speed particles, more penetrating than alpha particles. Symbolized by: 9.1 Natural Radioactivity

Beta Decay Upon decomposition, isotope of nitrogen-16 produces oxygen-16 and a beta particle. In beta decay, one neutron in nitrogen-16 is converted to a proton and the electron, the beta particle is released.

Gamma Rays Gamma rays (g) - pure energy or electromagnetic radiation. High energy. The most penetrating form of radiation Symbol is 9.1 Natural Radioactivity g

Gamma Production Gamma radiation occurs to increase the stability of an isotope. The atomic mass and number do not change. Usually gamma rays are emitted along with alpha or beta particles.

In General The penetrating power of the radiation determines the ionizing damage that can be caused. Alpha particle < beta particle < gamma rays. 9.1 Natural Radioactivity

Alpha particles are easy to stop, gamma rays are hard to stop.

Half-Life Half-life (t1/2) is the time required for a given substance to reach half quantity (half initial value). Each radioactive isotope has its own half-life. Ranges from a fraction of a second to a billion years. 9.3 Properties of Radioisotopes

Half-Lives of Selected Radioisotopes 9.3 Properties of Radioisotopes

Decay Curve for the Medically Useful Radioisotope Tc-99m

Units of Radiation Measurement The Curie is the amount of radioactive material that produces 3.7 x 1010 atomic disintegrations per second. The Roentgen is used for very high energy ionizing radiation only. The Rad is used for radiation absorbed dose. 9.8 Measurement of Radiation

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