3/2003 Rev 1 I.2.5 – slide 1 of 21 Part I Review of Fundamentals Module 2Basic Physics and Mathematics Used in Radiation Protection Session 5Nuclear Stability and Radionuclides Module I.2.5 IAEA Post Graduate Educational Course Radiation Protection and Safe Use of Radiation Sources

3/2003 Rev 1 I.2.5 – slide 2 of 21 Introduction  Nuclear stability and unstable nuclei will be discussed  Students will learn about atomic structure, the line of stability, and radioactive or unstable nuclei

3/2003 Rev 1 I.2.5 – slide 3 of 21 Content  Nuclear stability  Unstable nuclei  Radionuclides

3/2003 Rev 1 I.2.5 – slide 4 of 21 Overview  The atom, nuclear stability, and unstable nuclei will be discussed  Some common radionuclides used in the nuclear industry will be discussed

3/2003 Rev 1 I.2.5 – slide 5 of 21 Ernest O. Rutherford postulated atomic nucleus in 1911 Pioneering Nuclear Physicists

3/2003 Rev 1 I.2.5 – slide 6 of 21 Niels Bohr, 1913 atomic model Pioneering Nuclear Physicists

3/2003 Rev 1 I.2.5 – slide 7 of 21 The Atom

3/2003 Rev 1 I.2.5 – slide 8 of 21 Isotopes The number of protons determines the element. Elements with the same number of protons but different numbers of neutrons are called isotopes. Some isotopes are radioactive.

3/2003 Rev 1 I.2.5 – slide 9 of 21 J. J. Thomson, discovered electron in 1897 Discovery of the Electron

3/2003 Rev 1 I.2.5 – slide 10 of 21 James Chadwick, Discovered neutron in 1932 Discovery of the Neutron

3/2003 Rev 1 I.2.5 – slide 11 of 21 Basic Nuclear Structure

3/2003 Rev 1 I.2.5 – slide 12 of 21 Periodic Table of Elements

3/2003 Rev 1 I.2.5 – slide 13 of 21 Nuclear Stability  A stable or non-radioactive nuclide is one whose atoms do not decay  If one plots the stable nuclei, an interesting pattern emerges (shown in next slide)  The graph in the next slide shows a plot of neutron number N vs atomic number Z for the stable nuclei

3/2003 Rev 1 I.2.5 – slide 14 of 21 N > Z The Line of Stability

3/2003 Rev 1 I.2.5 – slide 15 of 21 Nuclear Stability  For the heaviest stable nuclei, N is about 1.5 times Z  The presence of the extra neutrons overcomes the positively charged protons’ tendency to repel each other and disrupt the nucleus  The nucleus is held together by a poorly understood force, the Nuclear Force

3/2003 Rev 1 I.2.5 – slide 16 of 21  The nuclear force is an extremely short- range force  It acts over a maximum distance of about two proton diameters  The nuclear force is responsible for the binding energy that holds the nucleus together Nuclear Stability

3/2003 Rev 1 I.2.5 – slide 17 of 21  Nuclei which do not fall on the line of stability tend to be unstable or “radioactive”  They are called “radionuclides”  A few radionuclides do fall on the line of stability but their rate of decay is so slow that for all practical purposes they are stable Unstable Nuclei

3/2003 Rev 1 I.2.5 – slide 18 of 21  Radionuclides undergo a process called radioactive transformation or disintegration  In this process, the nucleus emits particles to adjust its neutron (N) to proton (Z) ratio  This change in the N to Z ratio tends to move the radionuclide toward the line of stability Unstable Nuclei

3/2003 Rev 1 I.2.5 – slide 19 of 21 Some Common Radionuclides  Naturally occurring 235 U and 238 U  60 Co, 137 Cs, 90 Sr found in nuclear power plants  192 Ir used in radiography  99m Tc used in nuclear medicine  131 I used in treatment of thyroid conditions

3/2003 Rev 1 I.2.5 – slide 20 of 21 Summary  Atomic structure was reviewed  Principles of nuclear stability were discussed  Unstable nuclei were discussed  Some common radionuclides were listed

3/2003 Rev 1 I.2.5 – slide 21 of 21 Where to Get More Information  Cember, H., Introduction to Health Physics, 3 rd Edition, McGraw-Hill, New York (2000)  Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8 th Edition, 1999 update), Wiley, New York (1999)  International Atomic Energy Agency, The Safe Use of Radiation Sources, Training Course Series No. 6, IAEA, Vienna (1995)