Summary of Unit 18:Atomic and Nuclear Physics

  • There are two parts of an atom. Its central part is called the nucleus which contains neutrons and protons called nucleons. The nucleus is positively charged and electrons revolve around it in nearly circular orbits.
  • The number of protons present inside a nucleus is called the charge number or the atomic number and is denoted by the letter Z.
  • The sum of neutrons and protons present in a nucleus is called its atomic mass number. It is denoted by the letter A.
  • The atoms of same element with same atomic number but different atomic mass number are called isotopes.
  • The elements whose atomic number is greater than 82 are unstable. The process of decaying such elements into daughter elements is called natural radioactivity and such elements are called radioactive elements.
  • Radioactivity is a random process which does not depend on space and time.
  • The time during which the atoms of a radioactive element are reduced to one half is called the half-life of that element.
  • Background radiations are caused by some radioactive elements present in rocks,soil and water.
  • A process in which nucleus of an unstable heavy element breaks into two nuclei of lighter elements with the emission of radiation is called nuclear transmutation.
  • The isotopes which emit radiations are called radioactive isotopes. They are used in medicine, agriculture and industry for a variety of purposes.
  • The age of a dead human, animal or tree can be estimated by comparing the activity of carbon-14 in the live and dead tree. The technique is called carbon dating.
  • A process in which a heavy nucleus breaks into two nearly equal parts with the release of large energy is called nuclear fission.
  • A process in which  two light nuclei diffuse to form a heavier nucleus with release of enormous amount of energy is called fusion reaction.

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