The Nucleus.

Strong nuclear force holds neutrons and protons together to form a nucleus

Review of Atomic Terms •

Nucleons – particles found in the nucleus of an atom – neutrons and protons

  • Atomic Number (Z) – number of protons in the nucleus
  • Mass Number (A) – sum of the number of protons and neutrons
  • Isotopes – atoms with identical atomic numbers but different mass numbers
  • Nuclide – each unique atom.

KEYNOTE: Each Isotope has its own characteristic half-life. The rate of decay for an isotope is constant. It is unaffected by pressure, Temperature, Magnetic and Electric field, Chemical Reaction…

Radius Of the Nucleus.

Image result for radius of a nucleus

  Where A is the Atomic Mass, Fm is femtometer, it stands for 10 raised to the power of -15

The diameter of a Nucleus is D = 2r


Radioactivity was discovered in 1896 by the French physicist, Henri Becquerel working in Paris. In 1896, Henri Becquerel discovered, almost by accident, that uranium can blacken a photographic plate, even in the dark.

Radioactivity is the process by which nuclei emit particles and rays These penetrating particles and rays are called radiation.

Radioactivity is a phenomenon that occurs naturally in a number of substances. Atoms of the substance spontaneously emit invisible but energetic radiations, which can penetrate materials that are opaque to visible light. The effects of these radiations can be harmful to live cells but, when used in the right way, they have a wide range of beneficial applications, particularly in medicine.

Unstable isotopes can become stable by releasing different types of particles.

  • This process is called radioactive decay and the elements which undergo this process are called radioisotopes/radionuclides.

Therefore, Radioactive decay is a process by which the nuclei of a nuclide emit α, β or γ rays. A few naturally occurring isotopes and all of the man-made isotopes are unstable.

Uranium emits very energetic radiation – it is radioactive.


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