Monday, March 16, 2009


Atoms of the same element are identified by the same number of protons.

Nuclei that contain the same number of protons, but a different number of neutrons, are known as isotopes

The ratio of number of neutrons to the number of protons in a nucleus may indicate nuclear stability. Unstable isotopes undergo radioactive decay.

Those with 1:1 ratio are found to be stable. Nuclei having more protons than neutrons tend to be unstable.

Radioactive Decay

Nuclear radiation involves the atomic nucleus which has strong attractive nuclear force of interaction between protons but short-ranged (10-15 m) and is about zero at greater separation.

If there is an imbalance in these forces, the system will eventually shake off the excess and enter a more balanced state leading to the creation of a new element.

  • Too many protons:
Eject two protons and two neutrons as an alpha particle known as Alpha decay.
  • Too many neutrons:
Beta decay of a neutron to a proton with the ejection of an electron and a neutrino.
  • For excited nucleus:
Eject a gamma ray and settle into ground state. This spontaneous process called radioactive decay.


A radioactive nucleus that undergoes alpha emission emits a helium nucleus, 42He. The remaining nucleus has two fewer protons and two fewer neutrons: the atomic number declines by two and the mass number by four.BETA DECAY:

In nuclear physics, beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted. In the case of electron emission, it is referred to as "beta minus" (β−), while in the case of a positron emission as "beta plus" (β+).
(click her to learn more about beta decay)

Test your Logic

Suppose you were given three radioactive cookies, one is mixed with alpha particles, the second with beta and the third with gamma.

You are allowed to eat one, hold one and place one in your pocket.

Which cookie should be placed where so that you will receive the least radiation?
Analyze and note your explanation at the activity sheet of your microlesson.

Stability of Nuclides

Comment on the pattern according to your observation then answer these questions. post all of you answers here together with your name and section.
  1. What pattern of even or odd numbers do you see in the number of nucleons of stable nuclides?
  2. What pattern of even or odd numbers do you see in the number of nucleons of unstable nuclide?