Fra Angelica

Fra Angelico, The Virgin of Humility

Fra Angelico, The Virgin of Humility

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Radioactive Decay

Radioactive isotopes of elements have unstable arrangement of neutrons and protons in their nuclei. To become more stable, they emit alpha or beta particles. But this changes the number of protons and neutrons in the nucleus resulting in the formation of a new element. This process  is called radioactive decay.

The original nucleus is called the parent nucleus. The newly formed nucleus is called the daughter nucleus. The daughter nucleus and any other particles emitted are called the decay products.


Alpha decay:

After alpha decay, a new element is formed whose atomic number is 2 less  and mass number is 4 less than before.

For example, Radium-226 (atomic number 88) decays by alpha emission. The mass number drops to 222 and atomic number becomes 86. The new element formed is Radon-222.



Beta decay:

There are 2 kinds of beta decay – beta‾ decay and beta+ decay.


In Beta‾decay, a neutron  changes into a proton, an electron and an antineutrino (an uncharged, massless particle like the electron). The new element formed has an atomic number 1 more than before and the mass number remains unchanged.



In Beta+decay, a proton changes to a neutron, a positron and a neutrino. The new element formed has atomic number 1 less than before and the mass number remains unchanged.


Gamma emission:

The emission of alpha or beta particle from the nucleus leaves the protons and neutrons in an excited state. So as they rearrange to become more stable, they lose energy. This is emitted as a burst of gamma radiation.



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Sources of Nuclear radiation


Nuclear radiation can damage or destroy living cells or make cells grow abnormally causing cancer.

The most dangerous is radiation caused by radioactive materials absorbed by the body. Radioactive gas and dust may be taken into the body along with air, food or drink. Once absorbed, they are difficult to remove and cause damage to the cells. Inside the body, alpha radiation is the most dangerous because it is highly ionising.

There is lesser risk from radioactive sources outside the body. The intensity of the radiation decreases with distance from the source. Outside the body, beta and gamma radiations are more harmful as they can penetrate internal organs, while alpha particles can be stopped by the skin.


Sources of Nuclear radiation:


Background radiation:

There is a small amount of radiation around us all the time that comes from natural sources like soil, rocks, air,building materials, food and drink, space.

The biggest single source of natural background radiation is from a radioactive gas called radon which seeps out of rocks.


Artificial radiation:

The biggest source of artificial radiation if from medical X-rays. A small portion comes from radioactive waste from nuclear power stations and radioactive fallout from nuclear weapons testing.


Detecting radiation:

A Geiger-Muller tube is used to detect radiation.



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Nuclear Radiation


Henry Becquerel discovered radioactivity accidentally in 1896.


Nuclear radiation:

Some elements contain atoms with unstable nuclei. With time, the unstable nucleus disintegrates. While doing so, it shoots out a tiny particle and sometimes wave energy as well. Since the particles and the waves radiate from the nucleus, it is called nuclear radiation.


Radioactive isotopes:

These are particular isotopes of an element whose atoms have different number of neutrons in the nucleus.


List of radioactive isotopes:


Three main types of nuclear radiation:

Alpha particles (α) , Beta particles (β) and Gamma rays (γ)


Properties of alpha, beta and gamma radiation:






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m’s notes on nutrition











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