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Radioactivity. Some substances are radioactive . Their atoms release some of this energy as radiation. Radioactivity.

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Some substances are radioactive. Their atoms release some of this energy as radiation



Radiation in the environment and is caused by the radioactive in rocks, the air and our bodies, and also from cosmic rays from outer space we called it as “Background Radiation”.

Radiation detector

Radiation Detector

Gold Leaf electroscope

Geiger Muller Tube

Radiation detector1

Radiation Detector

Diffusion Cloud Chamber

Characteristics of and radiations

Characteristics of α, β, and γ Radiations

  • Ionizing Power

  • Penetrating Power

  • Deflection by Electric and Magnetic Fields

Ionizing power

Ionizing Power

Penetrating power

Penetrating Power

Deflection of and rays

Deflection of α, β, and γRays

Type of radiations

Type of Radiations

  • Alpha (α) particles

    > Helium Nucleus ( 42He)

    > Positive Charge

    > high mass

    > a few centimeters range in air

    > slight deflection in electric/magnetic fields.

    > strong ionization

    > can be stopped by thin paper

    > Pure source: Americium (Am-241)

Type of radiations1

Type of Radiations

  • Beta (β) particles

    > High-energy electron (0-1e)

    > Negative Charge

    > low mass

    > a few meters range in air

    > great deflection in electric/magnetic f.

    > weak ionization

    > can be stopped by aluminium (5mm)

    > Pure source: Strontium (Sr-90)

Type of radiations2

Type of Radiations

  • Gamma (γ) rays

    > High-energy electromagnetic radiation

    > un-charge

    > zero mass

    > a few hundred meters range in air

    > none deflection in electric/magnetic field.

    > very weak ionization

    > can be stopped by thick lead or concrete

    > source: Cobalt (Co-60) covered by aluminium

Radioactive decay

Radioactive Decay

  • After ejecting particles, a nucleus becomes the nucleus of a different element. It’s called radioactive decay.

  • If the new element is also unstable, the process of decay will continue until there are atoms with stable nuclei.

Radioactive decay1

Radioactive Decay


  • Alpha Decay.

Parent nuclide



Alpha particle

(helium nucleus)


Radioactive decay2

Radioactive Decay


  • Beta Decay.

Parent nuclide



Beta particle



Radioactive decay3

Radioactive Decay

  • Gamma Rays are usually given off during both Alpha decay and Beta decay.





Half life

Half Life

Half life1

Half Life


Plutonium-238 (plutonium oxide). The plutonium glows in the dark as a result of nuclear fission reactions which release enough energy to increase the metal's temperature to red-heat. The heat produced by plutonium has been used as an energy source on spacecraft.

Sample problems

Sample Problems

A radioactive source has a half-life of 10 minutes. What fraction is left in 1 hour?

Carbon-14 has a half-life of 5700 years. A 10 g sample of wood cut recently from a living tree has an activity of 160 counts/minute.

A piece of charcoal taken from a prehistoric campsite also weight 10 g but has an activity of 40 counts/minute. Estimate the age of the charcoal.

Sample problems1

Sample Problems

The ratio of the number of atoms of argon-40 to potassium-40 in a sample of radioactive rock is 1 : 3.

Assuming that there was no potassium in the rock originally and that argon-40 decays to potassium-40 with a half life of 1500 million years, estimate the age of the rock.

4. Radioactive Uranium-238 (U, proton number 92) decays to thorium (Th), emitting an alpha particle and gamma rays. Show this decay reaction as a nuclide equation

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