RADIOACTIVITY

Henri Bequerel : discovered radioactivity in 1896

Bequerel = 1 disintegration per second (dps)

Madam Curie : isolated radium 226

Curie = the number of disintegrations per second of 1 gram of radium

         = 3.7 X 10¹⁰ dps

Half Life : the amount of time required to reduce the radioactivity to ½ its present value (radioactivity is equal to activity)

• Disintegration of radioactive atoms are random, independent events
• We cannot tell which atom will undergo decay
• Need a group to make predictions

The equation to find the activity after a certain amount of time is :

 

The activity factor is :  

The half life of radium is 1622 years : this means that after 1622 years , the activity (radioacvtivity) is reduced by ½ its present value and therefore. Its associated dose rate (intensity) is also reduced by the same amount.

REVIEW OF THE ATOM:

Atom : is made up of a nucleus (protons and neutrons) and electrons

Nucleus : is made up of protons and neutrons

• Protons have a positive charge

Neutrons have no charge

Electrons : orbit the nucleus and have a negative charge

• 2000 electrons are equal to the mass of 1 neutron

Isotopes : atoms with the same number of protons and a different numbers of neutrons

Isotones : atoms with the same number of neutrons and a different number of protons

Isobars : same number of nucleons but different number of protons

Isomers : atoms having the same number of protons and neutrons but different nuclear energy levels

Radioactive Decay:

• property of the nucleus of an atom
• it is an instability in the nucleus which is manifested by an emmision of energy and/or particles
• it is independent of temperature and pressure

Types of Radioactive Decay:

Alpha Decay : likelihood it will occur with higher atomic number materials

• Alpha Particle: the nucleus of a helium atom that has a charge of +2
• needs 2 protons and 2 neutrons to leave the nucleus thus leaving the original atom or element with 2 protons and 2 neutrons less than it started with.

Example:

We start with Oxygen with 8 protons and 8 Neutrons:

• these protons and neutrons are moving around at great speeds in he nucleus and if 2 protons can join with 2 neutrons they now are able to leave the nucleus of the Oxygen atom

We see after the Alpha Particle leaves the nucleus of the atom we are left with a Carbon Atom with 6 protons and 6 neutrons: