Radioactivity

Radioactivity

1. Radioactivity is the spontaneous and random emission of radioactive rays from unstable radioactive materials after which they become more stable.

2. The process is said to be spontaneous because it is not influenced by any physical factors such as temperature, pressure, time, etc.

3. A nucleus is unstable if it is too big. All nuclei with z > 83 or A> 209 are unstable.

4. The emission of radioactive rays is random means that

• Emission occurs at irregular intervals.
• Emission does not occur at the same means.

5. There are three different types of radioactive emissions.

• Alpha particle- a
• Beta particle- B
• Gamma ray-r

6. Table below shows the characteristics of alpha particle, beta particle, and gamma particle.

Characteristic	Alpha particle	Beta particle	Gamma ray
Nature	Positively charged helium nucleus, He	Negatively charged electron, e	Neutral electromagnet ray
In an electric field	Bends to the negative plate	Bends to the positive plate	Does not bend, showing that it is neutral.
In magnetic field	Bends a little showing that it has a big mass. Direction of the bend indicates that it is positively charged.	Bends a lot showing that it has a small mass. Direction of the bend indicates that it is negatively charged.	Does not bend showing that it is neutral.
Ionising power	Strongest	Intermediate	Weakest
Penetrating power	low	Intermediate	High
Stopped by	A thin sheet of paper	A few millimeters of aluminium	A few centimeters of lead or concrete
Range in air	A few centimeters	A few metres	A few hundred metres
Speed	1/20 X the speed of light, c	3%-99% of the speed of light, c	The speed of light,c

Understanding the Nucleus of an Atom

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The Composition of the Nucleus

1. Matter is made up of very small particles called atoms.

2. Each atom has a very small and very dense core known as the nucleus.

3. Most of the mass of the atom is contained in the nucleus.

4. The electrons move in orbits around the nucleus.

5. The diameter of the nucleus is about 100 000 times smaller than the diameter of the atom.

6. This means that there are lots of empty spaces within an atom.

7. The subatomic particles in a nucleus are called nucleons.

8. The two types of nucleons are protons and neutrons.

9. The proton is a positively charged particle. It carries a charge of +e, where e is equal to 1.6 × 10-19 C.

10. The neutron carries no charge. The neutrons has approximately the same mass as the proton.

11. The number of protons in the nucleus of an atom is known as the proton number, Z.

12. The total number of protons and neutrons in the nucleus of an atom is known as nucleon number, A or mass number.

13. Then number of neutrons, N = A – Z

Nuclide Notation

1. A nuclide is a type of atom with a particular nucleon number. This term is also used for a type of nucleus.

2. The nuclide notation of an atom gives the symbol of the elements, the proton number and the nucleon number of the atom.

Isotopes

1. Isotopes are atoms of the same elements with the same numbers of protons but different number of neutrons.

2. isotopes have the same proton number but different nucleon numbers.

3. All isotopes of an element have the same chemical properties because their electrons are arranged in exactly the same way.

4. Their physical properties such as densities, boiling points and melting points are different.

5. Some elements in nature such as oxygen,carbon, and bromine consist of a mixture of isotopes.

6. Some isotopes of an element are stable while some are unstable. The unstable isotopes or radioisotopes.

7. Radioisotopes will undergo spontaneous decay to emit radioactive rays such as alpha, beta and gamma rays. After radioactive decay, the proton number and nucleon number of the radioisotope may be changed.

Relationship between Energy, Voltage, Current and Time

1. The potential difference or voltage,V, across two points is defined as energy,E, dissipated or transferred by coulomb of charge,Q, that moves through the two points.

Therefore:

Potential difference = Electrical energy dissipated / Charge

V= E / Q

2. Current is the rate of charge flow. Therefore, the total charge flows through the two points is given as:

Q = It                   I = current,  t = time in second

3. Since the energy dissipated or transferred is given by:

E= VQ

Therefore, the relationship between E, V,I and t can be written as:

E = VIt

4. From Ohm’s law, V =IR, therefore,

E = IR × It
E = I²Rt

5. From I = V / R = > ; E = V