This is a topic that is very broad, but I am going to take it step by step. First, let's get to know the name of the particles below.
⁴₂𑁛 ------- Alpha particle
⁴₂He ----helium particle use to represent Alpha particle
¹₁H---- Protium
²₁H----- Deuterium
³₁H----Tritium
²³⁴₉₀Th----. Thorium
⁰₋₁β ----- Beta particle
⁰₋₁e ------ Electron which is use to represent beta particle
¹₀n ---- Neutron
⁰₁U ------ Neutrino
⁰₊₁e ---- Positron
²³⁴₉₁Pa. ---- Protactinium
Radioactivity can be defined as a spontaneous emission of radiation by the disintegration or decay of an element. Such element is called radioactive element.
Question:What kind of elements undergo Radioactivity?
Answer: Unstable element
Question: why do they undergo Radioactivity?
Answer: for them to attain Stability.
Radioactivity can be classified into two. They are;
- Natural radioactivity
- Artificial radioactivity
Natural Radioactivity
This is the spontaneous disintegration of an element with the production of ionizing particles on its own. The decomposing element is called the parent nucleus while the resulting element is called daughter element. If the daughter element is not stable, there will be series of successive decay until stability is attain. This can be illustrated with the equations below.
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂𑁛
²³⁴₉₀Th →²³⁴₉₁Pa + ⁰₋₁e
Artificial Radioactivity
This is the type of radioactivity in which the nucleus of an element have to be bombarded with some particles before the emission of ionizing radiation can occur. Artificial radioactivity is a special type of radioactivity that involves both radioactive element and non- radioactive element.
For example, the bombardment of nitrogen atom with alpha particle will produce oxygen and protium while the bombardment of lithium with protium will produce two helium particles.
¹⁴₇N + ⁴₂𑁛 →¹⁷₈O + ¹₁H
⁷₃Li + ¹₁H → ⁴₂He + ⁴₂He
Types of ionizing Radiation
- Alpha particle (𑁛)
- Beta particle ( β)
- Gamma ray (ˠ)
Alpha particle & Decay
Alpha decay occur when alpha particles are given out during a radioactive decay. An alpha particle is represented as a helium nucleus having two protons and two neutrons. When a nucleus emit an alpha particle, it's atomic number and neutron number decreases by two while the mass number decreases by four. Examples are given below
²²⁶₈₈Ra →²²²₈₆Rn + ⁴₂He
¹²₆C → ⁸₄Be + ⁴₂He
Properties of Alpha particles
- It has a mass of about four times that of hydrogen atom.
- It has penetrating power.
- It has the highest ionizing power( ionizing power is the ability to make an atom to loose or gain electron)
- It is identify as helium particle i.e ⁴₂He
- They can be absorb by thin sheet of paper.
- It possesses a positive charge.
- It can be deflected by electric and magnetic field.
Beta Particle and Decay
This is observed when there is a transformation of a neutron into proton and vice versa. Beta particle are represented in form of electron. i.e ⁻¹₀e
When a nucleus undergo a beta decay, the neutron will decrease by one while the atomic number increases by one and the mass number remain the same.
¹⁴₆C →¹⁴₇N + ⁰₋₁e
²⁷₁₂Mg → ²⁷₁₃Al + ⁰₋₁e
Properties of beta particles
- They are fast moving electron similar to cathode ray
- They have the same mass and charge as an electron
- Their penetrating power is greater than alpha particles.
- Their ionizing power is lower than alpha particles
- They can be absorb by metallic foil
- They can be deflected by electrical and magnetic field.
Gamma Ray
Gamma ray are not particles but they are electromagnetic rays similar to visible light and X-rays but with very short wavelength. When a nucleus is in an excited state, it can decay to the ground state by the emission of gamma rays. This process is called gamma decay. In both alpha and beta decay, there are changes in atomic number and mass number and new element is form but in gamma decay, element does not change but the nucleus does from the excited state to ground state.
¹²⁵₅₂Te →¹²⁵₅₂Te + ˠ
²³⁶₉₂U → ²³⁶₉₂U + ˠ
Properties of gamma rays
- They have no charge
- They have no mass
- They travel through vacuum with the same velocity of light
- They have highest penetrating power.
- They have the lowest ionizing power.
- They can be absorbed by large lead block
- They can not be deflected by electric and magnetic field.
Nuclear Reaction
There are two types of Nuclear reactions, which are
- Nuclear Fission
- Nuclear Fusion
Lets take them one after the other.
Nuclear Fission
This can be defined as a process whereby a heavy nucleus decay or disintegrate to form 2-lighter nuclei of atoms of almost equal masses with the release of energy and radiations. Nuclear fission can occur either spontaneously or non spontaneously. A spontaneous nuclear fission can occur on its own while a non spontaneous nuclear fission usually involve particle bombardment. The particle usually use for the bombardment process is the neutron (¹₀n)
Question: why is neutron prefer for bombardment process?
Answer: This is because, it has no charge and it has an appreciable mass
The diagram above shows the disintingration of heavy nucleus into two lighter nuclei
Applications of Nuclear fission
- It is use in the production of atomic bomb
- It is use to produce nuclear energy in a nuclear reactor
Let's talk about Nuclear Reactor before we enter into Nuclear Fusion.
Nuclear Reactor
A nuclear reactor is also known as atomic pile. The generation of nuclear energy in a nuclear reactor is based on the process of nuclear Fission. This involves the fission of Uranium-235. The particle used to achieve this fission is the neutron. Below is an example to show the chain reaction.
Components of a Nuclear Reactor
- Uranium-235: This acts as a nuclear fuel because it is a fissionable material
- Moderator: These are used to slow down excess neutrons or the movement of fast moving neutrons. Examples of moderators are heavy water and graphite rod.
- Metallic absorber: These are used to absorb neutrons that are excess from a nuclear reactor inorder to stop the chain reaction when it is getting out of control.
Nuclear Fusion
These involves a combination of two lighter nuclei in order to form a heavy nucleus with the emission of energy and radiation. For Nuclear fusion to be achieve, sufficient heat energy must be supplied to the combination nuclei to overcome repulsive force. This is why nuclear Fusion is regarded as Thermonuclear Reaction.
The diagram shows the combination of two lighter nuclei forming a heavy nucleus
Applications of Nuclear Fusion
- It is use in the production of hydrogen bomb
- It is use by the sun to produce it's energy
Balancing of Nuclear Equation
In balancing nuclear Equations, the mass number and the atomic number of the reactant must be equal to the mass number and atomic number of the product. Let's see how it is done
- What are the values of X and Y in the given equation
²³⁴₉₀Th → ˣyPa + ⁰₋₁e
Answer
Let's take a look at the mass numbers
What do I add to 0 to get 234, the answer is 234 which means x = 234.
Look at the protons, what do i substract 1 from to get 90 the answer is 91, which means y= 91.
- ²³₁₁Na + X → ²⁰₉F + ⁴₂He What particle is X in the reaction above?
Answer
If you carry out the calculation well, X is neutron
- ¹⁴₇N + ⁴₂He → ¹⁷₈O + X.
In the equation above, the particle X is
(a) an α-particle (b) a β-particle (c) a proton (d) a neutron
Answer
If you carry out the calculation well, X is proton.
- During the nuclear reactions described by ²³⁵₉₂W → ²³⁵₉₃X → ²³¹₉₁Y, the particles emitted are respectively (a) α and α (b) β and β (c) α and β (d) β and α
Answer
The answer is d
Basic terms to know
- Artificial Transmutation:This is the transformation of one element to another during nuclear disintegration. It was first achieved by Lord Ernest Rutherford who succeeded in transmitting a Nitrogen isotope into an Oxygen isotope by bombarding the nitrogen isotope with alpha particles.
¹⁴₇N + ⁴₂He →¹⁷₈O + ¹₁H
- Binding Energy: This is the energy required to split the nucleons (proton or neutron) apart.
- Mass defects : This is the difference between the mass of the product and the mass of the reactants.
We shall be moving into another phase which is the calculation aspects.
Half life
This is the time taken for a radioactive element to decay to half of its original amount. What that statement means is that, if you have an element with original mass of 1000g, and after two yrs, it becomes 500g, another two yrs, it becomes 250g, another two yrs, it becomes 125g. It simply means that, the half life of that element is 2yrs.
Half life is represented as t1/2. The rate at which an element decays is called decay constant. It is represented as ⋋.
The relationship between half life and decay constant is that the shorter the half life, the higher the decay constant.
These are the formulae we use in solving questions on Radioactivity.
(1)
(2) when you are ask to find the remaining fraction, you use this
(3) when you are ask to find Decayed fraction, you use this
(4) when the question has to do with remaining amount and original amount.
(5) when you are asked to find Decayed amount
We are going to be solving questions using these formulae.
Questions
- A radioactive isotope has a decay constant of 10⁻⁵s⁻¹. Calculate its average life.
Solution
Average life means also half life.
- A radioactive substance has a half-life of 20 days. What fraction of the original radioactive nuclei will remain after 80days?
Solution
This question has to do with remaining fraction, t1/2 = 20 days, T = 80days, R.F =?
- A radioactive element has a half life of 4 days. The fraction that has decayed in 16 days is?
Solution
This question deals with decayed fraction.
t = 4days, T= 16days, D.F =?
- A piece of radioactive material contains 1000 atoms. If its half-life is 20 seconds, the time taken for 125 atoms to remain is?
Solution
This question has to do with remaining amount and original amount
Original Amount( O.A) = 1000 atoms, t= 20sec, Remaining amount(R.A) = 125 atoms, T= ?
- A radioisotope of halflife 5days decay for xdays. If the original amount of the radioactive material is 6.00g. Determine the value of x given that 5.25g of the radioisotope decayed
Solution
t=5days, T= xdays, Original amount (O.A) =6g, Decayed amount (D.A) = 5.25g
The count rate of a radioactive material is 800 count/min. If the half-life of the material is 4 days, what would be the count rate 16 days later?
Solution
Count rate is the number of decay per unit time. O.A= 800, t= 4days, T= 16days, R.A= ?
- The time it will take a certain radioactive material with a half-life of 50 days to reduce to 1/32 of its original number is
Solution
t= 50days, T = ?, R.A= 1/32 of O.A
Exercises
- A radioactive nucleus has a half-life of 20 years, starting with 100,000 particles, how many particles will be left exactly at the end of 40 years?
- If the fraction of the atoms of a radioactive material left after 120 years is 1/64, what is the half-life of the material?
- A certain radioactive element of initial mass 160g has a half life of 20 years. After a period of T years, only 5g of the element is left undecayed. The value of T is
- The radioisotope ²³⁵₉₂∪ decays by emitting two alpha particles, three beta particles and a gamma ray.What is the mass and atomic numbers of the resulting daughter element?
- A radioactive substance has a half-life of 20 days. What fraction of the original radioactive nuclei will remain after 80days?
- The particle that is responsible for nuclear fission in a nuclear reactor is (a) neutron (b) electron (c) proton (d) photon
- The particle emitted when ³⁹₁₉K decays to ³⁹₁₉K is (a) beta (b) alpha (c) gamma (d) electron
Solve the exercises and write your answers in the comment section below