Nuclear Chemistry: What is Nuclear Chemistry?

What is Nuclear Chemistry? Nuclear Chemistry is the chemistry and reactions involving the nucleus of an atom.

Nuclear reactions tend to release a lot of energy than normal chemical reactions. Nuclear reactions involve splitting the nucleus of a heavy atom(nuclear fission), coming together of smaller nuclei(nuclear fusion), or even changing the protons in a nucleus(artificial transmutation0.  

What is the difference between Nuclear reactions and Chemical Reactions?

A chemical reaction is a reaction involving electrons while nuclear reactions involve protons and neutrons.

When we talk about nuclear reactions, we talk about reactions that involve changes in the number of protons or neutrons.

Recall that there are sub-particles in an atom, the electrons that stay in the orbit and the protons and neutrons which stay in the nucleus.

The protons and neutrons are collectively called the nucleons or mass numbers.

What is a Nuclear reaction?

A nuclear reaction is a reaction in which the nucleus (protons and neutrons) is involved.

Difference between nuclear reactions and chemical reactions

Nuclear Reactions	Chemical Reactions
Involves protons and neutrons	Involves electrons only
A large amount of energy is involves	Little energy involved
Temperature does not affect the rate of nuclear reactions	The rate of chemical reactions is temperature-dependent

Examples of nuclear reactions

I will group the different nuclear reactions into four categories;

1. Natural radioactivity
2. Artificial transmutation
3. Nuclear fission
4. Nuclear fusion

Natural Radioactivity (Radioactive disintegration)

Natural radioactivity or radioactivity is the spontaneous disintegration of elements by the emission of radiations.

There are three basic radiations involved in radioactivity; alpha emission, beta emission, and gamma emission/

Radioactivity is an example of a spontaneous reaction though it is a nuclear reaction and any element that exhibits radioactivity is called a radioactive element.

Radiations can be captured and detected with instruments such as Geiger Muller counter, Scintillation Counter, Diffusion Cloud Chamber.

When a radioactive element disintegrates spontaneously or decays, there is always a change in the nucleus and heat is equally involved in the reaction.

What is radioisotope?

A radioisotope is an isotope of an element that is reduced in mass by the emission of radiation and energy i.e radioactive.

For example, carbon has three isotopes  ¹²C, ¹³C, and ¹⁴C but Carbon -14 is radioactive so it is a radioisotope.

The rate of decay or disintegrations of the radioisotope or radioactive element depends on the nature of the radioactive element. Different elements have different rates of disintegrations which is directly proportional to the half-life of the elements.

Analysis of the types of radiations

	Alpha decay(emission)	Beta decay (emission)	Gamma decay(emission)
Nature	Helium nucleus	Electrons	Electromagnetic radiation
Electrical charge	+2	-1	Nil
Relative Penetration	1	100	10000
Absorber /Stopper	Thin Paper	Metal Paper	Lead Block Suit
Velocity	About 1/20 speed of light	About 3-99% speed of light	Exactly the speed of light

Hint: Alpha particles can be stopped by thin paper.

Beta particles can be stopped or absorbed by metal.

Gamma rays can be stopped or absorbed using lead or depleted uranium materials.

Examples of radioactive reactions

Alpha decay is represented using  Helium particle   ₂⁴He  or ₂⁴α

Beta emission is represented using electron particle   _-1⁰e^– or _-1⁰β

Gamma emission is represented using ₀⁰γ

Dangers of Radiations

Alpha radiations are heavy and thus do not travel very fast and equally not very penetrating however through a cut can enter humans and these can destroy tissues in our body.

Beta radiations or emissions travel equally fast and can cause skin burns and also when swallowed or inhaled.

Gamma rays can penetrate even bones and teeth and if unhindered or stooped cause cancer, gene mutation and kill living cells.

Radioactive reactions are examples of first-order reactions and first-order reactions have a model formula for the calculations.

Examples of first-order calculations

Examples of Natural Radioactivity equations

 Alpha decay emission

   _B^AX à   _(B-2) ^(A-4)Y  + ₂⁴He

Examples of Alpha decay reactions

Example 1

If Uranium atoms undergo alpha decay to yield Thorium then the equation will be written as this;

 ₉₂²³⁵U – ₂⁴He  à ₉₀²³⁴Th  

This can be written as

    ₉₂²³⁵U à ₉₀²³⁴Th + ₂⁴He

Example 2

Thorium undergoes an alpha decay to yield Radium.

₉₀²³⁴Th – ₂⁴He à ₈₈²³⁰Ra

Rewritten

₉₀²³⁴Th à ₈₈²³⁰Ra + ₂⁴He

Beta decay emissions (Beta radiations)

  _B^AX à   _(B+1) ^(A)Y  + _-1⁰e^–

Examples of Beta emissions

Example 1

Thorium undergoes beta emission to form Protactinium as shown below:

₉₀²³⁴Th – ₁⁰e^– à   ₉₁²³⁴Pa

This could be rewritten as

₉₀²³⁴Th à    ₉₁²³⁴Pa + ₁⁰e^–

Example 2

Lead undergoes beta emission to form Bismuth as shown below;

  ₈₂²¹⁴Pb – _-1⁰e^– à  ₈₃²¹⁴Bi

This is rewritten as

₈₂²¹⁴Pb   à ₈₃²¹⁴Bi + _-1⁰e^–

Beta emissions

A beta emission neither accompanies the other radiations and does nor really affects the nucleus of the atom.

Rate and Half-life of radioactive elements

The rate of radioactive elements is independent of temperature and radioactive elements actually vary at different rates.

The rate of radioactive elements depends on how long it takes half the nucleus of the element to disintegrate spontaneously or decay.

The truth is that different radioactive elements have different half-lives, again the rate at which a radioactive element will decay solely depends on the half-life.

Half-life of a radioactive element is defined as the time taken for half of the total number of atoms in a given sample of an element to decay.

The formula involving Half life and Decay constant

Half life of a radioactive element can be calculated using   the formula stated below;

    t_½   = In2/K

    In (A₀/A_t) = Kt

Where     

       t_½  = half life of the radioactive element

         A₀ = original amount of the element

         A_t = Amount remaining after some time

          t =time of reference

          K = Decay constant

 Examples of calculations in Radioactivity

Example 1

If a radioactive element Z has a half life of 30 seconds. What percent of the radioactive element will remain after 90 seconds?

Solution

This is very simple to solve, all you need to do is to relate the half life with the percent.

Hint: Half life is time taken for half the mass of the nucleus to decompose.

100%  —-30s—— 50%

50%    —-30s—— 25%

25%    —-30s——12.5%

 When you add up, you will get 90s and 12.5%  will remain.

Example 2

Protactinium has half life of 1.18 minutes, what mass will remain after 400g of he radioactive has undergone decay for 4.8 minutes.

Solution

To solve this one, no need to use the formula. We have a half life which is 1.18 minutes.

400g  —–1.18 minutes——200g

200g —–1.18 minutes ——100g

100g —–1.18 minutes ——-50g

50g  ——1.18 minutes ——-25g

This will add up to 4.72 seconds, we will stop here because if you add another half life it will be more than the required time which is 4.8 seconds.

So the remaining mass is 25 grams after 4.72 seconds.

Example 3

The half life of Polonium- 214 is 1.6 x 10^-4 seconds. How long will it take 125g of the radioactive element to disintegrate to 25g?

Solution

First let’s get the decay constant

   t_1/2 = in2/K

    t_1/2 = 0.693 /K

    t_1/2 = 0.693 /1.6 X 10^-4

    K = 4331.25s^-1

   In(A_o/A_t) =Kt

    In(125/25) =Kt

    In(125/25) =433.25t

   t = 1.6094/4331.25

    t = 3.7158 x 10^-4s

Example 4

What is the amount remaining if 235g of Bismuth disintegrates for 1 hour with half life of 19.7 minutes?

Solution

First, we still need to get the decay constant

First, we still need to get the decay constant

t_1/2 = in2/K

t_1/2 = 0.693 /K

K = 0.693 /t_1/2

Change the time to seconds

1 minute = 60 seconds

19.7 minutes = 19.7 x 60 seconds

 1182 seconds

K = 0.693/1182

K=  0.00059S^-1

What amount will remain after one hour, it means after 3600 seconds.

Because 1 hour = 60 minutes

              1 minute = 60 seconds

In (A₀/A_t) = Kt

A₀/A_t = e^{0.00059 x 1182}

A₀/A_t = 2.190

    235/2.190 = A_t

    A_t = 107.3g

Artificial transmutation

This is the process of converting an isotope of an element to another isotope of an element by the bombardment of the element with radiations.

These radiations could be alpha, neutron, deuterons, and protons.

The artificial transmutation was first performed by Lord Rutherford when he bombarded nitrogen isotope to oxygen isotope.

Examples of Artificial Transmutation

Changing an element to a different element using neutron bombardment

₇¹⁴N + ₀¹n –> ₆¹⁴C + ₁¹P

Changing an element to a different element using Helium bombardment

₇¹⁴N + ₂⁴He –> ₈¹⁷O + ₁¹P

Changing an isotope of an element to a different isotope using neutron bombardment

₂₇⁵⁹Co + ₀¹He –> ₂₇⁶⁰Co

Nuclear Fission

This is the process in which the nucleus of a heavy element is split into two nuclei of nearly equal mass with a release of energy and radiation.

Examples of Nuclear Fission

₉₂²³⁵U + ₀¹n –> ₅₆¹⁴¹Ba + ₃₆⁹²Kr + 3 ₀¹n

Nuclear Fusion

This is the process by which two or more light nuclei fuse together to form a heavier nucleus with a release o energy or radiation.

Examples of Nuclear Fusion

₁²D  +  ₁³T –>  ₂⁴He +  ₀¹n + energy

Differences between Nuclear Fission and Nuclear Fusion

Nuclear Fusion	Nuclear Fission
This is coming together of smaller nuclei	This is the splitting of the nucleus
Energy released	Greater energy released
Nuclei of two atoms combine at high temperatures	Splitting of nucleus takes place at a temperature not as high as fusion

Uses of radioactivity

1. Americium is used in smoke detectors

2. Cobalt 60 used in Cancer treatment

3. Iodine 131 used in the treatment of thyroid gland

4. Carbon 14 is used in the dating and estimation of the age of material during an archeological excavation.

5. Nickel 63 used to detect explosives and voltage/current surge protection

6. Iridium 192 used to test the integrity of pipeline welds and boils

7. Cobalt 60 is used in checking faults in welds and castings

In conclusion, Nuclear chemistry is a branch of chemistry that studies the (alterations both splitting and merging ) made in the nucleus of an atom as well as the applications of the energy released during these reactions.