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  Nucleus and Radioactivity, Chemistry tutorial

Introduction:

The nucleus is basically the centre of positive charge and mass in an atom. The number of positive charges in the nucleus of a neutral atom finds out the number of electrons which surround the nucleus. The arrangement of the electrons around the nucleus establishes the chemical properties of the element.

At present there is no theory which predicts the stability of the nucleus however a number of empirical observations recommend that the presence of neutrons account partially for nuclear stability. Apart from for the hydrogen atom, all the nuclei comprise neutrons. As the proton number increases, the neutron number as well increases. For heavy elements, the neutron number far goes beyond the proton number in the nucleus.

Example: 82Pb208 has 82 protons and 126 neutrons

The Nucleus:

The nucleus occupies an extremely small volume of the atom. According to Rutherford the nucleus is round 1/100,000 times the size of the atom. Apart from, for hydrogen the whole elements encompass more than one proton in their nuclei. From your acquaintance of elementary magnesium in Physics, we are familiar that like charges repel each other while unlike charges attract one other.

How then can particles of the similar or identical charge stay so close in the nucleus devoid of repelling? As illustrated in the staring, no theory predicts the nuclear stability. Empirical observations recommend that the neutrons are partly responsible for nuclear stability. Some of the examinations are as follows:

1) All the nuclei apart from hydrogen include neutrons.

2) As proton number increases neutron number as well increases and far exceeds the proton number for heavy elements.

3) For several elements some of the neutron-proton combinations are unstable.

4) Several neutron-proton combinations are more plentiful than others for the similar element.

Table: Naturally occurring isotopes

Element

Isotope

Natural abundance

 

Carbon

6C12

98.89

6C13

1.11

6C14

trace

 

Oxygen

8O16

99.758

8O17

0.038

8O18

0.204

Nuclear Reactions:

Nuclear reactions include changes in the composition of nuclei leading to the conversion of one element to the other. On contrast to the hypothesize of Dalton, an element is destroyed and a new one is formed, whenever a radioactive element such as uranium disintegrates.

Similar to in simple chemical reactions symbols are employed to summarize the nuclear reaction in an equation. A nuclear reaction equation should be balanced to account for all particles and charge.

Example: 92U238 → 90Th234 + 2He4

Uranium 238, the uranium isotope containing an atomic mass of 238 is radioactive. It breaks down emitting the particles of Thorium and Helium.

Radioactivity:

A few nuclei are unstable and will spontaneously emit radiations. This is termed as radioactivity and is an illustration of a nuclear reaction.

Very heavy metals having atomic number more than 83 are radioactive. A few isotopes of light elements are as well radioactive. A radioactive isotope is termed as a radioisotope. Illustrations of radioisotopes are:

92U238 and 6C14

Radioisotopes decay at dissimilar rates. The half-life is the measurement of the stability of a radioisotope.

Half life is the time it takes for half of the radioactive substance to decay. 6C14 and 92U238 have half lives of 5570 and 4.47 x 109 years correspondingly. They are extremely stable as compared to 11Na23 and 84P214 having half lives of 60 seconds and 101 microseconds correspondingly.

Some of the stable isotopes of elements can be made radioactive.

7N14 + 0n1 → 6C14 + 1P1

The above equation is a reaction which takes place instantly in the nature by the bombardment of cosmic neutrons upon nitrogen. This assists to keep 6C14 activity constant in the atmosphere.

Nuclear radiations:

The radioactive element in its decay emits radiations. Such radiations are mostly of three kinds. They are known alpha (α); beta (β) and (γ) rays. The properties of α, β and γ rays are summarized in the table shown below. α, β and γ radiations are detected whenever they pass via an electric or magnetic field.

Table: Alpha (α), Beta (β) and gamma (γ) radiations

Alpha (α)

Beta (β)

Gamma (γ)

Positively charged 

Negatively charged

No charge

They are helium nuclei 2He4

They are electrons -1β0

Electromagnetic radiation

Deflected towards -ve pole

Deflected towards +ve pole  

No effect of electric field

Low penetrating power

Higher penetrating power

Very high penetrating power

High ionizing power on gases 

Low ionizing power on gases

Very low ionizing power on gases

The decay of heavy radioisotopes is generally accompanied by emission of all the three kinds of radiations. The decay of light radio isotopes is generally accompanied via one or at most two of the three radiations.

Nuclear fusion:

This is a procedure in which two or more light nuclei join to form a heavier nucleus having a discharge of energy. Nuclear fusion reactions need very high temperatures. Due to very high temperatures in sun, fusion reactions are assumed to take place and are responsible for the very high thermal energy which comes from the sun.

1H2 + 1H2 → 2He4 + energy

The equation above is supposed to be one of the reactions going on in the sun. The energy from a fusion reaction initiates more reactions. If not controlled, can lead to bang.

Nuclear fission:

The Nuclear fission is a procedure in which the nucleus of a heavy element is split to two nuclei of almost equivalent mass by a release of energy and radiation.

92U235 + 0n1 → 92U236 → 54Xe140 + 38Sr93 + 3 0n1 energy

This fission procedure is initiated via the absorption of a neutron. The reaction discharges three neutrons that can initiate more fission reactions. This is an illustration of a chain reaction. If the chain reaction is not controlled the fission reaction can become volatile. The energy from fission reactions is not as high as in fusion and the reactions in fission don't need very high temperatures to initiate. There is fission reactors employed in producing electricity.

Other illustrations of nuclear transformation reactions:

Nuclear transformation means changing one element to the other by the reactions of atomic nuclei. Such reactions are numerous. Most of the isotopes of elements have been made by this method and employed in chemical, biological and medical researches.

7N14 + 2He4 → 8O17 + 1H1

13Al27 + 2He4 → 15P30 + 0H1

For heavy elements, neutron bombardment is more general as they are neutral and are not repelled through nuclei by the use of particle accelerators. A few heavy elements have been generated by the radioactive action of alpha particles, that is, Helium atom.

92U238 + 2He4 → 94Pu239 + 3 0n1

Radioactivity uses:

Radioactivity consists of a huge number of uses that comprise:

1) Treatment of cancer.

2) Controlling the thickness of paper, metals and plastics.

3) Controlling the filling of containers and packets.

4) Sterilizing hospital equipment and devices.

5) Source of energy as in fission.

6) Tracing movement of the substance in a procedure.

7) Radioactive dating example: carbon dating.

Hazards of Radioactivity:

Gamma radiation is employed to demolish cancerous cells. F-radiation as well destroys healthy cells as well and too much exposure to it can do more harm than good. The amount of damage depends on the energy and kind of radiation. The effect of radiation is as well cumulative and small doses over a long period of time will as well cause serious damage to biological systems. Radioactive waste is extremely dangerous and should be disposed properly to avoid essential exposure to its risks.

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