Radioactivity

Understanding Radioactivity: The structure of atom consists of a protons, neutrons, and electrons. Rutherford during its experiment verified that atoms are mainly empty space but they also contain a tiny positive nucleus. The nucleus contains protons (which are positive), neutrons which are neutral and negative charge electrons revolve around the nucleus.

Remember that the number of protons is fixed for an element but the number of neutrons is not fixed. Isotopes are versions of an element with the same number of protons but different numbers of neutrons. A good example is a carbon which has got three common isotopes. All carbon atoms have got six protons.

Isotopes 126C 136C 146C
Protons 6 6 6
Neutron 6 7 8

However,126C isotopes got six neutrons. 136C isotopes got seven neutrons and 146C isotopes got eight neutrons.

What is Radioactivity?

Now when somebody says, some atoms are radioactive and what that means is that they release radiation from their nucleus. When a radioactive atom releases radiation it decayed. This decay is a totally random process scientists cannot predict. When an atom will decay it’s totally random and scientists cannot do anything to make them decay faster or slower.

There are three types of radiation and we’re going to look at them now.

  • The first type of radiation is called an alpha particle. It consists of two protons joined with two neutrons. An alpha particle is having the same nuclear of a helium atom which also consists of two protons and two neutrons.
  • A beta particle is an electron produced in the nucleus and released.
  • Gamma radiation is a high-energy electromagnetic wave at there like x-rays but carrying, even more energy.Radioactivity

Radioactivity Definition

Radioactivity is the phenomenon of the spontaneous emission of certain high active radiation by radioactive substances. Some examples of radioactive substances are radium, thorium, plutonium etc.

Who Discovered Radioactivity?

It was discovered by French physicist Henri BecquerelA year later, in 1896, Marie Curie found that besides uranium and its compounds, thorium was another element which possessed the property of radioactivity.

Radioactivity Discovery

The discovery of radioactivity was purely accidental. It was discovered by French physicist Henri Becquerel. He was working on the phenomenon of fluorescence. Fluorescence is the ability for certain substances to transform incident ultraviolet radiation into visible light. He kept the collection of various minerals required for his studies.These remained untouched for a long period of time. The minerals were kept in a box which also contained several unopened boxes of photographic plates. Thes plates were wrapped in thick black paper. When Henri Becquerel will use one of the plates and developed them he found them badly formed as if they were exposed to sunlight. The other plates kept in the box were also damaged.

He performed a series of experiments. He used to light-tight boxes in which he arranged one of the minerals pitchblende (uranium ore) and a photographic plate in one box. The uranium ore and photographic plate were kept in contact with each other while in the other box they were separated by thin sheets of aluminum. The results of the experiment indicated that the photographic plates were affected due to the radiation emitted by the uranium all in both the boxes.

Radioactivity Units

The unit of radioactivity is curie (Ci). It is the quantity of any radioactive substance which has a decay rate of 3.7 x 1010  disintegrations per second.

1 milli curie (mCi) = 3.7 x 107 disintegrations per sec. 

1 micro curie (LC) = 3.7 x 1014” disintegrations per sec.

There is another unit called Rutherford (Rd) which is defined as the amount of a radioactive substance which undergoes 106disintegrations per second.

1 milli rutherford = 103 disintegrations per sec.

1 micro rutherford = 1 disintegration per sec.

Types of Radioactivity

It appears nothing is to happen with all these radioactive substances. They keep on emitting nuclear radiation it’s invisible. An easy way of detecting it is to use a Geiger muller tube attached to a counter. There are three different types of nuclear radiation:

  • Alpha Radiation.
  • Beta  Radiation.
  • Gamma Radiation.
Characterstic Alpha Beta Gamma
Symbol α β γ
Mass(amu.) 4 1/2000 0
Charge +2 -1 0
Speed Slow Fast Speed of Light.
Ionisation ability High Medium
Penetrating Power Low Meduim High.
Stopped By Paper Alminium Lead.

Natural Radioactivity

All heavy elements from bismuth through uranium and a few of lighter elements have naturally occurring isotopes which possess the property of radioactivity. These isotopes have unstable nuclei and attain stability through the phenomenon of radioactivity. The property of disintegration of a radioactive material is independent of temperature, pressure and other external conditions.

Radioactivity is a nuclear phenomenon, i.e., the kind of intensity of the radiation emitted by any radioactive substance is absolutely the same whether the element is present as such or in any one of its compounds. The various experiments confirmed that the phenomenon of radioactivity does not depend on the orbital electrons but depends only on the composition of nucleus .

Artificial Radioactivity

The phenomena by which even light elements are made radioactive by artificial or induce method is called as artificial radioactivity. OR

The process in which a stable isotope is converted into a radioactive element by artificial transmutation is called artificial radioactivity. This was discovered by Irene Curie and F. Joliot in 1934. Example of artificial Radioactive:

2713Al + 10n →  2311Na + 42He

Application & Uses of Radioactivity

Modern industry uses radio isotopes in a variety of ways to improve productivity and in some cases to gain information that cannot be obtained in any other way. Nuclear techniques are increasingly used in industry and environmental management. The rapid response of nuclear techniques results in reduced cost with increased product quality.

  • Radioactive sodium is used to detect a clot in the human body. A different isotope of sodium is injected into the limb and its flow rate in the body is studied.
  • Radioactive cobalt due to its gamma radiation is used to treat cancer and kill cancer cells
  • The functioning of thyroid can be studied by iodine isotope.
  • Sealed radioactive sources are used in industrial radiography gauging applications and mineral analysis.
  • A short-lived radioactive material is used in flow tracing and mixing measurements in a nuclear plant.
  • Gamma sterilization is used for medical supplies some bulk commodities and increasingly for food preservation.
  • Agriculture radiation is also used in agriculture to sterilize (male pupae) an insect that could damage crops. These males are usually released to mate with females which produce unfertilized eggs. This is effective pest control as it reduces the population of insects.
  • Another agricultural use of radioisotopes is the genetic modification of plants and animals. It is used to confer high resistance to pests and disease early maturing improved productivity high nutritional value climate resistance adaptation etc.

Effects of Radioactivity

Radioactive pollution is naturally occurring or artificially produced radioactive materials. Terrestrial radiations from natural Radio isotopes originate from the use of radioactive materials. These materials are used in the production of nuclear weapons nuclear fuel and electric power. The radioactive material used in atom bombs is very destructive the impact of radioactivity on man and environment.

  • Radioactive wastes cause pollution the high-level products of nuclear wastes remain in the environment for hundreds of years leakage and nuclear reactors also cause large-scale environmental pollution the leakage might lead to several deaths.
  • Radioactive rays possessing high-energy pollute air, water, and soil.
  • All organisms are affected by radioactive pollution prolonged and frequent exposure to radioactive substances can cause cancer and leukemia and induce mutations. The mutated genes can persist in human animal and plant populations.

Radioactivity Detector

This is the most important factor need to know. Radiations produce ionization in the gases through which they are passed. This effect is used for quantitative measurement of radioactivity. The radiations cause a number of molecules of the gas to lose electrons and pass into positive ions. The electrons immediately become attached to the neutral molecules, thus making them negative ions. 

The total ions of one sign are equal to the total ions of the other type. The rate of production of these ions is proportional to the intensity of radiation. The extent, to which a definite quantity of a gas is rendered a conductor by a radioactive substance, is a measure of the radioactive power of a radioactive substance. The apparatus used for this purpose is called electroscope.

Geiger-Muller counter is based on this effect. The ionization chamber consists of 90% argon and 10% ethyl alcohol vapor at 10 m.m. pressure. Due to ionization, a flow of current occurs, which is measured after amplification.

 

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