radiation

Introduction

Ever wondered why sometimes just by observing the oven, without even touching it, we can tell whether it is warm or cold? Ever felt the heat transfer from sun and fire. We know that the space between Earth and Sun is so large and empty that there is no way of heat transfer by conduction or convection, but still, heat from the sun reaches the earth. These all are examples of heat transfer by radiation. It means the hot body emits the radiation/ electromagnetic waves which are absorbed by our skin, so in these cases, a medium for transfer is required. These electromagnetic waves have got different names depending upon their wavelength and frequencies. In this topic, we will study in detail the concept of radiations, their types, their frequencies, their wavelength, their applications and limitations.

All objects absorb or emit electromagnetic radiation. The amount of heat transfer by radiation largely depends upon the colour of the emitting or absorbing body. For example, people who live in extremely hot temperatures rarely prefer to wear black outfits, as dark colour absorbs more radiation. At the same time, a white colour reflects radiation just like a mirror does. The grey coloured objects have the uniform ability to absorb all parts of the electromagnetic spectrum. For instance, consider the infrared radiations that are more easily absorbed by our skin, making our skin sensitive to it. The amount/ rate of heat transfer by radiation can be determined by the Stefan-Boltzmann law of radiation. It is given by;

Qt = σeAT⁴

where σ is the Stefan-Boltzmann constant. it has a value of  5.67 × 10-8 J/s.m².K⁴,

T is the absolute temperature given in Kelvin

A is the surface area of the object and

e is the emissivity of an object ( it defines how well an object can radiate).

Types of Radiation 

The radiation travels from a medium before getting absorbed. The radiations can be classified basically into two types that are;

• the ionising radiation and 
• the non-ionising radiations

Ionising radiations:

The ionising radiations are named so because they have enough power to remove the tightly bound electrons from the outer shells of the atoms leading to charge generation or ionisations of the atom. The radiations that have high frequency and short wavelengths have more energy than the radiations having low frequencies and high wavelengths. The ionising radiations are generally harmful to us as they can damage the DNA and denature the proteins.

Types of Ionising radiations

The ionising radiations can take a few forms, which are ;

• Alpha radiations: These radiations are formed when an atom undergoes radioactive decomposition, giving rise to a particle known as an alpha particle. That consists of two protons and two neutrons (a nucleus of 4 helium atoms). Due to their property of charge and masses, the alpha particle strongly interacts with matter. They can only travel up to a few centimetres in the air. Alpha particles cannot penetrate the outer layer of dead skin cells, but they can do so if they are mistakenly ingested or inhaled by food or air. 
• Beta radiation: Beta radiation, after being emitted from an atom, takes the form of an electron or a positron ( a type of particle having the same size and mass as the electron but having a positive charge on it). As it has a smaller mass, it can easily travel high in the air up to a few metres and can easily be stopped by a thick piece of paper or plastic. It can penetrate skin cells up to a few centimetres.
• Gamma radiations: Unlike beta radiations or alpha radiations, the gamma rays do not have any particles. They consist of a photon of energy that is emitted from an unstable nucleus. They have no mass or charge and can travel more in air, losing up to half of their energy for every 500 feet. They can be stopped by thick or denser material having high atomic number molecules such as lead or depleted uranium.  
• X rays: These X-ray radiations are somehow similar to the gamma rays; the basic difference originates from their origin that occurs by an electron cloud. This is a cause of change in energy of electrons moving from high energy to lower energy leading to the release of excess energy.
• Neutron radiation:  These consist of a free neutron emitted as a result of induced nuclear fission. They can travel up to hundreds or thousands of metres high in the air. They can be stopped by Hydrogen rich materials like water or concrete. As they have no charge, they are commonly indirectly ionising, i.e., they are absorbed by a stable material, making it unstable and hence emitting or ionising radiation of another type. Neutrons are the only radiations that can turn other materials radioactive.

Non-ionising radiations:

This radiation does not cause ionisation. They produce heat which can cause burns. Their types are as follows;

• Ultraviolet radiations: The most practical source of UV rays is the sun.
• Visible light: This type of radiation can even be seen by the human eye. The longest wavelength is for the red light, and the shortest wavelength is for the violet light.
• Black body radiations – Radiations emitted by black bodies. These emissions consist of all sorts of wavelengths.
• Radio waves and microwaves: The microwaves that we use in our homes provide the right temperature for the cooking of food.
• Infrared radiations: They are used in emergency signals as they are visible from a wide range of distances.

Types of Nuclear Radiation 

Nuclear chemistry deals with the study of the chemical and physical properties of elements that are influenced by changes in the atomic structure of the nucleus. It is often termed Radiochemistry. Rutherford, in 1902, sorted out 3 types of radioactive radiations by passing them between two oppositely charged plates.

• The radiations that bent towards the positive plate carried the negatively charged particles and were known as Beta rays.
• The radiation that bends towards the negative plate carries the positive particles and  are called alpha rays.
• The radiations that did not bend at all carried neutral charged particles known as the gamma rays.

The nuclear reactions result in the transformation of one element into another. Due to this property, they are highly used in Nuclear power plants to gather nuclear energy. The three types of nuclear radiation are primarily:

• Alpha radiation: It can be defined as the emission part of alpha particles from the nucleus of an atom. When an atom releases an alpha particle, its atomic mass decreases by 4 units.
• Beta radiation: It can be defined as the conversion of a neutron into an electron and proton. The atomic mass of an atom is unaffected by the release of a beta particle whereas the atomic number increases by one.

• Gamma radiation: It involves the emission of energy from an atom’s nucleus. Their wavelength is less than 3 × 10-11 metres.

X-Ray Radiation

It is a type of electromagnetic radiation that has a wavelength from 0.01 to 10 nanometers, a frequency range of 30 petahertz(1015) to 30 exahertz(1018) and energies ranging from 100eV to 100keV.

Properties of X-ray radiations:

• They travel with the same speed of light and can also travel in a vacuum.
• They are invisible to human eyes.
• They always travel in a straight line
• They have high penetrating power
• They are not deflected by an electric or magnetic field.

Applications of X-ray radiations:

• They can detect defects in welding.
• They are used to scan luggage bags in airports, railways etc.
• They are used for doing x-ray scans of teeth, lungs, chest, kidney, bones, etc.

Conclusion:

Radiation can be defined as the amount of heat transfer that occurs due to the emission or absorption of heat from one body to another. The common applications of radiation lie in our daily life, but still, there are some limitations concerning the health hazards of radiation. The rate of heat transfer from a body/system depends on the surface area and the fourth power of absolute temperature. The energy of electromagnetic radiation depends upon the wavelength that ranges from small to large. A greater amount of heat is radiated at higher temperatures. The temperature change is accompanied by a colour change. The electromagnetic waves explain the concept of quantum physics and the electromagnetic spectrum.