Properties of Alpha Beta and Gamma Rays for IIT JEE

Radioactivity is essentially the nuclei decomposition process. It refers to the spontaneous decomposition of unstable atomic nuclei to form nuclei with higher stability. This process or stability achievement is called radioactivity. The process leads to the emission of radiation - called energy and particles. There may be two types of radioactivity - radioactivity that is natural or induced.

Natural Radioactivity: It is called natural radioactivity when unstable nuclei break down in nature.

Induced Radioactivity: As the name suggests, the decomposition is called induced radioactivity when unstable nuclei are prepared in the laboratory.

Law of Radioactive Decay: Radioactive decay law provides for how the decrease in the number of non-decayed nuclei of a given radioactive substance occurs over time. This can also be stated, in other words, as the number of atoms disintegrated per second at any moment is directly proportional to the number of radioactive atoms present in the sample at that moment.

If \[N_{0}\] be the total number of atoms at t = 0, N is the total number of atoms left in the sample at time t, then dN/it will be the rate of disintegration.

Radioactive Half-Life

The half-life for a given radioisotope indicates the time to undergo radioactive decay for half the radioactive nuclei in any sample. The remaining portion will be one-fourth of the original sample after two half-lives. Similarly, one-eighth of the original sample after three half-lives, and so on. In other words, radioactivity can also be defined as the time interval required to decay one-half of a radioactive sample's atomic nuclei or the time interval required to decrease by one-half the number of disintegrations per second of radioactive material.

This decay of the radioactive substance is entirely based on likelihood. Half-life is independent of the physical condition, temperature, pressure, or chemical compounds in which the nucleus is found. Therefore, no external factors can affect the half-life. Indeed, the only thing that can impact a radioactive particle's half-life is the direct nuclear interaction with an external particle. A high-energy collision in an accelerator, for example, could have an impact.

Average Life or Mean Life

In a given sample, there is no disintegration of all atoms together. In the very beginning, some atoms may disintegrate for which lifetime is zero. Therefore, their lifetime may vary from zero to infinity in the case of atoms that disintegrate between them. The total lifetime of all the element atoms divided by the total number of atoms originally present in the element's sample is called the Mean life.

Alpha, Beta, and Gamma Rays

Alpha rays, beta rays, and gamma rays are the rays emitted during a substance's radioactivity. We will now discuss the properties of all three one by one.

Alpha Radiation

Alpha rays are the radiation that is positively charged. An alpha particle is a helium nucleus, denoted by the symbol α. The alpha particle is called a helium atom that has lost two electrons and carries a + 2e charge. Its weight is about four times that of an atom of hydrogen. It initially escapes from its parent atom's nucleus and is further repelled by electromagnetism as both the alpha particles and the nucleus are charged positively. The speed of α-particles ranges from 5% to 7% of the light speed. They have very little power to penetrate a material medium but they have very high power to ionize. These rays are more massive than the beta rays and they contain a stream of positively charged particles, called alpha particles, which have an atomic mass of 4 and a positive charge of 2 (a helium nucleus). The emission from the nucleus of an alpha particle decreases the nucleus mass number by 4 and the atomic number decreases by 2. As in the reaction below, the alpha particle is the helium nucleus.

\[_{92}^{238}\textrm{U} \rightarrow _{4}^{2}\textrm{He} + _{234}^{90}\textrm{Th}\]

The alpha radiation consists of two neutrons and two protons attached to a helium atom's nucleus. These particles have an intense ionizing power which means that they can cause mutations when they come into contact with the atoms of living tissue and sometimes such reactions can even lead to cancer. Despite their high ionization power, these rays are not very harmful. These are, in fact, the least dangerous of the three rays as long as they are not inhaled. A few centimeters of air can stop alpha rays from penetrating through the skin. Particles with alpha rays have the least power to penetrate. They cannot travel very far in the air and they cannot even get through a piece of paper. They just find and join two electrons to become an atom of helium before they can result in any kind of harm. However, it does not imply that they are not dangerous. When inhaled, they are quite risky. They stick to the lungs if inhaled and can become a cause of lung cancer.

Beta Radiation

Beta radiations consist of a stream of electrons termed beta particles. β -particles are electrons moving at high speeds. They have greater penetrating power (in comparison with α-particles), but less ionizing power. Their speed of emission is almost the speed of light. They have a spectrum of energy as opposed to α-particles, i.e. beta particles have energy from a certain minimum to a certain maximum value. A β-particle is usually an electron, but it can be a position as well. A positron is a positively charged particle which is the antimatter equivalent of an electron. On the emission of a beta particle, a neutron in the nucleus gets converted to a proton and hence the mass number remains unchanged but the atomic number increases by one unit. The most common example of beta emission is the degradation of radioactive copper which after emitting one electron leaves behind a nickel atom: 

\[(^{64}Cu_{29}) \rightarrow (^{0}e_{-1}) + (^{64}Ni_{28})\]

Beta decline itself occurs in two types: one is positive β+ decline and the other is β- decline. β- emission occurs when one nucleus neutron is transformed into a proton, an electron, and antineutrino. The fission resulting from nuclear reactors or -products experience β-decline as the resulting product has an excess of neutrons.

β+ degeneration is a similar process, but it involves the transformation of a proton into a neutron, positron, and neutrino. Beta rays consist of electrons of high energy. They are less ionizing than alpha rays, but they are more harmful as they can penetrate the skin. With an aluminum sheet, they can be stopped.

Gamma Radiation

Gamma rays comprise ~10 - 12 m wavelength electromagnetic waves. Gamma radiation is a very powerful photon with a very short wavelength (0.0005 to 0.1 nm). Gamma emissions often accompany alpha and beta emissions as an excited nucleus falls into a lower and more stable state of energy. Gamma rays are high-frequency electromagnetic waves without mass and charge. This radioactive emission has the least power of ionization. These are emitted as a result of the transition from a higher energy state to a lower energy state of the excited nucleus. Once an alpha or beta decay takes place in a nucleus, excess energy is often left in an excited state. Just as an electron can move to a lower energy state by emitting a photon to an infrared range somewhere in the ultraviolet range, by emitting a gamma ray, an atomic nucleus loses energy. The penetration power is the highest for gamma rays. They have the least power to ionize any material, but they are the most dangerous. Gamma rays have the highest penetrating power and only a few centimeters of lead sheet or a few meters of concrete can stop them. In certain cases, they may even pass through them.

The following table gives a detailed description of the comparisons and differences in the properties characteristic of alpha, beta, and gamma rays:

Properties Characteristic of Alpha, Beta, and Gamma Rays

Detail Concept of Properties of Alpha Beta and Gamma Rays:

At the time of the radioactivity process the particles like alpha, beta & gamma rays are released by an atom due to an unstable atom trying to gain stability. Therefore, the atoms finally decay by secreting a particle that transforms when they are unstable and transforms the nucleus into a lower energy state. This process of decaying continues till the nucleus attains a stable stage.

There exist three major types of radiations produced by the radioactive particles namely:

• Alpha

• Beta

• Gama

These radiations are released from the nucleus of an atom. Their behavior differs from one another, though all three cause some ionization and carry some penetration power. 

Properties of Alpha:

Alpha particles are relatively slow and heavy in comparison with other forms of nuclear radiation. The particles travel at 5 to 7 % of the speed of light or 20,000,000 meters per second and have a mass approximately equivalent to 4 protons. Alpha particles as they are highly ionizing are unable to penetrate very far through matter and are brought to rest by a few centimeters of air or less than a tenth of a millimeter of biological tissue

Properties of Beta:

Beta particles have a mass that is half of one-thousandth of the mass of a proton and carry either a single negative (electron) or positive (positron) charge which has a very small  mass and can emit with high energy, so they can reach relativistic velocities. Small masses quickly lose energy by interacting with matter and have a random path as they travel through air and other matter. 

Beta particles are less ionizable than alpha particles and generally do less damage to a given amount of energy storage.

They typically have ranges of tens of centimeters in the air (energy-dependent) and a few millimeters in materials.

Properties of Gamma Rays:

The waves from the high-frequency end of the electromagnetic spectrum which do not have any mass are called gamma rays. They have the greatest power of penetration.