Fundamentals of Alpha Emission-IRadioactivity, Laws of Radioactivity, Alpha Emission, Occurrence of Alpha Emission, Uses of Alpha Emission, Practice Problems, FAQs

Let me share one report from WHO according to which cancer is the leading cause of death than any other natural or anthropogenic disasters in the world, accounting for nearly 10 million deaths in 2020. It has also been said that Tobacco use, a high BMI (Body Mass Index), alcohol consumption, a lack of fruits and vegetables, and a lack of physical activity account for roughly one-third of cancer deaths.

But do you know what actually happens in this cancer disease?

According to the WHO “cancer is a broad term that refers to a wide range of diseases that can affect any part of the body”. The rapid formation of abnormal cells that multiply beyond their normal boundaries and can then invade adjoining parts of the body and spread to other organs is a defining characteristic of cancer; this process is known as metastasis.

Many cancers can be cured if they are detected early and treated properly.

But do you know how it is being eradicated? By either or both chemotherapy (treatment with medicine) and Radiotherapy (treatment with radiation).

Alpha-emitting radionuclides are currently being used to eradicate cancerous tumours in three ways: as an infusible radioactive treatment that targets specific tissues (Radium-223), as a source of radiation inserted directly into tumours and as an attachment to a tumour-targeting molecule, such as an antibody to a tumour-associated antigen.

Let us learn more about alpha emission in this article.

Table of Content

• Radioactivity
• Laws of Radioactivity
• Alpha Emission
• Occurrence of Alpha Emission
• Uses of Alpha Emission
• Practice Problems
• Frequently Asked Questions-FAQs

Introduction to Radioactivity

By chance, Henry Becquerel discovered radioactivity. A Uranium compound was wrapped in black paper and placed in a drawer containing photographic plates. When the plates were eventually examined, it was discovered that they had been exposed! The concept of radioactive decay arose as a result of this exposure. Such manifestations of radioactivity exist.

Mainly there are three main types of emissions that take place in the radioactive disintegration which include:

• Gamma Radiation (Photons having high energy are emitted)
• Beta Degeneration (Emission consists of Electrons)
• Alpha Degeneration (Emission consists of Helium nucleus).

Radioactive reactions showing the emission of radiation are as follows:

$⬚zaX(mother nucleus)\to ⬚z-2a-4Y(daughter nucleus)+⬚24He(\alpha -particle)$

$⬚zaX(mother nucleus)\to ⬚z+1aY(daughter nucleus)+⬚-10e(beta-particle)⬚zaX(mother nucleus)\to ⬚azY(daughter nucleus)+hf(gamma-rays)$

Some elements, such as uranium, radium, polonium, and thorium, are unstable due to nuclear instability; the elements' nuclei undergo radioactive decay to form stable nuclei. Radioactivity is the spontaneous breakdown of unstable nuclei of elements to produce stable nuclei. Two forces, which include electrostatic repulsion and the nucleus's powerful forces of attraction, keep the nucleus together. In the natural world, these two forces are thought to be extremely powerful because the mass of the nucleus becomes very large when concentrated, and the likelihood of encountering instability increases as the size of the nucleus increases. The n/p ratio is used to calculate the stability of an element's nuclei.

Laws of Radioactivity

• The decay of the nucleus causes radioactivity.
• The rate of nucleus decay is independent of temperature and pressure.
• The law of charge conservation governs radioactivity.
• The daughter nucleus has different physical and chemical properties than the mother nucleus.
• Energy emitted by radioactivity is always accompanied by alpha, beta, and gamma particles.
• The decay rate of radioactive substances is determined by the number of atoms present at the time. Radioactivity follows first-order kinetic law.

Alpha Emission

Alpha decay is a type of radioactive decay process in which unstable atomic nuclei emit helium nuclei (alpha particles) and undergo a transformation into a more stable element. The emitted particle, known as the alpha particle, is composed of four nucleons: two neutrons and two protons. Alpha radiation reduces the proton-to-neutron ratio in the parent nucleus, resulting in a more stable configuration. A helium atom's nucleus is identical to an alpha particle.

The first observations and investigations into alpha decay were made by Ernest Rutherford, who used alpha particles in his gold foil scattering experiment. As the alpha particle, which is made up of two protons and two neutrons, exits the nucleus, the atomic number of the radioactive sample changes.

For example,

$⬚ZAM\to ⬚Z-2A-4N+⬚24He$

Here,

M represents the parent nucleus symbol

Z represents the atomic number of parent nuclei

A represents the mass number of parent nuclei

N represents the symbol of daughter nuclei

Z-2 represents the atomic number of daughter nuclei

A-4 represents the mass number of daughter nuclei

He represent the symbol of the helium atom

Let us consider the radioactive reaction in which uranium-238 is dissociated into thorium-234 and an alpha particle is emitted.

$⬚92238U\to ⬚90234Th+⬚24He$

Note: When the n/p value of the element lies below the zone of stability, they undergo -alpha emission, K-electron capture, or positrons emission.

-emission generally occurs when the nuclei of naturally occurring elements are present. K-electron capture or positron emission occurs in the case of an artificially prepared radioactive element.

Occurrence of Alpha Emission

Alpha decay of heavier ( atomic mass greater than 106 u) atoms is the most well-known source of alpha particles. The decay of uranium to thorium and radium to radon are two examples of nuclear transmutation by alpha decay.

All of the larger radioactive nuclei, including thorium, actinium, and radium, as well as the transuranic elements(element present after uranium), emit alpha particles. Alpha decay, unlike other types of decay, requires a minimum-size atomic nucleus to function. Beryllium-8 and the lightest tellurium (element 52) nuclides with mass numbers ranging from 104 to 109 are the smallest nuclei discovered to date capable of alpha emission.

Alpha decay occurs only in the heaviest elements. The nucleus of the element must be large enough or unstable enough to undergo spontaneous fission-like changes. In these elements, it is the most common type of decay. The alpha particles emitted from the nucleus have an energy level of about 5 MeV and a speed of about 5% of light. Because there are no electrons, alpha particles have a charge of +2, and because of this charge and its heavy mass, an alpha particle reacts vigorously with its surroundings, losing all of its energy almost immediately, and has high ionising power but low penetration power when compared to alpha and beta particles.

Uses of Alpha Particles

Some applications of alpha particles include:

• Americium-241 is an alpha emitter that is used in smoke detectors sold in the United States. The alpha particles emitted by the Americium sample ionise the air in the smoke detector chamber, resulting in a small current in the chamber. When smoke is detected in the chamber, it causes a drop in current, triggering the alarm. Although Alpha particles have a very short range, they are extremely lethal when in close proximity.

• Alpha decay can serve as a safe source of power for radioisotope thermoelectric generators used in space probes and artificial heart pacemakers.

• Alpha-emitting radionuclides are currently being used to eradicate cancerous tumours in three ways: as an infusible radioactive treatment targeted to specific tissues (Radium-223), as a source of radiation inserted directly into solid tumours (Radium-224), and as an attachment to a tumour-targeting molecule, such as an antibody to a tumour-associated antigen.

• Radium-224 is a radioactive atom that is used as a source of alpha radiation in a recently developed cancer treatment device known as DaRT Diffusing alpha emitters radiotherapy, also known as Alpha DaRT.

Practice Problems

Q1. Select the correct option with respect to the radiation emitted during the nuclear reaction.

1. In the case of beta emission mass number decreases by 4 units and the atomic number remains unchanged.
2. In the case of alpha emission mass number decreases by 4 units and atomic number decreases by 2 units respectively.
3. In the case of gamma emission mass number decreases by 2 units and the atomic number remains unchanged.
4. Both A and B are correct

Answer: (B)

Solution: In the case of alpha emission mass number decreases by 4 units and the atomic number decreases by 2 units respectively whereas, in the case of beta emission atomic number increases by one unit and the mass number remain unchanged and in gamma emission both mass number and atomic number remain unchanged. Therefore, option(B) is correct.

Q2. Which of the following options is correct with respect to the alpha emission?

1. -emission generally occurs when the nuclei of naturally occurring elements are present and n/p value is above the stability belt
2. -emission generally occurs when the nuclei of naturally occurring elements are present and n/p value is below the stability belt
3. -emission generally occurs when the nuclei of artificial occurring elements are present and n/p value is above the stability belt
4. Both A and B correct

Answer: (B)

Solution: When the n/p value of the element lies below the zone of stability, they emit -emission, K-electron capture, or positrons.

-emission generally occurs when the nuclei of naturally occurring elements are present. K-electron capture or positron emission occurs in the case of an artificially prepared radioactive element.

Q3. Polonium(94239Pu) undergo radioactive disintegration process to emit alpha particle then atomic number and mass number respectively for the daughter nuclei will be_______.

1. 90 and 235
2. 90 and 239
3. 92 and 235
4. 92 and 239

Answer: (C)

Solution: Alpha particles are also referred to as Alpha radiation or Alpha ray. It is a positively charged particle emitted by the radioactive decay of various materials. The mass of the alpha particle is due to the bonding of two protons and two neutrons. It is represented by the "" symbol, which stands for doubly ionized helium nucleus, which is made up of four units of atomic mass and two positively charged particles. When the alpha particle is emitted, the mass number and the atomic number of the daughter nuclei decrease by 4 and 2 units, respectively.

According to the given question,

Polonium $(⬚94239Pu)$ undergo radioactive disintegration process to emit alpha particle then,

$⬚94239Pu\to ⬚92235U+⬚24He$

Atomic number and the mass number of the daughter nuclei will be 92 and 235 respectively. Therefore, option(C) is correct.

Q4. Which of the following option is correct with respect to the laws of radioactivity?

1. The decay rate of radioactive substances is determined by the n/p value of the daughter nuclei emitted during radioactive decay.
2. The rate of nucleus decay is dependent on temperature but independent of pressure.
3. Energy emitted by radioactivity may not be accompanied by alpha, beta, and gamma particles.
4. The daughter nucleus has different physical and chemical properties than the mother nucleus.

Answer: (D)

Solution: According to the law of radioactivity,

• The decay rate of radioactive substances is determined by the number of atoms present at the time.
• The rate of nucleus decay is independent of temperature and pressure.
• Energy emitted by radioactivity is always accompanied by alpha, beta, and gamma particles.
• The daughter nucleus has different physical and chemical properties than the mother nucleus.

Therefore, option (D) is correct.

Frequently Asked Questions-FAQ

Q1. How to determine the stability of the nucleus?
Answer: The natural tendency of an atom nucleus to decay or change into another substance is referred to as nuclear stability. If an element's isotope (referred to as a nuclide) is unstable (not stable), the nuclide has an inclination to emit radiation and is referred to as an unstable radioactive nuclide. The neutron-proton ratio (n/p) is useful in determining nuclear stability. This ratio is close to one for atoms with low atomic numbers (less than about 20 protons).

The n/p ratio steadily rises as the atomic number increases, from an element greater than the atomic number calcium to element 84, polonium. Almost every element with an atomic number greater than 84 is unstable.

Q2. What is the difference between the alpha and beta particles in terms of their properties?
Answer:

Q3. List a few important characteristics of alpha particles.
Answer: Alpha particle is the stream of particles represented as a doubly ionised helium nucleus with +2 charge. It has high kinetic energy and can ionise a gas when passed through. It has a low penetration power due to its larger size and can be stopped by a sheet of paper or 0.01 mm thick aluminium foil. It travels at one-tenth the speed of light, but its exact velocity is determined by the nucleus from which it is emitted.

Q4. What is radioactive decay? Explain with the help of a suitable example.
Answer: Radioactive decay is the process by which an unstable atomic nucleus disintegrates to release energy (radiation) with or without additional particles. Nuclear decay, radioactivity, and nuclear disintegration are all terms used to describe the process. A radioactive material contains unstable nuclei. The most common types of decay are alpha decay (-decay), beta decay (-decay), and gamma decay (-decay), all of which involve the emission of one or more particles. For example,

Let us consider the radioactive reaction in which uranium-238 is dissociated into thorium-234 and an alpha particle is emitted.

$⬚92238U\to ⬚90234Th+⬚24He$