Alpha decay : Definition, Example, & Facts

Edited By Team Careers360 | Updated on Jul 02, 2025 05:31 PM IST

A nuclear process known as "alpha decay" releases a particle made up of two neutrons and two protons when an unstable nucleus transforms into another element. This ejected substance is referred described as an "alpha particle.". Ernest Rutherford investigated how radiation is deflected through magnetism to distinguish alpha decay from other types of radiation. Given that the alpha particles carry a +2e charge, the alpha decay would deflect a positive charge.

This Story also Contains

Describe Alpha Decay
Uses Of Alpha Decay
The Equation For Alpha Decay
How Does Alpha Decay Work?
Gamow's Alpha Decay Theory
Protection
History

Alpha decay : Definition, Example, & Facts

Describe Alpha Decay

A nuclear process known as "alpha decay" releases a particle made up of two neutrons and two protons when an unstable nucleus transforms into another element. The helium nucleus that is being ejected is termed an “alpha particle”. Positive charge and a sizable mass characterise alpha particles. Due to their high mass, alpha particles are unable to penetrate solids or the atmosphere very deeply. Alpha decay is rarely employed in requires medical radiation therapy because alpha particles only have an impact on surfaces.

Ernest Rutherford first identified alpha decay as distinct from other radiation types by studying the radiation's refraction via a magnetic field. Since alpha particles carry a+2e charge, alpha decay deflects as you would anticipate a positive particle

Uses Of Alpha Decay

Uses of alpha decay are:

Smoke detectors employ the alpha emitter americium-241. In an open ion chamber, the alpha particles ionise the air, which then experiences a little amount of current. The smoke detector sounds an alarm when smoke embers from the fire reach the chamber, decreasing the current.
Additionally, an alpha emitter is radium-223. It is employed to treat bone tumours (cancers in the bones).
Radioactive substances thermoelectric generators used in space missions and artificial heart pacemakers can be safely powered by alpha decay. Other types of radioactive decay are far more difficult to protect against than alpha decay.
Polonium-210, an alpha absorber, is frequently used in static eliminators to ionise the air, causing the "static cling" to disperse more quickly.

The Equation For Alpha Decay

While the atomic number decreases by two during -decay, the nuclear reaction's output nucleus' mass number is four less than the atomic nucleus. The alpha decay equation is typically shown as follows:

{}_{Z}^{A}X\to {}_{Z-2}^{A-4}\,Y\,+\,{}_{2}^{4}\,He

where:

The parent nucleus, or the initial nucleus, is {}_{Z}^{A}X .
The number of nucleons overall is A.
The number of protons overall is Z.
The offspring nucleus, or terminating nucleus, is { }_{Z-2}^{A-4} Y .
The expelled alpha particle is { }_2^4 \mathrm{He} .

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How Does Alpha Decay Work?

A typical radioactive decay process when a nucleus releases an alpha particle (a helium-4 nucleus). The nucleus releases an alpha particle or helium nucleus during alpha decay. Massive nuclei with a high proton-to-neutron ratio experience alpha decay. The parent nucleus becomes more stable as a result of alpha radiation's reduction of the protons to neutrons ratio.

Gamow's Alpha Decay Theory

The decay frequency of a radioactive element and the strength of the released alpha particles are related by the Geiger-Nuttall law or rule. In accordance with this relationship, half-lives and decay energy are exponentially related, meaning that very significant changes in half-life correspond to very modest changes in decay energy and, therefore, alpha particle energy.

This law dictates that short-lived isotopes release higher powerful alpha particles than long-lived isotopes. The name of this law was given in honour of Hans Geiger and John Mitchell Nuttall, two physicists who first proposed it in 1911.

Protection

The consumption of a material that experiences alpha decay is dangerous even when it doesn't penetrate very deeply since the released alpha particles can quickly cause internal tissue damage despite their limited range. Interaction with membranes and live cells led to this harm.

Depending on how the exposure occurs, alpha particles have different health implications. There may be long-lasting biological harm if the alpha emitter is ingested, absorbed, or absorbed into the body's bloodstream. The risk of cancer is raised by this damage. If the alpha emitter is breathed, alpha radiation is well-known to cause lung cancer in people. One of the main causes of alpha decay illnesses in humans is the intake of radon, an alpha emitter.

History

Ernest Rutherford originally mentioned alpha particles in his studies on radioactivity in 1899; by 1907, they had been recognized as He2+ ions. George Gamow had discovered a tunnelling solution to the idea of alpha decay by 1928. An inviting nuclear potential well and a repellent electromagnetic potential barrier hold the alpha particle inside the nucleus. The capacity to leave the nucleus is traditionally prohibited, but according to the rules of quantum mechanics, there is a very small chance of doing so.

Gamow derived the Geiger-Nuttall law, which had previously been discovered empirically, by solving a virtual potential for the nucleus and establishing from first principles the link between both the half-life of the emission and the energy of the decay.

Frequently Asked Questions (FAQs)

1. Alpha decay releases what?

A positive charge particle similar to the helium-4 nucleus is spontaneously released during alpha decay. Two protons and two neutrons make up this particle, also referred to as an alpha particle. Sir Ernest Rutherford made the discovery and gave it a name in 1899.

2. How can you tell if it's alpha decay or not?

The distinctions between radioactive decay of the alpha, beta, and gamma rays can be summed up as follows: Beta decay produces a new element that has one more proton and one fewer neutron while alpha decay creates a new element with some fewer protons and two fewer neutrons.

3. Is alpha decay a natural occurrence?

In general, there are two different kinds of natural radioactive decay: alpha decay, which is produced when radon gas emits particles "containing two neutrons and two protons," and nuclear decay caused by photon emission.

4. What characteristics does alpha decay have?

The positive charge particles are called alpha rays. The helium atom that makes up an alpha particle is extremely active and energetic and has two neutrons and protons. The least penetrating and most ionising particles are these. They have a high ionisation power, which means that if they enter the body, they can cause severe harm.

5. What elements lead to alpha decay?

Strong nuclear force and electromagnetic force are the two forces that work together to produce alpha decay. The strong nuclear force is a force of attraction that not only holds quarks together in the nucleus to create protons and neutrons as well as other forms of particles.

6. What is alpha decay?

Alpha decay is a type of radioactive decay where an atomic nucleus emits an alpha particle (two protons and two neutrons, equivalent to a helium-4 nucleus). This process reduces the atom's mass number by 4 and its atomic number by 2, transforming it into a different element.

7. What is the difference between alpha decay and cluster decay?

While alpha decay involves the emission of a helium-4 nucleus, cluster decay is a rare type of radioactive decay where the emitted particle is heavier than an alpha particle but lighter than a fission fragment. Examples include the emission of carbon-14 or neon-24 nuclei. Both processes involve the tunneling of a particle through the nuclear potential barrier.

8. What role does the strong nuclear force play in alpha decay?

The strong nuclear force plays a crucial role in alpha decay. It is responsible for holding the nucleons together in the nucleus. Alpha decay occurs when the electrostatic repulsion between protons overcomes the strong force in heavy nuclei. The balance between these forces determines the stability of the nucleus and the likelihood of alpha decay.

9. How does alpha decay affect the nucleus's moment of inertia?

Alpha decay reduces the nucleus's moment of inertia because it removes mass (four nucleons) from the nucleus. This change can affect the rotational properties of the nucleus, which is important in understanding nuclear structure and behavior, especially in studies of nuclear deformation and rotation.

10. What is the connection between alpha decay and nuclear shell structure?

The nuclear shell structure, which describes how nucleons are arranged in energy levels within the nucleus, influences alpha decay. Nuclei with "magic" numbers of protons or neutrons (corresponding to filled shells) are generally more stable. Alpha decay often results in daughter nuclei closer to these magic numbers, explaining why certain decays are more favorable than others.

11. What is the relationship between alpha decay and nuclear binding energy?

Alpha decay occurs when it results in an increase in the average binding energy per nucleon. The daughter nucleus and alpha particle have a higher total binding energy per nucleon than the parent nucleus, making the decay energetically favorable and contributing to the stability of the resulting products.

12. Why don't lighter elements typically undergo alpha decay?

Lighter elements don't typically undergo alpha decay because the strong nuclear force is sufficient to overcome the electrostatic repulsion between protons in their smaller nuclei. Additionally, the emission of an alpha particle would require more energy than is available in these lighter nuclei.

13. What is the tunneling effect in alpha decay?

The tunneling effect in alpha decay refers to the quantum mechanical phenomenon where alpha particles can escape the nucleus despite not having enough classical energy to overcome the potential barrier. This effect explains why alpha decay occurs at all and helps predict decay rates.

14. How does alpha decay contribute to nuclear fission?

While alpha decay itself is not nuclear fission, it can contribute to the process. In some cases, alpha decay can leave the daughter nucleus in an excited state, which may then undergo fission. Additionally, the study of alpha decay has contributed to our understanding of nuclear structure, which is crucial for understanding fission processes.

15. How does the mass defect relate to alpha decay?

The mass defect is the difference between the mass of a nucleus and the sum of its constituent nucleons. In alpha decay, the mass defect of the parent nucleus is greater than the combined mass defects of the daughter nucleus and the alpha particle. This difference in mass is converted to energy according to E=mc², providing the energy for the decay process.

16. What is the connection between alpha decay and the island of stability?

The island of stability is a theoretical region of the chart of nuclides where superheavy elements might have relatively long half-lives. Alpha decay is expected to be a primary decay mode for these elements. Understanding alpha decay mechanisms is crucial for predicting the stability and decay properties of these hypothetical superheavy elements.

17. Can alpha decay be induced artificially?

While alpha decay is typically a spontaneous process, it can be induced artificially in some cases. This can be done by bombarding certain nuclei with high-energy particles, causing them to become unstable and subsequently emit alpha particles. However, this is not common and is different from natural alpha decay.

18. What is the significance of Geiger-Nuttall law in alpha decay?

The Geiger-Nuttall law relates the decay constant (or half-life) of an alpha-emitting isotope to the energy of the emitted alpha particle. It demonstrates that isotopes emitting higher-energy alpha particles generally have shorter half-lives. This empirical law was crucial in early understanding of alpha decay and still provides a useful approximation for decay rates.

19. What is the role of alpha decay in the production of transuranic elements?

While alpha decay itself doesn't produce transuranic elements, understanding alpha decay is crucial in the study and production of these elements. Many transuranic elements decay via alpha emission, and predicting their half-lives and decay chains relies on our understanding of alpha decay mechanisms. Additionally, alpha decay studies have contributed to our knowledge of nuclear structure used in synthesizing these elements.

20. What is the significance of fine structure in alpha decay spectra?

Fine structure in alpha decay spectra refers to the observation that alpha particles can be emitted with slightly different energies from the same isotope. This occurs when the daughter nucleus is left in different excited states. Studying this fine structure provides valuable information about nuclear energy levels and helps refine models of nuclear structure.

21. Why do some atomic nuclei undergo alpha decay?

Atomic nuclei undergo alpha decay to achieve greater stability. This typically occurs in heavy nuclei (atomic number > 82) where the strong nuclear force can no longer overcome the electrostatic repulsion between protons. By emitting an alpha particle, the nucleus reduces its size and energy, becoming more stable.

22. How does alpha decay affect an element's position on the periodic table?

Alpha decay causes an element to move two positions to the left on the periodic table. This is because the loss of two protons changes the atomic number, which defines the element. For example, when uranium-238 undergoes alpha decay, it becomes thorium-234.

23. What is the difference between alpha decay and alpha radiation?

Alpha decay refers to the process by which an unstable nucleus emits an alpha particle. Alpha radiation is the stream of alpha particles emitted during this process. Alpha decay is the cause, while alpha radiation is the effect.

24. How does alpha decay change the neutron-to-proton ratio in a nucleus?

Alpha decay removes two protons and two neutrons from the nucleus. This tends to increase the neutron-to-proton ratio in the daughter nucleus, as heavy nuclei typically have more neutrons than protons. This shift often brings the nucleus closer to the stable neutron-to-proton ratio for its mass.

25. How does the atomic mass change during alpha decay?

During alpha decay, the atomic mass of the parent nucleus decreases by approximately 4 atomic mass units (amu). This is because an alpha particle, which has a mass of about 4 amu, is emitted from the nucleus.

26. What is the range of alpha particles in air?

Alpha particles typically have a range of only a few centimeters in air. This short range is due to their relatively large mass and charge, which causes them to interact strongly with surrounding matter, quickly losing energy through ionization.

27. Can alpha particles penetrate human skin?

No, alpha particles cannot penetrate human skin. They are stopped by a sheet of paper or the outer layer of dead skin cells. However, alpha-emitting materials can be dangerous if ingested or inhaled, as they can cause significant damage to internal tissues.

28. Why are alpha particles considered ionizing radiation?

Alpha particles are considered ionizing radiation because they have enough energy to remove electrons from atoms they encounter, creating ions. This ionization process can disrupt chemical bonds and damage biological molecules, which is why alpha radiation can be harmful to living tissues.

29. How does the energy of alpha particles compare to other types of radiation?

Alpha particles generally have higher kinetic energy than beta particles or gamma rays from the same radioactive source. However, due to their large mass and charge, they lose this energy quickly and have the least penetrating power of the three main types of radiation.

30. How does alpha decay contribute to the heat generation in Earth's interior?

Alpha decay of naturally occurring radioactive elements like uranium, thorium, and their decay products is a significant source of heat in Earth's interior. The kinetic energy of alpha particles is converted to heat as they interact with surrounding matter. This radioactive heating plays a crucial role in driving geological processes like mantle convection and plate tectonics.

31. How is alpha decay represented in a nuclear equation?

Alpha decay is represented in a nuclear equation as:

32. How does the half-life of an element relate to its alpha decay rate?

The half-life of an element undergoing alpha decay is inversely proportional to its decay rate. A shorter half-life indicates a faster decay rate, meaning more alpha particles are emitted per unit time. The relationship is given by the equation: λ = ln(2) / t₁/₂, where λ is the decay constant and t₁/₂ is the half-life.

33. What is the recoil effect in alpha decay?

The recoil effect in alpha decay refers to the movement of the daughter nucleus in the opposite direction of the emitted alpha particle, as required by the conservation of momentum. This recoil can affect the kinetic energy distribution between the alpha particle and the daughter nucleus and is important in precise measurements of decay energies.

34. How does alpha decay energy affect the probability of decay?

The energy of alpha decay, which is the Q-value of the reaction, directly affects the probability of decay. Higher energy alpha decays are generally more probable because the alpha particle has a greater chance of tunneling through the nuclear potential barrier. This relationship is described by the Geiger-Nuttall law, which shows that higher energy decays correspond to shorter half-lives.

35. How does alpha decay contribute to the concept of radioactive equilibrium?

In a decay chain, radioactive equilibrium occurs when the rate of production of a daughter isotope equals its rate of decay. Alpha decay is often a key step in these chains. Understanding alpha decay rates is crucial for determining when and how radioactive equilibrium is achieved, which is important in various applications of nuclear physics and geochemistry.

36. How does alpha decay contribute to radiometric dating?

Alpha decay is fundamental to several radiometric dating methods, particularly those involving long-lived isotopes like uranium and thorium. By measuring the ratio of parent to daughter nuclei produced by alpha decay, geologists can determine the age of rocks and minerals, providing crucial information about Earth's history and geological processes.

37. What is the importance of alpha decay in stellar nucleosynthesis?

Alpha decay plays a role in stellar nucleosynthesis, particularly in the production of certain heavy elements. In stars, alpha particles (helium nuclei) can be captured by heavier nuclei in a process called alpha capture. This process, along with subsequent decays, contributes to the formation of elements heavier than iron in stellar environments.

38. What is the significance of the alpha decay series?

The alpha decay series, also known as radioactive decay chains, are sequences of radioactive decays (primarily alpha decays) that begin with a long-lived parent isotope and end with a stable daughter isotope. These series are important in understanding the natural radioactivity of elements and in dating geological samples.

39. How does alpha decay contribute to the formation of helium in the Earth?

Alpha decay of naturally occurring radioactive elements like uranium and thorium in the Earth's crust and mantle is a significant source of helium production. The alpha particles emitted during decay capture electrons to form helium atoms, contributing to the helium reserves found in natural gas deposits.

40. What is the role of alpha decay in the production of radon gas?

Radon gas is produced through the alpha decay of radium, which is part of the uranium and thorium decay series. The alpha decay of radium-226, for example, produces radon-222, a radioactive noble gas. This process is significant for environmental and health concerns, as radon can accumulate in buildings and pose health risks.

41. How does alpha decay relate to the concept of magic numbers in nuclear physics?

Magic numbers in nuclear physics refer to specific numbers of protons or neutrons that result in exceptionally stable nuclei. Alpha decay often results in daughter nuclei with proton or neutron numbers closer to these magic numbers, contributing to the stability of the decay products. This relationship helps explain why certain alpha decays are more energetically favorable than others.

42. How does alpha decay affect nuclear spin?

Alpha decay can change the nuclear spin of the decaying nucleus. Since an alpha particle has zero spin, the change in nuclear spin depends on the orbital angular momentum carried away by the alpha particle. This can result in excited states of the daughter nucleus, which may then decay further through gamma emission.

43. How does the shell model of the nucleus explain alpha decay?

The shell model of the nucleus helps explain alpha decay by showing how nucleons are arranged in energy levels or "shells." Alpha decay is more likely to occur when it results in a daughter nucleus with a closed shell configuration (magic number of protons or neutrons), as this is energetically favorable. This model helps predict which nuclei are more prone to alpha decay.

44. What is the relationship between alpha decay and nuclear deformation?

Nuclear deformation, where nuclei deviate from a spherical shape, can influence alpha decay rates. Deformed nuclei may have different potential barriers for alpha emission depending on the direction of emission relative to the deformation axis. This can lead to anisotropic emission of alpha particles and affects decay rates and energies.

45. How does the pairing effect influence alpha decay?

The pairing effect in nuclear physics refers to the increased stability of nuclei with even numbers of protons and neutrons. This effect influences alpha decay because alpha particles (with two protons and two neutrons) are particularly stable. Nuclei with even numbers of protons and neutrons are more likely to undergo alpha decay, as the emission preserves the even-even nature of the nucleus.

46. How does alpha decay relate to the concept of nuclear isomers?

Nuclear isomers are excited states of atomic nuclei with relatively long half-lives. Some isomers can decay via alpha emission, similar to ground state nuclei. The study of alpha decay from isomeric states provides additional information about nuclear structure and decay mechanisms, as the decay properties can differ from those of the ground state.

47. What is the significance of alpha decay in cosmic ray spallation?

While alpha decay is not directly part of cosmic ray spallation, the products of spallation reactions can undergo subsequent alpha decay. Understanding alpha decay is important for interpreting the results of cosmic ray interactions with matter, both in the atmosphere and in space, which is crucial for cosmic ray dating techniques and studies of cosmic radiation effects.

48. How does alpha decay contribute to the study of superheavy elements?

Alpha decay is a primary decay mode for many superheavy elements. Studying the alpha decay properties of these elements provides crucial information about their nuclear structure and stability. The energy and half-life of alpha decay are key parameters used to identify and confirm the synthesis of new superheavy elements.

49. What is the connection between alpha decay and nuclear fission barriers?

Both alpha decay and nuclear fission involve overcoming potential barriers in the nucleus. The study of alpha decay, particularly the tunneling process, has contributed to our understanding of how nuclei overcome potential barriers. This knowledge is applicable to understanding fission barriers, which is crucial in predicting the stability and decay modes of heavy nuclei.

50. How does alpha decay affect nuclear magnetic moments?

Alpha decay can change the nuclear magnetic moment of a nucleus. The removal of two protons and two neutrons alters the distribution of nucleons, which can result in a different nuclear spin and magnetic moment for the daughter nucleus. This change is important in nuclear spectroscopy and in understanding the magnetic properties of nuclei.

51. What is the role of alpha decay in the production of medical isotopes?

While alpha decay itself is not typically used to produce medical isotopes, understanding alpha decay is important in the production and handling of certain medical isotopes. Some medical isotopes are produced in decay chains that involve alpha decay, and knowledge of these decay processes is crucial for predicting the purity and lifetime of the isotopes.

52. How does alpha decay contribute to our understanding of nuclear forces?

The study of alpha decay provides insights into the interplay between the strong nuclear force and electromagnetic force in nuclei. The fact that alpha particles can form and tunnel out of the nucleus gives information about nuclear structure and the strength of nuclear forces at different distances, contributing to refined models of nuclear interactions.

53. What is the significance of alpha decay in environmental monitoring?

Alpha decay is significant in environmental monitoring, particularly in detecting and measuring radioactive contamination. Many naturally occurring and man-made radioactive contaminants are alpha emitters. The short range of alpha particles makes them easy to detect without interference from background radiation, making alpha decay measurements valuable in environmental and health physics.