What is an Alpha Particle?
Radiation is one of the forms of energy that occurs when an unstable parent nucleus undergoes radioactive decay. Radiations travel a certain distance from their source in the form of energized waves/particles. The particles are alpha, beta, and gamma; these particles have different attributes and effects. We will focus on the alpha particle. Now, let’s understand what alpha particles are.
Alpha particles were named after the Greek alphabet ‘α’. The symbol for the alpha particle is α or α²⁺. As these particles are congruent to Helium nuclei. That’s why alpha particles can be written as He²⁺ or 24He indicating a Helium ion with a +2 charge (lacking two electrons).
Alpha particles are known as α-rays or alpha radiation; these particles comprise two protons and two neutrons bound together into a particle isotropic to Helium-4 nuclei. These particles are developed during the α-decay process.
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In this article, we will learn about alpha particles. So, let us get started with its characteristics.
Characteristics of Alpha Particle
Fundamental Properties of Alpha Particles
Alpha particles carry double the positive charge of the proton, i.e., equal to the charge on the Helium nucleus.
The mass of an α-particle is four times the mass of a Hydrogen atom, i.e., equivalent to the mass of the Helium atom.
(The above two properties prove that an alpha particle is equal to the Helium atom which has lost its two orbital electrons or a doubly ionized Helium atom).
The velocity of alpha particles ranges between 1.4 х 10⁷ m/s to 2.1 х 10⁷ m/s, relying on the source emitting/radiating it.
Because of the large mass of alpha particles, the penetrating power of these particles is lesser. It is 1/10³ times the penetrating power of beta rays and 1/10⁵ times that of the gamma rays.
Despite having a large size and low perforating power, alpha radiation can stop by a 0.02 cm thick aluminium sheet.
On being stopped, alpha particles give rise to heating effects. Though alpha particles have low perforating power, they can cause burns on the human body.
Because of their large mass and high-stepping speed, these particles have excessive ionizing efficiency. It means a single alpha particle can bring forth thousands of ions before being absorbed.
The distance an alpha particle travels in the air relies on the radioactive source creating it. At the normal pressure in air, the range of alpha particles deviates from 3 to 8 cm.
Alpha particles produce fluorescence in certain substances, like Barium-Platinocyanide and Zinc-Sulphide (ZnS).
Alpha particles fractionally affect the photographic plates.
Alpha particles are deflected by both electric & magnetic fields at smaller angles.
Alpha particles are garbled while passing through thin metal foils.
Most of the particles were disordered at small angles; however, a few of them deflected at an angle greater than the right angle.
Uses of Alpha Radiations
Alpha radiations are very popular in day-to-day applications. Some of its uses are:
For Treating Cancer Patients
We use alpha particles in cancer treatment. While treating the cancer patient, doctors use a technique called Unsealed Source Radiotherapy. This technique involves inserting alpha particles like Radium-226 in tiny amounts into cancerous masses. We use Radium-223 to treat bone cancer.
Static Eliminator
Static Eliminator is a common technique used in industries like paper mills. This technique helps eliminate static electricity in industries. What happens in this method is, alpha particles attract free electrons towards themselves; thereby, reducing the potential of the static electricity.
Pacemaker Battery
We can increase the life of a battery by using alpha radiation as the source of energy. Alpha radiations of Plutonium-238 serve as the best fuel source for heart pacemakers.
Oil Industries
Alpha particles are the best source of energy, especially in remote areas. Alpha radiations of Strontium-90 serve as the best source to increase the lifespan of batteries.
Smoke Detectors
Smoke detectors typically fall into the following two categories:
Photoelectric smoke detector
Ionization smoke chamber detector.
Ionization smoke chamber detectors are common household items that keep us safe by alerting smoke in our homes. These detectors use a small amount of isotope of Americium, i.e., Americium-241 as the source of alpha particles.
Alpha radiations ionize the air molecules, allowing a small current to flow between electrodes. This current rings an alarm.
Conclusion
Thus after reading this write-up on alpha particles we have understood what alphas particles are, how they are generated, their properties and characteristics and their uses. It has also helped us understand how important alpha particles are from the application point of view.
As a Physics student who will be handling such devices in the future, one must remember these particles are radioactive and can be damaging to your health. Thus when dealing with alpha particles a lot of care is taken.
Also by Vedantu
Vedantu suggests you go ahead and learn about beta particles (formed during beta decay) and gamma decay which produces gamma particles. Vedantu can also help you understand the topic of applications of Radioactivity in detail.
FAQs on Alpha Particle Mass
1. What is an alpha particle?
An alpha particle (α) is a positively charged particle that consists of two protons and two neutrons bound together. It is identical to the nucleus of a Helium-4 atom. As a result, it is often represented by the symbol ⁴₂He or He²⁺, indicating a Helium nucleus with a +2 elementary charge.
2. What is the precise mass and charge of an alpha particle?
The mass and charge of an alpha particle are fundamental properties used in nuclear physics calculations:
- Mass: Approximately 6.644 x 10⁻²⁷ kg, which is equivalent to 4.0015 atomic mass units (u).
- Charge: It has a positive charge of +2e, which is twice the elementary charge of a single proton. This equals +3.2 x 10⁻¹⁹ Coulombs.
3. Is the mass of an alpha particle simply the sum of the masses of two protons and two neutrons?
No, it is slightly less. The mass of an alpha particle is less than the total mass of two free protons and two free neutrons. This difference in mass is known as the mass defect. The 'missing' mass is converted into binding energy, which is the energy that holds the nucleus together, as described by Einstein's equation, E=mc². This binding energy is what makes the alpha particle a very stable configuration.
4. What are the key properties of alpha particles according to the NCERT syllabus?
Alpha particles have several distinct properties that are important for the CBSE Class 12 Physics syllabus:
- High Mass: They are relatively heavy compared to other forms of radiation like beta particles.
- High Ionizing Power: Due to their large mass and +2 charge, they are highly effective at knocking electrons off atoms they pass, creating many ion pairs.
- Low Penetrating Power: Their high ionizing ability causes them to lose energy quickly, so they can be stopped by a sheet of paper or a few centimetres of air.
- Velocity: They are typically ejected at speeds of about 5% to 7% the speed of light.
- Deflection: Being charged particles, their path is deflected by both electric and magnetic fields.
5. Why do alpha particles have low penetrating power but high ionizing power?
The two properties are inversely related. An alpha particle's high ionizing power is the direct cause of its low penetrating power. Because it is relatively large and has a strong +2 charge, it interacts intensely with the electrons of the atoms it passes. Each interaction (ionization) transfers some of the alpha particle's energy. Since it causes thousands of such ionizations over a very short distance, it quickly loses all its kinetic energy and stops, hence it cannot penetrate very far into a material.
6. How do alpha particles differ from beta and gamma radiation?
Alpha, beta, and gamma radiation differ significantly in their physical nature and properties:
- Composition: An alpha particle is a Helium nucleus (2p, 2n). A beta particle is a high-energy electron or positron. Gamma radiation is high-energy electromagnetic radiation (a photon).
- Charge: Alpha particles are +2e, beta particles are -1e (or +1e for positrons), and gamma rays are neutral (0).
- Mass: Alpha particles are the heaviest (~4 u). Beta particles are very light (~1/1837 u). Gamma rays are massless.
- Penetration: Gamma has the highest penetrating power, followed by beta, with alpha having the lowest.
7. What are some important real-world applications of alpha particles?
Alpha-emitting isotopes have several important applications:
- Smoke Detectors: Most common ionization-type smoke detectors use a small amount of Americium-241, an alpha emitter, to create an electric current in the air.
- Cancer Therapy: In a technique called Targeted Alpha Therapy (TAT), alpha emitters are attached to molecules that target cancer cells, delivering a high dose of destructive energy over a very short range to kill the tumour while sparing nearby healthy tissue.
- Power Sources: The heat generated by the alpha decay of isotopes like Plutonium-238 is used in Radioisotope Thermoelectric Generators (RTGs) to power spacecraft and rovers for deep space missions.
8. How does a household smoke detector use the properties of an alpha particle to detect smoke?
An ionization-type smoke detector contains a small amount of Americium-241, which continuously emits alpha particles. These particles bombard air molecules inside a chamber, knocking electrons free. This process, called ionization, allows a small, steady electric current to flow between two electrodes. When smoke enters the chamber, the smoke particles attach to the ions, neutralizing them and disrupting the flow of current. The detector's circuitry senses this drop in current and triggers the alarm.
9. What eventually happens to an alpha particle after it has been emitted and lost its energy?
After an alpha particle is emitted during radioactive decay, it travels through a medium, losing its kinetic energy by ionizing the atoms it encounters. As it slows down significantly, its strong positive charge allows it to capture two electrons from the surrounding material. Once it has captured two electrons, the alpha particle becomes a complete, electrically neutral, and stable Helium atom.
10. Is a Helium nucleus (He²⁺) exactly the same thing as an alpha particle?
Yes, for all practical purposes in the context of nuclear physics, a Helium nucleus is an alpha particle. The notation He²⁺ signifies a Helium atom that has lost its two orbital electrons, leaving only the nucleus, which consists of two protons and two neutrons. This is the precise definition of an alpha particle. The terms are used interchangeably.
