Alpha Particle Mass vs Proton, Electron, Deuteron: Full Table & FAQ
Alpha particles play a crucial role in modern physics, especially in nuclear science. An alpha particle is the nucleus of a Helium atom, consisting of two protons and two neutrons, and is often represented by the symbol α or He2+. Unlike a neutral helium atom, an alpha particle carries a positive charge because it lacks electrons.
Alpha Particle Mass: Definition and Key Values
The mass of an alpha particle is a well-established physical constant and is approximately four times the mass of a proton. Formally, the accepted value is:
- Mass in kg: 6.644657230(82) × 10-27 kg
- Mass in atomic mass unit (u): 4.001506179127(63) u
- Mass in energy units: 3.727379378(23) GeV/c2
- Charge: +2 (positive)
- Mass number: 4
The values in parentheses indicate the margin of experimental uncertainty. For calculation purposes, the rounded values above can be used.
Properties of Alpha Particles
| Property | Value | Unit |
|---|---|---|
| Mass | 6.644657230 × 10-27 | kg |
| Mass (amu) | 4.001506179127 | u |
| Mass (GeV/c2) | 3.727379378 | GeV/c2 |
| Mass Number (A) | 4 | – |
| Charge | +2 | (relative unit) |
| Symbol | α or He2+ | – |
Alpha particles are much heavier than electrons and protons. Their charge of +2 allows them to interact strongly with matter, resulting in high ionization but low penetration depth.
Comparison of Alpha Particle with Proton and Electron
| Property | Alpha Particle (α) | Proton | Electron |
|---|---|---|---|
| Approx. Mass (u) | 4.0015 | 1.0073 | 0.0005486 |
| Charge | +2 | +1 | -1 |
| Constituents | 2p, 2n | 1p | – |
Sources of Alpha Particles
Alpha particles primarily originate through the radioactive decay called alpha decay. In this process, heavy atomic nuclei (with atomic mass >106 u) emit an alpha particle, reducing their mass number by four. Alpha particles can also result from certain nuclear reactions in stars and constitute 10–12% of cosmic rays.
The phenomenon of ternary fission, although rare, can produce especially energetic alpha particles, often called long-range alphas due to their higher energy compared to typical alpha decay particles.
Applications of Alpha Particles
- Used in cancer therapy, especially via techniques like Unsealed Source Radiotherapy, by injecting substances such as Radium-226 or Radium-223 for targeted treatment.
- Employed in industrial static eliminators by attracting free electrons and reducing static electricity.
- Provide energy for battery-powered pacemakers; Plutonium-238 alpha radiation is commonly used as the fuel source.
- Enable ionization smoke detectors, which utilize a tiny amount of Americium-241 to detect smoke by sensing ionization changes in air.
Step-by-Step: Mass Calculations and Understanding
The mass of an alpha particle is not simply the sum of the masses of two protons and two neutrons. The binding energy (according to mass-energy equivalence) causes the actual mass to be slightly less—a phenomenon known as mass defect.
To convert the alpha particle mass from atomic mass units (u) to kilograms (kg), use:
For example, mass in kg = 4.001506 × 1.66053906660 × 10-27 ≈ 6.644657 × 10-27 kg.
Typical Features and Formulae
- Alpha particle mass ≈ 4 × mass of proton
- Charge = +2e
- Mass calculation: 2 × mass of proton + 2 × mass of neutron – binding energy/c2
Alpha Particle: Problem Example
Q: What is the ratio of the mass of an alpha particle to that of a proton?
• Mass of proton = 1.007276 u
• Ratio = 4.001506 / 1.007276 ≈ 3.97
More Learning & Practice
- Learn about Alpha Decay Process
- Explore Binding Energy in Nuclei
- Radioactivity: Alpha, Beta, Gamma Decay
- More on Atomic Physics Concepts
Summary Table: Alpha Particle Quick Facts
| Aspect | Alpha Particle |
|---|---|
| Structure | 2 protons + 2 neutrons (He2+) |
| Rest Mass | 6.644657230 × 10-27 kg |
| Mass Number | 4 |
| Electric Charge | +2e |
| Penetration | Low (stopped by paper/skin) |
| Ionizing Power | High |
Mastering the concept of alpha particle mass helps in understanding nuclear decay, energy emission, and the structure of nuclei. It supports the study of radioactivity and its applications in physics, medicine, and engineering.
For more resources and to deepen your understanding, explore related topics such as Nucleus of an Atom, Mass-Energy Equivalence, and Binding Energy on Vedantu.
FAQs on Alpha Particle Mass: Exact Value, Charge, Units & Comparison
1. What is the mass of an alpha particle?
The mass of an alpha particle is 6.644657 × 10-27 kg (kilograms) or 4.001506 u (atomic mass units).
• This value is sourced from the most recent NCERT, NTA, and CRC Handbook data.
• In nuclear physics, alpha particles are crucial for understanding radioactive decay and nuclear reactions.
2. What is the charge of an alpha particle?
An alpha particle carries a positive charge of +2e, which equals 3.204 × 10-19 coulombs.
• This is because an alpha particle consists of 2 protons and 2 neutrons.
• The strong positive charge gives alpha particles high ionizing power but limits penetration depth.
3. Is an alpha particle heavier than a proton?
Yes, an alpha particle is significantly heavier than a proton.
• Alpha particle mass: 4.001506 u
• Proton mass: 1.007276 u
• Alpha particles are nearly 4 times as massive as protons.
4. What is the mass number of an alpha particle?
The mass number of an alpha particle is 4.
• This is because it consists of 2 protons and 2 neutrons.
• Alpha particles are represented as 4He2+ or simply α.
5. Are alpha particles the same as helium nuclei?
Alpha particles and helium-4 nuclei are essentially the same in composition (2 protons and 2 neutrons), but
• Alpha particles have a charge of +2 (they lack electrons),
• A neutral helium atom has 2 electrons.
• In nuclear reactions, alpha particles are specifically He2+ ions.
6. How do you convert the mass of an alpha particle from amu to kg?
To convert alpha particle mass from amu (u) to kg:
1. Use: 1 u = 1.66053906660 × 10-27 kg
2. Multiply: 4.001506 × 1.66053906660 × 10-27 kg
3. Result: 6.644657 × 10-27 kg
7. What is the value of mass of alpha particle in MeV/c2?
The mass of an alpha particle is 3727.38 MeV/c2.
• Calculated as: 4.001506 u × 931.494 MeV/c2 per u
8. How does the alpha particle mass compare to electron and deuteron mass?
Alpha particle mass is much greater than electron mass and nearly twice the mass of deuteron.
• Electron: 0.0005486 u
• Deuteron: 2.013553 u
• Alpha particle: 4.001506 u
Thus, alpha >> deuteron >> electron (by mass).
9. What are the main properties and characteristics of an alpha particle?
Main properties of alpha particle:
• Mass: 4.001506 u (6.644657 × 10-27 kg)
• Charge: +2e (double positive)
• Mass number: 4
• Consists of 2 protons, 2 neutrons
• Symbol: α or He2+
• High ionizing power, low penetration
10. What are the main sources of alpha particles?
Alpha particles are commonly produced by:
• Radioactive alpha decay of heavy nuclei like Uranium-238 and Radium-226
• Certain nuclear reactions in stars
• Small amounts in cosmic rays and rare nuclear fission (ternary fission)
• Used in smoke detectors and medical therapies as isotopic sources
11. How is the alpha particle mass calculated from its components?
Alpha particle mass is the sum of 2 protons and 2 neutrons minus binding energy:
• mα = 2 × mproton + 2 × mneutron – Binding Energy mass deficit
• The actual measured mass is slightly less than the sum due to nuclear binding energy.
12. Why is the mass of an alpha particle not exactly equal to 4 times a proton’s mass?
The mass of an alpha particle is slightly less than 4 times the proton mass because:
- Nuclear binding energy causes a mass defect
- Some mass is converted to binding energy that holds the nucleus together
