Alpha Particle Mass: Definition, Value, Properties & Example

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Alpha Particle, alternatively known as Alpha Ray or Alpha Radiation, is a particle that is positively charged emitted when radioactive materials are decayed. The reason behind the mass of the alpha particle is the bonding between its two protons and two neutrons. In this article, we will learn more about the mass of the alpha particles, their properties, and their uses.

Keyterms: Atoms, Thomson's Atomic Model, Rutherford's Model, Atomic Spectra, Alpha-Radiations, Radiation, Alpha Ray, Proton, Neutron, Helium, Nucleus, Velocity


What is an Alpha Particle?

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Alpha particles, alpha rays, or alpha radiations, are all the names of a particle consisting of two protons and two neutrons which are known as alpha particles. The alpha particles actually are very similar to the helium nucleus emitted by some radioactive substances. The alpha particles are named after the first Greek alphabet, α. The alpha particles are generally produced during the alpha decay but there are various other ways to produce alpha particles. They have zero net spins. Alpha particles have a kinetic energy of 5 MeV, and a velocity of 4% of that of light.

Alpha particles

Alpha particles

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Properties of Alpha Particles

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  • The mass of the alpha particle is 6.644657230(82) x 10-27 kg. 
  • The speed of the alpha particle is 1.4 x 107 m/s to 2.1 x 107 m/s.
  • The penetrating power of alpha particles is very low due to their large size.
  • Alpha particles give rise to heating effects if they are stopped.
  • Alpha particles are produced in the high-energy particle accelerators.
  • Alpha particles are capable of producing fluorescence in certain substances.
  • They also affect photographic plates.
  • They have high ionization power.
  • Despite the low perforating power, alpha particles can result in burns on the human body.
  • At smaller angles, alpha particles are deflected by both magnetic and electric fields.

Radioactive Atom Releasing an Alpha Particle

Radioactive Atom Releasing an Alpha Particle

Some properties of alpha particles along with corresponding values and units are listed below:

Alpha Particles Value
Alpha particle mass number 4
Alpha particle Charge Positive
Alpha particle symbol α, He+2
Charge of alpha particle +2
Alpha particle mass (amu) 4.0015(63) amu
Alpha particle mass (Ev) 3.727 GeV/C2
Alpha particle mass (Kg) 6.644657230(82) × 10-27 Kg
Mass of alpha particle compared to proton Mass of alpha particle= 4 x mass of a proton
Spin 0
Composition Two protons, Two neutrons
Activeness Highly energetic and active

Uses of Alpha Particles

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  1. Alpha particles are used in cancer treatment in Unsealed Source Radiotherapy which works by inserting alpha particles in little amounts into the cancerous masses.
  2. Alpha particles are used to eliminate static electricity in industries like paper mills as the alpha particles work by attracting free electrons.
  3. Alpha particles also act as fuel sources for pacemakers.
  4. Alpha particles are also used in various experiments such as the Rutherford gold foil experiment, Geiger-Marsden experiment.
  5. Alpha particles are also used in smoke detectors by ionizing the molecules in the air which allows a small amount of current to pass through the electrodes, thus ringing an alarm.

Example of Alpha Particle

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Any alpha decay can be easily represented as:

Any alpha decay can be easily represented as

Hence, an example of alpha decay can be:

Hence, an example of alpha decay can be:

Here,\(^4_2He\)is the alpha particle.

Alpha particle

Alpha particle

Things to Remember

  • Alpha Particle, alternatively known as Alpha Ray or Alpha Radiation, is a particle that is positively charged emitted when radioactive materials are decayed.
  • The alpha particles are named after the first Greek alphabet, α.
  • The speed of the alpha particle is 1.4 x 107 m/s to 2.1 x 107 m/s.
  • Despite the low perforating power, alpha particles can result in burns on the human body.
  • Alpha particles are used to eliminate static electricity in industries as the alpha particles work by attracting free electrons.
  • Alpha particles are used in cancer treatment.

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Sample Questions

Ques. How are alpha particles represented? (2 marks)

Ans. The alpha particles are represented by the Greek symbol α. Alpha particles are similar to helium nucleus so can also be represented by

Ques. What is an alpha particle? (2 marks)

Ans. The alpha particles are originally considered as a ray. They are actually the helium nucleus emitted by some radioactive elements.

Ques. What is the mass of an alpha particle? (1 marks)

Ans. The mass of an alpha particle is 6.644657230(82)X 10-27 kg

Ques. How alpha particles are dangerous? (1 marks)

Ans. The alpha particles cause damage to the cells and the DNA. 

Ques. What is the speed of an alpha particle? (1 marks)

Ans. The speed of alpha particles is between 1.4X107 m/s to 2.1 X 107 m/s.

Ques. How do alpha particles lose energy? (2 marks)

Ans. The maximum amount of energy of the alpha particles is lost during the process of attracting the electron from large distances. Alpha particles constantly lose energy, slow down and finally stop and turn into neutral atoms.

Ques. Why do alpha particles have high ionizing power? (1 marks)

Ans. The mass of the alpha particle and the double-positive charge are the reasons behind the high ionizing power of alpha particles. Alpha particles are able to create multiple ionization within a very small distance.

Ques. What is the strongest ionizing radiation? (1 marks)

Ans- The alpha particle radiation is four times the mass of proton and neutron and large size, has the highest ionizing power, and has the greatest ability to damaged tissues.

Ques. Do alpha particles have mass? (1 marks)

Ans- Yes, alpha particles have a mass. The mass of alpha particles is equivalent to the mass of four protons.

Ques. State three properties of alpha particles. (2 marks) 

Ans. The properties of alpha particles are:

  • Alpha particles give rise to heating effects if they are stopped.
  • They also affect photographic plates and have high ionization power.
  • Alpha particles are capable of producing fluorescence in certain substances.

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CBSE CLASS XII Related Questions

  • 1.
    Three batteries E1, E2, and E3 of emfs and internal resistances (4 V, 2 \(\Omega\)), (2 V, 4 \(\Omega\)) and (6 V, 2 \(\Omega\)) respectively are connected as shown in the figure. Find the values of the currents passing through batteries E1, E2, and E3.
    Three batteries E1, E2, and E3 of emfs and internal resistances


      • 2.
        A charge \( -6 \mu C \) is placed at the center B of a semicircle of radius 5 cm, as shown in the figure. An equal and opposite charge is placed at point D at a distance of 10 cm from B. A charge \( +5 \mu C \) is moved from point ‘C’ to point ‘A’ along the circumference. Calculate the work done on the charge.
        work done on the charge


          • 3.
            A small spherical shell \( S_1 \) has point charges \( q_1 = -3 \, \mu C \), \( q_2 = -2 \, \mu C \) and \( q_3 = 9 \, \mu C \) inside it. This shell is enclosed by another big spherical shell \( S_2 \). A point charge \( Q \) is placed in between the two surfaces \( S_1 \) and \( S_2 \). If the electric flux through the surface \( S_2 \) is four times the flux through surface \( S_1 \), find charge \( Q \).


              • 4.
                The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:

                  • \( \frac{\alpha}{r} \)
                  • \( \frac{\alpha r^2}{2} \)
                  • \( \frac{\alpha}{2r^2} \)
                  • \( -\frac{\alpha}{r} \)

                • 5.
                  A rectangular glass slab ABCD (refractive index 1.5) is surrounded by a transparent liquid (refractive index 1.25) as shown in the figure. A ray of light is incident on face AB at an angle \(i\) such that it is refracted out grazing the face AD. Find the value of angle \(i\).
                  A rectangular glass slab ABCD (refractive index 1.5)


                    • 6.
                      In the circuit, three ideal cells of e.m.f. \( V \), \( V \), and \( 2V \) are connected to a resistor of resistance \( R \), a capacitor of capacitance \( C \), and another resistor of resistance \( 2R \) as shown in the figure. In the steady state, find (i) the potential difference between P and Q, (ii) the potential difference across capacitor C.
                      potential difference across capacitor C

                        CBSE CLASS XII Previous Year Papers

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