Radiation is an emission of energy in the form of waves or particles. This includes the emission of Alpha particle, Beta particle, and Gamma particle. Alpha particles are also denoted by Alpha rays or Alpha radiation. It has two protons and two neutrons.
Alpha particles are formed during α - decay of radioactive elements such as uranium, thorium, radium, and plutonium. Alpha particles are positively charged particles. The alpha particles can be denoted as α or α2+. As alpha particles are similar to helium nuclei they are also denoted as doubly ionized helium nuclei He2+. Due to their double positive power, they have high ionizing power but have low penetration depth. α - decay is a decay process in which the parent element emits an alpha particle thereby it decays into a different element. For example, uranium -238 undergoes α - decay emits α - particles and is transmuted into thorium - 234.
$$\mathrm{{289}_{92}U\:\rightarrow\:4_2He+234_{90}Th}$$
As uranium emits alpha particles during α - decay four units decreased from its mass number and two units decreased from its atomic number.
As an alpha particle is like that of a Helium atom its mass is equal to that of the mass of Helium. Mass of α - particles are,
$$\mathrm{\alpha_m= 6.644657230(82)×10^{-27}\:Kg}$$
| Parameters of Alpha particle | Values |
|---|---|
| Composition | Two protons and two neutrons |
| Mass in Kg | $\mathrm{\alpha_m= 6.644657230(82)×10^{-27}\:Kg}$ |
| Mass in amu | 4.001506179127(63)u |
| Mass in eV | 3.727379378(23) GeV/c2 |
| Electric charge | Positive (+2) |
| Spin | 0 |
| Symbols | $\mathrm{\alpha, \alpha^{2+}, He^{2+}}$ |
| Kinetic Energy | $\mathrm{5\: MeV}$ |
Table-1: Characteristics of an Alpha Particle
Alpha particles have high velocities ranging from $\mathrm{1.4 \times 10^7 to 1.7 \times 10^7 m/s}$.
They travel in a straight line.
They have intense ionisation power. Its ionisation power is 102 times greater than that of beta rays and 104 times greater than that of gamma rays. They can also ionise biological molecules.
Its ionisation power is high but has low penetration depth. They can even be blocked by paper.
As the mass of an alpha particle is high its penetrating power is less. It is 1/1000 times the penetrating power of beta rays and 1/100000 times the penetrating power of gamma rays.
Alpha particles interact with matter through coulomb forces.
Even though it has a high ionisation power it loses its kinetic energy quickly. So, the range of α - particles is short.
They are deflected by both electric and magnetic fields which show that they are charged particles.
Alpha particles produce both fluorescence and phosphorescence.
As it is a positive charge it deflects towards negative plates.
Alpha particles are scattered by heavy elements like gold.
They can produce a heating effect. This heating effect is due to the stoppage of α - particles. They affect photographic plates but it is very weak.
The mass of an alpha particle is four times that of a Hydrogen atom.
It is used to treat cancer in the medical field. Radium - 226 is inserted into the cancerous masses. It kills the cancer cells. But because of its less penetrating power, it does not affect human cells.
Americium - 241 is used in smoke detectors. Smoke entering the detector is ionised by americium - 241 and the ejected free electrons produce an electric current which triggers the alarm.
Batteries used in satellites and spacecraft are charged using Plutonium - 238 as a fuel source. During α - decay electricity is produced by converting the heat produced in the battery.
A pacemaker used to control the heart beat uses Plutonium - 238 as fuel for its batteries. But due to its toxicity and difficulties, it is no longer used.
In industries to reduce static electricity Polonium - 210 is used. The alpha particles produced during the α - decay attract the electrons as it is positively charged. It reduces the potential thereby it reduces the static electricity. It is mostly used in paper mills.
Alpha radiation from Strontium - 90 is used as a fuel source for oceanic buoys by the U.S coast. Here also the α radiation is used to energise the batteries.
Alpha particles originated from radioactive elements having two electrons and two protons bound together. These particles have high Ionisation power so they can penetrate through matter. Naturally, the alpha particles are radiated from radionuclides like U-238 and R-226 and artificially these are produced in reactors using the radioisotopes of plutonium, californium, and so forth. Alpha particles find application in various treatments like cancer treatment, smoke detectors, artificial heart pacemakers, thermoelectric generators, etc. As it has low penetration depth it cannot penetrate through the skin and cannot be affected.
Q1. How is the alpha particle detected?
Ans. Charged particles like alpha particles are detected using many methods. They are
Ionisation chamber
Scintillation counter
Semiconductor detector
Q2. How do alpha particles interact with matter?
Ans. Alpha particles emitted during alpha decay travel for only small distances but deposit their total energy over there. So, the energy transferred is high. As it is highly charged, it can have the energy to eliminate an electron from the atom. This is known as ionisation. Alpha particles have high ionisation power.
Q3. Compare the ionisation power and penetrating power of alpha particles with beta particles and gamma particles.
Ans. Alpha particles have intense ionisation power. Its ionisation power is 102 times greater than that of beta rays and 104 times greater than that of gamma rays. They can also ionise biological molecules.
As the mass of an alpha particle is high its penetrating power is less. It is 1/1000 times the penetrating power of beta rays and 1/100000 times the penetrating power of gamma rays.
Q4. Are alpha decay and alpha particles the same?
Ans. No. Alpha particles are particles that are emitted from the radioactive elements during alpha decay. Alpha decay is a process of emission of alpha particles.
Q5. What are the health effects caused by alpha radiation? How to protect ourselves from alpha radiation?
Ans. Alpha particles have high ionisation power but it has less penetration depth. So, it cannot penetrate through the outer skin and so it cannot affect the outer layer of skin. But if the alpha radiation is inhaled or consumed by a person it affects the inner parts.
If it is inhaled it reaches the lungs and may lead to cancer. If it is consumed through water, it reaches the kidneys and may lead to kidney diseases. High exposure to alpha radiation may lead to DNA damage. Large amounts of exposure lead to Acute radiation syndrome. Protection from alpha radiation
To avoid these health effects there are three possible ways. By reducing the time of exposure to alpha radiation, having a long distance from the exposure of alpha radiation, and making a shield these health hazards are reduced.
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