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Positron was discovered by American physicist Carl Anderson in 1933. The discovery of positrons was the first evidence of these particles and they belong to what is called antimatter. Positrons do not exist in the environment due to the movement of countless electrons around the atom. The process of annihilation exerts energy to create equal counts of positrons and electrons; both are opposite with varying properties.
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Key Terms:- Positron, Electron, subatomic particle, radioisotopes, Decay, mass of a positron, annihilation process.
Definition
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Positron is also known as antielectron having the same mass as that of the electron but positively charged subatomic particle. Not the mass but the magnitude of the charge is equal to that of the electron. It has a spin of ½ and an electrical charge of +1. Positron is also known as a positive electron and creates the antiparticle of the negative electron.
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| Topics Related to Positron | ||
|---|---|---|
| Polonium | Plutonium | Carbon dating |
| Nucleation | Cadmium | Nucleon |
How is Positron created?
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Positrons are formed during the decaying of nuclides that have an excess of Proton in the nucleus compared to the number of Neutron. Radio nuclides emit Positron and neutrino while decaying. Although neutrinos don’t interact with surrounding material, positrons interact with electrons and the process is called Annihilation.
Positron is similar to that of the proton as a positively charged subatomic particle. The main differentiating factor between proton and positron is their mass. The mass of a proton is quite higher than that of the positron.
Difference between Positron and electron:
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A positron is the antimatter counterpart of an electron. The antimatter is opposite to matter, in detail; it looks like matter however differ from the former at least one of its properties. Positrons are not found in an atom but formed in the + decay of radioisotopes. Alternately, electrons are found revolving around the nucleus of an atom. The process of annihilation takes place between positron and electron when the antimatter and matter meet each other.
The table shows the difference in properties of positron and electron.
| Properties | Positron | Electron |
|---|---|---|
| Mass | 9.109 E-31 Kg | 9.109 E-31 Kg |
| Spin | ½ | ½ |
| Charge | +e | -e |
| Symbols | E+, β+ | E-, β- |
| Nuclear symbol | 0 β +1 | 0 e -1 |
Characteristics of Positrons
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- Positrons are stable in a vacuum.
- They quickly react with electrons.
- β+ Decay of radioactive isotopes emits positrons. Positrons are emitted by the Positron Emitted Tomography man-made method.
- Remain stable when kept alone but undergoes a process of annihilation when meeting other particles of matter like an electron.
Mass of Positron
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The mass of a positron is equal to the mass of the electron and it is 0.000548756 amu. Positron is produced by decaying radioactive isotope so there is some loss of kinetic energy. The positron particle participates in the annihilation process after losing kinetic energy.
The encounter of positron with the electron obeys the Law of momentum or Law of energy conservation.
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Things to Remember
- It is a form of antimatter because when a positron encounters an electron both the particles annihilate to yield energy.
- It is not true that positrons have negative kinetic energy.
- Positrons are important in medical technology to scan the brain and nervous system.
- The PET scanner detects and maps the positron emission from the ingested substance that is annihilated by surrounding electrons.
Sample Questions
Ques. Does a positron particle have mass? (1 mark)
Ans: The positively charged positron particle has the same mass and magnitude as that of the electron. The positrons are produced in the decay of short-lived particles called muons.
Ques. What stops positrons? (1 mark)
Ans: A metal sheet can stop the emission of positron during the decaying of + radioactive isotopes. Also, the positron can penetrate few centimetres into a solid material.
Ques. Does a positron have a negative mass? (1 mark)
Ans: A negative mass does not exist as anti-gravity is not possible. No matter or subatomic particle exists with negative mass. The electron and positron have the same mass, same spin, and same magnitude of charge.
Ques. Is positron a stable particle? (1 mark)
Ans: Of course, the positively charged positron is stable in a vacuum. It quickly reacts with electrons of ordinary matter by annihilation to produce gamma radiation.
Ques. How does a positron identify? (1 mark)
Ans: PET uses a scanning device to detect the photon emitted by a radionuclide in an organ or tissue for examination. PET is the abbreviation of Positron Emission Tomography.
Ques. Can you touch antimatter? (1 mark)
Ans: When antimatter and regular matter touch or collide, they will destroy themselves by releasing lots of energy. The energy is measured as radiation. The radiation emitted in small quantities is completely safe to get in contact. If huge radiation (gamma) is emitted then it is more than enough to kill you.
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