Introduction to Radioactive Isotopes
Due to nuclear instability, the nucleus exhibits the phenomenon of Radioactivity. It is the phenomenon of the disintegration of heavy elements into comparatively lighter ones by emission in the form of radiation. It was discovered by Henri Becquerel in 1896. Energy is lost due to radiation emitted out of the unstable nucleus of an atom. The driving force of this phenomenon is the force of repulsion also known as electrostatic force, and the forces of attraction of the nucleus which keep the nucleus together. The two forces are considered extremely strong in the natural environment.
The instability of the atom increases as the size of the nucleus increases because the mass of the nucleus becomes a lot when concentrated. This is the main reason that atoms of Plutonium, Uranium are extremely unstable and undergo the phenomena of radioactivity. Emission and absorption are not noticed easily when it takes place in the atom.
Definition of Radioactive Isotopes
Radioisotopes are radioactive isotopes of an element. They are the atoms containing an unstable combination of neutrons and protons or excess energy in their nucleus. The excess of energy can be used in any of the ways during those processes, the radionuclide is said to undergo radioactive decay.
Radioactive decay is a property of naturally occurring elements and artificially produced isotopes of the elements. The rate at which a radioactive element decays is expressed in terms of its half-life which is the time required for one-half of any given quantity of the isotope to decay. We have discussed radioactive isotope definition, Radioisotopes, Half-life, Radioactive decay now we will discuss some application of radioactive isotopes.
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Laws of Radioactivity
The rate of decay of the nucleus is independent of the temperature and pressure.
It follows the law of conservation of charge.
The emission of energy from radioactivity is accompanied by alpha, beta, and gamma particles.
The rate of decay of radioactive substances is proportional to the number of atoms that are present at the time.
(Curie and Rutherford are the units of radioactivity.)
Uses of Radioactive Isotopes
Radioisotopes used in medicine have short half-lives, which means they decay quickly and are suitable for diagnostic purposes; others with longer half-lives take more time to decay, which makes them suitable for therapeutic purposes.
Radioactive isotopes have several other useful applications like they are used in medicine, for example, Cobalt-60 is extensively used as a radiation source to arrest the development of cancer.
Americium-241 an alpha emitter is used in domestic smoke detectors in the United States.
Iodine-131 is found effective in treating hyperthyroidism. Another important radioactive isotope is carbon-14, which is used in a breath test to detect the ulcer-causing bacteria Heliobacter pylori.
They are also used to measure the thickness of metal or plastic sheets, the precision of thickness is indicated by the strength of the radiations that penetrate the material being inspected.
Application of Isotopes
Isotopes of an element have the same atomic number but different mass numbers. Hydrogen is the first element present in the periodic table and has one proton. Hydrogen has three isotopes protium, deuterium, and tritium. The three isotopes are different because of the difference in the number of neutrons present in them. In protium, there is only proton and electron, whereas deuterium contains one neutron and tritium contains two neutrons. Out of these three isotopes of hydrogen, tritium is radioactive in nature which emits low energy particles. Some radioactive isotopes examples are Tritium, which is used in Boosting Nuclear weapons, Neutron initiator, Self-powered lighting, etc.
Another Radioactive isotopes example is Uranium, which is a weakly radioactive element with an atomic number 92 and symbol U. It has two isotopes U-235 and U-238. It is one of the heavy metals that can be utilized as a rich source of concentrated energy. Isotope U-235 is mostly used because it can be split readily and yield a large amount of energy when bombarded with a slow-moving neutron. Natural uranium is found as a mixture of two isotopes. U-238 accounts for 99.3% and U-235 around 0.7%.
Types of Radioactivity: Alpha, Beta, and Gamma Decay
Alpha Decay: The nuclear disintegration process that emits alpha particles is termed alpha decay. An example of alpha decay is uranium-238. The alpha decay of U -238 is given as:
92U238 → 4He2 + 234Th90
In the above nuclear change, the uranium atom is transformed into an atom of thorium and gives off an alpha particle. The bottom number in a symbol indicates the number of protons which signifies that the alpha particle has two protons in it that is lost by the uranium atom. The two protons also have a charge of +2. The top number 4 indicates the mass number or the total of the protons and neutrons in the particle.
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Beta Decay: A beta particle is a type of decay in which a high-energy electron is emitted from the nucleus. Nuclei don't contain electrons and yet during decay, an electron is emitted from a nucleus. At the equivalent time that the electron is being ejected from the nucleus, a neutron is becoming a proton. (It is unwise to picture this as a neutron breaking into two pieces are a proton and an electron.) That would be convenient for simplicity, but unfortunately, this is not what actually happens. For convenience, we'll treat decay as a neutron splitting into a proton and an electron. The proton stays within the nucleus, increasing the number of the atom by one. The electron ejects from the nucleus and is the particle of radiation which is called beta.
In order to insert an electron in the equation and to add up properly, a nucleon number is to be assigned to an electron. The mass number assigned to an electron is zero (0), which is reasonable since the mass number is the number of protons and neutrons, and an electron contains no protons and no neutrons. The number assigned to an electron may be a negative one (-1) because that permits a nuclear equation containing an electron to balance atomic numbers. In the example below Thorium is a nucleus that undergoes beta decay.
-1e0 or -1β0
234Th90 → 0e-1 + 234Pa91
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Gamma Ray: Gamma-ray is produced in nuclear reactions of all types. In the alpha decay of U -238 nucleus, two gamma rays of different energies are emitted in addition to the alpha particle.
238U92 → 4He2 + 234Th90 + 20γ0
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Summary
At the end of this discussion on Radioactive Isotopes, we can conclude the topic. Radioactive Isotopes are the atoms with an unstable nucleus regain stability by emitting radiation, which contains extra particles and energy. The process of radiation decay is known as radioactive decay. Each radioisotope's radioactive decay process is distinct, and its half-life is used to measure it. The time it takes for half of the unstable atoms to undergo radioactive decay is called a half-life.
Did You Know?
Radioactivity was discovered accidentally by Henry Becquerel in the year 1896. A Uranium compound was placed in a drawer containing photographic plates, wrapped in black paper. When the plates were examined thoroughly it was found that they were exposed. This exposure, later on, gave rise to the concept of Radioactive decay. The life of every radioactive element is finite.
FAQs on Radioactive Isotopes
1. What is a radioactive isotope? Provide an example.
A radioactive isotope, also known as a radioisotope, is an atom that has an unstable nucleus due to an excess of energy or an imbalanced ratio of neutrons to protons. To achieve stability, its nucleus undergoes spontaneous disintegration, a process called radioactive decay, where it emits radiation in the form of particles or energy. For example, Carbon-14 (C-14) is a radioactive isotope of carbon, whereas Carbon-12 (C-12) is stable.
2. How is a radioactive isotope different from a regular, stable isotope of the same element?
The primary difference lies in the stability of the nucleus. Both types of isotopes of an element have the same number of protons and electrons. However, they differ in the number of neutrons. In a stable isotope, the combination of protons and neutrons results in a stable nucleus. In a radioactive isotope, this combination is unstable, leading it to spontaneously decay and emit radiation to become more stable.
3. Why are some isotopes radioactive while others are not?
The stability of an atom's nucleus depends on the neutron-to-proton (n/p) ratio. For lighter elements, a stable ratio is close to 1:1. For heavier elements, more neutrons are needed to counteract the electrostatic repulsion between protons, so a stable ratio is closer to 1.5:1. An isotope is radioactive if its nucleus falls outside the 'band of stability' because it has too many or too few neutrons relative to its protons, making it unstable and prone to decay.
4. What is meant by the half-life of a radioactive isotope?
The half-life (t₁/₂) of a radioactive isotope is the specific time it takes for half of the atoms in a given sample to undergo radioactive decay. It is a constant value for each specific isotope and is not affected by external factors like temperature or pressure. For instance, if you start with 100 grams of an isotope with a half-life of 10 years, only 50 grams will remain after 10 years, and 25 grams will remain after another 10 years.
5. What are the key differences between alpha, beta, and gamma decay?
Alpha, beta, and gamma decay are three different ways an unstable nucleus releases energy and particles. They differ in what is emitted:
- Alpha (α) Decay: The nucleus emits an alpha particle, which is essentially a helium nucleus (2 protons and 2 neutrons). This reduces the atomic number by 2 and the mass number by 4.
- Beta (β) Decay: The nucleus emits a beta particle (a high-energy electron). This occurs when a neutron transforms into a proton. It increases the atomic number by 1 but leaves the mass number unchanged.
- Gamma (γ) Decay: The nucleus emits a gamma ray, which is a high-energy photon. This process does not change the atomic or mass number but allows the nucleus to release excess energy, often after an alpha or beta decay has occurred.
6. What are some important applications of radioactive isotopes in medicine and industry?
Radioactive isotopes have several critical applications. In medicine, Cobalt-60 is used in radiation therapy to target cancer cells, and Iodine-131 is used to diagnose and treat thyroid disorders. In industry, Americium-241 is used in smoke detectors, while other isotopes are used to measure the thickness of materials like plastic and metal sheets without contact.
7. If radioactivity can be harmful, how are radioisotopes used safely for medical diagnosis and treatment?
The safe use of radioisotopes in medicine relies on two key principles: dose and half-life. For diagnostic purposes, isotopes with very short half-lives are used in tiny amounts. They decay quickly, providing the necessary image or data while minimising the patient's radiation exposure. For therapeutic purposes, like cancer treatment, higher doses of radiation are precisely targeted at the cancerous cells to destroy them while sparing the surrounding healthy tissue as much as possible.
8. Does a sample of a radioactive isotope ever decay to zero?
Theoretically, a sample of a radioactive isotope never fully decays to zero. The process of decay is based on half-lives, meaning that in each half-life period, the amount of the radioactive substance reduces by half. This creates an exponential decay curve that approaches zero but never mathematically reaches it. For all practical purposes, after many half-lives, the amount of remaining radioactive material becomes so negligible that it is considered to have completely decayed.
