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Radioactivity

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Radioactivity

When we hear the word radioactivity, our mind tends to drift to catastrophic incidents, such as the nuclear fallout at Chernobyl. However, the same radioactivity that so many fear is used in medicine, academics, industry, and in generating electricity.

But what is radioactivity? Radioactivity occurs when an unstable atom emits radiation to achieve stability.

Why does radioactivity even occur?

Everything you see around you is made up of stable atoms. Otherwise, your carbon table would degenerate into something else.

Inside the atom's nucleus, some protons are positively charged, while neutrons are neutrally charged. The two are supposed to repel each other, except that there is a strong nuclear force that keeps the nucleons intact. This glue-like force has a very short range and depends on the ratio of protons and neutrons inside the nucleus.

An imbalance of protons and neutrons, therefore, affects this nuclear force. To be more precise, if the number of neutrons surpasses the number of protons, the element becomes unstable because atoms tend to expel excess energy to regain stability.

Carbon 12 is a stable element with six protons and six neutrons. Carbon 14, however, with eight neutrons and six protons, is an unstable isotope. Isotopes are formed when an atom's proton numbers are the same as the stable atom but the number of neutrons varies.

The scenarios above lay the foundations for unstable isotopes. Just as your body gets rid of waste material, the isotopes emit particles with energy to restore balance. However, during this emission of energy, isotopes form a new nucleus.

This property of turning from one thing into something else to attain stability is what we call radioactivity. And the process in which an unstable atomic nucleus releases energy to become stable is known as radioactive decay. Materials that have unstable nuclei are, therefore, radioactive.

Radioactivity: Radioactive decay

Unstable isotopes with three kinds of energy particles, which means that there are three types of radiation that are released by an unstable nucleus.

Radioactivity: Alpha (α)

An alpha particle has a helium nucleus that consists of two protons and two neutrons.

Radioactivity, Alpha particle, StudySmarterFigure 1. An alpha particle consists of two protons and two neutrons.

Alpha particles are somewhat heavy and only travel a few centimeters. Alphas are not that harmful either, as they can be easily halted by a sheet of paper or plastic.

Radioactivity: Beta (β)

An electron or a positron (a particle having the same mass as an electron and a numerically equal but positive charge) is emitted by a nucleus of a heavy element as the result of a conversion in which neutrons are converted into protons.

Beta particles have more energy than is found in alpha radiation, and they travel for longer distances than alpha particles. Beta particles can be held by a thin sheet of metal or by protective clothing.

Radioactivity, Beta particle, StudySmarterFigure 2. The emission of an electron or a positron constitutes a beta-minus or a beta-plus decay.

Radioactivity: Gamma (γ)

Gamma radiation is by far the most dangerous. After the emission of alpha and beta particles, if the nucleus is still at a high energy state and must return to a lower, stable energy state, then gamma rays, a form of high-energy light radiation, are released.

A nucleus can undergo these processes spontaneously. But how long does it take for the unstable element to attain stability? Answer to this can vary for different elements, as it may take seconds, weeks, months, years, or even centuries.

Radioactivity, Gamma rays, StudySmarterFigure 3. Gamma rays have the smallest wavelength and the highest energy amongst all waves in the electromagnetic spectrum.

The rate of decay is being determined by the half-life of the radioactive substance. The half-life of an isotope is the average time it takes for unstable nuclei to halve. Note that the half-life is not measured by counting nuclei but by measuring the time it takes for their activity to halve.

A long half-life can be dangerous because of the danger caused by radioactive elements. We need to be careful when it comes to storing or disposing of nuclear waste products because they can have a very long half-life and can damage the environment if radiation is released into the air, land, or water.

Do all radioactive isotopes decay at the same rate?

Isotopes do not all decay at the same rate. Most isotopes are stable. Hydrogen, for instance, has three isotopes, only one of which is radioactive while the other two are stable.

For elements that do decay, radioactive decay is a very random process. To predict which nuclei will decay and when is, therefore, difficult. However, if you take a very large number of nuclei, their behavior can reveal a certain pattern because the rate of decay for a given isotope over a specific period is constant. This means that during that period, a predictable number of nuclei will decay.

The rate of decay is measured by the decay constant (λ), which estimates how much a nucleus will decay per second. A larger value of λ indicates a faster rate of decay. For instance, when λ is twice as large, the decay rate per second is twice as high. See the formula below:

Activity = decay constant ⋅ number of nuclei

Radioactivity: Is radiation harmful?

Ionizing and nuclear radiation have been categorized as harmful for all biological beings. Some radiation can even be deadly.

However, low levels of radiation are not dangerous. Examples of this include the radiation emitted by your phone when you receive a call, the light bouncing off of your skin, and the food being heated in a microwave.

Even radioactive material can be put to good use. While exposure to limitless amounts of radioactive material can cause lethal amounts of genetic mutation and cancer, controlled amounts of the same material can be used to cure cancer. Radioactive iodine, for instance, is used in radiation therapy to treat cancer and for imaging in the thyroid gland.

Radioactivity - Key takeaways

  • Radioactivity is the emission of alpha, beta, or gamma particles from an atom to achieve stability.
  • An atom becomes unstable when the number of neutrons either exceeds or becomes less than the number of protons.

  • Alpha particles consist of two protons and two neutrons.

  • A beta particle is the emission of either an electron or a positron by a nucleus.

  • Gamma rays have the shortest wavelength but the highest amount of energy among all the waves in the electromagnetic spectrum.

  • Not all isotopes are radioactive.

  • The half-life of an isotope is the average time it takes for the unstable nuclei to halve.

  • The decay constant (λ) states the degree of probability of a nucleus decaying per second. The bigger the value of λ, the faster the rate of decay.

  • Ionizing or nuclear radiation is harmful to biological beings.

  • Radioactive iodine is used to treat cancer.

Frequently Asked Questions about Radioactivity

Radioactivity is the state in which an unstable atom emits radiation to achieve stability.

 Radioactive decay is the process by which an unstable atomic nucleus loses energy.

No, not all isotopes are radioactive.

Although the radioactivity has decreased with time, Chernobyl is still a radioactive area.

No, it is safe to live in Hiroshima.

Final Radioactivity Quiz

Question

What are the basic constituents of alpha radiation?

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Two neutrons and two protons.

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What are the basic constituents of beta radiation?

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An electron or a positron.

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What are the two types of beta decay?

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Beta plus decay and beta minus decay.

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Who was the main discoverer of radioactivity?

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Marie Curie.

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What did Paul Villard discover?

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Gamma radiation.

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What is the effect of ionising radiation on cells?

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Ionising radiation breaks chemical bonds and affects structures like DNA.

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What are the basic constituents of gamma radiation?

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High-energy photons.

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Which of the following is correct?

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Alpha and beta radiation are particle-like radiation and gamma radiation is wave-like radiation.

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There are conservation laws associated with disintegration processes.

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The more ionising a radiation, the less penetrating.

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We are exposed to non-damaging radiation every day.

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What is the name of the detectors of radioactivity used in nuclear power plants? 

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Geiger detectors.

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Is radiation used to fight tumours?

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Yes.

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What kind of damage can gamma radiation cause?

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Gamma radiation can cause burns.

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What is radioactive decay?

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A random process that occurs when an atom is unstable and wants to achieve stability.

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What is an unstable atom?

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An atom with an excess of particles and/or energy.

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Give two types of decay processes that emit massive particles.

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Alpha decay and beta decay.

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How many types of beta decays are there?

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There are two types: beta minus and beta plus decay.

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The law of exponential radioactive decay is derived from quantum mechanics.

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Radioactive decay occurs faster at earlier times than at later times.

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The rate of percentual decay is constant and depends only on the decay constant.

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Into which element does uranium-238 decay?

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Uranium-238 decays into lead. 

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What is the name of the time it takes the unstable nuclei of an element to decrease in half?

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Half life.

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Which element is used for estimating the age of organic structures?

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Carbon-14.

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Why does the exponential decay law work for samples of unstable elements with a high number of atoms?

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The exponential decay law works for samples of unstable elements with a high number of atoms because it is a statistical feature.

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Which decays do elements usually undergo to gain stability?

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Alpha and beta decay.

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Is the constant of radioactive decay universal?

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No, the constant of radioactive decay is specific to each element.

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Do electrons determine the instability of an atom?

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No, only neutrons and protons determine the instability of an atom. 

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Which particles can beta radiation emit?

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Electrons and positrons.

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Nuclear instability is caused by an excess of particles (instability) and energy (metastability).

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Alpha and beta radiation are forms of particle radiation and gamma radiation is a form of wave radiation.

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Alpha decay takes place for unstable heavy atoms.

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Gamma radiation usually takes place after other forms of nuclear decay.

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Nuclear instability allows us to produce energy when controlled.

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What is the N-Z curve?

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It is a curve where nuclei are represented according to their numbers of protons and neutrons.

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After which proton number do elements lose any form of stability?

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After 82 protons. 

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What is the stability island?

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It is a predicted set of heavy nuclei that are not unstable.

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What is the medical use for Technetium-99?

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Answer

Tracing and mapping bodies.

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How can nuclei go from a metastable state to a stable state?

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By emitting gamma radiation.

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Are alpha and beta all the possible forms of decay?

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No, there are other forms of decay like fission.

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Which element has the highest number of stable isotopes?

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Tin has the highest number of stable isotopes. 

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What types of beta decay are there?

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There are two types of beta decay: beta plus and beta minus.

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Do light nuclei tend to have the same number of protons and neutrons?

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Yes, light nuclei tend to have the same number of protons and neutrons. 

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Do heavy nuclei tend to have the same number of protons and neutrons?

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No, heavy nuclei do not tend to have the same number of protons and neutrons

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The closest approach method is not accurate because it assumes alpha particles are only affected by the electric force.

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According to quantum physics, the limit between waves and particles is artificial.

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The usual formula for the nuclear density assumes a uniform distribution and a spherical disposition.

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Alpha particles are made of two neutrons and two protons.

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The diffraction pattern of electrons has a peak of intensity that allows us to measure the radius.

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Question

Which method for measuring the nuclear radius uses alpha particles?

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Answer

The closest approach method uses alpha particles. 

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