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Radioactive Elements in Periodic Table

Last Updated : 19 Dec, 2023
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Radioactive Elements are the elements that emit radioactive waves like alpha waves, beta waves, and gamma waves. The Process is called Radioactivity. They are found throughout the Earth’s crust and have important applications in various fields, including medicines, energy production, etc. The radioactive elements are unstable because of the presence of excess nuclear charge inside their atomic nucleus. These atomic nuclei undergo radioactive decay to form stable nuclei. The elements that undergo radioactive decay are called radioactive elements.

Learn about, Types of Radioactivity

In this article, we will learn about radioactive elements, radioactive elements table, characteristics, examples, and applications of radioactive elements.

What are Radioactive Elements in Periodic Table?

Some elements are not stable in nature due to the excessive charge concentrated at the nucleus, and because all elements want to be stable in nature, these elements undergo radioactive decay in order to be stable nuclei. These unstable elements are known as radioactive elements. Thus, we can say that the elements that undergo radioactive decay are called radioactive elements.

In stable atoms, the neutron-proton ratio( ratio of neutron to the proton in the nucleus ) is typically close to 1:1 for small nuclei elements(Z<20). However, in unstable or radioactive isotopes, this ratio may be significantly different, which can affect their stability and decay behaviour. This ratio normally rises as Z(Atomic number) rises, reaching 1.587 for Uranium-238. There are a few exceptions to the above rule, such as 1H(Protium) and 3He(Helion), which both have more protons than neutrons and are still stable.

History of Radioactive Elements

In 1896, French physicist Henri Becquerel discovered spontaneous radioactivity in uranium salts while investigating a connection between phosphorescence and x-rays, which had just been discovered. Becquerel had been studying fluorescence and phosphorescence, a subject his father had been an expert in, and was skilled in photography. He found that the uranium salts emitted radiation without any stimulation from sunlight and confirmed that uranium was the element emitting the radiation. Becquerel’s discovery was accidental but significant and led to the study of other radioactive elements by Marie Cuire and Pierre Curie, who coined the term “radioactivity.” The accidental discovery of radioactivity is well-known in the history of physics. 

List of Natural Radioactive Elements

There are very few radioactive elements that occur naturally as radioactive elements are highly unstable and they tend to disintegrate very quickly to other elements. Some of the naturally occurring elements are,

  • Uranium
  • Polonium
  • Radium
  • Radon


Uranium, with the atomic number 92 and symbol U, is a naturally occurring radioactive element found in soil, air, and water. Uranium steadily decays into other elements like radium and radon. There are various isotopes of Uranium, but the most abundant isotope is U-238, which accounts for approximately 99% of all Uranium found on Earth.


Polonium is a rare, radioactive element with the atomic number 84 and the symbol Po. It was discovered by Marie and Pierre Curie in 1898 and was named after Marie’s home country of Poland. Polonium is a highly toxic substance, and its most stable isotope is polonium-210. It occurs naturally in small amounts in the Earth’s crust, but can also be artificially produced in nuclear reactors.  It gained attention after being used as a fatal toxin in the 2006 assassination of Russian dissident Alexander Litvinenko.


Radium is a rare and highly radioactive metallic element found in uranium and thorium ores at trace levels. Radium, discovered in 1898 by Marie and Pierre Curie, emits alpha, beta, and gamma rays and is one of the most unstable elements.


Radon is an atomic number 86 chemical element with the symbol Rn. It is a colourless, odourless, and tasteless radioactive gas produced naturally by radium decay. Radon is considered a health risk since it is the second leading cause of lung cancer after smoking.

What is Alpha Radiation?

Alpha radiation is a form of ionizing radiation composed of alpha particles (two protons and two neutrons). Although this sort of radiation has low penetrating strength and can be prevented by a sheet of paper or the outer layer of human skin, it can be hazardous if it enters the body by ingestion or inhalation. Alpha radiation is typically generated by heavy, unstable nuclei during the radioactive decay process.

List of Radioactive Elements on the Periodic Table

There are various radioactive elements on the periodic table, the radioactive element in the periodic table added below are shown using blue colour.

Periodic table with all the radioactive elements highlighted


Examples of Radioactive Elements

Examples of all periodic table radioactive elements, their most stable isotope, and their half-life are given in the table below,

ElementAtomic NumberMost Stable IsotopeHalf-life of Most Stable Isotope
Technetium43Tc-914.21 x 106 years
Promethium61Pm-14517.4 years
Polonium84Po-209102 years
Astatine85At-2108.1 hours
Radon86Rn-2223.82 days
Francium87Fr-22322 minutes
Radium88Ra-2261600 years
Actinium89Ac-22721.77 years
Thorium90Th-2297.54 x 104 years
Protactinium91Pa-2313.28 x 104 years
Uranium92U-2384.47×109 years
Neptunium93Np-2372.14 x 106 years
Plutonium94Pu-2448.00 x 107 years
Americium95Am-2437370 years
Curium96Cm-2471.56 x 107 years
Berkelium97Bk-2471380 years
Californium98Cf-251898 years
Einsteinium99Es-252471.7 days
Fermium100Fm-257100.5 days
Mendelevium101Md-25851.5 days
Nobelium102No-25958 minutes
Lawrencium103Lr-2624 hours
Rutherfordium104Rf-26513 hours
Dubnium105Db-26832 hours
Seaborgium106Sg-2712.4 minutes
Bohrium107Bh-26717 seconds
Hassium108Hs-2699.7 seconds
Meitnerium109Mt-2760.72 seconds
Darmstadtium110Ds-28111.1 seconds
Roentgenium111Rg-28126 seconds
Copernicium112Cn-28529 seconds
Nihonium113Nh-2840.48 seconds
Flerovium114Fl-2892.65 seconds
Moscovium115Mc-28987 milliseconds
Livermorium116Lv-29361 milliseconds
Oganesson118Og-2941.8 milliseconds

Most Radioactive Elements

The most stable naturally occurring element is Polonium. It is one of the most radioactive elements and has no stable isotopes. It is so radioactive that it causes gas particles around itself to excite and glow and so it appears to glow blue.

Radioactive Metals

Radioactive metals refer to natural and synthetic metals that can release alpha (α), beta (β), and gamma (γ) rays. They can be put to use in many ways for the benefit of human beings, such as power generation, energy resources for spacecraft, nuclear batteries, material engineering, and cancer treatment. In the entire chain from mining to the final disposal of the radioactive metals, membrane separation has the potential to improve the efficiency of many steps. Pilot scale tests or applications have been carried out in laboratories and power plants worldwide.

Radioactive Element Decay

A radioactive atom will naturally emit radiation in the form of energy or particles in order to transition into a more stable state. This procedure is called Radioactive Decay.

The nucleus before the decay is called the parent nucleus and the newly formed nucleus after decay is called the daughter nucleus.

The most common decays are Alpha Decay, Beta Decay, and Gamma Decays.

Radioactive nucleus emitting alpha, beta and gamma particles


Alpha Decay

The emission of alpha particles from the nucleus is known as alpha decay. Alpha particles resemble the helium nucleus in that they are made up of two protons and two neutrons.

Alpha Decal of Plutonium into Uranium and Alpha Particle


Where 2He4 is the Alpha particle that some radioactive element’s nucleus emits.

Beta Decay

The emission of beta particles from the nucleus occurs during beta decay. High-energy electrons or positrons are what are known as beta particles. Also, the emission of positron or neutrino is accompanied by its anti-particle antineutrino.

Beta Decay of C-14 into Nitrogen, positron and antineutrino


Where -1e0 is the beta particle and {}_0\bar{\nu}^0      is the antineutrino.

Gamma Decay

Gamma radiation is released from the nucleus during gamma decay. High-energy electromagnetic radiation known as gamma radiation is released when a nucleus changes from a higher to a lower energy state.

Gamma decay of Cobalt-60

Where -1e0 is the beta particle and 0γ0 is the gamma-ray particle.


Half-Life is the time period in which the radioactive substance goes through the process of radioactive decay and disintegrates into smaller more stable substances until its concentration remains half of the initial concentration. This time period is represented by t1/2 and as it is time, the unit of half-life is the same as time i.e., second, minute, hour, day, or year.

Half-Life Formula

Half-life can be calculated using the division of λ by 0.693, where λ is the decay/disintegration constant and the half-life is represented by t1/2. Mathematically Half-Life Formula is given by:

t1/2 = λ/0.693

Derivation of Formula of Half-Life

Let N be the concentration of the radioactive element at any given time t. If the decrease in the concentration of radioactive elements is dN in time interval dt, then the rate of radioactive decay is given by

dN/dt = -λt

[ where λ is the decay constant and the “-” sign represents the decrease in the concentration] 

Integrating the above equation, we get

\begin{aligned} &N_t=N_0 e^{-\lambda t} \\ & \text{for Half-Life}, N_t=\frac{N_o}{2} \text{and} t=t_{1 / 2} \\ &\Rightarrow \frac{N_0}{2}=N_0 e^{-\lambda t_{1 / 2}} \\ &\Rightarrow \frac{1}{2}=e^{-\lambda t_{1 / 2}} \\ &\Rightarrow \log _{e}{1 / 2}=-\lambda t_{1 / 2} \\ &\Rightarrow \log _{e}{2}=\lambda t_{1 / 2} \\ &\Rightarrow t_{1 / 2}=\frac{\log _e 2}{\lambda} \\ &\Rightarrow t_{1 / 2}=\frac{0.693}{\lambda} \end{aligned}

Example: A sample of radioactive material has a half-life of 10 days. If the initial mass of the sample is 100 grams, how much of it will remain after 30 days?


λ = ln(2)/t1/2

where ln(2) is the natural logarithm of 2, and t1/2 is the half-life of the radioactive material.

Given t1/2 =10 days 

So, λ = ln(2)/t1/2
⇒ λ = ln(2)/10
⇒ λ = ln(21/10)

⇒ Nt = N0 e-λt

\Rightarrow N_t = N_0\times e^{-\ln\left(2^{1/10}\right)t} \\ \Rightarrow N_t = N_0\times e^{-\ln\left(2^{t/10}\right)} \\ \Rightarrow N_t = 100\times\left((1/2)^{30/10}\right) \\

Nt = 100 x (1/2)3

Nt = 12.5

Thus, sample will reamain 12.5 gm after 30 days.

Characteristics of Radioactive Elements 

Radioactive elements have several characteristics, including:

  • Alpha, beta, or gamma radiation is produced as radioactive elements decay over time.
  • Half-life is the length of time it takes for half of a radioactive atom to transform into a more stable form.
  • There are radioactive isotopes of some elements, and as they degrade over time, the number of protons and neutrons in the nucleus changes.
  • Radiation from the radioactive decay process can be detrimental to living things because it releases energy in the form of radiation.
  • Because they have an excess of protons or neutrons in their nuclei, radioactive elements are unstable and can decay as a result.
  • Transmutation is the process by which an element transforms into another element as a result of radioactive decay.

Effects of Radioactive Elements 

The body can suffer substantial damage from radiation released by radioactive materials because radiation can destroy the structural integrity of DNA, leading to abnormalities in the human genome and possibly to gene mutation and further can cause cancer as well. 

Different effects of radiation with different exposure to the radiation are as follows,

Dose (rem)

Effect on the Human Body

5-20There can be seen late long-term effects as well as chromosomal damage.
20-100Drop in the white blood cell count for a brief period.

Mild radiation sickness within a few hours, including fatigue, nausea, and decreased

 resistance to infection.


Radiation exposure causes severe radiation sickness symptoms, including bleeding and 

100-200 rem, and is a lethal dose for 10-35% of the population after 30 days.

300-400Severe radiation illness, as well as intestinal and marrow damage.
400-1000Accelerated illness and early death.
1000-5000Accelerated illness and early death in some days.

Where the biological risk of exposure to radiation is measured in rem(Roentgen equivalent man, CGS system), also sieverts (Sv) is the MKS(S.I.) unit of the same. (Where, 1 rem = 0.01 Sv)

Toxicity of Radioactive Elements

Radioactive elements can cause high damage to human beings if we even con in close contact with them because of the,

  • Alpha rays
  • Beta rays
  • Gamma rays

These rays interact with human cells at DNA levels and cause changes to them which in turn cause various health implications resulting in serious diseases such as cancer and others. These radiations also cause mutation in the human body resulting in various damages to the human body.

Uses of Radioactive Elements

There are numerous significant uses for radioactive elements, including:

  • Medical Diagnosis and Treatment: Radioactive isotopes are used in radiotherapy and medical imaging to identify and cure diseases like thyroid problems and cancer.
  • Radioactive isotopes are employed in numerous scientific and industrial applications, such as radiography, tracer studies, and material analysis.
  • Energy Production: Nuclear power facilities produce electricity using radioactive isotopes like uranium.
  • Smoke Detectors: A few smoke detectors have a little quantity of radioactive material inside that ionizes the air and sounds an alarm when smoke particles are detected.
  • Radioactive isotopes like Carbon-14 dating and Uranium-Lead dating are used to date rocks and fossils, allowing scientists to better comprehend Earth’s history and the evolution of life. 
  • Food Preservation: By using radiation to kill bacteria and other microbes, food can be kept fresh, and spoiled is prevented. 

Resources related to Radioactive Elements

Radioactive Elements – FAQs

1. What are Radioactive Elements?

Elements having unstable nuclei are radioactive elements as they emit radioactive rays, i.e. alpha, beta and gama rays from their nucleus. Some examples of radioactive elements are, Uranium, Polonium, etc.

2. What are Examples of Radioactive Elements?

The most common Radioactive Elements are 

  • Uranium
  • Radium
  • Polonium
  • Thorium, etc.

3. How many Radioactive Elements are there?

There are 37 such elements in the periodic table which are radioactive in nature and they undegoes radioactive decay to form more stable and less dense nuclei. Some of them are naturally occuring and other are man made.

4. Who discovered Radioactive Element Radium? 

Radium was discovered in 1898 from a ore mine in Jachymov by Madam Curie and her husband Pierre Curie.

5. Which Radioactive Element is used in treatment of Cancer?

Radioactive elements that is used in the treatment of cancer is Radium.

6. What is Half-Life of  Radioactive Elements?

The time taken by radioactive material to decay its half of the mass content is called the half-life of the radioactive elements.

Carbon-14 5,700 years
Uranium-235700 million years
Uranium-238 4.5 billion years
Plutonium-239:24,110 years
Radon-222 3.8 days

7. What are Uses of Uranium?

Uranium is one of the radioactive material that occur naturally and has variety of uses. It has two main isotopes,

  • U-235
  • U-238 

Some uses of Uranium are,

  • Uranium is used to power nuclear reactors that produce electricity
  • Isotopes of Uranimum are used for medical, industrial, and defence purposes.

8. Do all radioactive elements decay?

Yes, all radioactive elements decay to gain stability.

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