List of Radioactive Elements

A radioactive element is one with an unstable nucleus, which radiates alpha, beta or gamma radiation and gets converted to a stable element. This article has a comprehensive list of radioactive elements and their properties.
This Buzzle article has a list of radioactive elements that abound in nature, arranged in the order of increasing atomic number, along with their decay modes.

Let us understand the phenomenon of radioactivity. Radioactivity arrived on the scene of world physics in the 19th century, just when people thought they knew everything in physics. With its discovery in 1896, radioactivity opened up a Pandora's box of questions and revealed a new world, waiting to be explored in the microcosm of the atomic nucleus.

What is Radioactivity?
Radioactivity is a very interesting phenomenon in nature. Classical Electromagnetism cannot explain radioactivity. It's a spontaneous and random phenomenon whereby nuclei of certain chemical elements like Uranium, radiate gamma rays (high frequency electromagnetic radiation), beta particles (electrons or positrons) and alpha particles (Helium Nuclei).

By the emission of these particles and radiation, the unstable nucleus gets converted into a stabler nucleus. This is called radioactive decay.

The Term 'Radioactive' - A Misnomer
A radioactive element is a fundamental element whose atomic nuclei demonstrates the phenomenon of radioactivity. The name 'radioactive' may suggest to you that radioactive elements radiate radio waves, but unfortunately that is not so! The name 'radioactivity' is a misnomer because these elements have nothing to do with radio waves! The reason is that energy and frequency of a gamma ray which is emitted by a radioactive element, is far beyond that of the radio band of electromagnetic spectrum! So, we are just stuck up with the name!

What Makes an Element Radioactive?
To understand radioactivity, we need to explore the structure of an atomic nucleus. Every nucleus contains neutrons as well as protons. Neutrons are neither positively charged, nor negatively charged, they are neutral particles. Protons are positively charged. As you might remember from high school physics, like charges repel each other while unlike charges attract each other. In the nucleus, protons and neutrons are cramped together in a really very small space.

The protons in the nucleus, all being positively charged, repel each other! So if all the protons repel each other, how does the nucleus stay glued together and remain stable? It is because of the 'Nuclear Force'.

This force is more stronger than the electromagnetic force, but the range of this force is only limited to size of the nucleus, unlike electromagnetic force whose range is infinite. This nuclear force acts between the protons and neutrons, irrespective of the charge and it's always strongly attractive. However, it has limitations of range. So, in the nucleus, there is a constant tussle between the repelling electromagnetic coulomb force of protons and the attractive strong nuclear force.

In a nucleus like Uranium, which has almost 92 protons, coulomb repulsive force becomes too much for the nuclear force to contain. Subsequently, the nucleus is very unstable and radioactive decay occurs and Uranium decays into a more stable element. Such an unstable nucleus like Uranium, when gently tapped by a neutron, splits up into two other nuclei through nuclear fission, releasing tremendous amount of energy in the process! This is the principle on which nuclear energy and nuclear weapons are based.

The radioactive elements listed below shows all the decay modes of Uranium. A full explanation of radioactivity can only be given, if we plunge deep into quantum physics and elementary particle physics.

Types of Radioactive Decay
This decay may occur in any of the following three ways:
  • Alpha Decay: Nucleus emits a helium nucleus (called an Alpha Particle) and gets converted to another nucleus with atomic number lesser by 2 and atomic weight lesser by 4.
  • Beta Decay: Beta decay could be of two types; either through emission of an electron or positron (the antiparticle of electron). Electron emission causes an increase in the atomic number by 1, while positron emission causes a decrease in the atomic number by 1. In some cases, double beta decay may occur, involving the emission of two beta particles.
  • Gamma Decay: Gamma decay just changes the energy level of the nucleus.
  • Electron Capture: One of the rarest decay modes is electron capture. In this phenomenon, an electron is captured or absorbed by a proton rich nucleus. This leads to the conversion of a proton into a neutron in the nucleus, along with release of an electron neutrino. This leads to a decrease in atomic number (transmuting the element in the process), while leaving the atomic mass number unchanged.
A radioactive element may have more than one decay mode.

Radioactive Isotopes
When two nuclei have the same atomic number, but different atomic weight or mass numbers, then they are said to be isotopes. Isotopes have the same chemical properties but different physical properties. For example, carbon has two isotopes, 6C14 and 6C12. Both have the same atomic number, but different number of neutrons. The one with the two extra neutrons is radioactive and undergoes radioactive decay. The radioactive isotope of carbon was used to develop carbon dating tool, which has made the dating of various relics possible.

Half-Life of a Radioactive Element
Half-life is the amount of time required, for half quantity of radioactive element to decay. For example C14has a half life of 5730 years. That is, if you take 1 gm of C14, then half of it will have been decayed in 5730 years. In the list presented below, half-lives of all the radioactive elements are presented.

Radioactive Elements List
Here is a detailed and comprehensive list of natural radioactive elements along with their atomic and mass numbers, decay modes and half-lives. Here 'Beta Decay (β-)' denotes electron emission while Beta Decay (β+) denotes positron emission.

Radioactive ElementAtomic NumberAtomic Mass NumberDecay TypeHalf-Life
Hydrogen (H)13Beta Decay (β-)12.32 years
Beryllium (Be)47Electron Capture (ε), Gamma Decay)53.12 Days
Beryllium (Be)48Alpha7 x 10-17 sec
Beryllium (Be)410Beta Decay (β-)1,360,000 years
Carbon (C)614Beta Decay (β-)5,730 years
Calcium (Ca)2041Electron Capture (ε)103,000 years
Calcium(Ca)2046Double Beta Decay (β-β-)> 2.8 x 1015 years
Calcium(Ca)2048Double Beta Decay (β-β-)> 4 x 1019
Iron (Fe)2654Double Electron Capture (ε)> 3.1 x 1022 years
Iron (Fe) (Synthetic)2655Electron Capture (ε)2.73 years
Iron (Fe) (Synthetic)2659Beta Decay (β-)44.503 days
Iron (Fe) (Synthetic)2660Beta Decay (β-)2,600,000 years
Cobalt (Co) (Synthetic)2756Electron Capture (ε)77.27 days
Cobalt (Co) (Synthetic)2757Electron Capture (ε)271.79 days
Cobalt (Co) (Synthetic)2758Electron Capture (ε)70.86 days
Cobalt (Co) (Synthetic)2760Beta Decay (β-), Double Gamma5.2714 years
Nickel (Ni)2859Electron Capture (ε)76,000 years
Nickel (Ni) (Synthetic)2863Beta Decay (β-)100.1 years
Zinc (Zn) (Synthetic)3065Electron Capture (ε), Gamma243.8 days
Zinc (Zn) (Synthetic)3072Beta Decay (β-)46.5 hours
Selenium (Se)3479Beta Decay (β-)3.27 x 105 years
Selenium (Se)3482Double Beta Decay (β- β-)1.08 x 1020 years
Krypton (Kr)3685Beta Decay (β-)10.756 years
Rubidium (Rb)3787Beta Decay (β-)4.88 x 1010 years
Strontium (Sr)3889Electron Capture (ε), Beta Decay (β-)50.52 days
Strontium (Sr)3890Beta Decay (β-)28.9 years
Yttrium (Y)3990Beta Decay (β-), Gamma2.67 days
Yttrium (Y)3991Beta Decay (β-), Gamma58.5 days
Zirconium (Zr)4093Beta Decay (β-)1.53 x 106 years
Zirconium (Zr)4094Double Beta Decay (β-)> 1.1 x 1017 years
Zirconium (Zr)4096Double Beta Decay (β-)2 x 1019 years
Niobium (Nb) (Metastable)4193Beta Decay (β-),Gamma16.13 years
Niobium (Nb)4195Beta Decay (β-), Gamma34.991 days
Molybdenum (Mo)4293Electron Capture (ε)4 x 103 years
Technetium (Tc)4399Beta Decay (β-)2.111 x 105 years
Ruthenium (Ru)44103Beta Decay (β-), Gamma39.26 days
Ruthenium(Ru)44106Beta Decay (β-)373.59 days
Palladium (Pd)46107Beta Decay (β-), Gamma6.5 million years
Silver (Ag)47111Beta Decay (β-), Gamma7.45 days
Tin (Sn)50126Beta Decay (β-)2.3 x 105 years
Antimony (Sb)51125Beta Decay (β-)2.7582 years
Tellurium (Te)52127Beta
Decay (β-), Gamma
9.35 hours
Tellurium (Te)52129Beta Decay (β-)69.6 minutes
Iodine (I)53123Electron Capture (ε), Gamma13 hours
Iodine (I)53129Beta Decay (β-)15.7 million years
Iodine (I)53131Beta Decay (β-), Gamma8.02070 days
Xenon (Xe)54125Electron Capture (ε)16.9 hours
Xenon (Xe)54127Electron Capture (ε)36.345 days
Xenon (Xe)54133Beta Decay (β-)5.247 days
Cesium (Cs)55134Electron Capture (ε), Beta Decay (β-)2.0648 years
Cesium (Cs)55135Beta Decay (β-)2.3 million years
Cesium (Cs)55137Beta Decay (β-), Gamma30.17 years
Cerium (Ce)58144Beta Decay (β-)285 days
Promethium (Pm)61147Beta Decay (β-), Gamma2.6234 years
Europium (Eu)63154Beta Decay (β-), Beta Decay (β+), Gamma16 years
Europium (Eu)63155Beta Decay (β-)2 years
Iridium (Ir) (Synthetic)77188Electron Capture (ε)1.73 days
Iridium (Ir) (Synthetic)77189Electron Capture (ε)13.2 days
Iridium (Ir) (Synthetic)77190Electron Capture (ε)11.8 days
Iridium (Ir) (Synthetic)77192Beta Decay (β-), Electron Capture (ε)73.827 days
Iridium (Ir) (Synthetic, Metastable)77192Gamma Decay241 years
Iridium (Ir) (Synthetic)77193Gamma Decay10.5 days
Iridium (Ir) (Synthetic)77194 Beta Decay (β-)19.3 hours
Iridium (Ir) (Synthetic, Metastable)77194Gamma Decay171 days
Lead (Pb)82210Beta Decay (β-), Alpha21 years
Bismuth (Bi)83210Alpha3 million years
Polonium (Po)84210Alpha138 days
Radon (Rn)86220Alpha, Beta Decay (β+)1 min
Radon (Rn)86222Alpha4 days
Radium (Ra)88224Alpha4 days
Radium (Ra)88225Beta Decay (β-)15 days
Radium (Ra)88226Alpha1,622 years
Thorium (Th)90228Alpha2 years
Thorium (Th)90229Alpha7,340 years
Thorium (Th)90230Alpha80,000 years
Thorium (Th)90232Alpha14 years
Thorium (Th)90234Beta Decay (β-)24 days
Proactinium (Pa)91234Beta Decay (β-)6.75 hours
Uranium (U)92233Alpha159,200 years
Uranium (U)92234Alpha245,500 years
Uranium (U)92235Alpha7.038 x 108 years
Uranium (U)92236Alpha2.342 x 107 years
Uranium (U)92238Alpha4.468 billion years
Neptunium (Np) (Synthetic)93237Alpha2.144 million years
Plutonium (Pu)94238Alpha87.74 years
Plutonium (Pu)94239Alpha2.41 x 104 years
Plutonium (Pu)94240Alpha6.5 x 103 years
Plutonium (Pu)94241Beta Decay (β-)14 years
Plutonium (Pu)94242Alpha3.73 x 105 years
Plutonium (Pu)94244Alpha8.08 x 107 years
Americium (Am)95241Alpha432.2 years
Americium (Am) (Metastable)95242Alpha, Gamma141 years
Americium (Am)95243Alpha7,370 years
Curium (Cm)96242Alpha160 days
Curium (Cm)96243Alpha29.1 years
Curium (Cm)96244Alpha18.1 years
Curium (Cm)96247Alpha15.6 million years

These radioactive isotopes have a lot of applications today, ranging from medicine to atomic energy. Since these radioactive elements are harmful, burning up radioactive waste or disposing it, is difficult. Every development in science and technology brings in new problems. Now, it's for us to decide, how we intend to use the power of technology placed in our hands.