Each element has at least one isotope with an unstable nucleus that can undergo radioactive decay.

* Nuclear cardiology: The use of nuclear medicine to visualize the uptake of an isotope by the heart using radioactive sources.

By observing which areas of the brain take up the radioactive isotope, we can see which areas of the brain are more active than other areas.

Calcium also has a cosmogenic isotope, radioactive < sup > 41 </ sup > Ca, which has a half-life of 103, 000 years.

The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology.

A less accessible but rather efficient method is introduction of a radioactive isotope into the reaction and monitoring how it changes over time and where it moves to ; this method is often used to analyze redistribution of substances in the human body.

It is a synthetic element ( an element that can be created in a laboratory but is not found in nature ) and radioactive ; the most stable known isotope, dubnium-268, has a half-life of approximately 28 hours.

Self diffusion, exemplified with an isotopic tracer of radioactive isotope < sup > 22 </ sup > Na

Stable and radioactive isotope studies provide insight into the geochemical evolution of rock units.

Helium-3 was hypothesized to be a radioactive isotope until helions were also found in samples of natural helium, which is mostly helium-4, taken both from the terrestrial atmosphere and from natural gas wells.

This explains why the radioactive isotope predominates in abundance compared to the stable one.

Naturally occurring lanthanum is composed of one stable (< sup > 139 </ sup > La ) and one radioactive (< sup > 138 </ sup > La ) isotope, with the stable isotope, < sup > 139 </ sup > La, being the most abundant ( 99. 91 % natural abundance ).

For example, a radioactive isotope lutetium-176 is used in nuclear technology to determine the age of meteorites.

All isotopes of lawrencium are radioactive ; its most stable known isotope is lawrencium-262, with a half-life of approximately 3. 6 hours.

The isotope < sup > 28 </ sup > Mg is radioactive and in the 1950s to 1970s was made commercially by several nuclear power plants for use in scientific experiments.

In this case, the bismuth would present some minor radiation problems, as it is not quite as transparent to neutrons, and can be transmuted to a radioactive isotope more readily than lead.

To conduct the scan, a short-lived radioactive tracer isotope is injected into the living subject ( usually into blood circulation ).

Rubidium has only one stable isotope, < sup > 85 </ sup > Rb, with the isotope < sup > 87 </ sup > Rb, which composes almost 28 % of naturally occurring rubidium, being slightly radioactive with a half-life of 49 billion years — more than three times longer than the estimated age of the universe.

All isotopes of radium are highly radioactive, with the most stable isotope being radium-226, which has a half-life of 1601 years and decays into radon gas.

Rhenium ( meaning: " Rhine ") was the last element to be discovered having a stable isotope ( other new radioactive elements have been discovered in nature since then, such as neptunium and plutonium ).

It is a synthetic element ( an element that can be created in a laboratory but is not found in nature ) and radioactive ; the most stable known isotope, < sup > 267 </ sup > Rf, has a half-life of approximately 1. 3 hours.

Radiometric dating ( often called radioactive dating ) is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.

For the imaging scan, I-123 is considered an almost ideal isotope of iodine for imaging thyroid tissue and thyroid cancer metastasis.

A third alternative is to use a radioactive label rather than an enzyme coupled to the secondary antibody, such as labeling an antibody-binding protein like Staphylococcus Protein A or Streptavidin with a radioactive isotope of iodine.

It also is being investigated as a radiation therapy against hepatocellular carcinoma, by being loaded with an isotope of iodine, iodine-131.

However, since the other 90 % of radiation ( beta radiation ) causes tissue damage without contributing to any ability to see or " image " the isotope, other less-damaging radioisotopes of iodine are preferred in situations when only nuclear imaging is required.

The isotope I-131 is still occasionally used for purely diagnostic ( i. e., imaging ) work, due to its low expense compared to other iodine radioisotopes.

I-131 has been the most widely used tagging isotope in an aqueous solution of sodium iodine.

Unavoidable in situ production of this isotope is important in nuclear reactor control, as it decays to < sup > 135 </ sup > Xe, the most powerful known neutron absorber, and the nuclide responsible for the so-called iodine pit phenomenon.

Due to its volatility, short half life, and high abundance in fission products, < sup > 131 </ sup > I, ( along with the short-lived iodine isotope < sup > 132 </ sup > I from the longer-lived < sup > 132 </ sup > Te with a half life of 3 days ) is responsible for the largest part of radioactive contamination during the first week after accidental environmental contamination from the radioactive waste from a nuclear power plant.

Iodine-125 is the only other iodine radioisotope used in radiation therapy, but only as an implanted capsule in brachytherapy, where the isotope never has a chance to be released for chemical interaction with the body's tissues.

Iodine-124 is a proton-rich isotope of iodine with a half-life of 4. 18 days.

Iodine-135 is an isotope of iodine with a half-life of 6. 6 hours.

Six astatine isotopes, with mass numbers of 214 to 219, are present in nature as the products of various decay routes of heavier elements, but neither the most stable isotope of astatine ( with mass number 210 ) nor astatine-211 ( which is used in medicine ) is produced naturally.

Its alpha radiation is rather weak – 1. 45 % with respect to the β-radiation – but is sometimes used to detect this isotope.

* The BCS theory reproduces the isotope effect, which is the experimental observation that for a given superconducting material, the critical temperature is inversely proportional to the mass of the isotope used in the material.

IUPAC prefers that isotope symbols be written in superscript notation when practical, for example < sup > 12 </ sup > C and < sup > 235 </ sup > U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used.

Techniques using mass spectrometry and a double spike isotope dilution have been used for K-Ca age dating.

Californium-252, with a half-life of about 2. 64 years, is the most common isotope used and is produced at the Oak Ridge National Laboratory in the United States and the Research Institute of Atomic Reactors in Russia.

The most common isotope of hydrogen is protium ( name rarely used, symbol < sup > 1 </ sup > H ) with a single proton and no neutrons.

The formulas below are valid for all three isotopes of hydrogen, but slightly different values of the Rydberg constant ( correction formula given below ) must be used for each hydrogen isotope.

The average molecular mass is often used for larger molecules since molecules with many atoms are unlikely to be composed exclusively of the most abundant isotope of each element.

Its most stable isotope, < sup > 237 </ sup > Np, is a by-product of nuclear reactors and plutonium production, and it can be used as a component in neutron detection equipment.

These can be used to create pulses of neutrons, they have been used for some activation work where the decay of the target isotope is very rapid.

For example geochemical signatures from rocks may help to discover when life first arose on Earth, and analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as the Permian – Triassic extinction event .< ref name =" Twitchett "> A relatively recent discipline, molecular phylogenetics, often helps by using comparisons of different modern organisms ' DNA and RNA to re-construct evolutionary " family trees "; it has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the " molecular clock ".

Practical applications exist only for chemical compounds of promethium-147, which are used in luminous paint, atomic batteries and thickness measurement devices, even though promethium-145 is the most stable promethium isotope.

PET technology can be used to trace the biologic pathway of any compound in living humans ( and many other species as well ), provided it can be radiolabeled with a PET isotope.

Edenists operate cloud scoops in gas giants in order to extract the rare isotope helium 3 which can be used for fusion energy.

They isolated the metastable isotope technetium-99m, which is now used in some ten million medical diagnostic procedures annually.

The naturally occurring isotope thorium-232 is a fertile material, and with a suitable neutron source can be used as nuclear fuel in nuclear reactors, including breeder reactors.

It is the most popular isotope used for thallium nuclear cardiac stress tests.