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Nuclear Stability

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
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Radioactive Decay and Radiometric Dating

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Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.

Nuclear Fission

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger binding energies per nucleon—that is, mass numbers and binding energies per nucleon that are closer to the “peak” of the binding energy graph near 56. Sometimes neutrons are also produced. This decomposition of a large nucleus into smaller pieces is called fission. The breaking is rather random with the formation of a large...

Radioactivity and Nuclear Equations

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Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
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Nuclear Binding Energy

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The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect indicates a “loss” in mass of 4.0331 amu – 4.0026 amu = 0.0305 amu. The loss in mass accompanying the formation of an atom from protons, neutrons, and electrons is due to the conversion of that mass into energy that is evolved as the atom forms. The nuclear binding energy is the energy produced when the atoms’ nucleons are bound...

Types of Radioactivity

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The most common types of radioactivity are α decay, β decay, γ decay, neutron emission, and electron capture.
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Related Experiment Video

Updated: Mar 9, 2026

Laser-heating and Radiance Spectrometry for the Study of Nuclear Materials in Conditions Simulating a Nuclear Power Plant Accident

Laser-heating and Radiance Spectrometry for the Study of Nuclear Materials in Conditions Simulating a Nuclear Power Plant Accident

Published on: December 14, 2017

Evidence against solar influence on nuclear decay constants.

S Pommé¹, H Stroh¹, J Paepen¹

¹European Commission, Joint Research Centre (JRC), Retieseweg 111, B-2440Geel, Belgium.

Physics Letters. [Part B]

|January 7, 2017

Summary

This study disproved the hypothesis that the Sun

Keywords:

Decay constant Half-life Neutrino Radioactivity Sun Uncertainty

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Area of Science:

Nuclear Physics
Astrophysics
Metrology

Background:

The hypothesis proposed that variations in Earth's proximity to the Sun could influence nuclear decay rates.
Such variations, if present, could impact precise measurements in nuclear science and dating techniques.

Purpose of the Study:

To experimentally test and disprove the hypothesis of Sun-proximity-induced variations in decay constants.
To establish precise upper limits for any potential annual oscillations in nuclear decay rates.

Main Methods:

Activity measurements of mono-radionuclide sources were conducted over extended periods (up to 40 years) at 14 international laboratories.
Analysis focused on residuals from exponential decay curves to detect annual oscillations and systematic deviations.
Instrumental and environmental factors were carefully considered to distinguish true decay variations from measurement artifacts.

Main Results:

No statistically significant annual oscillations in decay rates correlated with Earth's orbital distance were observed.
Systematic deviations were attributed to experimental conditions, not solar proximity.
Upper limits for the amplitude of annual oscillations were set between 0.0006% and 0.008%.

Conclusions:

The hypothesis of Sun-proximity-induced decay constant variations at the permille level is disproved.
No natural impediments to achieving sub-permille accuracy in half-life determinations were found.
This validates the reliability of nuclear dating, SI unit establishment (becquerel), and international activity standards.