Radionuclide metrology
======================

**Radionuclide metrology** is the science of measuring radioactivity with high precision and accuracy.
Its primary goal is to ensure the reliability and consistency of radioactivity measurements across the world
and across various applications, such as healthcare, environmental monitoring, and nuclear energy production.

National Metrology Institutes
-----------------------------

National Metrology Institutes (NMIs) around the world work coordinately to this goal.
Radionuclide metrology laboratories try to met this goal through:

- **Primary standardisation techniques**:
  Using methods like liquid scintillation counting and coincidence techniques,
  they realise the SI-derived unit for activity of a radionuclide, which is the becquerel (Bq),
  and provide the most accurate measurements of activity.

- **International comparisons**:
  Through key comparisons of their standards, they demonstrate international equivalence of the activity
  measurements worldwide.

- **Secondary standardisation techniques**:
  They provide the tools needed to convert a count rate in a detector into an activity measurement traceable to the
  International System of Units (SI).
  They provide certified radioactive sources for calibration, accurate half-life values, emission
  probabilities of various types of radiation (x rays, gamma rays, alpha particles, conversion electrons, Auger
  electrons), and evaluated decay schemes of the most important radionuclides.

Radionuclide standardization
----------------------------

In the context of radionuclide metrology, radionuclide standardization refers to the process of
establishing accurate and reliable measurements of the activity (radioactive decay rate) of radionuclides.
This is crucial for ensuring consistency and accuracy in various applications,
such as medical diagnostics, treatment, environmental monitoring, and nuclear power.

The key steps involved are:

- **Primary Standardization**:
  This is the direct measurement of the number of nuclear transformations per unit time without relying on other calibrations or standards.
  It forms the basis for physical measurement standards of activity.
- **Measurement Techniques**:
  Various techniques are used for primary standardization, including:
  Liquid scintillation counting (LSC), coincidence counting, triple to double coincidence ratio (TDCR) and
  CIEMAT-NIST efficiency tracing
- **Traceability**:
  Measurements are traceable to international standards, such as those maintained by the National Metrology Institutes (NMIs)
  Examples of NMIs are NIST (United States), NPL (United Kingdom), PTB (Germany), LNHB (France) and LMRI (Spain).
  This traceability ensures that results are comparable across different laboratories and applications.
- **Detector Modeling**:
  Detailed modeling of detectors using Monte Carlo radiation transport and interaction methods is important for
  uncertainty analysis and understanding the effects of impurities.

Key quantities
--------------

The standardization of a radionuclide involves determining several key quantities that characterize its radioactive properties.
These quantities ensure accurate and reliable measurements for various applications. Here are the main quantities:

- **Activity** (A): This is the rate at which a radionuclide decays, measured in becquerels (Bq), where 1 Bq equals one decay per second.
  It is a fundamental quantity in radionuclide standardization.
- **Half-life** (:math:`t_{1/2}`): The time required for half of the radioactive atoms in a sample to decay.
  This is crucial for understanding the longevity and decay behavior of the radionuclide.
- **Decay modes**: The types of radiation emitted during decay, such as alpha particles, beta particles, and gamma rays.
  Each decay mode has specific energy levels associated with it.
- **Energy of emissions**: The energy levels of the emitted particles or photons, typically measured in electron volts (eV).
  This helps in identifying the radionuclide and understanding its interaction with matter.
- **Specific activity**: The activity per unit mass of the radionuclide, often expressed in Bq/g.
  This is important for applications where the concentration of the radionuclide is critical.
- **Gamma-ray emission probabilities**: The likelihood of gamma-ray emissions per decay,
  which is essential for applications involving gamma-ray spectroscopy and imaging.
- **Branching ratios**: The probabilities of different decay paths that a radionuclide can take.
  This helps in understanding the complete decay scheme of the radionuclide.

Find more details about radionuclide metrology in this
`JRC technical report <https://publications.jrc.ec.europa.eu/repository/handle/JRC129308>`_
and in this
`academic article by R. Collé <http://doi.org/10.1007/s10967-009-0509-5>`_.
