plasmapy.particles.atomic.half_life(particle: plasmapy.particles.particle_class.Particle, mass_numb: Optional[numbers.Integral] = None) → astropy.units.quantity.Quantity

Return the half-life in seconds for unstable isotopes and particles, and numpy.inf in seconds for stable isotopes and particles.

  • particle (int, str, or Particle) – A string representing an isotope or particle, an integer representing an atomic number, or an instance of the Particle class.
  • mass_numb (int, optional) – The mass number of an isotope.

half_life_sec – The half-life of the isotope or particle in units of seconds.

Return type:


  • InvalidParticleError – If the argument does not correspond to a valid particle or contradictory information is provided.
  • MissingAtomicDataError – If no half-life data is available for the isotope.
  • TypeError – The argument is not an int or str or the mass number is not an int.


Accurate half-life data is not known for all isotopes. Some isotopes may have upper or lower limits on the half-life, in which case this function will return a string with that information and issue a MissingAtomicDataWarning. When no isotope information is available, then this function raises a MissingAtomicDataError.


>>> half_life('T')
<Quantity 3.888e+08 s>
>>> half_life('n')
<Quantity 881.5 s>
>>> half_life('H-1')
<Quantity inf s>