plasmapy.particles.nuclear.mass_energy(particle: plasmapy.particles.particle_class.Particle, mass_numb: Optional[int] = None) astropy.units.quantity.Quantity

Return a particle’s mass energy. If the particle is an isotope or nuclide, return the nuclear mass energy only.

  • particle (str, int, or Particle) – A Particle object, a string representing an element or isotope, or an integer representing the atomic number of an element.

  • mass_numb (int (optional)) – The mass number of an isotope, which is required if and only if the first argument can only be used to determine the element and not the isotope.


mass_energy – The mass energy of the particle (or, in the case of an isotope, its nuclide) in units of joules.

Return type


  • InvalidParticleError – If the inputs do not correspond to a valid particle.

  • ParticleError – If the inputs do not correspond to a valid isotope or nucleon.

  • TypeError – If the inputs are not of the correct types.


>>> mass_energy('He-4')
<Quantity 5.9719e-10 J>