An alternative definition of the effective atomic number is one quite different from that described above.

The total and partial effective atomic numbers are obtained and presented.

Analysis of the experimental data in terms of cross sections and effective atomic numbers is presented.

The effective atomic numbers for photoelectric and total gamma-ray interactions are derived and their variation with energy is discussed.

The effective atomic number for electron interactions may be calculated with a similar approach; see for instance Taylor et al. 2009 and Taylor 2011.

The 1s electron of Iron (the closest one to the nucleus) sees an effective atomic number (number of protons) of 25.

The effective atomic number is important for predicting how photons interact with a substance, as certain types of photon interactions depend on the atomic number.

Gadolinium oxysulfide is a promising luminescent host material, because of its high density (7.32 g/cm) and high effective atomic number of Gd.

As such, for polyenergetic photon sources (in particular, for applications such as radiotherapy), the effective atomic number varies significantly with energy (Taylor et al. 2008).

For bulk interaction properties, it can be useful to define an effective atomic number for a composite medium and, depending on the context, this may be done in different ways.

Because the two 1s electrons screen the protons to give an effective atomic number for the 2s electron close to 1, we can treat this 2s valence electron with a hydrogenic model.

An effective atomic number in this context is equivalent to the atomic number but is used for compounds (e.g. water) and mixtures of different materials (such as tissue and bone).

The 4s electrons in Iron, which are furthest from the nucleus, feel an effective atomic number of only 5.43 because of the 25 electrons in between it and the nucleus screening the charge.

Effective atomic number has two different meanings: one that is the effective nuclear charge of an atom, and one that calculates the average atomic number for a compound or mixture of materials.

The effective atomic number Z, (sometimes referred to as the effective nuclear charge) of an atom is the number of protons that an electron in the element effectively 'sees' due to screening by inner-shell electrons.

As such, Barium and Iodine can be used to increase the Effective Atomic Number of certain soft tissues and hence, increase their ability to stop x-rays reaching the film (and therefore make them appear white).

Mathematically, the effective atomic number Z can be calculated using methods known as "self-consistent field" calculations, but in simplified situations is just taken as the atomic number minus the number of electrons between the nucleus and the electron being considered.

Effective atomic numbers are useful not only in understanding why electrons further from the nucleus are so much more weakly bound than those closer to the nucleus, but also because they can tell us when to use simplified methods of calculating other properties and interactions.