The radiation that is identical in mass and charge to a helium nucleus is alpha radiation.

Here's why:

* Alpha radiation consists of two protons and two neutrons bound together, which is exactly the composition of a helium nucleus (Helium-4).

* Mass: Both alpha particles and helium nuclei have a mass number of 4.

* Charge: Both have a +2 charge due to the two protons.

Therefore, alpha radiation is essentially a helium nucleus emitted from a radioactive atom during radioactive decay.