There isn't a specific New Zealand physicist who is credited with "splitting the atom". The concept of nuclear fission, the process of splitting an atom, was a collaborative effort involving scientists from multiple countries and institutions.

Here's why:

* Discovery of Fission: The discovery of nuclear fission is primarily attributed to Otto Hahn and Fritz Strassmann in Germany in 1938. They observed the splitting of uranium atoms when bombarded with neutrons.

* Interpretation: The theoretical explanation of fission was provided by Lise Meitner and Otto Frisch in 1939.

* Manhattan Project: The development of the atomic bomb, a practical application of fission, was a massive international effort during World War II, largely spearheaded by the United States.

While New Zealand has made significant contributions to science, there isn't a single Kiwi scientist associated with the discovery or initial development of nuclear fission.

It's important to remember that scientific discoveries are often collaborative endeavors, involving contributions from many individuals across different disciplines and nationalities.