Besant and CWL did occult research on atom and their observations were published in 1908. While there was a lot of questions about them, here is a recent article by a well known Indian Scientist which appeared in an Indian Newspaper. Here are two quotes:           

‘According to M Srinivasan, former associate director of Bhabha Atomic Research Centre, (BARC), "One important piece of work, which brings out the extraordinary power of the human mind or consciousness in gaining 'direct knowledge of reality,' as practised by the Indian sages was done by the Theosophists Annie Besant and C W Leadbeater over a century ago. They carried out clairvoyant investigations into the detailed structure of atoms and nuclei.’

‘Srinivasan, a Theosophist, says, "Besant and Leadbeater have recorded that an atom of the
smallest element Hydrogen comprised 18 UPAs while at the upper end, an atom of the heaviest element Uranium comprised 4,267 UPAs. They clairvoyantly discovered the existence of isotopes and published the atomic weight of all the 92 naturally occurring elements and several of their isotopes correct to the second decimal place." This was done five years before Aston experimentally detected an isotope of Neon using his newly-invented instrument or the mass spectrometer, and for which he was later awarded the Nobel Prize. The observations of Besant and Leadbeater were published in the first edition of the book, Occult Chemistry, in 1908.’

Read the full article here: here.