Starting his scientific career in nuclear physics from Great Britain, Bhabha returned to India for his annual vacation prior to start of the World War II in September 1939, prompting Bhabha to remain in India, and accepted a post of reader in physics at the Indian Institute of Science in Bengaluru, headed by Nobel laureate C.V. Raman. During this time, Bhabha played a key role in convincing the Congress Party's senior leaders, most notable Jawaharlal Nehru who later served as India's first Prime Minister, to start the ambitious nuclear programme.
As part of this vision, Bhabha established the Cosmic Ray Research Unit at the institute, began to work on the theory of the movement of point particles, while independently conduct research on nuclear weapons in 1944. In 1945, he established the Tata Institute of Fundamental Research in Bombay, and the Atomic Energy Commission in 1948, serving its first chairman. In 1948, Nehru led the appointment of Bhabha as the director of the nuclear programme and tasked Bhabha to develop the nuclear weapons soon after. In the 1950s, Bhabha represented India in IAEA conferences, and served as President of the United Nations Conference on the Peaceful Uses of Atomic Energy in Geneva, Switzerland in 1955. During this time, he intensified his lobbying for developing the nuclear weapons, and soon after the Sino-Indo war, Bhabha aggressively and publicly began to call for the nuclear weapons.
Bhabha gained international prominence after deriving a correct expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His major contribution included his work on Compton scattering, R-process, and furthermore the advancement of nuclear physics. He was awarded Padma Bhushan by Government of India in 1954. He later served as the member of the Indian Cabinet's Scientific Advisory Committee and provided the pivotal role to Vikram Sarabhai to set up the Indian National Committee for Space Research. In January 1966, Bhabha died in a plane crash near Mont Blanc, while heading to Vienna, Austria to attend a meeting of the International Atomic Energy Agency's Scientific Advisory Committee.
He received his early education at Bombay's Cathedral and John Connon School and entered Elphinstone College at age 15 after passing his Senior Cambridge Examination with Honors. He then attended the Royal Institute of Science until 1927 before joining Caius College of Cambridge University.
Bhabha's father understood his son's predicament, and he agreed to finance his studies in mathematics provided that he obtain first class on his Mechanical Sciences Tripos exam. Bhabha took the Tripos exam in June 1930 and passed with first class. Meanwhile, he worked at the Cavendish Laboratory while working towards his doctorate in theoretical physics.
Conducting experiments on particles which also released tremendous amount of radiation, was lifelong passion of Bhabha, and his leading edge research and experiments brought great laurels to Indian physicists who particularly switched their fields to nuclear physics, one of the most notable being Piara Singh Gill.
In January 1933, Bhabha received his doctorate in nuclear physics after publishing his first scientific paper, "The Absorption of Cosmic radiation". In the publication, Bhabha offered an explanation of the absorption features and electron shower production in cosmic rays. The paper helped him win the Isaac Newton Studentship in 1934, which he held for the next three years. The following year, he completed his doctoral studies in theoretical physics under Ralph H. Fowler. During his studentship, he split his time working at Cambridge and with Niels Bohr in Copenhagen. In 1935, Bhabha published a paper in the Proceedings of the Royal Society, Series A, in which performed the first calculation to determine the cross section of electron-positron scattering. Electron-positron scattering was later named Bhabha scattering, in honor of his contributions in the field.
He accepted an offer to serve as the Reader in the Physics Department of the Indian Institute of Science, then headed by renowned physicist C. V. Raman. He received a special research grant from the Sir Dorab Tata Trust, which he used to establish the Cosmic Ray Research Unit at the Institute. Bhabha selected a few students, including Harish-Chandra, to work with him. Later, on 20 March 1941, he was elected a Fellow of the Royal Society .
Tata Trust for establishing 'a vigorous school of research in fundamental physics'. In his proposal he wrote :
“ There is at the moment in India no big school of research in the fundamental problems of physics, both theoretical and experimental. There are, however, scattered all over India competent workers who are not doing as good work as they would do if brought together in one place under proper direction. It is absolutely in the interest of India to have a vigorous school of research in fundamental physics, for such a school forms the spearhead of research not only in less advanced branches of physics but also in problems of immediate practical application in industry.
If much of the applied research done in India today is disappointing or of very inferior quality it is entirely due to the absence of sufficient number of outstanding pure research workers who would set the standard of good research and act on the directing boards in an advisory capacity ... Moreover, when nuclear energy has been successfully applied for power production in say a couple of decades from now, India will not have to look abroad for its experts but will find them ready at hand. I do not think that anyone acquainted with scientific development in other countries would deny the need in India for such a school as I propose.
The subjects on which research and advanced teaching would be done would be theoretical physics, especially on fundamental problems and with special reference to cosmic rays and nuclear physics, and experimental research on cosmic rays. It is neither possible nor desirable to separate nuclear physics from cosmic rays since the two are closely connected theoretically.”
The trustees of Sir Dorabji Jamsetji. Tata Trust decided to accept Bhabha's proposal and financial responsibility for starting the Institute in April 1944. Bombay was chosen as the location for the prosed Institute as the Government of Bombay showed interest in becoming a joint founder of the proposed institute. The institute, named Tata Institute of Fundamental Research, was inaugurated in 1945. When Bhabha realized that technology development for the atomic energy programme could no longer be carried out within TIFR he proposed to the government to build a new laboratory entirely devoted to this purpose.
For this purpose, 1200 acres of land was acquired at Trombay from the Bombay Government. Thus the Atomic Energy Establishment Trombay (AEET) started functioning in 1954. The same year the Department of Atomic Energy (DAE) was also established. He represented India in International Atomic Energy Forums, and as President of the United Nations Conference on the Peaceful Uses of Atomic Energy, in Geneva, Switzerland in 1955. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1958.
Bhabha is generally acknowledged as the father of Indian nuclear power. Moreover, he is credited with formulating a strategy of focussing on extracting power from the country's vast thorium reserves rather than its meagre uranium reserves. This thorium focused strategy was in marked contrast to all other countries in the world. The approach proposed by Bhabha to achieve this strategic objective became India's three stage nuclear power programme.
Bhabha paraphrased the three stage approach as follows:
“ The total reserves of thorium in India amount to over 500,000 tons in the readily extractable form, while the known reserves of uranium are less than a tenth of this. The aim of long range atomic power programme in India must therefore be to base the nuclear power generation as soon as possible on thorium rather than uranium… The first generation of atomic power stations based on natural uranium can only be used to start off an atomic power programme… The plutonium produced by the first generation power stations can be used in a second generation of power stations designed to produce electric power and convert thorium into U-233, or depleted uranium into more plutonium with breeding gain… The second generation of power stations may be regarded as an intermediate step for the breeder power stations of the third generation all of which would produce more U-233 than they burn in the course of producing power.