Dr. Homi J. Bhabha: A Short Biography

Homi Jehangir Bhabha was born into a prominent wealthy Parsi family on 30 October 1909. His father Jehangir Hormusji Bhabha was a well-known lawyer and his mother was Meheren. He attended the Cathedral and John Connon School in Bombay and entered Elphinstone College at age 15 after passing his Senior Cambridge Examination with Honours.

He then attended the Royal Institute of Science in 1927 before joining Caius College of Cambridge University. He completed his Mechanical Tripos with distinction and persuaded his parents to let him do a Mathematical Tripos as his interests were in Physics.

During the 1931–1932 academic year, Bhabha was awarded the Salomons Studentship in Engineering. He excelled in his mathematical studies under Paul Dirac to complete the Mathematics Tripos.

In 1932, he obtained first-class on his Mathematical Tripos and was awarded the Rouse Ball traveling studentship in mathematics, and had the wonderful opportunity of working for short periods with Wolfgang Pauli in Zurich and with Enrico Fermi in Rome. In January 1933, Bhabha published his first scientific paper, “The Absorption of Cosmic radiation“. 

The paper helped him win the Isaac Newton Studentship in 1934 which allowed him to complete his doctoral studies in theoretical physics under Ralph H. Fowler. In 1937, Bhabha was awarded the Senior Studentship of the 1851 exhibition, which helped him continue his work at Cambridge until the outbreak of World War II in 1939.

Bhabha came on a brief holiday to India in 1939. He could not go to England as planned as World War 2 broke out in September 1939. 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. He gathered some students to work with him in theoretical particle physics and one of them was Harish Chandra who later held a Professional Chair in Mathematics at the Princeton Institute of Advanced Studies.

On 20 March 1941, he was elected a Fellow of the Royal Society. With financial support from Sir Dorab Tata Trust and the Government of Maharasthra, Bhabha established the Tata Institute of Fundamental Research in Bombay in June 1945. Bhabha was the director of TIFR from 1945 till his untimely death in January 1966.

When Bhabha realized that technology development for the atomic energy program 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 were acquired at Trombay from the Bombay Government. Thus, the Atomic Energy Establishment Trombay (AEET) started functioning in 1954.

Bhabha’s advocacy led to the Indian Atomic Energy Act of 1948. In 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 was a keen member of the Scientific Advisory Committee of the Indian Cabinet and its Chairman from July 1964, until his death.

He was largely responsible for the introduction of the Indian space program through the set up in 1962 of the Indian National Committee for Space Research under the chairmanship of Dr. Sarabhai. Bhabha was appointed as the President of the International Union of Pure and Applied Physics from 1960-to to 1963.

He presided over the Warsaw General Assembly in 1963. Bhabha was a member of the International Atomic Energy Agency (IAEA) Scientific Advisory Committee and remained a member until his death. Bhabha made powerful contributions to the work of the I.A.E.A., both as a member of the Scientific Advisory Committee and as the Indian spokesman at the General Assembly of the Agency.

On 24 January 1966, Bhabha died in Air India Flight 101 plane crash near Mont Blanc, while heading to Vienna, Austria to attend a meeting of the International Atomic Energy Agency’s Scientific Advisory Committee. Misunderstanding between Geneva Airport and the pilot about the aircraft’s position near the mountain is the official reason for the crash.

References

1. Bhabha Atomic Research Center. (2009). Remembering Dr. Homi Bhabha, the Physicist. http://www.barc.gov.in/publications/tb/bhabha.pdf
2. Physics Today. (1966). Homi Jehangir Bhabha. 19 (3): 108. doi:10.1063/1.3048089.
3. IGCAR, Kalpakkam, Raj, B., & Amarendra, G. (n.d.). A legend lives on –Homi Jehangir Bhabha (1909-1966). Indira Gandhi Centre for Atomic Research. Archived from the original on 22 May 2013. Retrieved January 7, 2021, from https://web.archive.org/web/20171007155126/http:/www.igcar.ernet.in/press_releases/press29.htm
4. Singh, Virendra. (2009). Bhabha’s Contributions to Elementary Particle Physics and Cosmic Rays Research. Resonance.14, 430-454. DOI: https://doi.org/10.1007/s12045-009-0045-1
5. Penney, William George. (1967). Homi Jehangir Bhabha, 1909-1966. (PDF).  Biographical Memoirs of the Fellows of the Royal Society.  https://doi.org/10.1098/rsbm.1967.0002
6. Haine, Edgar A. (2000). Disaster in the Air. Associated University Presses. pp. 146–147. ISBN: 978-0-8453-4777-5.

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What are the important scientific contributions of Homi J. Bhabha?

What is Bhabha Scattering?

Bhabha investigated positron interactions in a number of papers using Dirac’s Hole Theory. He studied the creation of electron-positron pairs by fast-charged particles. He investigated electron-positron scattering a process known as Bhabha scattering.

In the quantum-mechanical description of scattering, the distinguishability of the particle is lost and the effect of particle exchange on scattering needs to be considered. If a positron is regarded as an independent particle that obeys the Dirac equation, the positron-electron scattering should show no exchange effects.

If, on the other hand, a positron is regarded as an electron in an unoccupied negative energy state then we should expect exchange effects. These two hypotheses would lead to different results. Except for the non-relativistic limit, the effect of the exchange was found to be considerable.

Bhabha looked at this extra-energy contribution as due to the annihilation of the electron-positron pair, followed by the simultaneous creation of a new electron-positron pair, and that such terms should be present in the scattering of any two particles which can annihilate each other and be created in pairs.

A consequence of this calculation was an expected considerable increase in the number of fast secondaries for positrons of higher energies. Bhabha’s theory was beautifully confirmed by experiments.

Bhabha Scattering formulas are now routinely used to calibrate the beams at large accelerators using positron or other antiparticle beams.

References

1. Bhabha, H. J. (1936). The scattering of positrons by electrons with exchange on Dirac’s theory of the positron. Proc. R. Soc. Lond. A154, 195–206. http://doi.org/10.1098/rspa.1936.0046
2. Bhabha, H., & Hulme, H. (1934). The Annihilation of Fast Positrons by Electrons in the K-Shell. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 146(859), 723-736. Retrieved January 5, 2021, from http://www.jstor.org/stable/2935492
3. Pauli, W., & Weisskopf, V. (1934). Uber die Quantisierung der skalaren relativistischen. Helv. Phys. Acta, 7, 708-731.
4. Baumann, K. (1953). Acta Physica Austriaca, Vol. 7, p.96.
5. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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What is Bhabha-Heitler theory?

The Bethe-Heitler Theory predicted large cross-sections for energy loss of electrons or positrons passing through the field of the nucleus by bremsstrahlung in a single encounter. The theory seemed to disagree with the observation of fast electrons at sea level which has traversed 8 km of the atmosphere.

It was believed that these observations signified the breakdown of quantum electrodynamics. Bhabha and Heitler showed through their Cascade Theory that quantum electrodynamics was quite consistent with the observed phenomenon. A fast electron loses all of its energy after passing through the matter for a short distance as predicted by the Bethe-Heitler formula.

The energy reappears in the form of radiation quanta which, for large initial velocities, have a large probability of moving in the direction of the original fast electron. There is a high probability that these radiation quanta are hard.

Again, in accordance with quantum electrodynamics, these radiation quanta materialize after traveling a short distance through matter into electron-positron pairs. Again, there is a high probability that the resulting pair consists of a fast electron and a fast positron moving in the direction of the disappearing hard quantum.

This process of conversion into photons and reconversion into electron-positron pairs can take place many times. The total effect is thus as if the original electron was losing its energy much more slowly than implied by the theoretical range as predicted by the Bethe-Heitler Theory.

These ideas of Bhabha and Heitler provided a natural explanation of cosmic ray showers. The Bhabha-Heitler Theory agreed very well with the observations of Rossi and Regener.

References

1. Regener, E., Pfotzer, G. (1935). Vertical Intensity of Cosmic Rays by Threefold Coincidences in the Stratosphere. Nature 136, 718–719. https://doi.org/10.1038/136718a0
2. Rossi, B. (1935). Some results arising from the study of cosmic rays, in: International Conference on Physics, London 1934: a Joint Conference organized by the International Union of Pure and Applied Physics and the Physical Society: Papers & Discussions, Vol. I. Nuclear Physics, The Physical Society, London, pp. 233–247.
3. Bonolis, Luisa. (2014). From cosmic ray physics to cosmic ray astronomy: Bruno Rossi and the opening of new windows on the universe. Astroparticle Physics, Vol. 53, pp. 67-85, ISSN-0927-6505. DOI: https://doi.org/10.1016/j.astropartphys.2013.05.008.
4. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Did Homi J. Bhabha work on penetrating components of Cosmic Rays?

It was understood from the work on the absorption of cosmic rays in lead by Rossi and others that cosmic rays consist of two components; soft and penetrating. The properties of the soft component could be completely accounted for by the Bhabha-Heitler Theory if it was electrons.

It was not possible for the quantum electrodynamics to account for the penetrating component if it was electrons. There was therefore a breakdown of quantum electrodynamics for higher energies or if the penetrating component did not consist of electrons.

Bhabha showed that the breakdown of quantum electrodynamics for the energy loss of electrons was not a viable alternative for the observed phenomenology of cosmic radiation. Bhabha showed that if the breakdown energy is around 10GeV or higher for electrons then no latitude effect would be seen at sea level.

Hence the penetrating component of cosmic radiation was thought to consist of particles other than electrons. Bhabha found out that the penetrating component of cosmic radiation consisted of particles whose charge could be of both signs and mass between the electron and proton mass, about 100 times the electron mass.

These particles are now called muons and were observed by Neddermeyer and Anderson in cosmic rays in 1938. Bhabha when he predicted the cosmic muons in October 1937 was not aware of Hideki Yukawa’s Meson Theory.

References

1. Bhabha, H. J. (1938). On the Penetrating Component of Cosmic Radiation. Proceedings of the Royal Society London. A164, 257–294. Print ISSN: 0080-4630, Online ISSN:2053-9169. DOI: http://doi.org/10.1098/rspa.1938.0017
2. Blackett, Patrick Maynard Stuart. (1937). Further measurements of the cosmic-ray energy spectrum. Proceedings of the Royal Society London. A159, 1-18, DOI: http://doi.org/10.1098/rspa.1937.0052
3. Neddermeyer, Seth H., Anderson, Carl D. (1937). Note on the Nature of Cosmic-Ray Particles. Physical Review, Vol. 51, Issue 10, 884. DOI: https://doi.org/10.1103/PhysRev.51.884.
4. Street, J. C., Stevenson, E. C. (1937). New Evidence for the Existence of a Particle of Mass Intermediate Between the Proton and Electron. Physical Review. Vol. 52, Iss. 9. 1003. DOI: https://doi.org/10.1103/PhysRev.52.1003.
5. Neddermeyer, Seth H., Anderson, Carl D. (1938). Cosmic-Ray Particles of Intermediate Mass. Physical Review. Vol. 54, Iss.1, 88. DOI: https://doi.org/10.1103/PhysRev.54.88.2
6. Rossi, B. (1934). Misure sulla distribuzione angolare di intensita della radiazione penetrante all’Asmara. Supplemento a la Ricerca Scientifica, 1, pp. 579.
7. Auger, P., & Leprince-Ringuet, L. (1934). Analyse du rayonnement cosmique en haute altitude. Academie des Sciences, Paris, Comptes rendus, 199, 785-787.
8. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Did Bhabha work on the Theory of Relativity?

Bhabha pointed out that positive (negative) mesons should spontaneously decay into positrons (electrons). This disintegration being spontaneous, the U-particle may be described as a clock, and hence it follows from relativity that the time of disintegration is longer when the particle is in motion. The U-particles referred to the mesons.

Thus the lifetime T of a particle moving with a velocity ν should be given by

This was confirmed by the experiments and is one of the tests for the special theory of relativity.

References

1. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1
2. Bhabha, H. (1938). Nuclear Forces, Heavy Electrons and the β-Decay. Nature, 141, 117–118. DOI: https://doi.org/10.1038/141117a0

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Did Homi J. Bhabha work on mesons?

The original Yukawa’s theory had considered mesons to be scalar particles i.e., having no spin and with positive parity. This assignment does not give rise to satisfactory nuclear force between the nucleons. Mesons, further, have to have integral spins and obey Bose-Einstein statistics.

Bhabha, therefore, considered the generalization that mesons are vector particles, i.e., having spin one and odd parity. Bhabha used Proca’s wave equation to describe the meson field. The coupled nucleon-meson field system was then quantized and nucleon-nucleon interaction was calculated using the second-order perturbation theory.

The interaction is therefore just of the required form consisting of Heisenberg and Majorana forces of the right sign so as to allow one to make the triplet state of the deuteron the lowest stable state. Bhabha also calculated the meson-nucleon scattering cross-section in the lowest order.

References

1. Bhabha, H. J. (1938). On the theory of heavy electrons and nuclear forces. Proceedings of the Royal Society London. A166, 501–528. DOI: http://doi.org/10.1098/rspa.1938.0107
2. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Classical Meson Theory

In order to overcome the limitations of the perturbation theory in the coupling constant in dealing with quantum meson field theory, Bhabha decided to investigate the classical meson field theory in interaction with a fermion. The meson field was described by the Proca wave equation but the meson field components were taken as commuting variables.

The fermion was taken as a point classical particle having a spin and moving along classical world-lines. This entailed the generalization of the method of Dirac used in treating the behavior of a classical point electron in the field of electromagnetic radiation.

The meson-fermion scattering cross-sections were calculated. These were analogous to Thomson scattering for zero mass photons and found to go smoothly to the limit as the meson mass went to zero.

Indeed, it was found that at high energies i.e., energies much larger than the meson mass, the behavior was the same as that in Dirac’s case. Before the advent of the Chew-Low theory, these were among the best theoretical attempts to deal with the meson-nucleon scattering problem.

References

1. Bhabha, Homi Jehangir. (1939). Classical theory of mesons. Proceedings of the Royal Society London. A172, 384–409. DOI: http://doi.org/10.1098/rspa.1939.0110
2. Dirac, Paul Adrien Maurice. (1938). Classical theory of radiating electrons. Proceedings of the Royal Society London. A167, 148–169. DOI: http://doi.org/10.1098/rspa.1938.0124
3. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Classical Relativistic Spinning Point Particle Theory – Bhabha-Corben Equations

Bhabha was drawn to the classical theory of relativistic point particles as a way to take into account the reaction of the emitted or scattered radiation, whether of electromagnetic quanta or of mesons, i.e., radiation reaction on the motion of fermions.

The quantum treatment of the interaction of point particles with fields, which depended on perturbation theory in the coupling constant, was not very satisfactory. It was even more so when the explicit spin-dependent interactions were taken into account.

The interactions tend to increase with energy. Bhabha pointed out that these effects are due to the neglect of radiation reaction and that the quantum treatment can be trusted only in the region of energy where this neglect of radiation reaction is justified.

Faced with this situation it was natural to go back to the classical limit where it is, in principle, possible to take radiation reaction into account either exactly or with controlled approximations. For spinless charged particles it was possible to do this by using Dirac’s work on the point electron theory.

In Dirac’s work, the spin of the electron was not taken into account. It was therefore necessary to generalize Dirac’s work to the case of spinning point particles. In the procedure of Dirac and Pryce, one assumes the validity of the field equations right up to the point particle worldline but one modifies the definition of the field energy in the presence of singularities.

This is also the procedure adopted by Bhabha and Corben. The effect of radiation reaction was, as expected by Bhabha, to reduce the scattering cross-section.

References

1. Dirac, Paul Adrien Maurice. (1938). Classical theory of radiating electrons. Proceedings of the Royal Society London. A167, 148–169. DOI: http://doi.org/10.1098/rspa.1938.0124
2. Bhabha, Homi Jehangir., Corben, H. C. (1941). General classical theory of spinning particles in a Maxwell field. Proceedings of the Royal Society London. A178, 273–314. DOI: http://doi.org/10.1098/rspa.1941.0056
3. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Meson Theory and Nucleon Isobars

Before the discovery of the pion in 1947, the muon was confused with Yukawa’s meson. The meson theorists had the unenviable task of explaining why meson-nucleon scattering is weak since muons do not scatter much on the nucleons and yet at the same time the nuclear forces arising from the exchange of the same mesons are strong.

Bhabha found out the scattering of the longitudinally polarized neutral vector mesons on nucleons shows a decrease as E^-2, E being the meson energy, for large energies in contrast to the scattering of longitudinally polarized charged mesons whose scattering on the nucleons increases as E².

This difference was traced by Bhabha as being due to the cancellation between the direct channel nucleon poles in the case of neutral mesons and the lack of such cancellation for charged mesons. For charged mesons, we do not have both direct and cross-channel exchanges possible if only nucleons of charge +1 and 0 exist.

In order to have the cancellation mechanism available, Bhabha, therefore, suggested that the nucleon may exist in charge states +2 and -1 also. The contribution from these charged states was needed to provide the cancellation. In general, nucleon isobars may have any charge and the neutron and the proton are the only light ones occurring in nature.

This was the first suggestion of the existence of nucleon isobars. Bhabha communicated the idea to Heitler and he also pursued it. This mechanism, referred to as the Bhabha-Heitler mechanism, for reducing meson cross-sections, was one of the major reasons for a study of the strong coupling theory of nucleon isobars.

The first nucleon isobar N* was discovered by Enrico Fermi in pion-nucleon scattering experiments in 1952.

References

1. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Cascade Theory

Bhabha-Heitler Theory had made a number of simplifying assumptions. In particular, it was assumed that one can ignore collision loss below a certain critical value, i.e., the energy at which the collision loss is equal to the radiation loss. Further, if the energy was above this critical value it was assumed that it would lead to an absorption of the cascade.

Snyder and Serber attempted to give an improved treatment by taking collision loss into account, but there were some doubts about the convergence of their series solutions. Bhabha and Chakrabarthy gave a solution to this problem in the form of a rapidly converging series.

Bhabha and Chakrabarthy used the asymptotic form of the Bethe-Heitler expressions in their solution. Using Mellin transformation techniques it was possible to obtain a series solution that was rapidly convergent.

It is possible to regard the Bhabha-Chakrabarthy solution as an analytical continuation of the results of Snyder and Serber. Bhabha and Chakrabarthy extended their calculations of the number of charged particles and quanta in 1948, to cover the case of showers in thin layers.

They brought to completion this part of their work on cascade theory which deals only with mean numbers of shower particles at various depths.

References

1. Snyder, H. (1938). Transition effects of cosmic rays in the atmosphere. Physical Review, 53(12), 960. DOI: https://doi.org/10.1103/PhysRev.53.960
2. Serber, R. (1938). Transition effects of cosmic rays in the atmosphere. Physical Review, 54(5), 317. DOI: https://doi.org/10.1103/PhysRev.54.317
3. Bhabha, H. J., & Chakrabarty, S. K. (1943). The cascade theory with collision loss. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 181(986), 267-303. DOI: https://doi.org/10.1098/rspa.1943.0007
4. Landau, L. D., & Rumer, G. (1938). The cascade theory of electronic showers. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 166(925), 213-228. DOI: https://doi.org/10.1098/rspa.1938.0088
5. Iyengar, K. S. K. (1942). Exact solution of the equations of the general cascade theory with collision loss. In Proceedings of the Indian Academy of Sciences-Section A (Vol. 15, No. 4, pp. 195-229). Springer India. DOI: https://doi.org/10.1007/BF03046014
6. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Stochastic Process in Cosmic Ray Showers

The study of the fluctuations of the number of shower particles is also of great importance in the study of cosmic ray showers. One of the conceptual difficulties in attacking the problem was that it involved a system whose state space was continuous and not discrete. The electrons and photons do not have a continuous variation in energy.

Bhabha, therefore, derived the product density function method for the continuous parametric systems and applied it to derive the equations of cosmic ray cascade theory which determine the mean numbers (i.e., Landau-Rumer equations) and the mean square deviations of the numbers. These equations were solved in a subsequent paper with Ramakrishnan.

References

1. Bhabha, H. J. (1950). On the stochastic theory of continuous parametric systems and its application to electron cascades. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 202(1070), 301-322. DOI: https://doi.org/10.1098/rspa.1950.0102
2. Bhabha, H. J., & Ramakrishnan, A. N. D. A. (1950). The mean square deviation of the number of electrons and quanta in the cascade theory. In Proceedings of the Indian Academy of Sciences-Section A (Vol. 32, No. 3, pp. 141-153). Springer India. DOI: https://doi.org/10.1007/BF03171089
3. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Experimental Cosmic Ray Work

In order to devise an experimental setup to study the hard component of the cosmic rays containing mesons, it was necessary to devise procedures to discriminate between the soft and the hard components experimentally. Bhabha studied this problem in 1943.

Bhabha came to the conclusion that the usual method of separating the two components of the cosmic rays by interposing absorbers such as lead of different thicknesses and measuring the cosmic ray absorption is not very reliable.

Bhabha devised a new method for this purpose. Bhabha showed that it would be able to take better advantage of shower multiplication by soft component to better discriminate between the soft and hard components. The experimental measurement of the vertical intensity of mesons was carried out in two airplane flights at Bangalore at a magnetic latitude of 3.3° N.

The measurements were taken up to 15,000 ft. A second flight carried measurements up to 30,000 ft. A comparison of the experimental measurements by Bhabha and his group in these flights with those of Schein, Jesse, and Wollan carried out at Chicago at a magnetic latitude of 52.5° N, showed that for meson intensity there was no marked increase even to latitudes corresponding to 275 mbar pressure.

This was quite in contrast to the total cosmic ray intensity which showed a marked increase of latitude effect up to these heights. Another flight making such measurements later extended the results up to an altitude of 40,000 ft above Bangalore with similar results.

The program of measuring the hard component of the cosmic ray intensity, at various Indian latitudes and its variation with altitudes was continued at Bombay. Towards these objectives, Bhabha organized a High Altitudes Studies Group whose main program was to organize balloon flights for these studies. The balloon flights were initially made from Bangalore and Delhi.

Bhabha reported these results at a conference in Kyoto, Tokyo in 1953. Bhabha made a preliminary beginning for nuclear emulsion work with cosmic rays by flying Ilford C2 planes loaded with Boron in an airplane at an average altitude of 8,000 ft for 72 hours in 1948.

An example of meson scattering with nuclear excitation was recorded and published by his student Roy Daniel. Later, Bhabha introduced Bernard Peters, of the University of Rochester to take over the nuclear emulsion group at Bombay in 1950. Peters was well known for his discovery of heavy nuclei in primary cosmic rays.

A 12-inch diameter cloud chamber, similar in design to one at Blackett’s laboratory at Manchester, which Bhabha had got built at Bangalore, was moved to Bombay, and work on the meson scattering continued.

Bhabha also started considering Kolar Gold Fields as a facility for deep underground experiments on cosmic rays around 1950. Prof. M. G. K. Menon joined the cosmic ray group from Prof. Powell’s group in 1956.

References

1. Bhabha, H. J. (1954). Proceedings of the International Conference on “Theoretical Physics”, Kyoto-Tokyo, 1953, (Sc. Council of Japan), p. 95.
2. Bhabha, H. J., & Daniel, R. R. (1948). Meson Scattering with Nuclear Excitation. Nature, 161(4101), 883-884. DOI: https://doi.org/10.1038/161883a0
3. Sreekantan, B. V., Udgaonkar, B. M., & Singh, V. (1985). HJ Bhabha: His contributions to cosmic ray physics. PRE-29120.
4. Bhabha, H. J., & Chakrabarty, S. K. (1943). The cascade theory with collision loss. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 181(986), 267-303. DOI: https://doi.org/10.1098/rspa.1943.0007
5. Bhabha, H. J. (1944, January). Note on the separation of the electronic and non-electronic components of cosmic radiation. In Proceedings of the Indian Academy of Sciences-Section A (Vol. 19, No. 1, p. 23). Springer India. DOI: https://doi.org/10.1007/BF03174816
6. Bhabha, H. J., Aiya, S. V. Chandrasekhar., Hoteko, H. E., & Saxena, R. C. (1945). Meson Intensity in the Substratosphere. Physical Review, Vol. 68, Iss. 7-8, 147. DOI: https://doi.org/10.1103/PhysRev.68.147
7. Schein, Marcel., Jesse, William P., Wollan, E. O. (1940). Intensity and Rate of Production of Mesotrons in the Stratosphere. Physical Review, Vol. 57, Iss. 10, 847. DOI: https://doi.org/10.1103/PhysRev.57.847
8. Millikan, Robert A., & Neher, H. Victor. (1935). The Equatorial Longitude Effect in Cosmic Rays. Physical Review, Vol. 47, Iss. 3, 205. DOI: https://doi.org/10.1103/PhysRev.47.205
9. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Bhabha Equations

Dirac, Fierz, and Pauli proposed relativistic wave equations for particles having an integral or half-odd integral spin. An unsatisfactory feature of the equations proposed by Dirac, Fierz, and Pauli for spin greater than one was the presence of the subsidiary conditions.

These conditions created difficulties when one considered these particles interacting with electromagnetic fields. The problem was connected to the fact that these could not be derived from a variational principle.

Bhabha, therefore, investigates general first-order relativistic wave equations without any subsidiary conditions, i.e., equations for a wave field of the form,

where,  

are four matrices (k=0,1,2,3) and is an arbitrary constant. Such equations are called Bhabha Equations.

References

1. Bhabha, H. J. (1945). Relativistic wave equations for the elementary particles. Reviews of Modern Physics, 17(2-3), 200. DOI: https://doi.org/10.1103/RevModPhys.17.200
2. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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Multiple Meson Production

In the center of the mass system, the two colliding nucleons suffer a relativistic contraction in the direction of motion and appear as colliding discs. Different mechanisms were invoked by Fermi and Heisenberg for the conversion of nucleon energy into mesons.

Bhabha suggested the hypothesis that the strong interactions get localized both due to relativistic contraction as well as due to the time of interaction being very small. In this picture, the energy available for meson production is much less than the total available c.m. energy.

The real surge of interest in multiple meson production had to wait till the early 1970s when sufficient high energy data became available. In Bhabha’s view, it is somewhat natural to assume not only that the strong interaction gets localized but that the production of mesons also gets localized, leading to the damping of transverse momenta.

Bhabha’s model thus can be regarded as a precursor of the Parton model which is the 1969 model of Feynman picturing protons and neutrons as made up of various point-like constituents.

References

1. Bhabha, H. J. (1953). Production of mesons and the localization of field energy. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 219(1138), 293-303. DOI: https://doi.org/10.1098/rspa.1953.0147
2. Narayan, D. S. (1971). Localization of strong interaction and random fragmentation as a model of high-energy collisions. Nuclear Physics B, 34(2), 386-396. DOI: https://doi.org/10.1016/0550-3213(71)90335-X
3. Singh, V. (2009). Bhabha’s contributions to elementary particle physics and cosmic rays research. Resonance, 14, 430–454. DOI: https://doi.org/10.1007/s12045-009-0045-1

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What are Homi J. Bhabha’s contributions to the Indian Nuclear Program?

In 1944, Bhabha wrote his historical letter to the Tata trust for support in setting up a center for research work in nuclear science, which could play a central role in the development of nuclear energy. This was just two years after 1942 when the first experimental demonstration of a nuclear reactor was made in the USA.

All the more so, the country was still under British rule and industrially undeveloped. There was a clear similarity in vision between the great Jamshedji Nusserwanji Tata and Bhabha with respect to the need for education, scientific research, and human resource development for economic prosperity.  

Based on this letter, Tata Trust supported him to set up a laboratory at Kenilworth, Bombay. Subsequently, the Tata Institute of Fundamental Research was formed and large-scale research in physics, chemistry, electronics, and mathematics commenced. 

Thus, Bhabha had converted the difficulty of not going back abroad into a great opportunity of setting up front-ranking research facilities within the country. During the growing days of the Atomic Energy Establishment at Trombay, Bhabha sent for training to the U. K. and the United States, many young physicists, metallurgists, and chemists as a nucleus for Trombay.

He also invited overseas scientists and technologists to work at Trombay, in particular, to advise him and his staff on the organization and program which would best fit the Centre to provide the support necessary for India’s Nuclear Power Industry.

Bhabha’s plan of working towards complete self-sufficiency in a national nuclear power program required a considerable effort in the procurement and processing of ores, uranium metal fabrication, fuel element development, and manufacture of irradiated fuel elements. Bhabha’s advocacy led to the Indian Atomic Energy Act of 1948.

A Commission was created in the Department of Scientific Research, and later in the ministry of Natural Resources and Scientific Research, to carry out the responsibilities of the central government given by the 1948 Act.

Bhabha was appointed Chairman of the Commission in August 1948. Using the authority of the 1948 Act, a separate ministry, the Department of Atomic Energy was created in August 1954 and was charged solely with the development of atomic energy for peaceful purposes.

The Department was in direct charge of the Prime Minister and Bhabha was appointed Secretary to the Government of India in the Department. The headquarters of the Ministry were located in Bombay in order to have close contact with the main center of its scientific activities, the Trombay Establishment.

In addition to the plants at Trombay, or in connection with the center at Trombay, several more atomic energy plants were constructed or started, while Bhabha was Secretary to the Government of India in the Department of Atomic Energy.

Bhabha chalked out focused research and minerals exploration programs for nuclear energy. He was such a visionary that he realized the importance of the nuclear power program way back in the 1950s and enunciated a three-stage nuclear program so as to meet the energy security of the nation.

Bhabha conceived a nuclear strategy that would work around our nation’s rather meager resources of Uranium. He also sought to exploit the country’s vast resources of thorium. The three-stage program consisted of the utilization of natural uranium, plutonium, and abundant thorium resources in thermal, fast, and advanced nuclear reactors with closed fuel cycles.  

He also had a balanced perspective on the role of other energy resources such as coal, oil, and solar.

A significant factor that contributed to the growth of nuclear sciences and its applications was Bhabha’s rapport with the then Prime Minister Pandit Jawaharlal Nehru, who reposed complete confidence in him.

Bhabha stated that while ‘in a line which is on the frontiers of knowledge, it is clearly impossible to give any assurance that heavy water will be required permanently, there was every indication that its uses in atomic energy are not likely to diminish’.

The water-moderated reactor systems require advanced Zirconium technology, and Bhabha started to research and development work on Zirconium at the Trombay Establishment, with a view to building a Zirconium fabrication plant in due course.

Accordingly, the Indian Government authorized the construction of a heavy water plant at Nangal as a part of a fertilizer project of the Fertilizer Corporation of India Ltd.  After his sudden death in an air crash, at a ceremony attended by many well-known international figures in atomic energy, on 12 January 1967, the Prime Minister of India, Mrs. Indira Gandhi, renamed the Trombay Establishment the Bhabha Atomic Research Center.

Due to the vision of Dr. Bhabha, India is a world leader in thorium research and development.

References

1. Penney, William George. (1967). Homi Jehangir Bhabha, 1909-1966. (PDF).  Biographical Memoirs of the Fellows of the Royal Society.  https://doi.org/10.1098/rsbm.1967.0002
2. IGCAR, Kalpakkam, Raj, B., & Amarendra, G. (n.d.). A legend lives on –Homi Jehangir Bhabha (1909-1966). Indira Gandhi Centre for Atomic Research. Archived from the original on 22 May 2013. Retrieved January 7, 2021, from https://web.archive.org/web/20171007155126/http:/www.igcar.ernet.in/press_releases/press29.htm
3. Rahman, M. (2011, November 1). How Homi Bhabha’s vision turned India into a nuclear R&D leader. The Guardian. https://www.theguardian.com/environment/2011/nov/01/homi-bhabha-india-thorium-nuclear?intcmp=239
4. Institute of Physics. (2010, October 1). A future energy giant? India’s thorium-based nuclear plans. Phys.Org. https://phys.org/news/2010-10-future-energy-giant-india-thorium-based.html

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What is Homi J. Bhabha’s contribution to International Science and Technology?

Most of Bhabha’s work in international science and technology stemmed from his atomic energy activities in India. He was appointed as the President of the International Union of Pure and Applied Physics from 1960-to 1963. He presided over the Warsaw General Assembly in 1963.

By unanimous vote, the General Assembly of the United Nations decided in December 1954 that an international technical conference should be held under the auspices of the United Nations to explore means of developing the peaceful uses of atomic energy through international cooperation.

The General Assembly also decided that the date and venue of the planned conference be decided by the United Nations Secretary-General and an Advisory Committee composed of representatives of seven countries, including India.

India was represented by Dr. Bhabha. In his letter to the invited nations, the Secretary-General of the United Nations informed that he had appointed Dr. Bhabha, the Chairman of the Atomic Energy Commission of India, as President of the Conference.

Bhabha’s Presidential address to the conference was a brilliant essay about energy and population and described in a simple direct style the changes in living conditions of man during the last 2,000 years, made possible by technology.

Bhabha also presented to the conference, a paper on the role of nuclear power in India and its immediate possibilities. In another outstanding address to the Conference in his concluding speech, Bhabha gave a clear summary of the world’s need for more energy and correctly expressed the confidence of the Conference that nuclear energy would make a vital contribution.

The International Atomic Energy Agency was created in 1955, and its headquarters was placed in Vienna. Bhabha certainly had some part in the choice of Vienna.

The Secretary-General of the IAEA decided that he needed a scientific advisory committee, and his proposal was accepted that the committee should have, on a personal basis, the same seven scientists who represented their countries on the United Nations Secretary General’s scientific advisory committee. Bhabha, therefore, became a member of the IAEA Scientific Advisory Committee and remained a member until his death.

Bhabha made powerful contributions to the work of the IAEA, both as a member of the Scientific Advisory Committee and as an Indian spokesman at the General Assembly of the agency. At the second United Nations Conference on the Peaceful Uses of Atomic Energy, which was held in Geneva in September 1958, Bhabha took the chair of session 4: the possibility of controlled fusion.

At the conference, Bhabha and W. B. Lewis also presented a paper on ‘The Canada-India reactor: an exercise in international collaboration’. The third United Nations Conference on the Peaceful Uses of the Atomic Energy, held in Geneva in September 1964, again showed Bhabha as one of the leading figures in nuclear power.

He presented a paper titled ‘World energy requirements and the economics of nuclear power with special reference to underdeveloped countries.’

References

1. Penney, William George. (1967). Homi Jehangir Bhabha, 1909-1966. (PDF).  Biographical Memoirs of the Fellows of the Royal Society.  https://doi.org/10.1098/rsbm.1967.0002

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What are Homi J. Bhabha’s contributions as the Government Advisor on Science and Technology?

Bhabha was a member of the Scientific Advisory Committee of the Indian Cabinet and its Chairman from July 1964 until his death. He was largely responsible for the introduction of the Indian Space Program through the set up in 1962 of the Indian National Committee for Space Research under the chairmanship of Dr. Vikram Sarabhai.

Bhabha was also Chairman of the Government Electronics Committee. Bhabha laid down the blueprint for a ten-year development of the electronics industry which he did as the Chairman of the Electronics Committee.

References

1. Penney, William George. (1967). Homi Jehangir Bhabha, 1909-1966. (PDF).  Biographical Memoirs of the Fellows of the Royal Society.  https://doi.org/10.1098/rsbm.1967.0002

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What are the Awards and Honours conferred upon Homi J. Bhabha?

1. Fellow of the Royal Society of London. (1941)
2. Adams prize (for a thesis on ‘The theory of the elementary particles and their interaction’). (1942)
3. Hopkins prize of the Cambridge Philosophical Society. (1948)
4. Melchett Award of the Fuel Institute in London.
5. Padma Bhushan. (1954)
6. Honorary fellow of Gonville and Caius College. (1957)
7. Honorary Fellowship of the Royal Society of Edinburgh. (1957)
8. Honorary fellowship of the American Academy of Arts and Sciences. (1959)
9. Foreign associate of the National Academy of Sciences of the United States. (1963)
10. Honorary doctoral degrees in science at Patna (1944), Lucknow (1949), Banaras (1950), Agra (1952), Perth (1954), Allahabad (1958), Cambridge (1959), London (1960), Padova (1961).

References

1. Penney, William George. (1967). Homi Jehangir Bhabha, 1909-1966. (PDF).  Biographical Memoirs of the Fellows of the Royal Society.  https://doi.org/10.1098/rsbm.1967.0002
2. Raj, Baldev., Amarendra, G. A legend lives on Homi Jehangir Bhabha (1909–1966). Indira Gandhi Centre for Atomic Research.  Archived from the original on 22 May 2013. Retrieved 1 January 2021.
3. American Academy of Arts and Sciences. (n.d.). Book of Members. Retrieved January 7, 2021, from https://www.amacad.org/sites/default/files/media/document/2019-10/ChapterB.pdf

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Homi J. Bhabha’s Legacy

After his death, the Atomic Energy Establishment in Mumbai has renamed the Bhabha Atomic Research Centre in his honor. The radio telescope in Ooty, Tamil Nadu was his initiative, and it became a reality in 1970. The Homi Bhabha Fellowship Council has been giving Homi Bhabha Fellowships since 1967.

Other noted institutions in his name are the Homi Bhabha National Institute, an Indian deemed university, and the Homi Bhabha Centre for Science Education, Mumbai, India.

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