Qualification:
Ph.D, M.Tech, MSc

Dr. Mahadevan S. currently serves as Deputy Dean of School of Engineering and Chairperson of the Department of Sciences at Amrita Vishwa Vidyapeetham, Coimbatore campus. His areas of research include Theoretical Nuclear Physics.

He has attended several national conferences and international conferences and presented papers in the field of Theoretical Nuclear Physics.

## Publications

### Publication Type: Journal Article

Year of Publication Title

2014

C. S. Shastr, Dr. Mahadevan S., and Aditya, K., “Unified approach to alpha decay calculations”, Pramana - Journal of Physics, vol. 82, pp. 868-878, 2014.[Abstract]

With the discovery of a large number of superheavy nuclei undergoing decay througha emissions, there has been a revival of interest in α decay in recent years. In the theoretical study of α decay the a-nucleus potential, which is the basic input in the study of a-nucleus systems, is also being studied using advanced theoretical methods. In the light of these, theWentzel-Kramers-Brillouin (WKB) approximation method often used for the study of a decay is critically examined and its limitations are pointed out. At a given energy, theWKB expression uses barrier penetration formula for the determination of the transmission coefficient. This approach utilizes the a-nucleus potential only at the barrier region and ignores it elsewhere. In the present era, when one has more precise experimental information on decay parameters and better understanding of a-nucleus potential, it is desirable to use a more precise method for the calculation of decay parameters. We describe the analytic S-matrix (SM) method which gives a procedure for the calculation of decay energy and mean life in an integrated way by evaluating the resonance pole of the S-matrix in the complex momentum or energy plane. We make an illustrative comparative study of WKB and S-matrix methods for the determination of decay parameters in a number of superheavy nuclei. © Indian Academy of Sciences.

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2010

Pa Prema, Dr. Mahadevan S., Shastry, C. Sa, and Gambhir, Y. Kb, “S-matrix-based unified calculation of Q-values and half-lives of α-decay of super heavy elements”, International Journal of Modern Physics E, vol. 19, pp. 2033-2043, 2010.[Abstract]

The Q-values and half-lives of several heavy α decaying systems are calculated using the relativistic mean field (RMF) theory-based microscopic α-daughter nucleus potential. A unified procedure is adopted, using analytic S-matrix method and treating α-decay as the decay of the resonance state of the α-daughter nucleus system. The resonance parameters are obtained from the pole positions of the S-matrix in the complex k-plane and using these Q-values and half widths are evaluated. The calculation reproduces the experimental results well. We find that the present unified approach gives a good description of the data and compare well with those obtained by empirical formulae. © 2010 World Scientific Publishing Company. More »»

2009

Dr. Umamaheswari A., Prema, P., Dr. Mahadevan S., and Shastry, C. S., “Quasi-bound states, resonance tunnelling, and tunnelling times generated by twin symmetric barriers”, Pramana, vol. 73, p. 969, 2009.[Abstract]

In analogy with the definition of resonant or quasi-bound states used in three-dimensional quantal scattering, we define the quasi-bound states that occur in one-dimensional transmission generated by twin symmetric potential barriers and evaluate their energies and widths using two typical examples: (i) twin rectangular barrier and (ii) twin Gaussian-type barrier. The energies at which reflectionless transmission occurs correspond to these states and the widths of the transmission peaks are also the same as those of quasi-bound states. We compare the behaviour of the magnitude of wave functions of quasi-bound states with those for bound states and with the above-barrier state wave function. We deduce a Breit-Wigner-type resonance formula which neatly describes the variation of transmission coefficient as a function of energy at below-barrier energies. Similar formula with additional empirical term explains approximately the peaks of transmission coefficients at above-barrier energies as well. Further, we study the variation of tunnelling time as a function of energy and compare the same with transmission, reflection time and Breit-Wigner delay time around a quasi-bound state energy. We also find that tunnelling time is of the same order of magnitude as lifetime of the quasi-bound state, but somewhat larger. More »»

2008

Pa Prema, Dr. Mahadevan S., Shastry, C. Sa, Bhagwat, Abc, and Gambhir, Y. Kde, “Study of alpha decay of super heavy elements using s-matrix and wkb methods”, International Journal of Modern Physics E, vol. 17, pp. 611-629, 2008.[Abstract]

A comparative study of the S-matrix and the WKB methods for the calculation of the half widths of alpha decay of super heavy elements is presented. The extent of the reliability of the WKB methods is demonstrated through simple illustrative examples. Detailed calculations have been carried out using the microscopic alpha-daughter potentials generated in the framework of the double-folding model using densities obtained in the relativistic mean field theories. We consider alpha-nucleus systems appearing in the decay chains of super heavy parent elements having A = 277 More »»

2007

Dr. Umamaheswari A., Dr. Mahadevan S., Prema, Pa, Shastry, C. Sa, and Agarwalla, S. Kb, “Transmission and scattering by an absorptive potential”, American Journal of Physics, vol. 75, pp. 245-253, 2007.[Abstract]

Transmission and scattering problems involving complex potentials are important in physics, in particular in describing nuclear collisions. We describe many pedagogical features of transmission in one dimension and scattering and absorption cross sections in three dimensions for a rectangular absorptive potential and compare the results with scattering from real barriers and a hard sphere. For a given energy in one dimension we show that the absorption reaches a maximum for a critical value of the absorption strength and then monotonically decreases with an increase in the absorption strength. An infinitely absorptive well becomes almost fully reflective and thus is similar to an infinitely high barrier. Similar results are found in three dimensions. We show that the absorption cross section in three dimensions diverges at a threshold energy, which is of critical importance for exothermic reactions. © 2007 American Association of Physics Teachers. More »»

2007

Dr. Mahadevan S., Prema, P., and Shastry, C. S., “Light Dominates Physics”, Physics Education Journal, vol. 24, pp. 119-131, 2007.

2006

Dr. Mahadevan S., Prema, Pa, Shastry, C. Sa, and Gambhir, Y. Kb, “Comparison of S-matrix and WKB methods for half-width calculations”, Physical Review C - Nuclear Physics, vol. 74, 2006.[Abstract]

The calculated Q values and half widths of α-decay of superheavy elements using both the S-matrix and the WKB methods are analyzed. The calculations are carried out using the microscopically derived α-daughter potentials for the parents appearing in the α-decay chain of super heavy element (A=277 More »»

2006

Dr. Mahadevan S., Prema, Pa, Agarwalla, S. Kb, Sahu, Bb, and Shastry, C. Sa, “Resonance-like tunneling across a barrier with adjacent wells”, Pramana - Journal of Physics, vol. 67, pp. 401-413, 2006.[Abstract]

We examine the behavior of transmission coefficient T across the rectangular barrier when attractive potential well is present on one or both sides and also the same is studied for a smoother barrier with smooth adjacent wells having Woods-Saxon shape. We find that presence of well with suitable width and depth can substantially alter T at energies below the barrier height leading to resonant-like structures. In a sense, this work is complementary to the resonant tunneling of particles across two rectangular barriers, which is being studied in detail in recent years with possible applications in mind. We interpret our results as due to resonant-like positive energy states generated by the adjacent wells. We describe in detail the possible potential application of these results in electronic devices using n-type oxygen-doped gallium arsenide and silicon dioxide. It is envisaged that these results will have applications in the design of tunneling devices. © Indian Academy of Sciences.

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2006

S. Ka Agarwalla, Mallick, G. Sb, Prema, Pc, Dr. Mahadevan S., Sahu, Ba, and Shastry, C. Sc, “Analysis of 16O + 28Si elastic scattering in the laboratory energy range 50.0 MeV to 142.5 MeV”, Journal of Physics G: Nuclear and Particle Physics, vol. 32, pp. 165-178, 2006.[Abstract]

We have successfully carried out an optical model analysis of 16O + 28Si differential scattering cross section σ() in the laboratory energy range EL from 50.0 MeV to 142.5 MeV and angular range from 0° to 100° using the LC potential suggested by Lee and Chan. This potential is very successful in explaining the differential cross section σ() at EL = 50.0 and 55.0 MeV in the entire centre of mass angle range reproducing the enhanced back angle oscillations correctly. The LC potential has only seven parameters, including the Coulomb radius parameter, which is much smaller than the number of parameters used in recent calculations on the system. In the light of an excellent fit to the data, we make a detailed analysis of different features of the LC potential and compare it with the typical heavy-ion potential having a Woods-Saxon (WS) form factor used in the analysis of 18O + 58Ni at EL = 60.0 MeV. These features include the behaviour of the real effective potential around grazing partial wave (ℓg), angular momentum (ℓ) dependence of classical deflection function (Θ), reflection function |Sℓ| and the term |1 - Sℓ|2 governing the total partial wave elastic cross section. We also calculate the barrier region resonance positions generated by the partial waves around ℓg. We find that the orbiting phenomenon generated by the flatter, surface transparent effective potential and the resulting coherent behaviour of only a small number of partial waves in the surface region, resulting in the interference of absorptive region and Coulombic region amplitudes, are primarily responsible for back angle oscillations. As a quantum-mechanical consequence of orbiting behaviour, we find close clustering of resonances corresponding to a set of partial waves around ℓg which is the special feature of the LC potential. On the basis of this, we envisage that 16O + 28Si is likely to show large enhanced back angle oscillations at EL = 66.0 and 72.0 MeV. It will be interesting if this is experimentally investigated. © 2006 IOP Publishing Ltd. More »»

2006

Dr. Mahadevan S. and Prema, P., “Emerging Technologies Relevance to India”, Science India, vol. 9, pp. 4-9, 2006.

2006

Dr. Mahadevan S., Dr. Umamaheswari A., Prema, P., Shastry, C. S., and , “Quantum mechanical transmission with absorption”, Phys. Educ, vol. 23, pp. 13–21, 2006.[Abstract]

Transmission and reflection across a rectangular barrier at energies below and above barrier is the most commonly studied topic in nonrelativistic quantum mechanics. However the subtle inter-relationship between the barrier problem and the corresponding well problem is not widely known, in particular when absorption is present. In this article we show that when a particle traverses an absorptive medium, at any given energy the absorption peaks for a particular value of absorption potential strength W0. Similarly we study the corresponding cases when incident energy E is increased keeping W0 constant. Further, we show that for a given E when W0. is made very large absorption gradually decreases and reflection overtakes it and tends towards unity. We also study the case of transmission across a potential barrier and well and interpret physically the behavior of absorption, transmission and reflection. More »»

### Publication Type: Conference Proceedings

Year of Publication Title

2012

K. Aditya, Dharani, Ma, Prema, P., Dr. Mahadevan S., and Shastry, C. S., “Calculation of Q values and Half lives of $\alpha$-decay for A= 152-181 using S-Matrix method”, Proceedings of the DAE-BRNS Symposium on Nuclear Physics, vol. 44. 2012.[Abstract]

The success in the description of half lives and Q-values of Super heavy elements (SHE) using the microscopic alpha daughter nucleus potential and S-Matrix method (SM) prompted us to extend the analysis to the nuclei in the rare earth regions with A=152-181. We have reported in 2010, the results of the half lives and Q-values for the nuclei A=152-181 using WKB method. In this paper we report the results obtained using the more accurate S-Matrix method. The microscopic alpha nucleus potential is generated in the double folding model (τρρ-approximation) using relativistic mean field (RMF) densities along with density dependent M3Ynucleon-nucleon interaction. This potential is then used in the SM method to calculate both Q-values and decay half lives

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### Publication Type: Conference Paper

Year of Publication Title

2012

Ma Dharani, Shastry, C. S., Sahu, B., and Dr. Mahadevan S., “Selective suppression of Eigen states with an absorptive delta potential”, in Proceedings of the DAE-BRNS symposium on nuclear physics. V. 57, 2012.[Abstract]

Delta function potentials are used to explain short range elastic impurities and nature of the spectrum generated by the delta function potential embedded in a box and to construct model atomic systems interacting with the electromagnetic fields leading to multi photon absorption and ionization process. Similar study can be carried out in a nuclear system to analyze different properties of radioactive ions. The resonances generated when particle traverses across two delta potentials in one-dimension (ID) are studied. In this contribution, a novel feature is demonstrated that an absorptive delta potential suitably placed within a potential pocket can be used to selectively manipulate and suppress the resonances generated by the pocket

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2007

Dr. Mahadevan S., Shastry, C. S., and Gambhir, Y. K., “Calculation of widths of very sharp quasi stationary states”, in Proceedings of the DAE symposium on nuclear physics. V. 52, 2007.

2006

P. Prema, Dr. Mahadevan S., Shastry, C. S., Agarwalla, S. K., Sahu, B. B., Sahu, B., and Mallick, G. S., “Resonances in the barrier region”, in Proceedings of the DAE-BRNS symposium on nuclear physics: V. 51, 2006.

### Publication Type: Book

Year of Publication Title

1998

Dr. Mahadevan S., A Laboratory Manual for the Second Pre-degree Students of Karnataka Pre- University Students. 1998.

Faculty Research Interest: