Research into accelerator driven systems using particle track detectors

In the interaction of relativistic protons with heavy and extended targets such as lead, large number of neutrons is produced in the course of the so-called spallation process. These neutrons can be used to drive a sub-critical nuclear assembly for energy generation and/or for the transmutation of the long-lived nuclear waste isotopes to environmentally safer nuclear species. Such nuclear assemblies are referred to as accelerator driven systems (ADS).

Knowledge of the neutron yield in the spallation process and an understanding of the behaviour of these neutrons in the desired sub-critical assembly are the most important and determining factors in the design and operation of these systems. Many parameters related to the neutronics of an ADS can be studied qualitatively as well as quantitatively using solid-state nuclear track detectors (SSNTD). In some circumstances SSNTDs provide the best and the most logical detector option for these investigations.

In this paper applications of the SSNTDs into research related to ADS are discussed and some experimental and theoretical results presented.     

Thermal hydraulic studies of spallation target for one-way coupled indian accelerator driven systems with low energy proton beam

BARC has recently proposed a one-way coupled ADS reactor. This reactor requires typically ∼1 GeV proton beam with 2 mA of current. Approximately 8 kW of heat is deposited in the window of the target. Circulating liquid metal target (lead/lead-bismuth-eutectic) has to extract this heat and this is a critical R&D problem to be solved. At present there are very few accelerators, which can give few mA and high-energy proton beam. However, accelerators with low energy and hundreds of micro-ampere current are commercially available. In view of this, it is proposed in this paper to simulate beam window heating of ∼8 kW in the target with low-energy proton beam. Detailed thermal analysis in the spallation and window region has been carried out to study the capability of heat extraction by circulating LBE for a typical target loop with a proton beam of 30 MeV energy and current of 0.267 mA. The heat deposition study is carried out using FLUKA code and flow analysis by CFD code. The detailed analysis of this work is presented in this paper.      

The physics of accelerator driven sub-critical reactors

In recent years, there has been an increasing worldwide interest in accelerator driven systems (ADS) due to their perceived superior safety characteristics and their potential for burning actinides and long-lived fission products. Indian interest in ADS has an additional dimension, which is related to our planned large-scale thorium utilization for future nuclear energy generation. The physics of ADS is quite different from that of critical reactors. As such, physics studies on ADS reactors are necessary for gaining an understanding of these systems. Development of theoretical tools and experimental facilities for studying the physics of ADS reactors constitute important aspect of the ADS development program at BARC. This includes computer codes for burnup studies based on transport theory and Monte Carlo methods, codes for studying the kinetics of ADS and sub-critical facilities driven by 14 MeV neutron generators for ADS experiments and development of sub-criticality measurement methods. The paper discusses the physics issues specific to ADS reactors and presents the status of the reactor physics program and some of the ADS concepts under study.      

Nuclear data requirements for accelerator driven sub-critical systems — A roadmap in the Indian context

The development of accelerator driven sub-critical systems (ADSS) require significant amount of new nuclear data in extended energy regions as well as for a variety of new materials. This paper reviews these perspectives in the Indian context.      

Accelerator driven systems from the radiological safety point of view

In the proposed accelerator driven systems (ADS) the possible use of several milliamperes of protons of about 1 GeV incident on high mass targets like the molten lead-bismuth eutectic is anticipated to pose radiological problems that have so far not been encountered by the radiation protection community. Spallation reaction products like high energy gammas, neutrons, muons, pions and several radiotoxic nuclides including Po-210 complicate the situation. In the present paper, we discuss radiation safety measures like bulk shielding, containment of radiation leakage through ducts and penetration and induced activity in the structure to protect radiation workers as well as estimation of sky-shine, soil and ground water activation, release of toxic gases to the environment to protect public as per the stipulations of the regulatory authorities. We recommend the application of the probabilistic safety analysis technique by assessing the probability and criticality of different hazard-initiating events using HAZOP and FMECA.      

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

The relativistic effective core potential (RECP) approach combined with the spin-orbit DFT electron correlation treatment was applied to the study of the bonding of eka-mercury (E112) and mercury with hydrogen and gold atoms. Highly accurate small-core shape-consistent RECPs derived from Hartree-Fock-Dirac-Breit atomic calculations with Fermi nuclear model were employed. The accuracy of the DFT correlation treatment was checked by comparing the results in the scalar-relativistic (spin-orbit-free) limit with those of high level scalar-relativistic correlation calculations within the same RECP model. E112H was predicted to be slightly more stable than its lighter homologue (HgH). The E112-Au bond energy is expected to be ca. 25–30 % weaker than that of Hg-Au. The role of correlations and magnetic (spin-dependent) interactions in E112-X and Hg-X (X=H, Au) bonding is discussed. The present computational procedure can be readily applied to much larger systems and seems to be a promising tool for simulating E112 adsorption on metal surfaces.     

Evaluation of dynamical properties of open quantum systems using the driven Liouville-von Neumann approach: methodological considerations

Methodological aspects of using the driven Liouville-von Neumann (DLvN) approach for simulating dynamical properties of molecular junctions are discussed. As a model system we consider a non-interacting resonant level uniformly coupled to a single Fermionic bath. We demonstrate how a finite system can mimic the depopulation dynamics of the dot into an infinite band bath of continuous and uniform density of states. We further show how the effects of spurious energy resolved currents, appearing due to the approximate nature of the equilibrium state obtained in DLvN calculations, can be avoided. Several ways to approach the wide band limit, which is often adopted in analytical treatments, using a finite numerical model system are discussed including brute-force increase of the lead model bandwidth as well as efficient cancellation or direct subtraction of finite-bandwidth effect. These methodological considerations may be relevant also for other numerical schemes that aim to study non-equilibrium thermodynamics via simulations of open quantum systems.     

Role of (<Emphasis Type="Italic">n,xn</Emphasis>) reactions in ADS,IAEA-benchmark and the Dubna Cascade Code

Dubna Cascade Code (version-2004) has been used for the Monte Carlo simulation of the 1500 MW_t accelerator driven sub-critical system (ADS) with ²³³U + ²³²Th fuel using the IAEA benchmark. Neutron spectrum, cross-section of (n, xn) reactions, isotopic yield, heat spectra etc. are simulated. Many of these results that help in understanding the IAEA benchmark are presented. It is revealed that the code predicts the proton beam current required for the 1500 MW_t ADS for K _eff = 0.98 to be 11.6 mA. Radial distribution of heat is fairly in agreement with other codes like the EA-MC and it needs nearly 1% less enrichment than given by other codes. This may be because the code takes care of the role of larger order of the (n, xn) reactions. It is emphasized that there is a strong need to study (n, xn) reactions both theoretically and experimentally for better design. This talk is dedicated to the fond memory of late Professor V S Barashenkov, JINR, Dubna     

Universal high-frequency behavior of periodically driven systems: from dynamical stabilization to Floquet engineering

We give a general overview of the high-frequency regime in periodically driven systems and identify three distinct classes of driving protocols in which the infinite-frequency Floquet Hamiltonian is not equal to the time-averaged Hamiltonian. These classes cover systems, such as the Kapitza pendulum, the Harper–Hofstadter model of neutral atoms in a magnetic field, the Haldane Floquet Chern insulator and others. In all setups considered, we discuss both the infinite-frequency limit and the leading finite-frequency corrections to the Floquet Hamiltonian. We provide a short overview of Floquet theory focusing on the gauge structure associated with the choice of stroboscopic frame and the differences between stroboscopic and non-stroboscopic dynamics. In the latter case, one has to work with dressed operators representing observables and a dressed density matrix. We also comment on the application of Floquet Theory to systems described by static Hamiltonians with well-separated energy scales and, in particular, discuss parallels between the inverse-frequency expansion and the Schrieffer–Wolff transformation extending the latter to driven systems.     

Thermodynamic treatment of nonphysical systems: Formalism and an example (Single-lane traffic)

An effort is made to introduce thermodynamic and statistical thermodynamic methods into the treatment of nonphysical (e.g., social, economic, etc.) systems. Emphasis is placed on the use of theentire thermodynamic framework, not merely entropy. Entropy arises naturally, related in a simple manner to other measurables, but does not occupy a primary position in the theory. However, the maximum entropy formalism is a convenient procedure for deriving the thermodynamic analog framework in which undetermined multipliers are thermodynamic-like variables which summarize the collective behavior of the system. We discuss the analysis of Levine and his coworkers showing that the maximum entropy formalism is the unique algorithm for achieving consistent inference of probabilities. The thermodynamic-like formalism for treating a single lane of vehicular traffic is developed and applied to traffic in which the interaction between cars is chosen to be a particular form of the follow-the-leader type. The equation of state of the traffic, the distributions of velocity and headway, and the various thermodynamic-like parameters, e.g., temperature (collective sensitivity), pressure, etc. are determined for an experimental example (Holland Tunnel). Nearest-neighbor and pair correlation functions for the vehicles are also determined. Many interesting and suggestive results are obtained,     

Geometrical properties of local dynamics in Hamiltonian systems: The Generalized Alignment Index (GALI) method

We investigate the detailed dynamics of multi-dimensional Hamiltonian systems by studying the evolution of volume elements formed by unit deviation vectors about their orbits. The behavior of these volumes is strongly influenced by the regular or chaotic nature of the motion, the number of deviation vectors, their linear (in)dependence and the spectrum of Lyapunov exponents. The different time evolution of these volumes can be used to identify rapidly and efficiently the nature of the dynamics, leading to the introduction of quantities that clearly distinguish between chaotic behavior and quasiperiodic motion on N-dimensional tori. More specifically we introduce the Generalized Alignment Index of order k () as the volume of a generalized parallelepiped, whose edges are k initially linearly independent unit deviation vectors with respect to the orbit studied whose magnitude is normalized to unity at every time step. We show analytically and verify numerically on particular examples of N-degree-of-freedom Hamiltonian systems that, for chaotic orbits, tends exponentially to zero with exponents that involve the values of several Lyapunov exponents. In the case of regular orbits, fluctuates around non-zero values for 2≤k≤N and goes to zero for N<k≤2N following power laws that depend on the dimension of the torus and the number m of deviation vectors initially tangent to the torus: ∝t^{−2(k−N)+m} if 0≤m<k−N, and ∝t^−(k−N) if m≥k−N. The is a generalization of the Smaller Alignment Index (SALI) (). However, provides significantly more detailed information on the local dynamics, allows for a faster and clearer distinction between order and chaos than SALI and works even in cases where the SALI method is inconclusive.     

Nipponium as a new element (Z=75) separated by the Japanese chemist, Masataka Ogawa: a scientific and science historical re-evaluation

This review article deals with a new element 'nipponium' reported by Masataka Ogawa in 1908, and with its scientific and science historical background. Ogawa positioned nipponium between molybdenum and ruthenium in the periodic table. From a modern chemical viewpoint, however, nipponium is ascribable to the element with Z=75, namely rhenium, which was unknown in 1908. The reasons for this corrected assignment of nipponium are (1) its optical spectra, (2) its atomic weight when corrected, (3) its relative abundance in molybdenite, the same being true with rhenium. Recently some important evidence was found among the Ogawa's personal collection preserved by his family. Deciphering the X-ray spectra revealed that the measured spectra of the nipponium sample that Ogawa brought from University College, London clearly showed the presence of the element 75 (rhenium). Thus was resolved the mysterious story of nipponium, which had continued for almost a century. It is concluded that nipponium was identical to rhenium.     

Polymerization of 2‐(hydroxyethyl)methacrylate by two different initiator/accelerator systems: a Raman spectroscopic monitoring

The control of monomer polymerization is important when preparing biocompatible devices. The compound 2‐(hydroxyethyl)methacrylate can be polymerized by redox systems using benzoyl peroxide (BPO) (as accelerator) and a substituted amine (as initiator). However, this system is associated with a highly exothermic polymerization, and end‐products with inflammatory properties are produced. We have used ascorbic acid (AA) to induce BPO fragmentation and have compared the kinetics of the reaction, by Raman microscopy, with that obtained with a substituted amine. The breaking of the C bond (Raman stretching vibration at 1641 cm⁻¹) could be monitored in both cases and reflected the incorporation of new monomer molecules into the chain. The AA‐induced polymerization was slower than with the substituted amine and was accompanied by the appearance of a new band at 1603 cm⁻¹, assigned to the stretching vibrations of  COOH species incorporated into the chains. Raman microscopy appears to be a powerful tool in the study of polymeric biomaterial preparation. Copyright © 2008 John Wiley & Sons, Ltd.     

Processing of poly(1,3-bis-(p-carboxyphenoxy propane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20:80) by matrix-assisted pulsed laser evaporation for drug delivery systems

We have demonstrated successful thin film growth of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) by matrix-assisted pulsed laser evaporation using a KrF* excimer laser (λ = 248 nm, τ = 25 ns, ν = 10 Hz). The deposited thin films have been investigated by Fourier transform infrared spectroscopy, and atomic force microscopy. We have demonstrated that the main functional groups of poly(1,3-bis-(p-carboxyphenoxy, propane)-co-(sebacic anhydride)) (20:80) are present in the deposited film. The effect of matrix on both thin film structure and surface morphology was also examined. The goal of this work is to explore laser processing of this material to create suitable constructs for drug delivery applications.     

Complementarity in atomic (finite-level quantum) systems: an information-theoretic approach

We develop an information theoretic interpretation of the number-phase complementarity in atomic systems, where phase is treated as a continuous positive operator valued measure (POVM). The relevant uncertainty principle is obtained as an upper bound on a sum of knowledge of these two observables for the case of two-level systems. A tighter bound characterizing the uncertainty relation is obtained numerically in terms of a weighted knowledge sum involving these variables. We point out that complementarity in these systems departs from mutual unbiasededness in two significant ways: first, the maximum knowledge of a POVM variable is less than log (dimension) bits; second, surprisingly, for higher dimensional systems, the unbiasedness may not be mutual but unidirectional in that phase remains unbiased with respect to number states, but not vice versa. Finally, we study the effect of non-dissipative and dissipative noise on these complementary variables for a single-qubit system.     

Towards a compact high-order method for non-linear hyperbolic systems. I: The Hermite Least-Square Monotone (HLSM) reconstruction

A new Hermite Least-Square Monotone (HLSM) reconstruction to calculate accurately complex flows on non-uniform meshes is presented.     

Revisitation of the molecular mobility of the amorphous solid 4,4′-methylenebis(N,N-diglycidylaniline) (MBDA): New contributions from the TSDC technique

In the present work we revisit the previously published study by Thermally Stimulated Depolarisation Currents (TSDC) of the slow molecular mobility in the amorphous solid state of 4,4′-methylenebis(N,N-diglycidylaniline), MBDA (H. P. Diogo, J. J. Moura Ramos, J. Mol. Liq. 129(2006)138–146) in order to add two important points dealing with recent uses of the TSDC technique. One of them concerns a new method to account for nonexponentiality in Thermally Stimulated Depolarisation Currents (TSDC) data treatment which affects the analysis of the alpha relaxation peak and the determination of the fragility index of the glass-forming system. The other point concerns the analysis of the secondary relaxations in MBDA. It is shown that two kinds of secondary relaxations are differently influenced by aging. The faster components of the secondary relaxation are negligibly dependent on aging and may be ascribed to intramolecular modes of motion, while the slower motional modes show a significant dependence on aging and correspond to the genuine Johari-Goldstein β-relaxation.     

29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)3 spin systems: experiments and simulations

We consider ²⁹Si and ¹⁹F MAS NMR spectra of isolated ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems in two organosilicon compounds of the type RR’SiF₂ and RSiF₃(R,R′=organic ligands). Experimental spectra are analysed by means of numerical simulations. It is found that the SiF₃ group in RSiF₃ is reorienting rapidly around the molecular Si–C bond direction in the solid state. The two ¹⁹F shielding tensors in RR’SiF₂ have strongly differing orientations relative to the two Si–F bond directions in the molecule. Possibilities and limitations of straightforward MAS NMR approaches for the full characterisation of ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems and other dipolar coupled two and three-spin systems are discussed.     

Strong binding and shrinkage of single and double nuclear systems (K?pp,K?ppn,K?K?p and K?K?pp) predicted by Faddeev-Yakubovsky calculations

Non-relativistic Faddeev and Faddeev-Yakubovsky calculations were made for K⁻pp, K⁻ppn, K⁻K⁻p and K⁻K⁻pp kaonic nuclear clusters, where the quasi bound states were treated as bound states by employing real separable potential models for the K⁻-K⁻ and the K⁻-nucleon interactions as well as for the nucleon-nucleon interaction. The binding energies and spatial shrinkages of these states, obtained for various values of the interaction, were found to increase rapidly with the interaction strength. Their behaviors are shown in a reference diagram, where possible changes by varying the interaction in the dense nuclear medium are given. Using the Λ(1405) ansatz with a PDG mass of 1405 MeV/c² for K⁻p, the following ground-state binding energies together with the wave functions were obtained: 51.5 MeV (K⁻pp), 69 MeV (K⁻ppn), 30.4 MeV (K⁻K⁻p) and 93 MeV (K⁻K⁻pp), which are in good agreement with previous results of variational calculation based on the Akaishi-Yamazaki coupled-channel potential. The K⁻K⁻pp state has a significantly increased density where the two nucleons are located very close to each other, in spite of the inner NN repulsion. Relativistic corrections on the calculated non-relativistic results indicate substantial lowering of the bound-state masses, especially of K⁻K⁻pp, toward the kaon condensation regime. The fact that the recently observed binding energy of K⁻pp is much larger (by a factor of 2) than the originally predicted one may infer an enhancement of the interaction in dense nuclei by about 25% possibly due to chiral symmetry restoration. In this respect some qualitative accounts are given based on “clearing QCD vacuum” model of Brown, Kubodera and Rho.     

Prebiotic Aggregates (Tissues) Emerging from Reaction–Diffusion: Formation Time,Configuration Entropy and Optimal Spatial Dimension

For the formation of a proto-tissue, rather than a protocell, the use of reactant dynamics in a finite spatial region is considered. The framework is established on the basic concepts of replication, diversity, and heredity. Heredity, in the sense of the continuity of information and alike traits, is characterized by the number of equivalent patterns conferring viability against selection processes. In the case of structural parameters and the diffusion coefficient of ribonucleic acid, the formation time ranges between a few years to some decades, depending on the spatial dimension (fractional or not). As long as equivalent patterns exist, the configuration entropy of proto-tissues can be defined and used as a practical tool. Consequently, the maximal diversity and weak fluctuations, for which proto-tissues can develop, occur at the spatial dimension 2.5.