Inter University Accelerator Centre Research Articles

Lifetime measurements in the yrast band of 187Hg

Lifetimes of excited nuclear states in 187Hg have been measured using the 159Tb (32S, p3n)187Hg reaction at a beam energy of 154 MeV at the Inter University Accelerator Center, Delhi. In the experiment, the lifetimes of the five lowest yrast states have been determined using the recoil distance Doppler-shift (RDM) method. The extracted transition quadrupole moments show a sharp increase with increasing level spin, indicating a major shape transition happening in this nucleus. For a better insight into the predicted shape coexistence picture in 187Hg nucleus, the experimental results are compared with the results of the total Routhian surface calculations. The results indicate the shifting of deformed structures from weakly prolate at low-spins to strongly prolate at high spins in 187Hg nucleus.

Fabrication of 208Pb and 193Ir targets on Al-backing using high/ultra-high vacuum deposition technique for low-energy nuclear reaction experiments

Aiming to study the interplay of different nuclear reactions at low incident energies, thin targets of enriched stable isotopes, 208Pb and 193Ir, have been fabricated at the target development laboratory of the Inter-University Accelerator Centre (IUAC), New Delhi. As a means of preparing a large number of thin isotopically pure targets, physical vapour deposition techniques, (a) resistive heating, for fabrication of 208Pb targets of mass thickness 160-340μg/cm2, and (b) electron-gun evaporation technique, for fabrication of 193Ir targets of mass thickness 17-60μg/cm2, have been employed. The fabricated targets were characterized using Rutherford Backscattering Spectrometry (RBS) and Field Emission Scanning Electron Microscopy (FE–SEM). The thickness of targets was estimated based on the evaporation rate and measured by RBS. The RBS was employed to analyse the samples for trace- and heavy impurities, provided the measurements and analysis suggest that the targets prepared in the present work do not contain any impurities. FE-SEM was employed to examine the surface morphology and microstructure in high resolution. This technique enables the detection of any morphological changes induced by the irradiation process, offering insights into the effects of irradiation on the target films. The targets have been successfully deployed to measure complete and incomplete fusion excitation functions, mass distribution of fission fragments, and forward ranges of target-like recoils in 12C + 208Pb, 193Ir reactions from sub- to above barrier energies. Preliminary data analysis suggests the achievement of high-quality 208Pb and 193Ir target foils.

Fabrication and characterization of highly enriched thin 176Yb targets for the reaction dynamic studies on fission mass distribution

The fabrication, transfer, and storage of a highly enriched isotopic target is very much crucial because of air gases and moistures being chemically active at room temperature. One must limit the amount of time that the target surface is exposed to the atmosphere during the transfer of air sensitive targets. The highly interactive targets are not easy to store for longer time and demand an in-vacuum transfer facility. Getting an alternative technique to remove all such imperative is a need of the hour specially for the nuclear physics community, more particularly for reaction dynamic studies of fission fragment mass distribution induced by stable and radioactive ion beams. Highly enriched materials are rare and very expensive, so an effective and highly efficient technique is needed to deal with such materials. Here, an attempt has been made to fabricate 96.63% enriched thin targets of 176Yb by evaporation techniques enabling ≈129.1 μg/cm2 thickness with a ≈25.93 μg/cm2 carbon backing to increase its stability and durability. Numerous trials have been performed using natural Yb to optimize the evaporation setup and associated growth parameters for efficient Yb isotope deposition with thin film deposition unit and diffusion pump based coating unit at Inter University Accelerator Centre (IUAC), New Delhi. Thickness and elemental composition of the targets have been analysed using characterization techniques such as X-ray diffraction, α-energy loss technique, Rutherford backscattering spectroscopy and energy dispersive X-ray spectroscopy. Essentially no significant impurities are found by these measurements, describing high purity and robustness of the fabricated targets. During the nuclear experiments, 30Si and 16O beams of intensity of the order of ≈1010 particles per second were bombarded on the targets for 5–6 days and no ill effects on the target were observed. Isotopic abundance of the target has been obtained experimentally, which ensured the isotopic purity of the target required for the reaction studies. This article will admire our readers about the qualitative nature of the fabrication technique, measurement and characterization citing valuable insights, aiding in a comprehensive understanding of their quality.

Fabrication and characterization of thin 94Zr target with gold backing for nuclear lifetime measurements using DSAM

For lifetime measurements of excited nuclear states in the sub-picosecond range, a thin target with a thick backing of high-Z material is required. To meet these specifications, a thin isotopic94Zr target of thickness 1.14 ± 0.05 mg/cm2, with backing of 4.7 ± 0.2 mg/cm2 thick Au layer, has been fabricated using the cost-effective cold rolling technique at the target laboratory of Inter-University Accelerator Centre (IUAC), New Delhi. The thickness verification and purity check of the fabricated target have been carried out by non-destructive Energy Dispersive X-ray Fluorescence (EDXRF) and Rutherford Backscattering Spectrometry (RBS) techniques. The results of these measurements are in good agreement with each other. The elemental composition, purity and surface morphology have been explored by Energy Dispersive X-ray Spectrometry (EDS) and Scanning Electron Microscopy (SEM) techniques. The fabricated target has been successfully used with a16O ion beam in a recent γ-ray spectroscopy experiment for lifetime measurements using the Doppler Shift Attenuation Method (DSAM) at IUAC, New Delhi.

Fabrication and characterization of self-supporting and backed 107Ag targets for lifetime measurements using RDM and DSAM

Self-supporting and Au backed 107Ag targets have been fabricated from material in the form of powder at the Inter-University Accelerator Centre (IUAC), New Delhi. The method described in this report (using the combination of cold rolling and e-beam melting technique) is efficient in such a way that targets are fabricated without any significant loss of material and are free from major contamination. Consequently, this method of fabricating targets is useful for materials which are very expensive. Various techniques for thickness measurements and characterizations have been carried out, viz., α-transmission method, Rutherford Backscattering Spectrometry (RBS), X-ray Diffractometry (XRD), Energy Dispersive X-ray Fluorescence (EDXRF), Energy Dispersive X-ray Spectroscopy (EDS) and Scanning Electron Microscopy (SEM). The thickness of self-supporting 107Ag and backed 107Ag is ≈1.43± 0.08 and ≈1.11± 0.07 mg/cm2, respectively. One of the fabricated targets has been used successfully in nuclear physics experiment.

Indications of octupole correlation in 84Sr

Excited states in the 84Sr nucleus were investigated via the 76Ge(12C,4n)84Sr reaction at a beam energy of 58 MeV. The de-excited γ-rays were detected using the Indian National Gamma Array (INGA) spectrometer at Inter-University Accelerator Center, New Delhi. Directional Correlation from Oriented (DCO) states ratio and the polarization asymmetry (Δ) measurements were done to confirm the spin-parity of the low-lying states. Eight new γ-ray transitions were placed in the level scheme of 84Sr. The systematic behaviour of energy staggering S(I) of the γ-band (Band 1 and Band 2) was compared with the γ-bands in the mass A ≈ 80 region and the nuclei of other mass regions with similar behaviour (odd-I down). The E1 character is confirmed for strong γ-ray transitions connecting Band 3 to the Yrast band. Comparison of new results such as B(E1)/B(E2) ratio, frequency ratio ω −/ω + and energy displacement ΔE in 84Sr with those of 72Se, 150Sm, 152Gd, 220Ra and 224Th nuclei suggests the presence of octupole correlations in 84Sr.

Examining the correlation between multi-neutron transfer and inelastic excitations in sub-barrier fusion enhancement

Background: Heavy-ion fusion cross-sections at sub barrier energies are found to be enhanced by orders of magnitude as compared to the predictions of one-dimensional barrier penetration model (1-D BPM). The coupling of various internal degrees of freedom has been employed to decrypt the mechanism responsible for the observed sub-barrier fusion enhancement. However, the unambiguous role of multi-neutron transfer channels in the sub-barrier domain is still elusive.Purpose: We aim to explore and disentangle the effects of multi-neutron transfer channels from the inelastic excitations in the vicinity of the Coulomb barrier.Method: The fusion excitation functions for $^{28}\mathrm{Si} + ^{116,120,124}\mathrm{Sn}$ systems were measured from $\ensuremath{\approx}14%\phantom{\rule{0.222222em}{0ex}}$ below to $\ensuremath{\approx}15%\phantom{\rule{0.222222em}{0ex}}$ above the Coulomb barrier by detecting the evaporation residues (ERs) at the focal plane of the Recoil Mass Separator (RMS), Heavy Ion Reaction Analyzer (HIRA) at the Inter-University Accelerator Centre (IUAC), New Delhi.Results: The extracted fusion cross sections for the investigated systems at sub-barrier energies are significantly enhanced as compared to the predictions of 1-D BPM calculations. To probe the underlying mechanism responsible for the observed sub-barrier fusion enhancement, the coupled-channels (CC) formalism was employed. Coupled reaction channels (CRC) calculations by incorporating the one-neutron transfer channel to elucidate the significance of the transfer channel on the fusion dynamics were performed. Further, the semiempirical coupled channels (ECC) approach was explored to decipher the possible cause of the observed fusion excitation function trend. A systematic analysis of the neighboring systems available in the literature was also performed.Conclusions: CC calculations were able to reproduce the measured fusion excitation functions for $^{28}\mathrm{Si} + ^{116,120}\mathrm{Sn}$ systems to a reasonable extent. However, observed sub-barrier fusion enhancement in $^{28}\mathrm{Si}+^{124}\mathrm{Sn}$ system could not be explained using CC calculations. The influence of multi-neutron transfer channels was highlighted in the coupled-channels calculations. The interplay of collective excitations and neutron transfer was observed.

Nuclear reaction and structure studies using experimental facilities at Inter-University Accelerator Centre (IUAC)

Nuclear reaction and structure studies using experimental facilities at Inter-University Accelerator Centre (IUAC)

Study and improvements of a radially coupled coaxial Fast Faraday cup design toward lower intensity beams

A radially coupled coaxial fast Faraday cup design was presented in Carneiro et al. [Int. J. Mod. Phys. A 34(36), 1942013 (2019)] for high-intensity non-relativistic proton beams. In this work, we discuss a modification of that design in the context of a relatively lower intensity ion beam for longitudinal charge profile measurements. Particle-in-cell and time domain electromagnetic simulations of the new design with a focus on avoiding field dilution while generating enough signal for relatively lower intensity ion beams at the upcoming High Current Injector Program at the Inter-University Accelerator Center, New Delhi [A. Roy, Curr. Sci. 76(2), 149–153 (1999); Kanjilal et al., in 3rd Asian Particle Accelerator Conference (Pohang Accelerator Laboratory, 2004), p. 73], is discussed. Profile distortions from secondary electron emission are estimated, and strategies to suppress them are discussed.

Development of 187Re targets for heavy ion induced reactions

To perform nuclear reaction experiment, very good quality, uniform and thin targets are necessary. In order to carry out evaporation residue cross section measurement of 19F+187Re reaction using Hybrid Recoil mass Analyzer (HYRA) facility at Inter - University Accelerator Center (IUAC) 187Re targets of thickness 200 μg/cm2 are required. More than 20 targets of 187Re of 200 μg/cm2 thickness with thin carbon backing have been prepared using 70 mg of 187Re. Being one of the highest melting points of all elements, high temperature involved in the process and limited amount of available isotopic material are the major constraints during the target development of 187Re. The targets have been successfully used for the nuclear reaction experiment. The method used for the development of several 187Re targets with minimum material consumption and the detailed characterization techniques applied for studying the targets are discussed in detail.

Statistical assessment of long-term performance for AMS measurements at IUAC, New Delhi

A 500 kV ion Accelerator based Accelerator Mass Spectrometer (AMS) system was established in 2015 at the Inter-University Accelerator Centre (IUAC), New Delhi, India (14C Lab Code: IUACD) and is being used routinely for 14C, 10Be and 26Al measurements. The AMS System is backed by three automated graphitization equipment (AGE), a carbonate handling system (CHS) in graphitization laboratory and an appropriate clean laboratory for the chemical processing of samples in case of 10Be and 26Al measurements. In view of the increasing demand for 14C based studies, a major portion of the machine time goes into 14C measurements as compared to other isotopes.It is imperative to assess, monitor and establish the consistency of the performance of the AMS measurements over time since its inception. We have evaluated the short- and long-term performance of 14C measurements with the AMS set-up at IUAC, New Delhi, in terms of the reproducibility, accuracy, precision and calculation of random machine error (RME) in a routine laboratory environment using the International Atomic Energy Agency (IAEA) secondary standards (C1-C9) and chemical blanks in each session. A comparison of the analytical figures of merit between the short- & long-term usages of the AMS facility is presented through a statistical approach highlighting the importance of the measurements and evaluation of primary standards, secondary standards, blanks, and replicates in each of the experiments. A comparison of the analytical performances between the initial set-up and later adoption of a modified analytical protocol has also been made.

CHRONOLOGY OF FOSSILIFEROUS LOCALITIES IN MANJRA VALLEY, DISTRICT LATUR, MAHARASHTRA, INDIA

ABSTRACTThe present paper is an announcement of first absolute age dating directly on fossilized bones and teeth of the Pleistocene mammalian fauna from the Manjra valley, District Latur, Maharashtra, India. The fossilized samples were measured using the AMS facility at Inter-University Accelerator Centre, New Delhi, India. The results gave the time frame of 21,423 BP to 24,335 BP that correspond close to and the threshold of LGM and sheds important light on the palaeoecology of the area that supported diverse megafaunal species in the Upper Manjra valley. These calendar dates not only have wider significance in terms of first ever approximate chronological frame for the Pleistocene fauna in Peninsular India but also offer methodological innovations especially when the adequate bioapatite is absent in the fossilized bones and teeth from the fossil record.

NEW AMS 14C DATES OF A MULTICULTURAL ARCHAEOLOGICAL SITE FROM THE PALEO-DELTAIC REGION OF WEST BENGAL, INDIA: CULTURAL AND GEO-ARCHAEOLOGICAL IMPLICATIONS

ABSTRACTThis study is on the absolute age dating of a multicultural site of Erenda, East Medinipur district, in coastal West Bengal, India. Charcoal samples were collected and measured using the accelerator mass spectrometry (AMS) facility at the Inter-University Accelerator Centre, New Delhi, India. These samples were collected from secured stratigraphic context of two excavated trenches. A careful collection of samples from two trenches provided us with the first calendar dates, 950 BCE and 1979 BCE, of protohistoric sites in coastal West Bengal. These calibrated calendar dates not only have wider significance in terms of archaeology but also methodological implications to understand the relevance of application of AMS from the dynamic coastal landscape in the humid tropics during the late Holocene period.

INTER-UNIVERSITY ACCELERATOR CENTRE, NEW DELHI (IUACD) RADIOCARBON DATE LIST II

ABSTRACTAccelerator mass spectrometry (AMS) activities at the Inter-University Accelerator Centre (IUAC) in New Delhi, India, started with its 15UD Pelletron accelerator and cosmogenic radionuclide (CRN) measurements of 10Be and 26Al. Realizing the demand of a radiocarbon (14C) AMS facility in India, a 500kV Pelletron accelerator based AMS system was installed in 2015. This facility was designated with the lab code IUACD for 14C measurements. 14C dates measured in 2015 and 2016 were published in the first radiocarbon date list (see text for details). The present list is the second 14C date list and consists of dates measured from January to December 2017.

Fabrication and characterization of [formula omitted]Tm target for Nuclear Lifetime Measurements

A self-supporting 169Tm target was fabricated by rolling of 99.9% enriched 169Tm foil in the target laboratory of Inter-University Accelerator Centre, New Delhi. The sample was characterized using standard characterization techniques and confirmation of elemental purity was obtained. The XRD characterization shows that the target is crystalline in nature and free of strain. The prepared target was used to measure the lifetime of short lived excited states in 183Ir via Doppler Shift Attenuation Method.

Fabrication and characterization of thin 64Zn and 68Zn targets for nuclear reaction measurements

Isotopically enriched targets of 64,68Zn were prepared for heavy ion fusion and multi-nucleon transfer reactions. In view of the fragility of the targets under the ion current and during characterization, multiple targets of each isotope were required. Thin films of 64,68Zn isotopes were fabricated via vapor deposition in the target laboratory at Inter-University Accelerator Center (IUAC), New Delhi. Multiple targets of 64,68Zn in the thickness range 150 μg/cm2–300 μg/cm2, were synthesized on a carbon backing of 10 μg/cm2 using only 30 mg amount of available enriched material for each isotope. The use of a pin source and carbon foils as substrate allowed the fabrication of Zn targets without employing previously suggested methods of substrate cooling and forced condensation for thin film fabrication of volatile elements. The deposition results have been estimated quantitatively. The thickness measurement of the targets was carried out using the α particle energy loss technique and Rutherford Back Scattering (RBS) method. The elemental composition of the targets was examined using RBS and Dispersive Wavelength X-ray Fluorescence (DWXRF) to investigate the contamination. Morphological analysis of the films was performed using Scanning Electron Microscope (SEM) to study homogeneity and the impact of ion bombardment on the targets.

Ground state and excited state multinucleon transfer channels in interactions of 28Si with 90,94Zr in near barrier region

Multinucleon transfer reactions were measured in interactions of 28Si with 90,94Zr at a near barrier energy using recoil mass separator, Heavy Ion Reaction Analyzer (HIRA) at Inter University Accelerator Centre (IUAC), New Delhi. The effects of shell closure, positive Q-value transfer channels on the relative strengths of ground state and excited state transfer in multinucleon transfer processes were investigated. The kinematic coincidence technique was employed to reduce the background. The m/q ambiguity was resolved by time of flight (TOF) technique. Based on the Q-value considerations, it was observed that pickup channels were predominantly of neutron transfer, whereas, stripping channels were mainly of proton transfer. A 14-element BGO array was used to extract the relative strength of excited state transfer. In interactions of 28Si with 90Zr, it was observed that the ground state and excited states competes for populating all the transfer channels. In reactions of 28Si with 94Zr, nearly similar behavior was observed except for two-neutron pickup channel, where excited state transfer was dominant and four-neutron pickup channel where ground state transfer was dominant.

Compensation scheme for non-linear beam defocusing inside planar undulator

The Delhi Light Source (DLS), is a compact THz facility based on the principle of pre-bunched FEL, which is at the commissioning stage at Inter University Accelerator Centre (IUAC), New Delhi. The facility will produce relativistic electron beam in the energy range 4 to 8 MeV to generate THz radiation in the range 0.18–3.0 THz. To study the effect of the undulator U48 on this low energy range of the electron beam, a 3D field map of U48 was generated with the help of measured magnetic field data. Beam tracking simulations were performed with the generated field map at the minimum gap of U48. Simulations showed that the quadrupole component of the transverse field roll-off, which is the dominant component within the width of the vacuum chamber can introduce a substantial growth of the beam size in the wiggling plane and result in severe beam loss while propagating through the vacuum chamber inside the undulator. To compensate the dynamic quadrupolar field, an extended quadrupole field correction coil was implemented in the simulation by superimposing its field on the magnetic field of U48. Such a correction scheme showed a remarkable improvement to contain the beam transverse growth.

Analysis of Ethernet Control Network

Building a reliable communication network is a challenging task using the standard Ethernet as the medium for control and data acquisition networks. Such sensor-actuator networks could be distributed across multiple locations across a building. Packet retransmissions and losses could be critical when Ethernet is used for closed-loop controls and measurements. There could be multiple design challenges to build such networks such as total-traffic, compact node design, bandwidth limitations, packet retransmissions, delays, drops etc. In this paper, we report how we implemented a reliable http-based automation network of large interconnected microcontroller-based nodes with a careful design of hardware, firmware components and a new application-layer faulty-node-filter-algorithm. It analysed some of the top causes of poor network performance within such control networks using a popular network protocol-analyser “Wireshark”. Though Ethernet seemed the most future promising, it has the single drawback of nondeterministic packet transfers. Additional research is carried out to prove that IEEE 802.3 standard Ethernet could be used in applications like our slow-cryogenics-control systems of linear Accelerators to build an error-free, near deterministic control-application. This approach allowed the continued use of conventional Ethernet networking components. even for the control networks and the same communication medium. The tested system is distributed within a private LAN of more than 50 embedded servers each of which is built out of on-chip TCP/IP stacks implemented on ARM processors as nodes, for a successfully implemented Cryogenic control network of Superconducting linear Accelerator at Inter University Accelerator Centre, New Delhi, India.

Fabrication and characterization of thin [formula omitted]Nd targets for the study of dynamics of heavy-ion induced reactions

The fabrication of targets from rare earth elements are extremely difficult due to their highly active reacting properties. Hence, the fabrication, transfer, and storage of these types of targets using in-vacuum transfer facilities is found to be the ideal solution. However, the required instrument for this purpose is very expensive and not easy to maintain for a long period of time. Search for an alternate simplified method and its effective usage for fabrication and preservation of rare earth targets is the need of the hour. The present manuscript describes such a method which has been successfully used in the case of fabricating thin targets from the enriched Neodymium (Nd) isotopes. Since the target materials of enriched Nd-isotopes are expensive, devising a procedure which can produce a maximum number of targets with the use of minimum amount of material is very important. Isotopically enriched thin, uniform and durable Neodymium (142,150Nd) targets of ∼150μg/cm2 thickness have been fabricated by using electron beam bombardment technique within a diffusion pump based High Vacuum (HV) coating unit. The targets have been fabricated at the target laboratory of the Inter University Accelerator Centre (IUAC), New Delhi. The sandwiched targets have been prepared with a carbon backing layer of thickness ∼25μg/cm2 and a carbon capping layer of thickness ∼10μg/cm2. The present article brings out different aspects such as: (i) the detailed fabrication procedure along with the various challenges faced (heat damage, peeling off, oxidizing nature of the target etc.) has been reported in this article; (ii) the measurements involving Energy Dispersive X-ray Spectroscopy (EDS), and Rutherford Backscattering Spectrometry (RBS) have been carried out to assess the purity, uniformity, and elemental composition of the targets. The analysis of the acquired data from the measurements suggests that the prepared targets are found to be free from any high-Z contaminating elements. These targets have successfully been used in heavy-ion induced nuclear physics experiments using the General Purpose Scattering Chamber (GPSC) available at IUAC, New Delhi.