Variable Energy Cyclotron Centre Research Articles

Characterization of the first beam from the [formula omitted]500 superconducting cyclotron at VECC

The K500 superconducting cyclotron, developed at the Variable Energy Cyclotron Centre (VECC), is now delivering heavy ion beams for the experiments. This article provides a comprehensive description of the first beam characterization. Key parameters for precision measurements with this machine include beam energy and its resolution, which have been determined in this work using two different techniques. The measured beam energy was compared with the estimation (based on the cyclotron’s RF) and was found to be consistent within the experimental uncertainty. Energy of the first beam (14N) delivered was found to be 252.0 ± 1.0 MeV with a resolution of 580 ± 5 keV. The techniques described in this article were used to verify the beam energy of 20Ne at several energies. Finally, the measured beam energies were studied as a function of RF of the cyclotron to determine the calibration constant. This was found to be 1.852 ± 0.032 and is consistent with the estimated value using the machine parameters.

Effect of Oxygen Ion Irradiation on Nb-1Zr-0.1C Alloy Characterized Using X-Ray Diffraction Line Profile Analysis

One of the proposed materials for structural application in compact high-temperature reactors (CHTRs) is Nb-1Zr-0.1C alloy. Using the Variable Energy Cyclotron at the Variable Energy Cyclotron Centre, Kolkata, Nb-1Zr-0.1C alloy was irradiated with a 160-MeV oxygen (O6+) ion up to three different doses. Emulation of neutron irradiation by ion irradiation could be achieved as the weighted recoil spectra of the oxygen ion are found to be similar to the neutron recoil spectra of CHTRs within recoil energy ranging from 100 eV to 100 keV. The irradiated materials along with one as-received sample were characterized using different X-ray diffraction line profile analyses (XRDLPAs) to systematically evaluate microstructural parameters. A decrease in the domain size with an increase in microstrain and dislocation density is observed at first dose and then found to saturate with further irradiation. An increase in the Wilkens arrangement parameter indicates the formation of less correlated dislocations (clusters) after irradiation. Transmission electron microscopy analysis of as-received and highest-dose samples shows the formation of densely populated defect clusters after irradiation. Nanohardness increased after irradiation due to pinning of the dislocation movement by point defects and defect clusters/loops, as well as carbides in the matrix. The results extracted from the XRDLPAs are compared with our earlier studies of light ion–irradiated (H+) Nb-1Zr-0.1C alloy and oxygen-irradiated pure Nb to understand the effect of the type of ion and the alloying elements, respectively, on the evolution of the microstructure. It may be concluded that changes in dose and dose rate affect the movement of point defects toward sinks. Hence, possible correlated dislocation formation is observed in light ion–irradiated Nb alloy, but correlation is found to decrease with dose for heavy ion–irradiated Nb alloy. On the other hand, the presence of finely dispersed carbides restricts the formation of dislocation loops by making complexes with the defects in heavy ion (O6+)–irradiated Nb-1Zr-0.1C alloy, which is in contrast to pure Nb irradiated using the heavy ion (O6+) in a similar environment.

Different manifestations of triaxial shapes of the positive and negative parity bands in Os187

The excited states of $^{187}\mathrm{Os}$ have been studied via $^{186}\mathrm{W}(^{4}\mathrm{He},3n)^{187}\mathrm{Os}$ reaction at a beam energy of 36 MeV. The $\ensuremath{\gamma}$ rays were detected using the Indian National Gamma Array at the Variable Energy Cyclotron Centre having seven Compton-suppressed clover high-purity germanium (HPGe) detectors and one low-energy photon spectrometer (LEPS) detector with a digital data acquisition system. The level scheme of $^{187}\mathrm{Os}$ has been extended substantially up to $\ensuremath{\approx}$3.86 MeV of excitation energy and $37/2\phantom{\rule{0.16em}{0ex}}\ensuremath{\hbar}$ of spin with the placement of more than 90 new $\ensuremath{\gamma}$ rays. All known bands have been extended and new band structures have been identified. The results show evidence of triaxial shapes for different configurations of $^{187}\mathrm{Os}$ and different manifestations of nonaxial shape have been observed in the same nucleus. A comparison of the observed band crossing frequency in $^{187}\mathrm{Os}$ with neighboring nuclei gives evidence of a deformed shell gap at $N=110$. The experimental results are well explained using total Routhian surface calculations.

Design and development of high power RF amplifier for 88 in. room temperature cyclotron at Variable Energy Cyclotron Centre (VECC), Kolkata.

A tetrode based high power radio frequency (RF) amplifier has been designed, developed, and commissioned at Variable Energy Cyclotron Centre, Kolkata, India, for the 88-in. room temperature K130 cyclotron. The amplifier feeds power to a RF cavity based on the quarter-wave cantilever-type resonating structure to develop a high accelerating voltage for particle acceleration. The initial design of this amplifier was based on tetrode tube, which has already become obsolete. A new design of the RF amplifier has been made with a different tetrode of much lower power to satisfy the requirement of the cyclotron. This paper gives detailed insight into the various issues of the tetrode amplifier design and operational experience for the K130 cyclotron RF system.

Major Accelerator Facilities for Nuclear Physics in Asia Pacific

Asian Nuclear Physics Association (ANPhA) is the central organization representing nuclear physics in Asia Pacific. ANPhA is now preparing a list of accelerators applicable for nuclear physics experiments in Asia Pacific. Among the listed facilities, world-class “major” accelerator facilities are mainly located in China (Heavy Ion Research Facility in Lanzhou (HIRFL), and its future extension in Huizhou, i.e. HIAF/CiADS, Beijing Tandem Accelerator National Laboratory (BTANL), which is now upgraded to Beijing RI beam Facility (BRIF), in India (Variable Energy Cyclotron Centre (VECC) in Kolkata), in Korea (RISP/rAoN), and in Japan (RIBF at Riken, J-PARC, RCNP, and ELPH/LEPS). World class facilities based on the tandem accelerator are locating at Mumbai and New Deli in India, at Tokai-mura in Japan, and at Canberra in Australia. Characteristics of these “majof” facilities including their facility developments will briefly be reviewed in comparing with similar facilities in Europe and North America.

Optimization Calculations for Neutron Production Target at Variable Energy Cyclotron Centre, Kolkata with 50 MeV Electron Linear Accelerator

Optimization Calculations for Neutron Production Target at Variable Energy Cyclotron Centre, Kolkata with 50 MeV Electron Linear Accelerator

ChAKRA : The high resolution charged particle detector array at VECC

A large 4$\pi$ array of charged particle detectors has been developed at Variable Energy Cyclotron Centre to facilitate high resolution charged particle reaction and spectroscopy studies by detecting event-by-event the charged reaction products emitted in heavy ion reactions at energy $\sim$ 10-60 MeV/A. The forward part ($\theta \sim \pm $ $7^{0}$ - $\pm 45^{0}$) of the array consists of 24 highly granular, high resolution charged particle telescopes, each of which is made by three layers [single sided silicon strip($\Delta$E) + double sided silicon strip (E/$\Delta$E) + CsI(Tl)(E)]of detectors. The backward part of the array consists of 112 CsI(Tl) detectors which are capable of detecting primarily the light charged particles (Z $\le$ 2) emitted in the angular range of $\theta \sim \pm $ $45^{0}$ - $\pm 175^{0}$. The extreme forward part of the array ($\theta \sim \pm $ $3^{0}$ - $\pm 7^{0}$) is made up of 32 slow-fast plastic phoswich detectors that are capable of detecting light (Z $\le$2) and heavy charged particles (3 $\le$ Z $\lesssim$ 20) as well as handling high count rates. The design, construction and characterization of the array has been described.

Into the Fission Valley of 'magic Nucleus' Polonium

The word radioactive was first coined by Marie Curie when she, along with her husband Pierre Curie, discovered the element Polonium. The nucleus 210Po is a testing ground for many theoretical and experimental aspects of nuclear structure as well as nuclear fission dynamics as it is a magic nucleus with neutron number N=126. At Variable Energy Cyclotron Centre, Kolkata the fission of Polonium nuclei is being studied in order to understand the survival of nuclear shell effects that is known to be the key for the stability of super heavy elements (SHE).

Performance studies of oil-free bakelite multi-gap resistive plate chamber with cosmic rays

The Multi-gap Resistive Plate Chamber (MRPC) is an upgraded version of Resistive Plate Chamber (RPC) with excellent time resolution. They have found suitable applications in several High Energy Physics (HEP) experiments and also in medical physics like Positron Emission Tomography (PET) imaging. We have successfully developed and tested with cosmic rays a prototype MRPC using bakelite sheets without any oil treatment. In this document, we report the cosmic ray test performance of the second similar prototype. This effort is towards the development of a prototype set-up for PET imaging in Medical Imaging Laboratory at Variable Energy Cyclotron Centre, Kolkata, India.

Effect of neutron alignments on the structure of Tl197

The excited states of $^{197}\mathrm{Tl}$ have been studied via $^{197}\mathrm{Au}(^{4}\mathrm{He}$, $4\mathrm{n})^{197}\mathrm{Tl}$ reaction at a beam energy of 50 MeV from the K-130 cyclotron at the Variable Energy Cyclotron Centre (VECC). The $\ensuremath{\gamma}$ rays were detected using the VECC array for Nuclear Spectroscopy (VENUS) with six Compton-suppressed clover HPGe detectors. An improved level scheme of $^{197}\mathrm{Tl}$ has been proposed from this work, which has been extended to 5.1 MeV of excitation energy and 39/2 $\ensuremath{\hbar}$ of spin from the placement of 28 new $\ensuremath{\gamma}$-ray transitions. Band crossings in the known one- and three-quasiparticle (qp) bands have been identified for the first time in this work. Two new bands, based on 3-qp and 5-qp configurations, have been observed for the first time in this nucleus; both of which are identified as the magnetic rotational (MR) in nature. The excitation energies of these bands are similar to that of the doubly degenerate bands observed for the similar 3-qp and 5-qp configurations in $^{195}\mathrm{Tl}$. These indicate a transition from an aplanar geometry of the neutron, proton, and the core angular momentum vectors to a planar one for neutron number $N\ensuremath{\ge}116$ in Tl isotopes. The total Routhian surface calculations suggest a change in shape from oblate for the 1-qp configuration to a near-spherical one for the 3- and 5-qp configurations. This is consistent with the observed MR nature of the bands with multi-qp configuration. The MR bands are well reproduced by a model calculations in the frame work of the shears mechanism with the principal axis cranking.

Design of a spiral inflector and transverse beam matching for K130 cyclotron at the Variable Energy Cyclotron Centre

This paper describes the design of a spiral inflector for inflecting heavy ion beams into the existing central region of the $$\text {K} = 130$$ Variable Energy Cyclotron at Kolkata. Simulation results of transverse beam dynamics through the spiral inflector and the effect of the fringe field on beam phase ellipses at its exit have been discussed in the absence of space charge effect. We have also made an effort to minimise the effect of inflector fringe field by properly adjusting the inflector voltage. The proper matching conditions in the central region have been obtained by optimising the system parameters of the existing axial injection line of K130 cyclotron. The tracking of particles that belong to the boundary of the optimised phase ellipses at the matching point has also been carried out in the computed electric and magnetic fields in the central region. Simulation results confirm that the optimised beam condition reduces beam losses for further acceleration in the cyclotron.

Experimental nuclear physics research using the cyclotron at VECC

The cyclotron at Variable Energy Cyclotron Centre (VECC), Kolkata, has recentlyrecently completed its 40 years of operation in 2017. During the past four decades, VECC has been able to cross several milestones in exploring the properties of nuclei with the help of low energy light as well as heavy ions accelerated by the cyclotron. In this review, we endeavour to present an overall picture of the intense research activities in various branches of nuclear physics carried out in the past four decades using cyclotron, with special emphasis on the important achievements in each field.

Design development and testing of high voltage power supply with crowbar protection for IOT based RF amplifier system in VECC

This paper described the detailed design, development and testing of high voltage power supply (−30 kV, 3.2 A) and different power supplies for biasing electrodes of Inductive Output Tube (IOT) based high power Radio Frequency (RF) amplifier. This IOT based RF amplifier is further used for pursuing research and development activity in superconducting RF cavity project at Variable Energy Cyclotron Centre (VECC) Kolkata. The state-of-the-art technology of IOT-based high power RF amplifier is designed, developed, and tested at VECC which is the first of its kind in India. A high voltage power supply rated at negative polarity of 30 kV dc/3.2 A is required for biasing cathode of IOT with crowbar protection circuit. This power supply along with crowbar protection system is designed, developed and tested at VECC for testing the complete setup. The technical difficulties and challenges occured during the design of cathode power supply, its crowbar protection techniques along with other supported power supplies i.e. grid and ion pump power supplies are discussed in this paper.

Optimization of beam dump shielding for K-130 cyclotron at VECC

A compact and efficient beam dump shield has been designed using Monte Carlo simulation code FLUKA to facilitate low background measurement of neutron and gamma rays using K130 cyclotron at Variable Energy Cyclotron Centre, Kolkata (VECC). Iron, lead and high density Polyethylene (HDPE) were considered in the design of the beam dump shield. Representative FLUKA simulation results have been validated using in-beam experiment performed on the same beam dump constituents. Experimental neutron and gamma-rays energy spectra have been found to be in fair agreement with the simulation results. Activation of various beam dump shield components were also carried out.

Radioactive ion beams of 111In using ECR plasma sputtering method.

Radioactive ion beams of 111In (indium-111, half-life 2.8 days) have been produced using the plasma sputtering method in an electron cyclotron resonance (ECR) ion source at the Variable Energy Cyclotron Centre RIB facility. Indium isotopes were first produced by bombarding a natural silver target with a 32 MeV, 40 μA alpha particle beam from the K-130 cyclotron. After radio-chemical separation, about 25 mCi In-chloride was deposited on an aluminum electrode and inserted in the plasma chamber of the ECR. Indium ions produced by ion induced sputtering in the plasma were extracted from the ion source, isotopically separated, and a pure 111In beam was measured at the focal plane of the separator. The measured 111In beam intensity was 2.67 × 105 particles/s for a beam energy of 5 keV.

Theoretical and experimental investigation of magnetic field related helium leak in helium vessel of a large superconducting magnet

The helium vessel of the superconducting cyclotron (SCC) at the Variable Energy Cyclotron centre (VECC), Kolkata shows a gradual loss of insulation vacuum from 10−7mbar to 10−4mbar with increasing coil current in the magnet. The insulation vacuum restores back to its initial value with the withdrawal of current. The origin of such behavior has been thought to be related to the electromagnetic stress in the magnet. The electromagnetic stress distribution in the median plane of the helium vessel was studied to figure out the possible location of the helium leak. The stress field from the possible location was transferred to a simplified 2D model with different leak geometries to study the changes in conductance with coil current. The leak rate calculated from the changes in the leak geometry was compared with the leak rate calculated from the experimental insulation vacuum degradation behavior to estimate the initial leak shape and size.

Conceptual design of 4He film suppressor in Still of Dilution Refrigerator

The capacity of a dilution refrigerator in terms of its cooling power and base temperature is primarily governed by the flow rate of the isotopic mixture of helium. In the process of circulation of gas mixture, geometrical configuration of 3He distillation chamber (Still) maintained at a temperature of around 0.7 K plays a significant role in controlling the flow rate. We have already employed a still in our existing dilution refrigerator, however, a new conceptual design is presented here and it is envisaged that this novel design will improve the gas circulation efficiency. Even though, thermodynamic conditions are major issues in eliminating unwanted 4He film as compared to 3He molecules, this design based on a new geometry is likely to enhance the pressure and the temperature at the still that helps in burning out the super-fluid 4He film. The conceptual design of film suppressor and its relevance in the recently commissioned indigenous dilution refrigerator at Variable Energy Cyclotron Centre is presented in this paper.

Decay measurements of43K(β−)43Ca by HRS and TAS

In this work, decay spectroscopy of neutron-rich 43 K has been performed at the Radioactive Ion Beam (RIB) facility at Variable Energy Cyclotron Centre (VECC), Kolkata by producing it with an 18-MeV alpha beam on 40 Ar gas target. The beam was delivered from the K130 Cyclotron and the gas jet recoil transport system was used to move the products to a low-background site. The β-feeding intensities were measured by both high resolution γ-ray spectroscopy and total absorption γ-ray spectroscopy methods in order to address mainly the anomalies (if any) in the feeding to ΔJ ≥ 1 levels reported earlier. The decay half-life of 43 K was also measured to be 22.4(1) hrs.

Long term performance studies of large oil-free bakelite resistive plate chamber

Several high energy physics and neutrino physics experiments worldwide require large-size RPCs to cover wide acceptances. The muon tracking systems in the Iron calorimeter (ICAL) experiment in the India based Neutrino Observatory (INO), India and the near detector in Deep Underground Neutrino Experiment (DUNE) at Fermilab are two such examples. A single gap bakelite RPC of dimension 240 cm × 120 cm, with gas gap of 0.2 cm, has been built and tested at Variable Energy Cyclotron Centre, Kolkata, using indigenous materials procured from the local market. No additional lubricant, like oil has been used on the electrode surfaces for smoothening. The chamber is in operation for > 365 days. We have tested the chamber for its long term operation. The leakage current, bulk resistivity, efficiency, noise rate and time resolution of the chamber have been found to be quite stable during the testing peroid. It has shown an efficiency > 95% with an average time resolution of ∼ 0.83 ns at the point of measurement at ∼ 8700 V throughout the testing period. Details of the long term performance of the chamber have been discussed.

Shape coexistence inHo153

The high-spin states in 153Ho, have been studied by 139 57 La(20Ne, 6n) reaction at a projectile energy of 139 MeV at Variable Energy Cyclotron Centre (VECC), Kolkata, India, utilizing an earlier campaign of Indian National Gamma Array (INGA) setup. Data from gamma-gamma coincidence, directional correlation and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. We have suggested a few additions and revisions of the reported level scheme of 153Ho. The RF-gamma time difference spectra have been useful to confirm the half-life of an isomer in this nucleus. From the comparison of experimental and theoretical results, it is found that there are definite indications of shape coexistence in this nucleus. The experimental and calculated lifetimes of several isomers have been compared to follow the coexistence and evolution of shape with increasing spin.