Inter University Accelerator Centre Research Articles

Multinucleon transfer reactions for theSi28+Zr90,94systems in the region below and near the Coulomb barrier

Measurements on multinucleon transfer reactions for $^{28}\mathrm{Si}+^{90,94}\mathrm{Zr}$ systems were performed at sub- and near-barrier energies. The fact that $^{90}\mathrm{Zr}$ has a closed neutron shell ($N$ $=$ 50) and $^{94}\mathrm{Zr}$ has four neutrons outside the closed shell, allows us to investigate the effects of shell closure and pairing correlation on multinucleon transfer mechanism. The experiment was performed with pulsed $^{28}\mathrm{Si}$ beam using the Heavy Ion Reaction Analyzer (HIRA) at Inter University Accelerator Centre (IUAC), New Delhi. Based on the $Q$-value considerations, it turned out that pickup channels were neutron transfer whereas stripping channels were proton transfer. For the $^{28}\mathrm{Si}+^{90}\mathrm{Zr}$ system, the values of the slope parameter for two-neutron pickup turned out to be less than that for one-neutron pickup. The values of the slope parameter were almost the same for two-, three-, and four-neutron pickup channels in the case of the $^{28}\mathrm{Si}+^{94}\mathrm{Zr}$ system. The transfer probabilities in the case of the $^{28}\mathrm{Si}+^{94}\mathrm{Zr}$ system were much larger than those for the $^{28}\mathrm{Si}+^{90}\mathrm{Zr}$ system, further supporting the fact that there is a correlation between the transfer channels and sub-barrier fusion cross-section enhancement. An odd-even staggering was observed in the extracted transfer probabilities at the barrier radius implying the role of pairing correlation in transfer reactions.

Steady-state conduction behaviour of 100 MeV Ag ion-irradiated polyetherimide

The effect of high-energy ion irradiation on the steady-state conduction behaviour of polyetherimide (PEI) has been investigated. PEI samples of 25 μm thickness were irradiated with 100 MeV Ag ions (fluences of 5.6×1010, 1.8×1011 and 1.8×1012 ions/cm2) at the Inter University Accelerator Centre, New Delhi. Measurements under steady-state conditions at different temperatures (40–250 °C) were made at different electric fields ranging from 40 to 600 kV/cm. The ionic jump distance estimations indicate the possibility of ionic conduction at low and moderate temperatures. At high temperatures, the Schottky and Poole–Frenkel-type conduction mechanisms occur, depending on the fluence of irradiance. A decrease in charge carrier mobility (μ) with field has been associated with the radiation-induced disorders in PEI. An anomalous variation in μ with fluence shows the occurrence of a secondary radiation-induced crystalline phase. The activation energies were determined to be 0.05 and 2.3 eV below and above the glass transition, temperature, indicating the presence of more than one type of trapping centre in irradiated PEI.

ER cross section measurement in16O+194Pt reaction using gas-filled mode of HYRA

Evaporation residue (ER) excitation function in the complete fusion of 16O with 194Pt is measured around the Coulomb barrier using gas-filled mode of the HYbrid Recoil mass Analyser (HYRA) at the Inter University Accelerator Centre (IUAC), New Delhi. Measured ER excitation function is compared with statistical model calculation. Nuclear dissipation strength β = 1.5 is required to explain the experimental data at higher excitation energies.

Angular momentum distribution for the formation of evaporation residues in fusion of 19F with 184W near the Coulomb barrier

We present γ-ray multiplicity distributions for the formation of evaporation residues in the fusion reaction 19F + 184W → 203 83Bi 120 at beam energies in the range of 90–110 MeV. The measurements were carried out using a 14 element BGO detector array and the Heavy Ion Reaction Analyzer at the Inter University Accelerator Centre. The data have been unfolded to obtain angular momentum distributions with inputs from the statistical model calculation. Comparison with another neighboring system, viz. 19F + 175Lu → 194 80Hg 114 with nearly similar entrance-channel mass asymmetry, hints at the depletion of higher angular momenta after crossing of the Z = 82 shell in the compound nucleus.

Indian National Gamma Array at Inter University Accelerator Centre, New Delhi

A 4π multi-detector gamma-ray spectrometer named the Indian National Gamma Array (INGA) has been set up at the Inter University Accelerator Centre, New Delhi, for nuclear structure studies. The array is designed to incorporate twenty four Compton-suppressed Clover germanium detectors with a total photopeak efficiency ∼5%. The spectrometer along with sub-systems developed in-house like, mechanical support structure, high voltage power supplies, automatic liquid nitrogen filling system, front-end electronics and data acquisition system are described. The mechanical support structure facilitates the use of the Clover Germanium array with a recoil mass separator. The array has been used in a number of nuclear spectroscopic investigations. The in-beam and off-beam performance of the array are reported.

Evaporation residue excitation function from complete fusion ofF19withW184

Evaporation residue cross sections for $^{19}\mathrm{F}+^{184}\mathrm{W}$ have been measured at beam energies in the range of 90--130 MeV using the Heavy Ion Reaction Analyzer at the Inter University Accelerator Centre. A new approach, based on Monte Carlo calculations, has been adopted for estimating evaporation residue (ER) transmission efficiency. The challenges in the detection of ERs caused by the presence of isomeric states with longer half-lives have been thoroughly discussed. Measured cross sections have been fitted with statistical model calculations treating the fission barrier as an adjustable parameter. Comparison with other neighboring systems with nearly similar entrance-channel mass asymmetry indicates the onset of instability in the compound nucleus ${}_{83}^{203}{\mathrm{Bi}}_{120}$ after crossing of the $Z=82$ shell.

Fourier transform infrared and ultraviolet-visible investigation of swift heavy 100 MeV Ag-ion- and 75 MeV oxygen-ion-irradiated polyvinylidene fluoride thin films

Polyvinylidene fluoride (PVDF) polymer films (9, 12, and 20 μm) were irradiated with 100 MeV Ag ion (fluence: 1.875×1011 ions/cm2) and 75 MeV oxygen ion (fluences: 5.625×1011 and 5.675×1012 ions/cm2) using the PELLETRON facility at the Inter University Accelerator Centre, New Delhi, to study swift heavy ion (SHI) irradiation effects in thin films. The change in chemical, optical, and structural properties was analysed by comparing Fourier transform infrared (FTIR) and ultraviolet (UV)-visible spectra of pristine and irradiated films. The FTIR spectra show no major change in characteristic bands on irradiation, except that some weak bands appear because of the evolution of volatile species, unsaturated bond formation, decomposition of the free radicals, and subsequent cross-linking. The spectra of the irradiated films show some broadening and a decrease in intensity in characteristic bands when compared with the pristine samples. The FTIR results indicate that the overall chemical structure of PVDF is stable under SHI irradiation. The UV-visible absorption spectra of irradiated samples reveal hyperchromic shift, bathochromic shift, and hypsochromic shift. The spectra also estimate the direct optical band gap around 3.6 eV. The band gap decreases on irradiation, and the decrease is dependent on ion beam and fluence rate. The present study opens up the scope for the applicability of SHI-irradiated PVDF thin films as microsensors and actuators.

Positron annihilation lifetime and Doppler broadening study in 50MeV Li3+ ion irradiated polystyrene films

Abstract Swift heavy ion (SHI) irradiation of polymeric materials results in the change of their free volume properties which have strong correlation with their macroscopic properties. The modification depends on the polymer and ion beam parameters, namely ion energy, fluence and ion species. Polystyrene films were irradiated with Li3+ ions of energy 50 MeV from 15 UD Pelletron accelerators at Inter University Accelerator Centre (IUAC), New Delhi, India to the fluences of 1011, 1012 and 1013 ions/cm2. Nanosized free volume parameters in the polymer have been studied by positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS). From o-Ps lifetime τ3, free volume hole radius, mean free volume of microvoids and fractional free volume are computed and modification in free volume with the fluence is studied. Free volume parameters change slowly with ion fluence with a decrease at the highest fluence of 1013 ions/cm2. The decrease in τ3 and I3 (reflecting the number of free volume holes) may be interpreted on the process of cross-linking. S parameter obtained from DBS measurements showed a minor decrease with increasing fluence.

Studies of emittance of multiply charged ions extracted from high temperature superconducting electron cyclotron resonance ion source, PKDELIS

For the high current injector project at Inter University Accelerator Centre, a high temperature superconducting electron cyclotron resonance (ECR) ion source, PKDELIS, would provide the high charge state ions. The emittance of the ECR ion source is an important parameter to design further beam transport system and to match the acceptances of the downstream radio frequency quadrupole and drift tube linac accelerators of the high current injector. The emittance of the analyzed beam of PKDELIS ECR source has been measured utilizing the three beam size technique. A slit and two beam profile monitors positioned at fixed distances from each other were used to measure the beam size. The digitized beam profiles have been analyzed to determine the emittance of various multiply charged ions. The variation of emittance with gas mixing, ultrahigh frequency power, and extraction energy are discussed in this presentation.

Fabrication of 90,94Zr targets on carbon backing

Isotopic targets of 90,94Zr, with thickness of 280 μg/cm 2, have been prepared in ultra-high vacuum chamber by electron beam deposition method on carbon backing of 45 μg/cm 2 thickness at Inter University Accelerator Centre (IUAC), New Delhi. Amounts of 50.9 and 58 mg isotopic materials were utilized for preparation of 90Zr and 94Zr targets, respectively. These targets have been successfully used in nuclear physics experiments at IUAC.

Preparation and preservation of praseodymium targets at IUAC

A praseodymium target of 700 μg/cm 2 thickness on gold backing of 20 mg/cm 2 thickness has been prepared in high-vacuum environment by a resistive heating method at the Inter University Accelerator Centre (IUAC). Without disturbing the vacuum a thin gold layer of 200 μg/cm 2 thickness was deposited to protect the freshly prepared praseodymium thin film from oxidation. The praseodymium target preparation and protection of the layer are equally important. The successful methods adopted for the fabrication as well as the preservation are discussed.

Conversion of 160Gd 2O 3 to 160Gd by vacuum reduction-distillation

An enriched 160Gd target of 632 μg/cm 2 on a tantalum backing of 1 mg/cm 2 had been prepared in an ultra-high vacuum environment by the reduction-distillation method at the Inter University Accelerator Centre (IUAC). The target was used in static nuclear electromagnetic moment measurements at IUAC. The reduction of the 160Gd 2O 3 powder to 160Gd metal, the preparation of a tantalum-backing foil and details of the ultra-high vacuum evaporator facility of the IUAC are discussed. Further, X-ray fluorescence (XRF) analysis was performed to check the impurity of the reduction agent in the target.

English

Swift heavy ions (SHI) available with 15 million Volt Pelletron accelerator at Inter University Accelerator Centre (IUAC) Delhi, formerly known as Nuclear Science Centre, (NSC), provide a unique opportunity to researchers for accelerator based materials science research. The major research areas can be broadly categorised as electronic sputtering, interface modifications, synthesis and modification of nanostructures, phase transitions and ion beam-induced epitaxial crystallisation. In, general, SHI irradiation based-materials may not be economically feasible, still it could be of interest for very specific cases in defence and space research. The paper gives a glimpse of the current research activities in materials science with SHIs, at IUAC.Defence Science Journal, 2009, 59(4), pp.401-412, DOI:http://dx.doi.org/10.14429/dsj.59.1540

Energy loss of light ions in polypropylene absorber foils

The energy loss of Li, C and O ions in polypropylene absorber foils has been measured using 15 UD Pelletron Accelerator facility at Inter University Accelerator Centre (IUAC), New Delhi, India. The actual experiment has been performed in low flux chamber attached to the General Purpose Scattering Chamber (GPSC). These experimental energy loss values have been compared with the computed values based on various empirical/semi-empirical formulations. Some interesting trends have been observed.

Dielectric response of makrofol-KG polycarbonate irradiated with 145 MeV Ne6+ and 100 MeV Si8+ ions

The passage of heavy ions in a track detector polymeric material produces lattice deformations. These deformations may be in the form of latent tracks or may vanish by self annealing in time. Heavy ion irradiation produces modifications in polymers in their relevant electrical, chemical and optical properties in the form of rearrangement of bonding, cross-linking, chain scission, formation of carbon rich clusters and changes in dielectric properties etc. Modification depends on the ion, its energy and fluence and the polymeric material. In the present work, a study of the dielectric response of pristine and heavy ion irradiated Makrofol-KG polycarbonate is carried out. 40 μm thick Makrofol-KG polycarbonate films were irradiated to various fluences with Si8+ ions of 100 MeV energy from Pelletron at Inter University Accelerator Centre (IUAC), New Delhi and Ne6+ ions of 145 MeV from Variable Energy Cyclotron Centre, Kolkata. On irradiation with heavy ions dielectric constant (ɛ′) decreases with frequency where ɛ′ increases with fluence for both the ions. Variation of loss factor (tan δ) with frequency for pristine and irradiated with Si ions reveals that tan δ increases as the frequency increases. Tan δ also increases with fluence. While Ne irradiated samples tan δ shows slight variation with frequency as well as with fluence. Tan δ has positive values indicating the dominance of inductive behavior.

Study of optical band gap and carbon cluster sizes formed in 100 MeV Si8+ and 145 MeV Ne6+ ions irradiated polypropylene polymer

A wide variety of material modifications in polymers have been studied by using ion irradiation techniques. Extensive research has focused on to Swift Heavy Ions (MeV’s energy), probably because of good controllability and the large penetration length in polymers. High energy ion irradiation tends to damage polymers significantly by electronic excitation and ionization. It may result into the creation of latent tracks and can also cause formation of radicals such as ablation, sputtering, chain scission and intermolecular cross-linking, creation of triple bonds and unsaturated bonds and loss volatile fragments. Polypropylene polymer films of thickness 50 μm were irradiated to the fluences of 1 × 1010, 3 × 1010, 1 × 1011, 3 × 1011, 6 × 1011 and 1 × 1012 ions/cm2 with Si8+ ions of 100 MeV energy from Pelletron accelerator at Inter University Accelerator Centre (IUAC), New Delhi and Ne6+ ions of 145 MeV to the fluences of 108, 1010, 1011, 1012 and 1013 ions/cm3 from Variable Energy Cyclotron Centre, Kolkata. Optical modifications were characterized by UV towards the red end of the spectrum with the increase of the fluence. Value of optical band gap Eg shows a decreasing trend with ion fluence irradiated with both kinds of ions. Cluster size N, the number of carbon atoms per conjugation length increases with increasing ion dose. Cluster size also increases with the increase of electronic stopping power.

Oxygen (O6+) ion beam irradiation effects on etching parameter in lexan polymeric track detector

The polymer Lexan was irradiated to 80MeV O6+ ion beam using the 15UD pelletron at Inter University Accelerator Centre, New Delhi. The ion fluence ranging from 1011 to 3 × 1012 ions/cm2 has been used to study the dose effects of irradiation on Lexan. By using the etching technique, it is observed that the bulk etch rate of the sample increases with increasing the ion influence, while the activation energy associated with it show a decreasing trend which can be explained on the basis of polymer degradation.

SHI induced nano track polymer filters and characterization

Swift heavy ion irradiation produces damage in polymers in the form of latent tracks. Latent tracks can be enlarged by etching it in a suitable etchant and thus nuclear track etch membrane can be formed for gas permeation / purification in particular for hydrogen where the molecular size is very small. By applying suitable and controlled etching conditions well defined tracks can be formed for specific applications of the membranes. After etching gas permeation method is used for characterizing the tracks. In the present work polycarbonate (PC) of various thickness were irradiated with energetic ion beam at Inter University Accelerator Centre (IUAC), New Delhi. Nuclear tracks were modified by etching the PC in 6N NaOH at 60 (±1) °C from both sides for different times to produce track etch membranes. At critical etch time the etched pits from both the sides meet a rapid increase in gas permeation was observed. Permeability of hydrogen and carbon dioxide has been measured in samples etched for different times. The latent tracks produced by SHI irradiation in the track etch membranes show enhancement of free volume of the polymer. Nano filters are separation devices for the mixture of gases, different ions in the solution and isotopes and isobars separations. The polymer thin films with controlled porosity finding it self as best choice. However, the permeability and selectivity of these polymer based membrane filters are very important at the nano scale separation. The Swift Heavy Ion (SHI) induced nuclear track etched polymeric films with controlled etching have been attempted and characterized as nano scale filters.

Superconducting linac at Inter-University Accelerator Centre: Operational challenges and solutions

A superconducting linear accelerator based on niobium quarter wave resonators has recently become operational to boost the energy of the heavy ion beams available from the existing 15 UD (unit doubled) Pelletron accelerator. The niobium resonators typically performed at an accelerating field of $3--6\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ at 6 watts of input power in the test cryostat. When they were tested in the linac cryostat, the accelerating fields were drastically reduced and a number of other problems were also encountered. At present, all the problems have been diagnosed and solved. Many design modifications, e.g., in power coupler, mechanical tuner, helium cooling system, etc. were incorporated to solve the problems. A novel method of vibration damping was also implemented to reduce the effect of microphonics on the resonators. Finally, the accelerated beam through linac was delivered to conduct experiments.

Monitoring radon and its progeny in the environment of the vertical 15 UD Pelletron accelerator facility

Environmental radioactivity due to radon and its progenies in the ambient air at the vertical 15 UD Pelletron accelerator facility of the Inter University Accelerator Centre, New Delhi, India was evaluated to calculate the annual effective dose to the workers and users. The radon activity was measured with an active monitor. The activity concentrations of the radon progenies were measured simultaneously using grab aerosol sampling and absolute beta counting. The effect of in situ meteorological parameters such as the temperature and relative humidity along the height of the Pelletron tower on the activity of radon and its progenies was studied. The measurements were carried out in the winter and rainy seasons. The values for the temperature, relative humidity (in percentage), radon activity concentration, radon Equilibrium Equivalent Concentration (EEC), annual exposure, annual inhalation and annual effective dose were recorded/calculated for locations with air conditioning and without air conditioning. Elements such as 218Po, 214Pb, 214Bi, radon and EEC activity concentrations were found to decrease with the height and relative humidity and increase with increasing temperatures. The dose levels observed in the facility were below the International Commission on Radiological Protection (ICRP) and United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) recommendations, even for the general public (1.2 mSv).