Manoj Sharan

We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

A comparative study has been performed on Resistive Plate Chambers (RPC) made of two different grades of bakelite paper laminates, produced and commercially available in India. The chambers, operated in the streamer mode using argon, tetrafluroethane and isobutane in 34:59:7 mixing ratio, are tested for the efficiency and the stability with cosmic rays. A particular grade of bakelite (P-120, NEMA LI-1989 Grade XXX), used for high voltage insulation in humid conditions, was found to give satisfactory performance with stable efficiency of >96% continuously for more than 130 days. A thin coating of silicone fluid on the inner surfaces of the bakelite RPC is found to be necessary for the operation of the detector.

Fission fragment angular distributions have been measured for the systems $^{11}\mathrm{B}+^{235}\mathrm{U}$ and $^{14}\mathrm{N}+^{232}\mathrm{Th}$, at sub and near-barrier energies. Complete and incomplete momentum transfer fission components have been separated around $90\ifmmode^\circ\else\textdegree\fi{}\phantom{\rule{0.3em}{0ex}}\text{c.m.}$ for $^{14}\mathrm{N}+^{232}\mathrm{Th}$. The contribution of incomplete momentum transfer events is found to be about $8%$ over the present energy range of investigation. In the $^{14}\mathrm{N}+^{232}\mathrm{Th}$ case, anisotropy data are found to be anomalous throughout the energy range, where as corresponding data for $^{11}\mathrm{B}+^{235}\mathrm{U}$ are found to be normal, with respect to the saddle-point statistical model predictions. The large ground state spin values of $^{11}\mathrm{B}$ and $^{235}\mathrm{U}$ are found to play a major role at the sub-barrier region in influencing the anisotropy values.

Angular distributions of the elastic and breakup cross sections of 42 MeV 7Li-projectile on 58Ni target are measured at wide angles beyond the grazing angle. Coincidence measurements are done at unequal angle pairs. In this angular region, the direct breakup is found to be very small and strongly dominated by the nuclear breakup process, while the sequential breakup contributions from the decay of the 72−, 4.63 MeV resonant state of 7Li remain significantly large within its corresponding sequential cone. Some indications of contributions from the higher sequential states (52− 6.68 MeV, 52− 7.46 MeV) are found.

Abstract Thin films of CdSe grown by non-catalytic displacement plating (NCDP) are characterised electrochemically and photoelectrochemically in polysulphide electrolyte; using Cyclic Voltametry in dark and under intermittent illumination, band edges of NCDP-plated CdSe are located. A depletion width of 2 μm is calculated across the CdSe ∥ S 2− S 2 2− interface. Charge-transfer mechanism across this junction is discussed. Electrochemical and photoelectrochemical stabilities of NCDP-plated CdSe electrode are studied. Efficiency and fill factor of as-fabricated photoelectrochemical (PEC) cell are found to be 1.02% and 0.34, respectively.

Fission fragment angular distributions have been measured for ${}^{11}\mathrm{B}\mathrm{}{+}^{235}\mathrm{U}$ and ${}^{14}\mathrm{N}\mathrm{}{+}^{232}\mathrm{Th},$ both leading to the same compound nucleus ${}^{246}\mathrm{Bk}$ and lying on either side of the Businaro-Gallone critical asymmetry parameter. At comparable excitation energies, even though $〈{l}^{2}〉$ of the compound nucleus for ${}^{14}\mathrm{N}\mathrm{}{+}^{232}\mathrm{Th}$ are smaller than that of ${}^{11}\mathrm{B}\mathrm{}{+}^{235}\mathrm{U},$ the anisotropies measured for the former are found to be significantly larger than that from the latter. Further, while the measured anisotropies in the case of ${}^{11}\mathrm{B}\mathrm{}{+}^{235}\mathrm{U}$ are found to be consistent with the statistical saddle-point model, the corresponding data for ${}^{14}\mathrm{N}{+}^{232}\mathrm{Th}$ are found to be ``anomalous'' indicating the presence of entrance channel dependent noncompound nuclear contributions.

A measurement of cosmic muon flux, in the newly established underground laboratory at the Uranium Corporation of India Limited (UCIL), Jaduguda, Jharkhand, India, has been carried out. Several future low background experiments are planned in this laboratory. The experimental set up for muon flux measurements consists of four plastic scintillators, with three of these coupled to photomultiplier tubes (PMT) to generate a coincidence trigger for acquiring data. The fourth scintillator has been coupled to a Silicon Photomultiplier (SiPM) whose signals were processed with respect to the coincidence trigger. In this scintillator, a mean light yield of 22 photoelectrons per muon event was observed and the measured time resolution was 1.3 ns. The muon flux measurement at the underground laboratory at 555 m (1554±45 m w.e.) depth level was (2.79±0.13(stat)±.20(syst))×10−7cm−2sec−1sr−1. This agrees well with model predictions. This paper describes the detector system, analysis techniques, and results of measurement at the surface and the underground laboratory.

Abstract Orthorhombic WO3 film, has been prepared by the vacuum evaporation of polycrystalline WO3 powder. Effect of the substrate temperature and the post annealing on the morphology of the film have been studied by X-ray diffraction studies, TEM, including selected area diffraction pattern studies and X-ray/ultraviolet photoelectronscopy studies. The band gap of the orthorhombic WO3 film has been determined by an optical method for film as deposited, annealed and for hydrogen reduced films. The film deposited at temperatures below 300 K are amorphous with a band gap of 3.7 eV (direct) and 3.2 eV (indirect) which on annealing at 825 K becomes crystalline with a band gap of 3.6 eV (direct) and 2.8 eV (indirect). There is no effect of hydrogen reduction on the band gap of these films.

A readout box prototype for the CMS Hadron Forward calorimeter upgrade was built and tested in the CERN H2 beamline. The prototype was designed to enable simultaneous tests of different readout options for the four anode upgrade PMTs, new front-end electronics design and new cabling. The response of the PMTs with different readout options was uniform and the background response was minimal. Multi-channel readout options further enhanced the background elimination. Passing all the electronic, mechanical and physics tests, the readout box proved to be capable of providing the forward hadron calorimeter operational requirements in the upgrade era.

The present paper describes the measurement of high energy gamma rays (\ensuremath{\sim}5--22 MeV) in the reaction $^{16}\mathrm{O}$${+}^{181}$Ta. Singles measurements were performed at E${(}^{16}$O)=84, 89, and 107 MeV and the multiplicity gated measurements along with the angular distributions were made at E${(}^{16}$O)=94 MeV. It is seen that the Tl nuclei are nonspherical at the excitation energies and spins relevant for the present work. The angular distribution data can be explained only by incorporating large orientation fluctuations. An attempt has been made to extract information on shape fluctuations directly from the \ensuremath{\gamma} spectra. Under the restriction of using a common ``intrinsic'' strength function characterized by ${\mathit{E}}_{0}$ and ${\mathrm{\ensuremath{\Gamma}}}_{0}$ for the multiplicity gated data sets, a small increase of the effective mean deformation and a drive towards triaxiality (\ensuremath{\gamma}\ensuremath{\sim} 30\ifmmode^\circ\else\textdegree\fi{}) with angular momentum is brought out. If this restriction is relaxed, however, the data can be understood also with a smaller value of \ensuremath{\gamma}. The singles data can be understood within the same framework with a higher value of ${\mathrm{\ensuremath{\Gamma}}}_{0}$. \textcopyright{} 1996 The American Physical Society.

Resistive Plate Chambers (RPC), planned to be used in the ICAL detector of the Indian Neutrino Observatory (INO) project, need precise mixing of four different gases, as well as precise control of the flow rate of the mixed gas. The designed system has the capability to pre-mix the gases (static mode), which can be stored in a pressurized vessel for subsequent use. The unit can also dynamically control the ratio of the four constituent gases (dynamic mode) and deliver it at a controlled flow rate through the mixing volume to the RPC.

Fission fragment angular distributions have been measured for the fusion of ${}^{16}\mathrm{O}$ with deformed ${}^{181}\mathrm{Ta}$ target, in the energy range 90 MeV to 110 MeV. Combining with the existing data of evaporation residue and fission cross sections in the literature, the fusion cross sections have been determined in the range $1.1<~{E/V}_{B}<~1.6.$ Detailed statistical model analysis of the entire data set has been performed and it has been shown that fission fragment anisotropies calculated are in good agreement with the experimental data. Even at the lowest energy studied, ${(E=1.1V}_{B})$ as there is good agreement between the data and the calculation, it can be concluded that the quasifission effect is negligible at this energy.

Polycrystalline thin films of n-type CdSe (thickness 1–2 μm) were grown on Zn substrates by noncatalytic displacement plating using aqueous solutions of CdSO4 and SeO2 in acidic pH. Thickness measurement was performed by the chemical stripping method as well as by the capacitance method. The electrical characterization comprises ohmic contact study, resistivity, conductivity, and impedance measurements. The optical characterization was determined by photocurrent action spectrum and visible reflectance spectrum studies. Crystallographic structure and surface morphology were analyzed by X-ray diffraction and scanning electron microscopy. Average grain size of the order of micrometers and well-defined grain boundaries were observed.

\ensuremath{\gamma}-ray yields in the energy range \ensuremath{\sim}5--35 MeV have been measured in the reactions \ensuremath{\alpha}${+}^{197}$Au and $^{159}\mathrm{Tb}$ at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=40 MeV and \ensuremath{\alpha}${+}^{197}$Au, $^{116}\mathrm{Sn}$, $^{\mathrm{nat}}\mathrm{Ag}$, and $^{59}\mathrm{Co}$ at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=50 MeV at ${\mathrm{\ensuremath{\theta}}}_{\ensuremath{\gamma}}$=90\ifmmode^\circ\else\textdegree\fi{}. Angular distribution measurements have been carried out for the heaviest and the lightest target at ${\mathit{E}}_{\mathrm{\ensuremath{\alpha}}}$=50 MeV. A reasonably good agreement with the statistical model calculations is obtained for photon energies up to the giant dipole resonance region. A nonstatistical component is observed at higher \ensuremath{\gamma}-ray energies for all the systems studied. An attempt to understand the production mechanism of the nonstatistical part is made in terms of the potential bremsstrahlung and the incoherent nucleon-nucleon bremsstrahlung processes. While the calculations give the right order of magnitude of the measured cross sections for the highest \ensuremath{\gamma}-ray energies, they fail to reproduce the measured angular distributions and the cross sections in the entire \ensuremath{\gamma}-ray energy range.

Abstract Photosensitive thin films of binary and ternary phase semiconductors have been deposited on metallic substrates by non-catalytic displacement plating (NCDP). Various preparative parameters are optimized for deposition of CdSe, CdTe and ZnCdSe on Zn and Ti substrates. Bandgap of ZnddCdxSe has been tailored from 1.68 to 2.53 eV for various Zn/Cd molar ratios. Photoelectrodes thus prepared are found to yield a short circuit current up to 2 μA and an open circuit voltage up to 0.45 V in S2−/S22− electrolyte.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

The Phase I upgrade of the CMS Hadron Endcap Calorimeters consists of new photodetectors (Silicon Photomultipliers in place of Hybrid Photo-Diodes) and front-end electronics. The upgrade will eliminate the noise and the calibration drift of the Hybrid Photo-Diodes and enable the mitigation of the radiation damage of the scintillators and the wavelength shifting fibers with a larger spectral acceptance of the Silicon Photomultipliers. The upgrade also includes increased longitudinal segmentation of the calorimeter readout, which allows pile-up mitigation and recalibration due to depth-dependent radiation damage. As a realistic operational test, the responses of the Hadron Endcap Calorimeter wedges were calibrated with a 60Co radioactive source with upgrade electronics. The test successfully established the procedure for future source calibrations of the Hadron Endcap Calorimeters. Here we describe the instrumentation details and the operational experiences related to the sourcing test.

A Comparative study has been performed on Resistive Plate Chambers made of different grades of bakelite paper laminates, produced and commercially available in India. The chambers, operated in the streamer mode using argon : tetrafluroethane : isobutane in 34:59:7 mixing ratio, are tested with cosmic rays for the efficiency and the stability with cosmic rays. A particular grade of bakelite (P-120, NEMA LI-1989 Grade XXX), used for high voltage insulation in humid conditions, was found to give satisfactory performance with stable efficiency of > 96% continuously for more than 110 days. A silicone treatment of the inner surfaces of the bakelite RPC is found to be necessary for operation of the detector.