Position Sensitive Surface Barrier Detector Research Articles

Branching ratios in dissociative recombination of formyl and isoformyl cations

The energy dependence of the branching ratios in dissociative recombination of DCO+ with a known small admixture of DOC+ has been measured for collision energies from 0 to 25eV using an energy- and position-sensitive surface barrier detector which is designed for the analysis of multi-fragment events occurring in a molecular fragmentation study. The measurements are compared with theoretical calculations on the direct mechanism of dissociative recombination of HCO+ including the contribution from HOC+ at the experimental abundance fraction. At low collision energies, dissociative recombination of HCO+ is dominated by dissociation into H + CO. For collision energies above 2eV there is a transition into dissociation to HC+O, which can be explained by electron capture into resonant states. Signatures of DOC+ dissociative recombination are found experimentally and confirmed by the calculations for HOC+. Three-body breakup becomes important for collision energies above 6eV.

Study of evaporation residues produced in reactions of207,208Pb with50Ti

Evaporation residues produced in heavy-ion fusion-reactions of50Ti and207Pb,208pb have been investigated. They were separated from the projectile beam by the velocity filter SHIP and identified after implantation into position-sensitive surface-barrier detectors, where their α decay or their decay by spontaneous fission was measured. The production of weakly excited compound nuclei in reactions of projectiles and targets close to the doubly magic48Ca and208Pb was confirmed by the observation of the 1n deexcitation channel in the reaction50Ti +208Pb.

Detector system for investigation of proton radioactivity and new elements at ship

The velocity separator SHIP has been built at GSI, Darmstadt, for the investigation of evaporation residues produced in heavy ion compound nuclear reactions. Low level spectroscopic investigations down to production cross sections of 10 pb and half lives of 1 μs became possible due to the extremely high degree of separation from the projectile beam. The advantages of SHIP have been further improved with a newly developed position and time correlation method. 33 new nuclei could be identified in the element region between gadolinium and lead by correlation of successive alpha-decays of nuclei implanted into position-sensitive surface barrier detectors. In a search experiment for proton radioactivity in this region, the first proton radioactive nucleus beyond the proton dripline 151Lu could be identified, indicating the limit of radioactive nuclei on the neutron deficient side. In the region of the heavier elements ( Z ⩾ 98), nine new isotopes have been identified by parent daughter correlations. The decay properties of the heaviest known element, Z = 109, A = 266 could be measured in a decay of a single nucleus. Such an event has been observed in a two week irradiation of 209Bi targets with 58Fe projectiles.

The new isotopes247Md,243Fm,239Cf, and investigation of the evaporation residues from fusion of206Pb,208Pb, and209Bi with40Ar

The evaporation residues produced in heavy ion fusion reactions between40Ar and206Pb,208Pb, and209Bi, respectively, were investigated. They were separated in-flight using a velocity filter (SHIP) and identified after implantation into an array of position sensitive surface barrier detectors by measuring their decay characteristics. Three newα-emitting isotopes were found:247Md,243Fm, and239Cf.247Md was identified by correlation to its known daughter decay243Es, and243Fm and239Cf were observed as correlated decays. Moreover, all previously known deexcitation channels, characterized by spontaneous fission or byα decay, could be observed for the first time in one experimental setup. Our results for formation cross sections and decay characteristics are in agreement with known data.

Pseudostructures in the spectra from position sensitive detectors caused by digital data acquisition

In the course of the analysis of spectroscopic data taken with a position sensitive surface barrier detector, the resulting energy and position spectra showed unphysical substructures. This effect — caused by the digitizing of the analog detector signals — was reproduced by computer simulation. A simple method to correct data for these pseudostructures is given.

Charge States of 29.2- to 45.7-MeV Uranium Ions Emerging from Solid Foils

The equilibrium-charge-state distributions of uranium ions have been measured in carbon at 29.2 and 45.7 MeV, in aluminum at 29.1 MeV, in silver at 29.7 MeV, and in gold at 29.6 MeV (energy is the exit-beam energy). Following the passage of monoenergetic uranium ions from the Oak Ridge tandem accelerator through each thin-foil target, the charge states in the emergent beams were spatially separated in an electrostatic analyzer and measured with a position-sensitive surface-barrier detector. The foil thicknesses, derived from $\ensuremath{\alpha}$-particle energy-loss measurements, were 34 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ for carbon, 51 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ for aluminum, 58 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ for silver, and 110 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ for gold. Non-Gaussian charge-state distributions were observed. The most probable charge states are in reasonable agreement with published semiempirical formulas, although some deviations are noted.

The response of position-sensitive detectors to fission fragments and other heavy ions

Position-sensitive surface barrier detectors have been used for the measurement of energy and angular distributions of fission fragments and other heavy ions. The techniques used to calibrate such detectors are described. It is possible to determine the position of an incident ion with a resolution of about 0.25 mm for a 50 mm detector length, the position response being independent of the energy of the ion. However, the position response curve is non-linear, showing its largest curvature at one end of the detector. The pulse height versus energy calibration was determined for a variety of heavy ions produced by elastic scattering of 32S and 16O. The ions Ni, Ag and Au exhibited pulse-height defects, which were measured as a function of ion energy, and were found to be approximately equal to those for a “heavy ion” type surface barrier detector. The pulse height versus energy calibration is a function of position, but is linear at a given position. In spite of the slow rise time of the pulses, it was possible to obtain fast timing signals, with a resolution of 3.5 nsec (fwhm) at a fixed position and fixed energy. The time dependence on position, however, is very large with about 50 nsec difference between the center of the detector and the ends.

A particle-gamma ray correlation apparatus

An angular correlation apparatus is described in which particles are detected at zero degree with respect to the incident beam by a position sensitive surface barrier detector located at the focal point of a magnetic spectrometer. Four 7.6 cm × 10.2 cm NaI(Tl) crystals are simultaneously used to detect coincident γ-rays at angles between 60° and 160°. Details of precautions taken to reduce γ-ray and particle backgrounds are given. Data are accumulated in three parameter mode using a computer-analyzer system.

Four-parameter coincidence study of the 6Li( 6Li, α)2α reaction

The 6Li( 6Li, α)2α reaction was studied at E 6 Li = 2.75 MeV. A four-parameter data acquisition system employing two position-sensitive surface-barrier detectors, four pulse-height analysers and a general-purpose computer, provided simultaneous measurement of coincident energy spectra for any pair of angles within the 40° angular intervals subtended by each detector. No statistically correlated component appears in the energy or angle correlations. Regions of the coincidence spectra which correspond to the intense continuum observed in singles spectra, were found to exhibit pronounced structure which varied rapidly with angle. Contributions to these spectra from the decay of high-lying excited states of 8Be provide limited explanations for the observed structure. Angles and energies which satisfy the kinematic conditions for the zero momentum transfer of a deuteron tend to coincide with the highest coincidence rates in the angular range covered, in accord with a simple direct reaction model. However, no single hypothesis based upon decay of states of 8Be or a special reaction mechanism accounts for all of the observed structure.

An array of position sensitive surface barrier detectors for use in a broad range magnetic spectrograph

Position sensitive surface barrier detectors were developed with an effective length of 5 cm 1). The position dependent signal is linear within 1% and the resolution obtained is better than 1 mm for particles of 10 MeV. For use in a magnetic spectrograph these detectors have been combined to a multidetector array. The energy and the position pulses are stored in a two dimensional multi-channel analyser. The electronic equipment will be described. A device of 6 detector elements has been checked in the spectrograph and two spectra of the 27Al(d,d′) and 27Al(d,α) reactions will be shown, which were measured simultaneously.

Utilization of Web Silicon for Position-Sensitive Detectors

Position-sensitive surface-barrier detectors have been made with web silicon, a hyper-pure silicon in ribbon form. Several characteristics of this material are especially suited for position detectors, i.e., long lengths, flexibility and high surface lifetimes. In addition, the structural stability, thickness uniformity, and thin cross sections make this material attractive for standard or position sensitive dE/dx detectors. Counters with active areas of 2-3.5 cm × 2-4 mm have been tested with 5.5-MeV alpha particles yielding spectra sensitive in position to less than 1%. A region of twin planes is exhibited within the material by changes in the slope of the plots of detector capacitance and leakage current as functions of reverse bias. The effect of the twin planes on the carrier collection efficiency has been investigated with several samples and found to be significant in certain cases. These results are discussed in terms of carrier lifetimes.