Surface Barrier Detector Research Articles

Ion microbeam facility at the Wakasa Wan Energy Research Center

Two microbeam lines for an ion microprobe and a cell irradiation have been installed in a 5 MV tandem accelerator at the Wakasa Wan Energy Research Center (WERC), Japan. In the ion microprobe beam line, a magnetic quadrupole doublet is equipped for focus of the ion beam on the target point in a scattering chamber. It is utilized for the ion microprobe analysis such as particle induced X-ray emission and Rutherford backscattering spectroscopy. The beam spot size was obtained to be 0.8 μm ( x) × 0.6 μm ( y) (FWHM) for a beam current of 1 pA, and to be 2.0 μm ( x) × 2.5 μm ( y) (FWHM) for a beam current of 140 pA. In the cell irradiation beam line, a beam is extracted in air through a glass capillary with a 10 μm inner diameter in the vertical direction. A total dose to the cell is measured with a silicon surface barrier detector mounted under the sample stage.

Determination of the 8B Neutrino Spectrum

We have measured the total energy of the alpha particles following the beta decay of 8 B by implanting 8 B into a planar silicon surface barrier detector. Calibration was performed using alpha particles following the betadecay of 2 0 Na, similarly implanted. The alpha spectrum is used to infer the 8 B neutrino spectrum which is an important input in the interpretation of experiments that detect energetic neutrinos from the Sun. The alpha spectrum reported here is in disagreement with the previous best measurement which used two detectors in coincidence.

First on-line test of the LINAC superbuncher at nuclear science centre

An on-line test of the LINAC superbuncher at Nuclear Science Centre has been successfully performed. DC O7+ beam of nominal energy 92 MeV was accelerated through the superbuncher resonator, operating at a field of 4.54 MV/m. The total energy gain of the beam was measured to be 4.5 MeV. For the pulsed beam test a phase locked bunched beam of O7+ of nominal energy 92 MeV, FWHM 1.3 ns from the pre-tandem multiharmonic buncher was injected into the superbuncher. By properly adjusting the phase and amplitude of the resonator, the best FWHM of the bunched beam was measured to be 185 ps near the entrance of the first LINAC module. Fully depleted cooled surface barrier detector was used for measuring the time width. In a separate experiment the intrinsic time resolution of the same detector was measured to be 134 ps. Consequently the intrinsic time width of the bunched beam, after correcting for the detector resolution, would be 127 ps. Details of the experiment and results are presented.

A zero-to-few-hundred eV proton beam for calibrations of neutron β decay experiments

We have constructed a system using a duoplasmatron source to produce a beam of low-energy (0 – few hundred eV) protons with the principal goal of testing and calibrating detectors used to detect protons from neutron β decay. The system is stable and produces beams by simply turning on the associated power supplies without the need of careful tuning. As an example we show data from calibration of a surface barrier detector in the emiT apparatus. Protons from the system were scattered from an Al target and used to calibrate detectors in the emiT apparatus.

Dissociative recombination of D+(D2O)2 water cluster ions with free electrons

Dissociative recombination (DR) of the water cluster ion D+(D2O)2 has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Cluster ions were injected into the ring and accelerated to an energy of 2.28 MeV. The stored ion beam was merged with an almost monoenergetic electron beam, and neutral fragments produced by DR were detected by an energy-sensitive surface barrier detector. The first experimental determinations of the absolute DR cross section and branching ratios for a cluster ion are reported. The cross section for the process D+(D2O)2+e− is large and reaches 6⋅10−12 cm2 at a low center-of-mass collision energy of 0.001 eV. The cross section has an E−1.19±0.02 dependence in the energy range 0.001–0.0052 eV, and a steeper slope with an E−1.70±0.12 dependence for E=0.052–0.324 eV. The general trends are similar to the results for previously studied molecular ions, but the cross section is higher in absolute numbers for the cluster ion. Thermal rate coefficients for electron temperatures of 50–2000 K are deduced from the cross section data and the rate coefficients are consequently also large. Branching ratios for the product channels are determined with a grid technique. Break-up into 2D2O+D is the dominating dissociation channel with a probability of 0.94±0.04. The channel resulting in the fragments D2O+OD+D2 has a probability of 0.04±0.02, and the probability for formation of D3O+D2O is 0.02±0.03. The results are compared with data for molecular ions, and the cluster dissociation dynamics are discussed.

Relative cross sections for the electron impact single detachment on Li−

The electron impact single detachment process on Li− targets was studied using thestorage ring CRYRING located at the Manne Siegbahn Laboratory in Stockholm,Sweden. The Li− ions, first stored in the storage ring, were merged with a cold, 1.4cm in diameter, electron beam. The neutral Li atoms, originating from theprocess under scrutiny, were recorded by an energy-sensitive surface barrierdetector in order to measure the relative electron single detachment crosssection. The findings are the following. The cross section increases smoothlyabove the 1.4 eV detachment threshold and reaches a maximum at about12 eV. At even larger energies a slow decrease, which follows the ln (E)/Eenergy dependence predicted by the Bethe–Born approximation, is observed.

Experience in long-term neutron dose equivalent measurements using etched track detectors with (n,alpha) converters in moderators.

Etched track Makrofol detectors combined with Kodak BN-1 boron (n,alpha) converters were used inside a 30 cm diameter polyethylene (PE) sphere for the measurement of the neutron ambient dose equivalent. We found unexpectedly high values for the neutron dose equivalent of about 250 microSv instead of 25 microSv for 3 months' exposure in the natural environment. Results from such detectors etched in the authors' labortories revealed that the tracks could only be induced by spontaneous particle emission from the converter. This was confirmed by track diameter analysis and additional special etching of deeper detector layers. Eight surface barrier detectors were used simultaneosly for several days to measure the alpha spectra of the converters. The overall count rate in the energy range 2.5-7.5 MeV was 10 alpha particles d(-1) x cm(-2) for most of the converters and about 10 times less than this for some of them. To identify the nuclides responsible for alpha emission within the converters, gamma spectra of converters were measured for 8 days using a highly sensitive low-background gamma spectrometry system The spectra clearly indicated a small contamination (10 +/- 3 mBq) of the converter foils with 225Ra (T(1/2) = 5.7 y) typically originating from 232Th.

Nuclear models for proton induced upsets: a critical comparison

This work studies the status of the nuclear models used for estimating single event upsets sensitivity and other radiation effects, induced by protons in microelectronic devices. An extended comparison is made between the calculations of the two most developed models, the intranuclear cascade model (used for instant by the HETC code) and the pre-equilibrium exciton (PEqEx) model. The new data base ENDF/B-VI (calculated using PEqEx) is used to clarify the role of the various interactions of primary protons with Si nuclei in the energy deposition in silicon. In particular, we consider the light nuclear reaction products: secondary protons and /spl alpha/ particles. A comparison of simulated deposition spectra of surface barrier detectors with experimental data is shown. The role of reaction products created in the surrounding of the sensitive volume is discussed.

Neutron detector based on lithiated sol–gel glass

A neutron detector technology is demonstrated based on 6Li/ 10B doped sol–gel glass. The detector is a sol–gel glass film coated silicon surface barrier detector (SBD). The ionized charged particles from ( n, α) reactions in the sol–gel film enter the SBD and are counted. Data showing that gamma-ray pulse amplitudes interfere with identifying charged particles that exit the film layer with energies below the gamma-ray energy is presented. Experiments were performed showing the effect of 137Cs and 60Co gamma rays on the SBD detector. The reaction product energies of the triton and alpha particles from 6Li are significantly greater than the energies of the Compton electrons from high-energy gamma rays, allowing the measurement of neutrons in a high gamma background. The sol–gel radiation detection technology may be applicable to the characterization of transuranic waste, spent nuclear fuel and to the monitoring of stored plutonium.

Trajectory and charge state dependence of energy loss of relativistic heavy ions channeled in a silicon surface barrier detector

We measured the emerging charge-state distribution of hydrogen-like 390 MeV/u Ar 17+ ions planar channeled in a silicon surface barrier detector for the ΔE measurement, and observed their energy deposition in the detector simultaneously. We simulated the energy loss spectrum of specific emerging charge state, and succeeded in reproducing it with an adjusting parameter for the cut-off momentum transfer between close and distant collisions.

Energy dependence of the total reaction cross section of isomeric18Fmon silicon below 400 MeV

A 25 MeV/nucleon primary O-17 beam was used to produce an isomeric state F-18(m) beam via the single-nucleon transfer reaction O-17 (C-12, B-11)F-18(m). The total nuclear reaction cross section, sigma(R), of F-18(m) (metastable) on silicon was measured using a stack of silicon surface barrier detectors that included a position sensitive silicon detector (PSD). The total reaction cross sections were determined as a function of bombarding energy up to 400 MeV by measuring the energy loss in each detector. The reaction cross sections were measured both for a mixture of metastable- and ground-state ions and for a pure ground-state beam. The reaction cross sections for N-14 and O-16 beams were also measured simultaneously. The reaction cross sections for the metastable beam were deduced from the mixed- and the ground-state cross sections, corrected for the measured purity of the mixed-state beam. The observed reaction cross sections for F-18(m) are larger at low energies than the cross sections measured for the ground state. The isomeric cross sections can be reproduced by an optical model potential having a diffuseness of 0.8 fm, compared to a more conventional diffuseness parameter of 0.5 fm, which is adequate to reproduce the N-14, O-16, and F-18(g.s.) cross sections measured in this experiment.

Implantation sites of Ce and Gd in diamond

The implantation sites of rare earth (RE) probes 141 Ce ( t 1/2=32 d) and 149 Gd ( t 1/2=9.28 d) in diamond have been investigated using the emission channeling (EC) technique. Parent isotopes 141 Cs and 149 Dy were implanted into type IIa diamond samples at an energy of 60 keV at the online isotope separator ISOLDE at CERN. 141 Cs decays through the chain 141 Cs– 141 Ba– 141 La– 141 Ce– 141 Pr. EC measurements were made on the 102 keV conversion electrons emitted in the decay of 141 Pr to its ground state. The decay of 149 Dy follows the chain 149 Dy– 149 Tb– 149 Gd– 149 Eu– 149Sm. EC measurements were made on the 101 keV electrons emitted in the decay of 149 Eu. Two-dimensional channeling patterns of the conversion electrons were obtained along 〈1 1 0〉 and 〈1 1 1〉 axial directions by raster scans with a Si surface barrier detector. Comparison of the observed patterns with simulated spectra show that in diamond 45–50% of the RE atoms are located near substitutional sites, unlike the case in Si.

Response of Si p-i-n diode and Au/n-Si surface barrier detector to heavy ions

Pulse height versus energy calibrations of a Si p-i-n diode and a Au-/n-Si surface barrier detector have been studied for heavy ions with atomic number ( Z 1) from 3 to 79 in a range from 0.1 to 0.8 MeV per nucleon as a function of bias voltage and detector tilting angle. The detector response is simultaneously measured using a time of flight-energy elastic recoil detection analysis set-up with recoils produced over a wide energy range from a thick target of each element. Prior to impinging on the Si detector, the individual recoil is tagged by its energy determined from the time of flight and tabulated isotopic mass. For both detectors, the pulse height-energy calibration for recoils with a given Z 1 is described well by a linear relationship with small systematic deviations. The linear-fit parameters show similar, but not identical dependence on both Z 1 and bias voltage (collecting field strength) for the surface barrier detectors and the p-i-n diode. These results suggest that the efficiency of electron–hole pair collection is markedly dependent on the different electric field configurations for the two detector structures.

Doping Silicon with Lanthanides as a Method for the Optimization of Parameters of Ionizing-Radiation Detectors

A method for the optimization of parameters of surface-barrier ionizing-radiation detectors based on Gd-doped silicon is described. It is shown that the introduction of lanthanide into the molten zone removes impurities (Au, Cu, C, and Na) from single crystals grown by the crucibleless zone melting. This results in an increase in the nonequilibrium-carrier lifetime by a factor of ∼3 and in the single-crystal homogeneity from 25 to 60%. At room temperature, for the 239Pu α particles with an energy of 5.4 MeV, the energy resolution of the detectors based on the p-Si:Gd was by a factor of two better (33 keV) than that of the detectors based on conventional material (60 keV). For the n-Si:Gd under similar conditions, an energy resolution of 16 keV was attained.

Preparation of Thick Americium Targets and Synthesis of 259Db

A new isotope of Db has been produced via the reaction Am(Ne, 4n) at Elab = 118 MeV, and its half-life of 0.51± 0.16 s and α-decay energy of 9.47 MeV were determined in this work. The americium targets with thickness ranged from 0.7 to 1.0 mg/cm were prepared by molecular plating method through a single electrodeposition cycle. The reaction products were transported and collected using a helium-jet technique and a rotating wheel apparatus. The α decays of both the products and their daughter nuclides were detected by a series of Si(Au) surface barrier detectors arranged ingeniously. The identification of Db was performed based on the genetic relationship between the new activity and the known Lr established by α-recoiled milking measurement. The Qα value of Db derived from the present experiment is in good agreement with theoretical prediction.

Evaluation of 210Pb and 210Po in cigarette tobacco produced in Brazil

Cigarette smoking is one of the pathways that might contribute significantly to the increase in the radiation dose reaching man, due to the relatively large concentrations of 210Pb and 210Po found in tobacco leaves. In the present study, the concentrations of these two radionuclides were determined in eight of the most frequently sold cigarette brands produced in Brazil. 210Pb was determined by counting the beta activity of 210Bi with a gas flow proportional detector after radiochemical separation and precipitation of PbCrO 4. 210Po was determined by alpha spectrometry using a surface barrier detector after radiochemical separation and spontaneous deposition of Po on a copper disk. The results showed concentrations ranging from 11.9 to 30.2 mBq per gram of dry tobacco for 210Pb and from 10.9 to 27.4 mBq per gram of dry tobacco for 210Po. The collective committed effective dose resulting from the use of cigarettes produced in Brazil per year is estimated to be 1.5×10 4 man-Sv.

MeV carbon cluster-induced pulse height defect in a surface barrier detector

The pulse height defect (PHD) of surface barrier detectors (SBDs) bombarded by carbon clusters C n ( n=2–10) with energies of 1 and 2 MeV per carbon atom was measured. At the same projectile velocity the difference between residual cluster PHD and the n-fold PHD of each of the n cluster constituents is found to be proportional to n( n−1). This difference decreases when the thickness of the gold entrance window of the detector is increased. This is due to the smaller energy deposited in the depletion zone of the detector and not due to the separation of the cluster constituents while passing the window. Large radial separation distances of the cluster constituents must be achieved before the PHD vanishes. The model of Finch et al. [Nucl. Instr. and Meth. 163 (1979) 467] developed for atomic ions reproduces the data qualitatively.

Evaluation of Si(Li) detectors by a combination of the copper plating method and X-ray analytical microscopy

Copper mapping for copper-plated lithium-ion compensated Si(Li) wafers was performed by a microbeam X-ray fluorescence method. Positional distribution of copper across a cross section of the Si(Li) wafers treated at 120/spl deg/C for 20 h with no bias applied after complete compensation clearly showed deviation from those that did not undergo the thermal treatment. The surface-barrier detectors fabricated from the thermally treated wafers were found to have better energy resolution both for conversion electrons from /sup 207/Bi and for /spl alpha/-particles from /sup 241/Am. Correlation between the performance of the Si(Li) detectors and the lithium distribution in the intrinsic region was studied on the basis of the experimental results.

The new external beam facility of the Oxford scanning proton microprobe

This paper describes the development of a high spatial resolution external beam facility on one of the beamlines of the Oxford scanning proton microprobe tandem accelerator. Using a magnetic quadrupole doublet to focus the beam through the Kapton exit window a beam diameter of <50 μm full width at half maximum (fwhm) can be achieved on a sample located at 4 mm from the exit window. The facility is equipped with two Si–Li X-ray detectors for proton-induced X-ray emission (PIXE) analysis of light and trace elements respectively, a surface barrier detector for Rutherford backscattering spectrometry (RBS) analysis and a HP-Ge detector for γ-ray detection. The mechanical and beam-optical design of the system is described.

Angular distribution measurements of 6Li(p, α) 3He reaction at 140 keV proton energy using nuclear track detectors

Angular distributions of a 6 Li( p,α) 3 He reaction were measured at six angles for 140 keV proton energy using nuclear track detectors (NTDs). The measurements were carried out over 60°–160° lab. angles in 20° increments using a scattering chamber of 80° beam line of the 350 kV accelerator. A semiconductor silicon surface barrier (SSB) detector was placed at +160° and was used as a monitor. The results have shown that the CR-39 detector has excellent capabilities to distinguish 1.4– 2.7 MeV α+ 3 He particles from the 6 Li( p,α) 3 He reaction and 8– 9.4 MeV α -particles from the 7 Li( p,α) 4 He reaction through their track diameters. However, it was not possible to distinguish between the 2.3 MeV 3 He ions and the 1.7 MeV 4 He ions from the 6 Li( p,α) 3 He reaction from their track diameter measurements, but it was possible to differentiate between the two, from the darker contrast of the 3 He particles caused by its deeper tracks as compared to those of 4 He .