Silicon Surface Barrier Detector Research Articles

Determination of 228Ra, 226Ra and 224Ra in natural water via adsorption on MnO 2-coated discs

A fast procedure based on sorption of Ra on MnO 2 coated polyamide discs is presented for determination of radium isotopes (i.e. 228Ra, 226Ra, 224Ra) in aqueous samples. The sample discs can be used directly for low-level α-spectrometry without the need for further separation and preparation methods to produce planar sample sources. While the activity of α-emitting 224Ra and 226Ra can be determined during a first measurement, β-emitting 228Ra is obtained via ingrowth of the progeny 228Th on the same sample disc after a standing time of about six months. Calculations are presented for optimizing the analytical accuracy as well as for predicting the sorption yield or chemical recovery of radium on the sample disc as a function of exposure time because the sorption uptake proceeds with first-order kinetics. The analyses can be carried out on small samples of 0.5–1 l and, for long counting times of one week and use of high-purity silicon surface barrier detectors, a detection limit of 0.15 mBq l −1 is obtained for 226Ra. Since the half-life of 224Ra is only 3.7 d and since 228Th (as a measure for 228Ra) is built up only partially on the sample disc, a slightly higher detection limit of 0.24 mBq l −1 results for the latter isotopes. The procedure is therefore sufficiently sensitive to allow the investigation of Ra isotope relationships in aquifers at typical environmental levels.

A Position-Sensitive Photodetector for Studying the Spatial–Time Radiation Intensity Distribution in a Laser Beam

A position-sensitive nine-sectional photodetector for studying the spatial–time distribution of the radiation intensity in a laser beam is described. The photodetector was developed according to the technology used in the production of silicon surface-barrier detectors of nuclei fission fragments. Its sensitivity at a wavelength of 1.06 μm is 0.1 A/W, and the mutual interference of its sections is within 10%. The device was used in studies of the spatial–time evolution of the optical characteristics of an active medium based on an uranium-containing liquid during nuclear pumping on a pulsed reactor.

Measurement of the radioisotope 129I at the NSF-Arizona AMS laboratory

With the recent addition of a high-energy analysis beam line, the capability to measure 129I has been developed at the NSF-Arizona AMS Laboratory. Preliminary measurements have been made using the +4 and +5 charge states at 2.1 MV with a gas stripper. The current system employs a 90° injection magnet ( r=0.36 m) following the ion source. Analysis components following the accelerator include an electrostatic quadrupole doublet lens, a 15° electrostatic deflector ( r=1.25 m), a 90° analysis magnet ( r=1.27 m) and a 77° spherical electrostatic analyzer ( r=2.0 m). Detection of 129I is accomplished with a silicon surface barrier detector. Operation of this system with various iodine samples will be discussed.

Neutron detection based upon a lithiated sol–gel glass

The addition of dopants in the wet chemistry formation of glass in sol–gel technology is used for many purposes. Among the uses are the fabrication of films sensitive to pH, temperature, the presence of dissolved chemicals in solutions and many others. This paper describes the use of sol–gel technology for the doping of B-10, Li-6 and U-235 into glass films applied to silicon surface barrier (SSB) detectors. Using a commercial preamp/amplifier and an IEEE-488 NIM counter, the response was recorded of the neutron profile in a neutron activation source. A portable personal computer recorded the thermal neutron map as the detector was lowered in 1.27-cm steps down a Numec thermal neutron activation source. The lithiated glass film on the SSB gave about four times the count rate of the boron-10 doped glass film. The U-235 doped glass film gave a much lower count rate, but maintained a constant output signal due to the presence of the alpha activity from the U-235 and the trace of U-234 present in the sample.

Analysis of the surface technology of silicon detectors for imaging of low-energy beta tracers in biological material

Using silicon surface barrier detectors, the counting sensitivity of low-energy beta tracers is considerably influenced by surface technology applied in detector manufacturing. Original diagnostic procedure, using a mixture of uranium fission products, is described to trace the behaviors of different admixtures as in the etching bath as in the water used during development of the detector surface. In combination with some other described analyses, the detectors produced with the developed surface control are used in a PC – controlled scanning equipment reaching at room temperature an FWHM of 3.4 keV for 241Am. Such detectors make it possible to image distribution, of e.g., 3H, 125I, 3 H+ 14 C and other beta tracer combinations applied in life and environmental sciences.

A compact multiparameter acquisition system for radon concentration studies

A compact device suitable to acquire and display, at the same time, radon concentrations in a given atmosphere, and the environmental parameters characterising the atmosphere, is presented and described. It consists of two main blocks: (i) a detection section including a set of sensors for measuring pressure, humidity and temperature, and a set of silicon surface barrier detectors mounted in electrostatic cells collecting the ionised radon daughters; (ii) a single NIM module featuring an eight channel 12 bit ADC and the linear electronics to shape the signals from the silicon detectors. The system is controlled by a computer via a RS232 port. The software, implemented in Visual Basic, allows to display the energy distribution of the pulses coming from the alpha detectors and to initialise and control all phases of the acquisition. The results of preliminary tests show the high reliability of the system.

A detector for low-energy (few hundred eV–20 keV) X-rays in the presence of a high background of high-energy X-rays

The Vanderbilt University FEL Center project for the production of monochromatic X-rays uses Compton backscattering of the infrared light from the FEL by the 40 MeV electron LINAC to produce nearly monochromatic pulses of X-rays in the 10–20 keV range. Detecting these requires the ability to distinguish the small flux of 15 keV X-rays produced by the backscattering from the large flux of X-rays from low energy to many MeV resulting from scattered electrons from the beam. We have constructed a detector using two thin silicon surface–barrier detectors as calorimeters, separated by an aluminum absorber, so that the front detector sees both high- and low-energy X-rays, and the back one sees only high-energy X-rays. Using a carefully balanced differential amplifer chain, we can detect a soft X-ray flux which is only about 5% of the broadband flux observed by our detector.

Stopping powers of Al and Mo for protons from 0.3 to 3.0 MeV

Stopping powers of Al and Mo have been measured for protons in the respective energy ranges of 0.3–3.0 and 0.4–3.0 MeV with a surface barrier silicon detector. The uncertainty of the present results is ±0.35%. Above 0.8 MeV the present results for Al agree well with the Aarhus data of Anderson et al. [Phys. Rev. A 16 (1977) 1929] and the tabulated values of ICRU Report 49 (Stopping Powers and Ranges for Protons and Alpha Particles (International Commission on Radiation Units and Measurements, 1993)) (ICRU values). Below 0.8 MeV, however, ratios of the present data for Al to ICRU values show a slight decrease with decreasing proton energy. The decrease amounts to ∼1% at 0.3 MeV. In the case of Mo the ratios also decrease with decreasing proton energy below 2.0 MeV. The decrease reaches ∼8% at around the lowest energy, 0.4 MeV. Because the Bethe–Bloch formula is known to well reproduce stopping powers for protons above ∼1 MeV, the mean excitation energies, the I values, of Al and Mo have been extracted from the results for 1–3 MeV protons. These I values are compared with published values.

Parameterization of the pulse height defect and resolution for low-Z ions incident on silicon barrier detectors

Abstract The pulse height output of silicon charged particle detectors has been studied for low Z particles having energies in the range of 1–5 MeV/amu. Particle beams of 7Li, 9Be, 11B, 12C, and 16O nuclei were scattered from 197Au targets and their energies were measured with two silicon surface barrier detectors. For alpha-particle detection, both beam particles and those from a calibrated 228Th source were used. The data are anomalous in that the pulse heights for different ions of the same energy increase with atomic number, contrary to observations for fission fragments. It is found that the pulse height output of the detectors and the width of the pulse height distribution (FWHM) increase with the Z and Z2, respectively, of the detected particle.

Study of nuclear reactions with intense, high-purity, low-energy radioactive ion beams using a versatile multi-configuration dual superconducting-solenoid system

A new device (TwinSol) installed at the Nuclear Structure Laboratory at the University of Notre Dame implements a pair of large-bore 6 T superconducting solenoids for producing relatively pure, high-intensity beams of exotic light nuclei at low-energies (10–80 MeV). Typical beams include 8Li and 6He (T 1/2<1 s). The device efficiently produces, collects and focuses beams onto (or implants into) suitable target foils and test materials. The system uses various combinations of the following detection schemes: XY position sensitive gas counters for time-of-flight and ion ray-tracing; multiple stacks of silicon surface barrier detector telescopes mounted at various angles on a rotating table; 2D position-sensitive silicon detectors (PSDs) for high precision angular measurements; multi-annular, multisectored “CD” detectors for large solid angle (nearly 2π in lab frame), high-collection efficiency (multi-hit) particle detection; and ion-implanted stacks of target foils for off-line detection. Also available are a set of HPGe detectors which will be implemented upon completion of a low-background gamma cave. TwinSol represents an advancement in the application of large-bore superconducting magnet technology, capable of running in persistent mode for weeks without liquid helium (LHe) refill or measurable degradation of magnetic field (<0.1%).

Stopping powers of N2 and O2 for protons from 4.0 to 13.0 MeV

Stopping powers of N2 and O2 for protons from 4.0 to 13.0 MeV were measured with an accuracy of ±0.8% using a surface barrier silicon detector set inside a sealed gas cell. Energy loss in the gases was obtained from the peak shift of the proton pulse heights measured separately with and without gas filling. One-half of the experimental data obtained for molecules N2 and O2 was compared with that of experimental data for 4.4 MeV protons reported by Brolley and Ribe [Phys. Rev. 98 (1955)1112], the calculated values given in ICRU Report 49 [Stopping Powers and Ranges for Protons and Alpha Particles (International Commission on Radiation Units and Measurements, 1993)], and the values calculated by Andersen and Ziegler's formula [Hydrogen Stopping Powers and Ranges in All Elements (Pergamon, New York, 1977)] for atoms N and O. By analyzing the experimental results with the modified Bethe–Bloch formula that includes the Barkas correction term, we extracted the mean excitation energies, the I values, for N and O. The I values were compared with other reported values.

Neutron spectrometry at Strasbourg University Reactor

A neutron spectrometer incorporating two silicon surface barrier detectors and a 6LiF target has been designed, constructed and used to determine neutron energy distributions in three irradiation sites of the Strasbourg University Reactor (SUR). The spectrometer is compared with other spectrometer designs using the same detectors and target by means of the energy resolution observed for a thermalized neutron beam. The spectrometer considerations including the detection efficiency, the geometrical function and the spectrometer response function of coincident detection of the two emitted particles, i.e., tritium and α, are presented. Gold’s method of spectral unfolding was applied to reconstruct the energy distribution at two irradiation sites of SUR.

A TOF spectrometer for elastic recoil detection

A time-of-flight spectrometer was built for the ERD-TOF (Elastic Recoil Detection by Time Of Flight) and heavy ion RBS (Rutherford Backscattering Spectrometry) experiments with a 1.7 MV tandem Van de Graaff accelerator. The spectrometer consists of two time pick-off detectors and a SSB (Silicon Surface Barrier) detector with variable flight lengths. The time detector uses an electrode to accelerate and to focus the electrons from a thin carbon foil to a MCP (Micro Channel Plate). The advantage of this type of time detector is the good efficiency and no obstacles in the beam path at the cost of a small uncertainty in the flight length. The efficiency of the spectrometer was measured for the ions lighter than neon in the energy range of a few hundred keV to 7 MeV, and was better than 98% for the particles heavier than B. The intrinsic resolution of the time detector is about 220 ps. The time resolution of the spectrometer was measured as a function of incident particle type and energy. The mass resolution is below 1 amu for the particles of interest.

Elastic recoil detection using time-of-flight for analysis of TiN/AlSiCu/TiN/Ti contact metallization structures

The ability of elastic recoil detection (ERD) with time-of-flight (TOF) to quantify multilayer TiN/AlSiCu/TiN/Ti contact metallization structures on Si and SiO 2 has been demonstrated. In the technique a single microchannel plate (MCP) detector assembly and a silicon surface barrier detector (SSBD) were used. Technically high quality multilayer structures that have important applications in VLSI/ULSI devices were produced in a commercial Varian M2000 cluster tool by sputtering techniques. Several device process parameters such as annealing temperature (450°C, 500°C and 550°C), TiN oxidation, TiN ARC layer, TiN diffusion barrier thickness (50 and 90 nm) and types of substrate (Si and SiO 2) have important consequences on the performance of the product. The effect of changes in the above mentioned parameters on the elemental composition have been reliably studied by ERD. All the elements from H to Cu including substrate Si of a contact structure have been quantitatively and simultaneously profiled in a single experiment. The reproducibility of the major concentrations (N, O, Al, Si and Ti) in a multilayer test sample in every batch was within ±5%. Grazing angle X-ray diffraction (XRD) and the analyses of the ternary and quaternary phase diagrams complemented by the ERD investigations have been used to identify various phases in the layers. These results were then correlated with the measured electrical properties.

A new setup for elastic recoil analysis using ion induced electron emission for particle identification

We describe a new setup for elastic recoil detection analysis (ERDA) using our recently developed particle identification method. Before the ions and elastic recoil atoms from the target reach a silicon surface barrier detector for energy analysis, they penetrate a set of thin foils (e.g. carbon). The ion induced electron emission yield from the foils depends on the nuclear charge of the penetrating ion and it is roughly proportional to the energy loss in the foil. The emitted electrons are accelerated towards a microchannel plate (MCP), which gives a signal amplitude proportional to the number of emitted electrons. This signal is measured in coincidence with the energy signal from the surface barrier detector using our dual-parameter multichannel analyzer system M2D. Since the energy resolution is not measurably deteriorated by the particle identification our setup offers optimum depth resolution for light elements. Due to the compact design large solid angles for high sensitivity can be achieved. A new measuring chamber has been built which offers considerable improvements. The ERDA scattering angle (30° or 45°) and the target orientation can be selected for optimum depth resolution or sensitivity. Element separation for light elements has been enhanced by several improvements: A new geometry of the foil setup improves the collection efficiency for ion induced electrons onto the MCP, coating of the carbon foils with insulators enhances the electron emission yield. Finally, a new data evaluation procedure has been developed in which the pulse height spectrum of the MCP is considered to be a linear combination of individual spectra from the incident ion and of the recoil atoms. The normalized shapes of these spectra are taken from calibration measurements, the intensities are then calculated using a linear fitting algorithm and finally give the depth profiles of the elements in the target. For hydrogen in near surface layers even isotopic separation is possible. Examples for 1H and 2H in a Be matrix will be given.

A new compact 60 kV Mott polarimeter for spin polarized electron spectroscopy

A compact 60 kV Mott polarimeter has been constructed, tested, and calibrated especially for the local analysis of surface and two-dimension magnetism by means of electron spectroscopy with spin resolution. The use of construction combining spherical accelerating field with the absence of retarding potential after electron scattering provides low sensitivity of the polarimeter to movements of the analyzed electron beam and changes in its diameter. Special silicon surface-barrier detectors with large electron-optical acceptance provide efficiency ∈(≡Seff2×I/I0) about ≈2.5×10−4. The unique fast electronics allow to work with maximum count rate of detected electrons up to 5×106 counts/s. As a result, there is the possibility to calibrate the polarimeter (to calculate the effective Sherman function Seff) by extrapolation of the measured asymmetry to the high level of discrimination. This instrument is compact, fully UHV compatible and may be used in other fields of solid state physics, atomic physics, and physics of high energies.

On line measurements of proton flux by high energy backscattering spectroscopy

Proton radiotherapy is typically based on 70–200 MeV protons to irradiate limited volumes of diseased biological tissues. The absorbed dose is determined by the amount of proton energy released in the target i.e. the proton flux, the stopping power and the irradiation time. In this paper an experimental method is reported to make an on line measurement of proton flux, energy and beam stability. The facility is constructed at the 15 MV Tandem accelerator of the INFN-LNS in Catania (Italy) where preliminary studies are in progress. Investigations are performed at a proton energy of about 30 MeV, lower with respect to the therapeutic ones, but useful to simulate the clinical beams and to discover problems arising from their use. With the aim to use 70 MeV protons delivered by the LNS superconducting cyclotron for eye therapy, a gold scatterer is used to broaden the beam and to get a good uniformity over some centimeters in air. The scatterer is also used to produce the backscattered protons component which is detected with a thick silicon surface barrier detector. The detected yield is proportional to the beam flux and gives information about the beam energy and the current stability.

Identification and Rutherford Backscattering Measurement of MeV Carbon Cluster Ions

The MeV carbon cluster ions provided by 1.7 MV tandem accelerator were identified and Rutherford backscattering spectra of MeV carbon cluster ions on the gold film were measured with silicon surface barrier detector.

Depth resolution calculations for heavy-ion microbeam RBS analysis

A detailed study has been made on the use of MeV heavy ions ( Z 1 = 6–8) for microbeam Rutherford backscattering (RBS) analysis, to improve the depth resolution of this technique. The algorithm for determination of the depth resolution was created and applied to the Zagreb microbeam facility. Theoretical estimates of depth resolution for C and O ion RBS analysis of thin oxide films and semiconductors, using annular silicon surface barrier detector (SSBD), are compared to those for proton backscattering analysis. Depth resolution in certain cases may be improved by increasing the heavy-ion energy. Therefore, by the proper choice of the heavy ion and the heavy-ion energy, the depth resolution may be improved, maintaining the efficiency of the RBS method.

A note on collected-charge fluctuations in silicon surface-barrier detectors at heavy ion registration

Experimental results on charge losses and resolution in surface-barrier detectors under irradiation by 136Xe ions with an energy of about 1 MeV/amu are presented. It is shown that the dependence of resolution on charge losses and on the electric field intensity changes slope in a weak electric field region. It is supposed that this effect implies a mechanism of averaging charge losses due to the radial extension of a plasma column by the ambipolar diffusion.