Position Sensitive Particle Detectors Research Articles

Digitized signal acquisition of gas-filled, multiwire, neutron detector with delay-line readout

Multiwire counters are likely to remain a reliable and cost-efficient option for a large class of instruments. Delay-line position encoding is widely used in multiwire position sensitive particle detectors. Improvement of several detector parameters is a continuous demand such as count rate or position resolution. Digitization of the analog detector signals retains all information about the detected events at the highest count rate. Neutronic measurement results on our standard detector with 200mm × 200mm active area are presented with different acquisition algorithms. The analog signals were digitized by a high speed, multichannel Acqiris digitizer with 1 ns sampling resolution.

A deceleration system at the Heidelberg EBIT providing very slow highly charged ions for surface nanostructuring

Recently, it has been demonstrated that each single-impact of a slow (typically 1–2 keV/u) highly charged ion (HCI) creates truly topographic and non-erasable nanostructures on CaF 2 surfaces. To further explore the possibility of nanostructuring various surfaces, using mainly the potential energy stored in such HCIs, projectiles with kinetic energies as low as possible are required. For this purpose a new apparatus, capable of focusing and decelerating an incoming ion beam onto a solid or gaseous target, has been installed at the Heidelberg electron beam ion trap (EBIT). An X-ray detector and a position-sensitive particle detector are utilized to analyze the beam and collision products. First experiments have already succeeded in lowering the kinetic energy of HCIs from 10 keV/q, down to ∼30 eV/q, and in focusing the decelerated beam to spot sizes of less than 1 mm 2, while maintaining the kinetic energy spread below ∼20 eV/q.

Patterning large-area devices with a 5:1 reduction stepper

Contact or proximity aligners or 1:1 projection aligners are conventionally used for patterning large-area devices like silicon strip detectors for high-energy particle detection. Reduction steppers offer a far better pattern fidelity and an increased productivity but a very limited field size. This paper describes methods to overcome the field size limitations to pattern large-area position-sensitive particle detectors automatically and accurately with a 5:1 reduction stepper.

A position-sensitive particle detector for Coulomb excitation experiment

For Coulomb excitation experiments using a γ-ray detector array, a position-sensitive particle detector system that has a good angular resolution, capability of managing a high-counting rate, robustness for a radiation damage, compactness (under 110 mm φ) and easiness of handling is necessary. For this purpose we developed a new device utilizing plastic and yttrium aluminum perovskite activated by cerium (formula YAlO3:Ce abbreviated YAP Ce) scintillators and a position-sensitive photomultiplier tube. The detector system could operate at a high-counting rate (about 105), and with a good position resolution of 0.5–1.2 mm, which was enough for Doppler correction of the γ rays. It could sustain the radiation damage caused by Coulomb excitation experiments with heavy ions for more than 50 days. The detector chamber was well fitted in the 110 mm φ diameter of the internal space of a compact γ-ray detector array, GEMINI. This was much easier to handle than the position-sensitive gas counter. In Coulomb excitation experiment utilizing this device, the nucleus Ge74 has been Coulomb excited using a Pb target. The transitional E2 matrix elements have been determined and the device has turned out to be useful in Coulomb excitation experiments with heavy-ion beams.

The charge collection properties of CVD diamond

The charge collection properties of CVD diamond have been investigated with ionising radiation. In this study two CVD diamond samples, prepared with electrical contacts have been used as solid state ionisation chambers. The diamonds have been studied with beta particles and 10 keV photons, providing a uniform ionisation density and with protons and alpha particles which are absorbed in a thin surface layer. For the latter case a strong decrease of the signal as function of time is observed, which is attributed to polarisation effects inside the diamond. Spatially resolved measurements with protons show a large variation of the charge collection efficiency, whereas for photons and minimum ionising particles the response is much more uniform and in the order of 18%. These results indicate that the applicability of CVD diamond as a position sensitive particle detector depends on the ionisation type and appears to be promising for uniform ionisation densities as provided by relativistic charged particles.

Current-biased superconducting strips as position-sensitive particle detectors

The feasibility of superconducting strips as position-sensitive detectors for α particles was investigated. For this purpose films have been prepared of different materials and dimensions using standard evaporation and laser ablation in an UHV system. Films were patterned into strips and current-biased strips were irradiated with 5.5 MeV α particles. The energy deposited by the particle in the strip creates a normal-conducting region, which in turn causes a voltage drop. The time evolution of the voltage drop across the strip as a function of bath temperature and bias current has been investigated. Information about the site of the strip hit by the α particle was obtained from monitoring the propagating normal-conducting zones. A lateral position sensitivity of ±30 μm for a tantalum strip detector has been achieved. The propagation of normal-state zones in the strip cannot provide information on the energy of the particle. A model describing the time evolution of a normal-conducting zone in a current-biased superconducting strip was used to test and interpret the experimental results and allows one to estimate the thermal conductivity of the strip material and the heat transfer from the strip into the substrate.

Superconducting strip detectors as position sensitive particle detectors

The feasibility of using of current-biased superconducting strips for radiation detection is investigated. Narrow Ta strips are exposed to 5.5 MeV α-particle radiation and the rise-time of the induced voltage pulses is measured as function of temperature and bias current. The rise-time of the voltage signal strongly depends on the site on the strip which is hit by the α-particle. In order to determine the spatial resolution of a superconducting strip detector, position-sensitive measurements were performed. The maximum lateral resolution estimated so far is 25 μm in a 7 μm wide, 340 nm thick and 0.6 mm long Ta-strip.

Phase space compression of muon beams

A phase space compression technique applicable to short-lived particles is proposed. Its specific feature is that it treats each single particle separately by measuring its phase via position sensitive particle detectors and steers it via pulsed electromagnetic deflection. By applying the method to muons, very high quality low energy beams can be obtained. A specific design is presented that should allow to achieve a 50 keV muon beam with 0.1 π mm mrad transverse emittance and 10 4 s −1 intensity. These muons can be further decelerated to ultralow energies so that for example a 50 eV beam with 3 π mm mrad and Δp/ p = 10 −3 is obtained. The overall phase space compression compared to the entrance beam exceeds 10 15. With such beams, stopping of muons in atomic beams or on the first atomic layer of a solid can be envisioned. A short list of possible physics applications is given.

A position-sensitive particle detector with a meander-type delay line

A position-sensitive parallel plate avalanche detector with delay-line readout is described. The delay line is formed by two mutually shifted bent meanders. The characteristics of the operation are discussed. The position resolution is found to be 2 mm in accordance with the chosen geometry and the energy resolution is about 25%. Possible applications and ways for further developments are presented.

High-energy scattering of atoms and molecules

Research on atom-molecule interactions by high-energy scattering (at energies ~ 1 keV) through small angles (10−4–10−2 rad) is reviewed. The present state of experimental methods for this research is discussed. Theoretical aspects of research on potential-energy surfaces by means of high-energy scattering are analyzed. The results of recent research are summarized. In particular, there are discussions of research on elastic and inelastic scattering, a new effect (the vibrational rainbow) discovered in the scattering of atom-molecule systems, and measurements of the spectra of the total energy loss. Some possible directions for the further development of experiments are pointed out. Further experimental progress will require the assimilation of laser methods and position-sensitive particle detectors.

Analysis of time-spectra from coincidence measurements with high stop-rates

The development of new types of particle detectors makes possible coincidence measurements of low probabilities with very high particle stop-rates (>MHz). A consequence of a high stop-rate is, however, a loss of true coincidences, which are included in the random background. This effect becomes more severe if the position channels of a position-sensitive particle detector are used to stop a single TAC (time-to-amplitude-converter). An analytical description of time-spectra is developed and tested by a simulated coincidence experiment. A procedure is described, which can be used to determine the contents of the time-peak and to correct for the loss of the true coincidence.

Application of position-sensitive particle detection techniques to photon-atom coincidence experiments

Microchannel plates have been applied as position-sensitive particle detectors in photon-scattered-atom coincidence experiments. The time required to obtain a complete coincident angular distribution of the inelastically scattered atoms is reduced considerably as compared with previous experiments. The capability of the new technique is demonstrated in two different collision experiments. (a) The authors report the circular polarisation of the Li 2P to 2s photons emitted in 1000 eV Li-He collisions as a function of the scattering angle. (b) They report the probability for exciting the Li 2p state in (500 to 1000 eV) Li-surface (tungsten) collisions as a function of the projectile's scattering angle.

An inexpensive method for testing position sensitive particle detectors

A low cost method using a simple microprocessor has been demonstrated for the testing of the linearity and sensitivity of one-dimensional position-sensitive gas proportional neutron detectors. Results are given for a counter of nominal active length of 22″.

Position-Sensitive Semiconductor Particle Detectors Fabricated by Ion Implantation

The advantages and problems associated with the use of ion implantation for the fabrication of position-sensitive particle detectors are discussed. Analysis of the noise and pulse risetime properties of such devices shows the desirability of using a high sheet resistance in the distributing resistive layer for optimum position resolution while restricting the RC of the detector to values approximately equal to the clipping times used in the measuring circuits in order to obtain good position linearity. From both detector noise and pulse rise-time considerations it is found desirable to use equal pulse shaping in the energy and the position signal measuring systems. Detectors were made by implantation of 60 keV boron and phosphorus ions into 4000 ohm-cm n-type silicon. Representative results are shown for a 4×32 mm2 one dimensional detector which shows integral and differential position nonlinearity of less than one percent and position resolution of less than 0.2 mm. Extension to one dimensional detectors up to 50 mm and to 10×10mm two dimensional detectors is discussed.