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An ultrasensitive resonance ionization mass spectrometer that can be applied to evaluate krypton (Kr) contamination in xenon (Xe) dark matter detectors has been developed for measuring Kr at the parts-per-trillion (ppt) or sub-ppt level in Xe. The gas sample is introduced without any condensation into a time-of-flight mass spectrometer through a pulsed supersonic valve. Using a nanosecond pulsed laser at 212.6 nm, 84Kr atoms in the sample are resonantly ionized along with other Kr isotopes. 84Kr ions are then mass separated and detected by the mass spectrometer in order to measure the Kr impurity concentration. With our current setup, approximately 0.4 ppt of Kr impurities contained in pure argon (Ar) gas are detectable with a measurement time of 1000 s. Although Kr detection sensitivity in Xe is expected to be approximately half of that in Ar, our spectrometer can evaluate Kr contamination in Xe to the sub-ppt level.

As a part of the quality assurance procedure of the ATLAS SCT (Semiconductor Tracker) barrel modules, the response of the microstrip detector is measured by injecting focused Nd:YAG laser at each strip. The test is sensitive to sensor originated problems and a cross check to the results obtained from the electrical tests performed with the test pulse system implemented in the readout ASICs. Combining these results with the probing results obtained by the silicon sensor manufacturer, we verified the reliabilities of these tests and classified the type of defects for overall performance evaluation of the modules.

More than 2000 silicon modules need to be placed and fastened on the ATLAS SCT barrel tracker. A semi-automatic pick-and-place work robot was designed and developed to cope with the module placement for the SCT barrel assembly. We found that this robot could place modules to a mechanical precision of better than 25 μm.

In order to suppress the high electric field at the edge of the p-stop structure, a novel p-stop structure with DC field-plate was proposed. An n-in-n detector with the novel p-stop structure showed no onset of microdischarge, before and after proton irradiation of fluences of 3×10 13 and 3×10 14 p/cm 2 .

We applied the surface build-up Cu-polyimide flex-circuit technology with laser vias to the ATLAS SCT barrel hybrid to be made in one piece from the connector to the electronics sections including cables. The hybrids, reinforced with carbon–carbon substrates, provide mechanical strength, thermal conductivity, low-radiation length, and stability in application-specific integrated circuit (ASIC) operation. By following the design rules, we experienced little trouble in breaking the traces. The pitch adapter between the sensor and the ASICs was made of aluminum traces on glass substrate. We identified that the generation of whiskers around the wire-bonding feet was correlated with the hardness of metallized aluminum. The appropriate hardness has been achieved by keeping the temperature of the glasses as low as room temperature during the metallization. The argon plasma cleaning procedure cleaned the contamination on the gold pads of the hybrids for successful wire bonding, although it was unsuccessful in the aluminum of the pitch adapters.

We have developed a semi-automated assembly system and constructed 124 silicon microstrip modules so far for the ATLAS SCT barrel. This article describes the assembly procedure, evaluations of precisions and the module survey results. A precision of ∼2 μm is achievable with this assembly system.

In order to investigate the p-side strip isolation, position sensitivity and charge collection of type-inverted double-sided silicon microstrip detectors, signal amplitude and charge sharing of adjacent strips were measured by using a laser test stand, following the irradiation with a flux of 3.8×1013 /cm2 of 12 GeV protons. The irradiated detectors indicated high bulk resistivity, which results in maintaining a position sensitivity of the ohmic contact side even below the full depletion voltage. This fact suggests a possibility of operation of a double-sided detector whose full depletion voltage becomes higher than its breakdown limit because of a radiation damage.

Prototypes of ATLAS-SCT modules with ABCD readout chips were tested in a 4 GeV/c pion beam at KEK's proton synchrotron. Of both SCT module geometries—barrel and forward—three identical modules were placed in the beam. One module of each type had been irradiated to 3×1014 protons/cm2 in the CERN PS previous to the beam test. A method has been developed to reconstruct the time-resolved shaper pulse from the binary hit information, allowing a more detailed study of the timing properties of the ABCD. The present results will be compared to a simulation of the charge collection and Front End electronics response.

The ATLAS Semiconductor Tracker (SCT) consists of four barrel cylinders and 18 end-cap disks. This paper describes the SCT modules of the barrel region, of which more than 2000 are about to be constructed. The module design is fixed. Its design concept is given together with the electrical, thermal and mechanical specifications. The pre-series production of the barrel modules is underway using mass-production procedures and jigs. The pre-series modules have given satisfactory performances on noise, noise occupancy, electrical as well as mechanical and thermal properties. In addition, irradiated modules were demonstrated to work successfully. Also first results from a 10-module system test are given.

In a program of developing radiation-hard silicon sensors for the LHC-ATLAS experiment, we have irradiated various types of silicon sensors with 12 GeV protons at KEK. Among the other properties, we made a comparative study of characteristics of the sensors with two wafer planes 〈1 1 1〉 and 〈1 0 0〉 . The studied sensors are p-on-n type, which satisfy the ATLAS-SCT specifications. Possible dependence on the substrate orientation could result from different dangling-bond configurations. The compared characteristics are the charge collection efficiency, interstrip capacitance, and noise levels. The noise levels were measured with a real ATLAS-SCT electronics system. A substantial difference is observed in the interstrip capacitance at ∼10 kHz , while the difference is small at >1 MHz . The differences in the charge collection efficiency and in the noise levels appear to be small.

A double-sided, double metal, AC coupled readout silicon microstrip sensor (DDSMS) has been developed for the SVX-II, the upgrade vertex detector for CDF. Key issue in the development is to achieve sufficient radiation hardness for survival in the radiation environment of several kGy/yr. The required high-voltage capability and the reduction of the readout capacitance of the double-metal side were critical design goals. Detailed design methods to radiation-hard silicon sensors are discussed.

We have constructed a new massive ion beam system for the studies on well-defined microclusters. The laser-ablation-type cluster source is equipped for cluster generation separated from the ionization system. Two types of ionization systems are prepared: an ArF-excimer laser (193 nm, 0.8 mJ/pulse, 3 ns) or F2-excimer laser (157 nm, 0.3 mJ/pulse, 3 ns) and an electron impact ionizer. The energy and charge state of cluster ions are analyzed with a high accuracy by the sector-type 60° electrostatic analyzer with an orbital radius ρE=200 mm. The size of clusters with a specific energy and charge state is defined by the 60° magnetic analysis system characterized by an orbital radius ρM=650 mm and the maximum field strength Bmax=1.4 T. The massive ion beam system enables one to provide well mass-selected stable clusters, e.g. CuqN with sizes ranging as follows N=1–31 for q=+1 at energy E=20 keV, N=10–63 for q=+2 at E=40 keV, N=44–94 for q=+3 at E=60 keV, and N=121–126 for q=+4 at E=80 keV.

We describe a start-timing detector for the PHENIX experiment at the relativistic heavy-ion collider RHIC. The role of the detector is to detect a nuclear collision, provide precise time information with an accuracy of 50ps, and determine the collision point along the beam direction with a resolution of a few cm. Technical challenges are that the detector must be operational in a wide particle-multiplicity range in a high radiation environment and a strong magnetic field. We present the performance of the prototype and discuss the final design of the detector., Comment: 12 pages, LaTeX, 9 gif and 4 ps figures. Submitted to NIM A

Results are reported from a beam test of prototype silicon microstrip detectors and front-end electronics developed for use in the LHC detector ATLAS. The detector assemblies (“modules”) were 12 cm long and were read out with binary electronics. Both irradiated and unirradiated modules were measured in a 1.56 T magnetic field for efficiency, noise occupancy, and position resolution as a function of bias voltage, binary hit threshold, and detector rotation angle with respect to the beam direction.

The performance of the silicon strip detector prototypes developed for use in ATLAS at the LHC is reported. Baseline detector assemblies (“modules”) of 12 cm length were read out with binary electronics at 40 MHz clock speed. For both irradiated and unirradiated modules, the tracking efficiency, noise occupancy, and position resolution were measured as a function of bias voltage, binary hit threshold, and detector rotation angle in a 1.56 T magnetic field. Measurements were also performed at a particle flux comparable to the one expected at the LHC.

We have investigated the micro-discharge (micro-breakdown) phenomenon which is potentially a serious problem in operating in a high radiation environment. Numerical calculation of field strength for the model structure of the microstrip sensor gives us a quantitative understanding of each different cause of micro-discharge. The structure of the microstrip sensor can be optimized through this field calculation for suppressing the micro-discharge. We propose a new strip structure to suppress the micro-discharge.

We report on the construction of a new laser test stand equipped with a 1064 nm pulsed infrared YAG laser for simulating the passage of a charged particle in a silicon detector. The standard semiconductor repairing tool, the so-called laser-cutter, has been modified to have a newly developed optics which has the ability to reduce the light by the order of 10 6 –10 8 and to adjust the spot size to several microns. As an application we measured the position dependence of the induced signals in a silicon-strip detector when the laser light hits in the region between the strips. The measurement has show that this device is very effective in evaluating the detailed response of a silicon detector without using charged particles generated by accelerators.

The monitoring of the performance of silicon strip systems with binary readout is discussed. Due to the fact that neither pulse height nor noise level are recorded, the system is monitored with the efficiency and noise occupancy. As an example, on-line monitoring of the binary silicon strip system at the ATLAS H8 beam test at CERN is described.

We have examined experimentally some existing ideas for improving the radiation hardness of silicon microstrip sensors. We confirm that the extended electrode and the deep implant-strip proposed on the basis of simulation studies works effectively to suppress micro-discharge as well as junction breakdown of the bias or guard ring. For an integrated coupling capacitor a double layer structure of SiO 2 and Si 3 N 4 provides better radiation hardness than that of single SiO 2 coupling in our design conditions. The onset voltage of the micro-discharge on the bias/guard ring has been studied for an extended electrode and a floating guard ring.

A full-size prototype microstrip sensor for the silicon tracker of the SDC detector to be used at the Superconducting Super Collider has been fabricated at Hamamatsu Photonics. The sensor is double-sided, using an AC-coupled readout with 50 μm pitch strips. The sensor size is 3.4 × 6.0 cm 2 . Polycrystalline silicon is used as a bias feeding resistor on both surfaces. Each ohmic strip is isolated by a p + blocking line. The detailed requirements for the silicon tracker and the corresponding specifications as well as how to achieve them are discussed. The static performances of this prototype sensor are presented.

Microdischarge at the edges of strips in AC-coupled silicon strip sensors has been investigated. A steep increase in the leakage current (breakdown) and a sudden onset of burst noise were observed at a low reverse-bias voltage when the bias potential was across the AC-coupling capacitor. This can be explained by the occurrence of microdischarges along the edges of strips. These discharges have been confirmed by observing IR light emission. A calculation of the field strength at the strip edge suggests that a fringe field of the external electrode generates the microdischarge at the strip edge when the bias voltage is 50–80 V. This is consistent with our observations. We discuss a design for AC-coupled sensors that eliminates this discharge problem.

A new type of polarimeter for gamma-rays of over a hundred MeV was built. It is based on a principle in which the polarization is obtained from the azimuthal angular distribution of recoil electrons in electron-positron pair productions in the Coulomb fields of electrons.

A charged particle detector system for Coulomb excitation experiments with the multi-γ-ray detector system, NORDBALL, has been designed and constructed. The system consists of five position sensitive Si detecors and an annular type Si detector, which are installed in the central space of a BaF2 inner ball. The experiments have been carried out by using the beams of 32S, 48Ti and 58Ni ions. The combination of the new charged particle detector system and NORDBALL proves to have an excellent performance for heavy-ion-induced Coulomb excitation experiments.