G. Mahler

A large, high performance, curved 2D position-sensitive neutron detector ☆

Abstract A new position-sensitive neutron detector has been designed and constructed for a protein crystallography station at LANLs pulsed neutron source. This station will be one of the most advanced instruments at a major neutron user facility for protein crystallography, fiber and membrane diffraction. The detector, based on neutron absorption in 3He, has a large sensitive area of 3000 cm 2 , angular coverage of 120°, timing resolution of 1 μs , rate capability in excess of 10 6 s −1 , position resolution of about 1.5 mm FWHM, and efficiency >50% for neutrons of interest in the range 1– 10 A . Features that are key to these remarkable specifications are the utilization of eight independently operating segments within a single gas volume, fabrication of the detector vessel and internal segments with a radius of curvature of about 70 cm , optimized position readout based on charge division and signal shaping with gated baseline restoration, and engineering design with high-strength aluminum alloy.

Use of high-granularity position sensing to correct response non-uniformities of CdZnTe detectors

CdZnTe (CZT) is a promising medium for room-temperature gamma-ray detectors. However, the low production yield of acceptable quality crystals hampers the use of CZT detectors for gamma-ray spectroscopy. Significant efforts have been directed towards improving quality of CZT crystals to make them generally available for radiation detectors. Another way to address this problem is to implement detector designs that would allow for more accurate and predictable correction of the charge loss associated with crystal defects. In this work, we demonstrate that high-granularity position-sensitive detectors can significantly improve the performance of CZT detectors fabricated from CZT crystals with wider acceptance boundaries, leading to an increase of their availability and expected decrease in cost.

An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras

We developed a robust and low-cost array of virtual Frisch-grid CdZnTe detectors coupled to a front-end readout application-specific integrated circuit (ASIC) for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6 × 6 × 15 mm(3) detectors grouped into 3 × 3 sub-arrays of 2 × 2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays performance and reduction of their cost are possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.

Status of the R&D towards electron cooling of RHIC

The physics interest in a luminosity upgrade of RHIC requires the development of a cooling-frontier facility. Detailed calculations were made of electron cooling of the stored RHIC beams. This has been followed by beam dynamics simulations to establish the feasibility of creating the necessary electron beam. The electron beam accelerator will be a superconducting Energy Recovery Linac (ERL). An intensive experimental R&D program engages the various elements of the accelerator, as described by 24 contributions to the 2007 PAC.

Unique features in magnet designs for R&D energy recovery linac at BNL

In this paper we describe the unique features and analysis techniques used on the magnets for a R&D Energy Recovery Linac (ERL) [1] under construction at the Collider Accelerator Department at BNL. The R&D ERL serves as a test-bed for future BNL ERLs, such as an electron-cooler-ERL at RHIC [2] and a future 20 GeV ERL electron-hadron at eRHIC [3]. Here we present select designs of various dipole and quadrupole magnets which are used in Z-bend merging systems [4] and the returning loop, 3-D simulations of the fields in aforementioned magnets, particle tracking analysis, and the magnets influence on beam parameters. We discuss an unconventional method of setting requirements on the quality of magnetic field and transferring them into measurable parameters as well as into manufacturing tolerances. We compare selected simulation with results of magnetic measurements.

A position-sensitive ionization chamber for thermal neutrons

A position-sensitive neutron detector based on /sup 3/He is being developed for a national crystal backscattering spectrometer (CBS) at a pulsed neutron source. It comprises a single gas volume, of constant depth, in the form of an annulus that is also part of a truncated cone. Charge from each event is collected on one or two anode strips, out of a total 336 around the annulus, yielding an angular resolution of about 1/spl deg/. Low-noise signal processing, in the form of a monolithic preamplifier/shaping amplifier connected to each anode strip, provides electronic noise that is small enough to permit detector operation in an ionization mode. In addition, the segmented anodes ensure near complete induced charge collection. This new detector therefore has significant advantages over previous detectors used in CBS instruments, which primarily consisted of arrays of individual /sup 3/He filled cylindrical counters with dead regions and nonuniform detection efficiency. The optimization of gas mixture/pressure, drift field, and shaping time is significant in achieving successful performance in the new detector.

A new thermal neutron detector for protein crystallography

A new position-sensitive detector is being developed for protein crystallography studies at a spallation source. Based on eight, independent, wire proportional chamber segments housed in a curved pressure vessel, the device covers a scattering angle of 120 degrees, and has a collecting area of 1.5 m by 20 cm. The position resolution will be about 1.3 mm FWHM, with a total counting rate in excess of one million per second. Timing resolution, essential for a spallation source application, is of order 1 /spl mu/s and provides neutron energy determination that is well suited for crystallography. Advanced features of this device include a digital centroid finding scheme, a seamless readout between segments, and a wire array design that minimizes anode modulation. Details of the mechanical design are given, together with digital centroid measurements that illustrate accurate, uniform response.

Design Considerations and Testing of Virtual Frisch-Grid CdZnTe Detector Arrays Using the H3D ASIC

We discussed the design implementation and results from testing 2 × 2-, 3 × 3-, and 2 × 4-arrays of 6×6 ×15 mm3 CdZnTe virtual Frisch-grid detectors. In these measurements we employed a data acquisition system based on the H3D ASIC developed by BNLs Instrumentation Division in collaboration with the University of Michigan for 3D position-sensitive detectors. We used CZT crystals with a range of performance attributes to evaluate practical array configurations and detector-assembling procedures. The detector ratings were assigned based on the pulse-height spectra and correlated with data from X-ray diffraction topography measurements and X-ray response mapping obtained at BNLs National Synchrotron Light Source. The results helped us to better understand the performance limits of these detectors, and to identify future improvements in the arrays design and requirements for the new readout ASIC.

Diagnostics of BNL ERL

The ERL Prototype project is currently under development at the Brookhaven National Laboratory. The ERL is expected to demonstrate energy recovery of high- intensity beams with a current of up to a few hundred milliamps, while preserving the emittance of bunches with a charge of a few nanocoulombs produced by a high- current SRF gun. To successfully accomplish this task the machine will include beam diagnostics that will be used for accurate characterization of the three dimensional beam phase space at the injection and recirculation energies, transverse and longitudinal beam matching, orbit alignment, beam current measurement, and machine protection. This paper outlines requirements on the ERL diagnostics and describes its setup and modes of operation.

LSST DETECTOR MODULE AND RAFT ASSEMBLY METROLOGY CONCEPTS.

The LSST camera focal plane array will consist of individual Si sensor modules, each 42×42mm2 in size, that are assembled into 3×3 raft structures, which are then assembled into the final focal plane array. It is our responsibility at Brookhaven National Lab (BNL) to insure that the individual sensors provided by the manufacturer meet the flatness requirement of 5 μm PV and that the assembled raft structure be within the 6.5 μm PV flatness tolerance. These tolerances must be measured with the detectors operating in a cryogenic environment at -100C in a face-down configuration. Conventional interferometric techniques for flatness testing are inadequate to insure that edge discontinuities between detector elements are within the tolerances because of the quarter-wave phase ambiguity problem. For this reason we have chosen a combination of metrology techniques to solve the discontinuity ambiguity problem that include both a full aperture interferometer and a scanning confocal distance microscope. We will discuss concepts for performing flatness metrology testing with these instruments under these conditions and will present preliminary results of measurement sensitivity and repeatability from tests performed on step height artifacts.