J. Harder

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.

Construction and expected performance of the hadron blind detector for the PHENIX experiment at RHIC

A new hadron blind detector (HBD) for electron identification in high density hadron environment has been installed in the PHENIX experiment at RHIC in the fall of 2006. The HBD will identify low momentum electron-positron pairs to reduce the combinatorial background in the e + e - mass spectrum, mainly in the region below 1 GeV/c 2 . The HBD is a windowless proximity-focusing Cherenkov detector with a radiator length of 50 cm, a CsI photocathode and three layers of gas electron multipliers (GEM). Pure CF 4 is used as a radiator and a detector gas. This proceeding describes the construction details and the expected performance of the HBD.

High rate, high resolution, two-dimensional gas proportional detectors for X-ray synchrotron radiation experiments

Two-dimensional, gas proportional detectors are being developed for use with X-ray synchrotron radiation. Two new types of interpolating cathode structures have been investigated, both of which can operate with a significantly smaller number of readout nodes along each sensing axis than previous cathodes. Lumped parameter delay lines are used as the position encoders. Timing signals from fast, low noise shaping electronics are fed to a new, dual TDC system developed for this purpose. Operating with a clock frequency of 500 MHz, the TDCs have an intrinsic differential non-linearity of 0.1%. The complete system can handle X-ray fluxes in excess of 10{sup 6} per sec without distortion of the position information. A resolution of approximately 100 {mu}m FWHM and differenfial non-linearity of {plus minus}4% have been achieved. Application of a detector with active area 10 cm {times} 10 cm using synchrotron radiation is described.

Front-end electronics for high rate, position sensitive neutron detectors ☆

Advanced neutron detectors for experiments at new spallation sources will require greater counting rate capabilities than previously attainable. This necessitates careful design of both detector and readout electronics. As part of a new instrument for protein crystallography at LANSCE, we are constructing a detector whose concept was described previously (IEEE Trans. Nucl. Sci. NS-46 (1999) 1916). Here, we describe the signal processing circuit, which is well suited for 3He detectors with a continuous interpolating readout. The circuit is based on standard charge preamplification, transmission of this signal over 20 meters or so, followed by sample and hold using a second order gated baseline restorer. This latter unit provides high rate capability without requiring pole-zero and tail cancellation circuits. There is also provision for gain-adjustment. The circuits are produced in surface mounted technology.

A fast time-to-digital converter for position-sensitive radiation detectors with delay line readouts

Abstract A fast time-to-digital converter (TDC) has been developed for use with position-sensitive radiation detectors having delay line readouts. The device is recommended for detector applications where high position resolution and low distortion are required at high rates. The device has 2 ns time resolution, less than 0.1% differential nonlinearity, and a recovery time of 70 ns. When used with a detector system having a delay line of temporal length τ, the following performance has been achieved: (1) a position digitization of 1 position resolution element per ns of delay line; (2) an average dead time of ( 3 4 τ+70) ns ; (3) a maximum incident radiation rate of ⋍ 4 τ ; and (4) a maximum conversion rate of ⋍ 1 (3τ) . Discriminator circuits reduce pile-up distortion to neglible levels for rates as high as those listed above. Finally, two converters may be connected together for synchronous operation as required by 2-dimensional ( x - y ) detectors.

Prototype Tests and Construction of the Hadron Blind Detector for the PHENIX Experiment

A Hadron Blind Detector (HBD) has been constructed as part of the detector upgrade program for the PHENIX experiment at RHIC. The HBD is a proximity focused windowless Cherenkov detector operated with pure CF4 that will be used to detect single and double electrons in relativistic heavy ion collisions and provide additional rejection power against Dalitz pairs and photon conversions. The detector consists of a 50 cm long radiator directly coupled to a set of triple GEM detectors equipped with CsI photocathodes to detect UV photons produced by electrons emitting Cherenkov light. A full scale prototype of the HBD was built and tested in order to study its performance under beam conditions. Tests with the prototype demonstrated good separation between electrons and hadrons using pulse height discrimination and cluster size. The final detector has now been constructed and installed in PHENIX and is presently undergoing commissioning in preparation for its first round of data taking during the next heavy ion run at RHIC. Results of the beam test of the prototype, as well as on the construction and initial testing of the final detector, are presented in this paper.

The PHENIX Time Expansion Chamber

Abstract The TEC/TRD subsystem will track all charged particles and contribute to the particle identification by the measurement of energy loss. The design, construction and testing of the TEC chambers are described.

A hadron blind detector for the PHENIX experiment at RHIC

A hadron blind detector (HBD) is being developed for an upgrade of the PHENIX experiment at RHIC. The HBD is a windowless Cherenkov detector, operated with pure CF/sub 4/ in a special proximity focus configuration. The detector consists of a 50 cm long radiator, directly coupled to a triple GEM detector which has a CsI photocathode evaporated on the top surface of the uppermost GEM foil, and a pad readout at the bottom of the GEM stack. Detailed studies of the detector performance, including hadron rejection, figure of merit, N/sub 0/, number of photoelectrons and efficiency are presented. These studies include measurements performed with a UV lamp, an /sup 55/Fe X-ray source and an /sup 241/Am alpha source. Results will also be given on aging studies of the GEM foils and the CsI photocathode in pure CF/sub 4/.

A faster digitizer system for the Hadron Blind Detector in PHENIX

A Hadron Blind Detector (HBD) has been installed in the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). A 2300 channel compact 12-bit 60 MHz digitizer system has been built to read the HBD system. The raw signals are shaped with 70 ns rise time and are directly digitized. The time and charge of the raw signals can be calculated from the multiple samples. The system is designed to handle Level 1 (L1) trigger rates up to 25 kHz with 5 L1 event buffers. Large amounts of data are generated after the ADC. Issues regarding clock distribution, data handling, event buffers, and L1 trigger primitive generations have been addressed. The overall system performance will also be discussed.

Detectors for High Photon Rates

The increasing flux of photons available from synchrotron radiation sources requires x-ray detectors with greater and greater range in the counting rate capability. Dynamic studies of biological systems in which structural changes can be observed on a short time scale are of particular interest. No detector at present comes close to satisfying all the requirements simultaneously, such as counting rate capability, large dynamic range, high quantum efficiency over a wide range of energies, high position resolution, fast gating and consecutive time-slicing capability. Each detection principle developed so far has some good properties and some serious limitations, and the only practical approach for the near future is to find the best compromise for a particular experiment of interest. For example, some interesting detectors have a sufficiently large number of position elements (pixels) and can operate at high counting rates, but have a limited dynamic range and a long readout time. Thus consecutive time-slicing is not possible, and repetitive excitation and exposures of the sample are necessary.