A high spatial resolution event counting neutron detector using microchannel plates and cross delay line readout

Improved efficiency of high resolution thermal and cold neutron imaging

Experimental study of spatial resolution of MCPs for compact high-resolution neutron radiography system

We describe the design and report on the experimental results of a novel thermal and cold neutron imaging detector utilizing neutron sensitive (10B-doped) microchannel plates (MCPs). In this detector, the incoming neutron interaction products produce secondary electrons at the pores adjacent to the absorption point within the MCP glass. This electron signal is then multiplied by a stack of conventional MCPs within those adjacent pores limiting the spread of the signal to less than two pore diameters (currently 6-10 mum pores on 8-12 mum centers). The event position then can be encoded by a number of readout techniques already developed for photon/charged particle counting applications. This paper presents the results of experimental evaluation of neutron sensing MCP detector with Medipix2 readout allowing operation at high counting rate mode (>100 MHz level) at a spatial resolution limited by the 55 mum pixel size of the Medipix2 readout. Other attractive features of MCP neutron detectors are their high detection efficiency (approaching 50% levels) for thermal and cold neutrons and the absence of readout noise.

At Los Alamos National Laboratory we are developing a new imaging sensor which combines high spatial and high temporal resolution over a large area format, while maintaining single-photon counting sensitivity and sustaining a high count rate. The detector is called a microchannel plate with crossed delay line readout, or MCP/CDL. This detector is ideally suited to the observation of weak transient events, such as stellar flares from red dwarf flare stars in our Galaxy. At present we are initiating an experiment with the MCP/CDL detector which will utilize a 30-cm aperture f/7 telescope to characterize U-band, B-band, and V-band emission from such low-luminosity flare stars, and to search for weak optical transients associated with other astrophysical sources.

Sealed tube MCP detectors have provided a valuable platform for high spatial resolution photon counting detectors. Specifically, electronic readout microchannel plate (MCP) based sensors have been used as photon counting, imaging, event time tagging detectors for astronomy, time resolved biological imaging, imaging LIDAR, Cherenkov (RICH), scintillation detection, and neutron imaging [1]–[10]. For future applications we have been developing novel atomic layer deposited MCPs, UV optimized photocathodes and high resolution cross strip readouts for sealed tube detectors. The Photonis Planacon is a useful sealed detector format (~50 mm square active area) to employ and demonstrate these novel technologies. The Planacon standard geometry has been used, but the standard anode pad array is replaced with a cross strip anode that demonstrates ~20 µm FWHM spatial resolution for single photon events at electron gains of the order 106. Atomic layer deposited MCPs with 10µm pores have been used in place of conventional MCPs, providing tight pulse amplitude distributions, enhanced gain stability and reduced gamma ray sensitivity. The entrance window (Sapphire or MgF2) permits the high UV sensitivity of bialkali photocathodes (>30% @180nm) to be utilized. Event encoding electronics implemented in surface mount components also provides high resolution imaging at event rates of up to 5 MHz. ASIC versions of the encoding electronics are in the prototype phase and show considerable promise for enhanced performance with lower power and smaller footprints.

The Cosmic Origins Spectrograph (COS) was installed on the Hubble Space Telescope (HST) in May 2009 during Servicing Mission 4 (SM4). This paper discusses the initial on-orbit performance of the HST-COS far ultraviolet (FUV) detector designed and built by the Experimental Astrophysics Group at the Univ. of California, Berkeley. The HST-COS FUV detector is an open face, photon counting, microchannel plate (MCP) based device employing a cross delay line (XDL) readout. The detector consists of two separate, end-to-end segments (2x 85mm x 10mm - 179mm x 10mm total with a gap between segments), each digitized within a 16384x1024 space. The input surface is curved to match the Rowland circle of HST-COS. The CsI photocathode and open face nature result in sensitivity from <900Å to ~1750Å. Spatial resolution is approximately 25-30μm. Comparisons of on-orbit behavior relative to expectations from ground testing are performed. Areas of discussion include background (rate and morphology), sensitivity (system throughput and short wavelength response), and imaging performance (apparent spatial resolution and flat field fixed pattern). A measured increase in the MCP gain relative to ground testing is also discussed.

Detection efficiency, spatial and timing resolution of thermal and cold neutron counting MCP detectors

Neutron radiography plays an important role in the development of safer and more efficient nuclear power plants by providing valuable information for the irradiated nuclear fuel, nuclear waste containers and other critical components. Neutron sensitive microchannel plate (nMCP) doped with boron and gadolinium is a popular neutron imaging detector. It has been successfully employed in neutron resonances imaging of irradiated nuclear fuel, providing the possibility in mapping the elemental composition of reactor components. However, the exiting of gadolinium in nMCP degrades the spatial resolution and neutron-gamma discrimination capability, because of the long range and low energy deposition of the electrons generated by gadolinium. nMCP doped with boron has advantages on spatial resolution and neutron-gamma discrimination capability. In this paper, performances of boron doped nMCP were studied. According to the simulation, the theoretical detection efficiency of nMCP doped with 20mol% 10B2O3 could reach 34%, and the spatial resolution can be close to the pore size at the same time. Moreover, it is expected to achieve good neutron-gamma discrimination ability. The detection efficiency for nMCP which doped with 10mol% natB2O3 was experimented detailly at CSNS. Results show that the detection efficiency is 4.55% for 2.9 Å neutron and 7.26% for 4.8 Å neutron, which agrees well with simulation results. These results indicate that the excellent performance of boron doped nMCP is possible to be achieved. In the future, nMCP doped with 20mol% 10B2O3 will be fabricated and it will be a promising scheme for the application of neutron radiography in nuclear reactors.

The microchannel plate, delay line, detectors developed for the far ultraviolet spectroscopic explorer mission to be launched in 1998 are described. The two FUSE detectors have a large format (approximately equals 184 mm by 10 mm split into two 88.5 by 10 mm segments), with high spatial resolution (less than 20 micrometers by 50 micrometers FWHM, greater than 9000 by 200 resolution elements) and good linearity (plus or minus 25 micrometers), high image stability, and counting rates in excess of 4 by 10<SUP>4</SUP> events sec<SUP>-1</SUP>. KBr opaque photocathodes have been employed to provide quantum detection efficiencies of 30 - 40% in the 900 - 1200 angstrom range. Microchannel plates with 10 micrometer pores and an 80:1 pore length to diameter ratio, with a 95 mm by 20 mm format have been used in a Z stack configuration to provide the photon amplification (gain approximately equals 2 by 10<SUP>7</SUP>). These show narrow pulse height distributions (less than 35% FWHM) even with uniform flood illumination, and good background levels (less than 0.3 event cm<SUP>-2</SUP>sec<SUP>-1</SUP>). Flat field images are demanded by the microchannel plate multifiber boundary fixed pattern noise and are stable.

ALD-GCA-MCPs are a technology advancement that affords microchannel plates (MCPs) with significant performance benefits compared to conventional MCP technology. Incom now routinely produces ALD-GCA-MCPs with dimensions up to 20 cm x 20 cm. Notable advancements and benefits over conventional lead-oxide based MCPs are larger size and higher mechanical stability, high and stable gain (>1e4for single MCP @ 1000 V, stable gain to ≥ 1 C/cm2 extracted charge), low dark counts (≤ 0.05 cts/sec/cm2), ~3x lower gamma-ray sensitivity, and the unique ability to individually customize and control the MCP resistance and secondary electron emission (SEE) amplification characteristics. ALD-GCA-MCPs find application in a variety of photon and charged particle counting applications and are particularly suited for applications that require fast timing, high spatial resolution, radiation hardness, and long detector life times, such as Ion-TOF, electron spectroscopies, and a variety of other analytical instruments. They can also be incorporated into low-power, low-background photodetectors suitable for applications in extreme environments such as remote sensing applications in rugged environments, in space flight instrumentation, as well as in high-energy physics and nuclear physics experiments. In this paper we will provide a brief ALD-GCA-MCP technology overview highlighting recent developments that focused on improving the glass capillary array (GCA) substrate, and their implications for large-area photodetectors and spectrometers used in nuclear and high energy physics, space science, and other sensing applications.

High-resolution UV, alpha and neutron imaging with the Timepix CMOS readout

Microchannel plate based detectors are widely used for photon counting spectroscopy and imaging in astronomical, high energy physics and remote sensing applications^1-15. We present progress in the development of imaging cross strip readout detectors using novel microchannel plates functionalized by atomic layer deposition (ALD). ALD microchannel plates have established formats of 10 cm with 10 μm pore sizes and 20 cm with 20 μm pores. ALD MCPs show with high quantum efficiency (&gt;50% @115 nm) using opaque alkali halide photocathodes and very low background levels (0.05 events cm^-2) have been achieved. Readout systems have also evolved and now cross-strip anodes and encoding electronics enable high spatial resolution (&lt;20 μm) at low gain (10⁶) and over large formats (10 cm) with high dynamic range (&gt;5 MHz). These characteristics are essential for UV instrument concepts currently under study for NASA including the Large UV/Optical/IR Surveyor (LUVOIR)¹⁶, the Habitable Exoplanet Imaging Mission (HABEX)¹⁶, and Cosmic Evolution Through UV Spectroscopy (CETUS)¹⁶.

We have implemented cross strip readout microchannel plate detectors in 18 mm active area format including open face (UV/particle) and sealed tube (optical) configurations. These have been tested with a field programmable gate array based parallel channel electronics for event encoding which can process high input event rates (> 5 MHz) with high spatial resolution. Using small pore MCPs (6 μm) operated in a pair, we achieve gains of >5 x 10 5 which is sufficient to provide spatial resolution of <35 μm FHWM, with self triggered event timing accuracy of ~2 ns for sealed tube optical sensors. A peak quantum efficiency of ~19% at 500 nm has been achieved with SuperGenII photocathodes that have response over the 400 nm to 900 nm range. Local area counting rates of up to >200 events/mcp pore sec -1 have been attained, along with image linearity and stability to better than 50 μm.

과학위성 1호의 주탑재체인 원자외선 분광기의 검출기 전자부에 대한 특성을 분석하였다. FIMS (Far-ultraviolet Imaging Spectrograph)는 교차 지연선 양극을 가진 MCP(micro-channel plate)를 사용하여 입사된 원자외선 광자의 위치를 검출한다. MCP에 입사하는 광자는 MCP을 통해 전자형태로 변환되고 증폭된다. 증폭된 전하운의 중심은 양분되어 연결된 지연선을 통해 양단으로 나가게 되고, 지연선의 양단에서 전하운의 도착시간 차이를 구하여 입사된 광자의 위치를 판독한다. FIMS의 경우 2개의 MCP 검출기를 갖고 있으며, 각각 25mm<TEX>$\times$</TEX>25mm의 유효 크기를 갖고있다. 또 신호처리계는 1채널의 신호처리 회로계를 통해 2개의 검출기에 대한 영상검출이 가능하도록 함으로써 신호처리계의 복잡성을 피하고 아울러 전력과 무게 비용을 줄였다. 이 시스템을 통해 높은 시간 및 공간 분해능(<<TEX>$35{\times}75$</TEX>ps FWHM)을 얻었으며, 6W 이하의 저전력 시스템을 구현하였다. We describe some performance of the detector electronics system for the FIMS (Far-ultraviolet Imaging Spectrograph) mission. The FIMS mission to map the far ultraviolet sky uses MCP (micro-channel plate) detectors with a crossed delay line anode to record photon arrival events. FIMS has two MCP detectors, each with a ~25mm<TEX>$\times$</TEX>25mm active area. The unconventional anode design allows for the use of a single set of position encoding electronics for both detector fields. The centroid position of the charge cloud, generated by the photon-stimulated MCP, is determined by measuring the arrival times at both ends of the anode following amplification and external delay. The temporal response of the detector electronics system determines the readout's positional resolution for the charge centroid. High temporal resolution (<<TEX>$35{\times}75$</TEX>ps FWHM) and low power consumption (< 6W) were achieved for the FIMS detector electronics system.

Weather radar networks are an excellent tool for quantitative precipitation estimation (QPE), due to their high resolution in space and time, particularly in remote mountain areas such as the Tropical Andes. Nevertheless, reduction of the temporal and spatial resolution might severely reduce the quality of QPE. Thus, the main objective of this study was to analyze the impact of spatial and temporal resolutions of radar data on the cumulative QPE. For this, data from the world’s highest X-band weather radar (4450 m a.s.l.), located in the Andes of Ecuador (Paute River basin), and from a rain gauge network were used. Different time resolutions (1, 5, 10, 15, 20, 30, and 60 min) and spatial resolutions (0.5, 0.25, and 0.1 km) were evaluated. An optical flow method was validated for 11 rainfall events (with different features) and applied to enhance the temporal resolution of radar data to 1-min intervals. The results show that 1-min temporal resolution images are able to capture rain event features in detail. The radar–rain gauge correlation decreases considerably when the time resolution increases (r from 0.69 to 0.31, time resolution from 1 to 60 min). No significant difference was found in the rain total volume (3%) calculated with the three spatial resolution data. A spatial resolution of 0.5 km on radar imagery is suitable to quantify rainfall in the Andes Mountains. This study improves knowledge on rainfall spatial distribution in the Ecuadorian Andes, and it will be the basis for future hydrometeorological studies.