The upgrades of ATLAS and CMS for the High Luminosity LHC (HL-LHC) highlighted physics objects timing as a tool to resolve primary interactions within a bunch crossing. Since the expected pile-up is around 200, with an r.m.s. time spread of 180 ps, a time resolution of about 30 ps is needed. The timing detectors will experience a 1-MeV neutron equivalent fluence of about Phi(eq) = 10(14) and 10(15) cm(-2) for the barrel and end-cap regions, respectively. In this contribution, deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. To improve the detector's timing performance, the APDs are used to directly detect the traversing particles, without a radiator medium where light is produced. Devices with an active area of 8 x 8 mm(2) were characterized in beam tests. The timing performance and signal properties were measured as a function of position on the detector using a beam telescope and a microchannel plate photomultiplier (MCP-PMT). Devices with an active area of 2 x 2 mm(2) were used to determine the effects of radiation damage and characterized using a ps pulsed laser. These detectors were irradiated with neutrons up to Phi(eq) = 10(15) cm(-2) .

Recent interest in pile-up mitigation through fast timing at the HL-LHC has focused attention on technologies that now achieve minimum ionising particle (MIP) time resolution of 30 picoseconds or less. The constraints of technical maturity and radiation tolerance narrowed the options in this rapidly developing field for the ATLAS and CMS upgrades to low gain avalanche detectors and silicon photomultipliers. In a variety of applications where occupancies and doses are lower, devices with pixel elements of order 1 cm(2), nevertheless achieving 30 ps, would be attractive. In this paper, deep diffused Avalanche Photo Diodes (APDs) are examined as candidate timing detectors for HL-LHC applications. Devices with an active area of 8 x 8 mm(2) are characterised using a pulsed infrared laser and, in some cases, high energy particle beams. The timing performance as well as the uniformity of response are examined. The effects of radiation damage on current, signal amplitude, noise, and timing of the APDs are evaluated using detectors with an active area of 2 x 2 mm(2). These detectors were irradiated with neutrons up to a 1-MeV neutrons fluence Phi(epsilon q) = 10(15) cm(-2). Their timing performance was characterised using a pulsed infrared laser. While a time resolution of 27 +/- 1 ps was obtained in a beam test using an 8 x 8 mm(2) sensor, the present study only demonstrates that gain loss can be compensated by increased detector bias up to fluences of Phi(epsilon q) = 6.10(13) cm(-2). So it possibly falls short of the Phi(epsilon q) = 10(14) cm(-2) requirement for the CMS barrel over the lifetime of the HL-LHC.

For their operation at the CERN High Luminosity Large Hadron Collider (HL-LHC), the ATLAS and CMS experiments are planning to implement dedicated systems to measure the time of arrival of minimum ionizing particles with an accuracy of about 30 ps. The timing detectors will be subjected to radiation levels corresponding up to a 1-MeV neutrons fluence (Φeq) of 1015 cm−2 for the goal integrated luminosity of HL-LHC of 3000 fb−1. In this paper, deep-diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. These APDs are operated at 1.8 kV, resulting in a gain of up to 500. The timing performance of the detectors is evaluated using a pulsed laser. The effects of radiation damage on current, signal amplitude, noise, and timing performance of the APDs are evaluated using detectors irradiated with neutrons up to Φeq = 1015 cm−2.

Ultraviolet detection is often required to be made in the presence of a strong background of solar radiation which needs to be suppressed, but materials limitations at these wavelengths can impact both filter and sensor performance. In this work, we explore the use of 1D photonic bandgap structures integrated directly onto a Si sensor that can operate with solar blindness. These filters take advantage of the improved admittance with silicon to significantly improve throughput over conventional stand-alone bandpass filter elements. At far ultraviolet wavelengths these filters require the use of non-absorbing dielectrics such as the metal fluoride materials of MgF2, AlF3 and LiF. The latest performance of these 1D multilayer filters on Si photodiodes and CCD imaging sensors is demonstrated. We have also extended these 1D structures to more complex multilayers guided by the design concepts of metamaterials and metatronics, and to 2D patterned plasmonic hole array filters fabricated in aluminum. The performance of sensors and test filter structures is presented with an emphasis on UV throughput.

In this paper we report on the fabrication and characterization of tin- and lead-loaded, polystyrene-based plastic scintillators for nuclear security applications. These metal-loaded plastic scintillators have been scaled up to 4 inch diameter sizes and shown to have improved gamma-ray spectroscopy, as well as fast neutron detection and spectroscopy capabilities by means of pulse shape discrimination (PSD).

•We have grown 9-Phenylcarbazole by the solution growth technique.•The largest crystals were grown from acetone.•9-Phenylcarbazole crystals have high light yields of up to 25,000 ph/MeV.•9-Phenylcarbazole crystals have excellent pulse shape discrimination with a Figure of Merit of 1.9 at 120 keVee.•Fast neutron detection was achieved using a 252Cf source.

In this work, we show that the direct integration of ultraviolet metal-dielectric filters with Si sensors can improve throughput over external filter approaches, and yield devices with UV quantum efficiencies greater than 50%, with rejection ratios of visible light greater than 10(3). In order to achieve these efficiencies, two-dimensional doping methods are used to increase the UV sensitivity of back-illuminated Si sensors. Integrated filters are then deposited by a combination of Al evaporation and atomic layer deposition of dielectric spacer layers. At far UV wavelengths these filters require the use of non-absorbing dielectrics, and we have pursued the development of new atomic layer deposition processes for metal fluorides materials of MgF2, AlF3 and LiF. The performance of the complete multilayer filters on Si photodiodes and CCD imaging sensors, and the design and fabrication challenges associated with this development are demonstrated. This includes the continued development of deep diffused silicon avalanche photodiodes designed to detect the fast 220 nm emission component of barium fluoride scintillation crystals, while optically rejecting a slower component at 300 nm.

Barium fluoride crystals are the baseline choice for the calorimeter of the Mu2e experiment at Fermilab. By the fast (decay time 0.9ns) 220nm scintillation component and discriminating against the larger slow (decay time 630ns) 300nm component, it is possible to build a radiation-hard calorimeter with good energy and time resolution and high rate capability. This requires a solid state photosensor with high quantum efficiency at 220nm, discrimination against the 300nm component and good rise and decay times. Progress on the development of such a sensor is presented.

Barium fluoride crystals are the baseline choice for the calorimeter of the Mu2e experiment at Fermilab. By utilizing the fast 220 nm scintillation component (0.9 ns decay time) and discriminating against the larger slow component at 300 nm (650 ns decay time), it is possible to build a radiation hard calorimeter with good energy and time resolution and high rate capability. This requires a solid state photosensor with high quantum efficiency at 220 nm, discrimination against the 300 nm component, and fast rise and decay times. Progress on the development of such a sensor will be discussed.

Nuclear non-proliferation applications and monitoring of special nuclear materials (SNMs) prefer low-cost detector solutions that provide efficient gamma-ray and neutron detection in combination with neutron/gamma pulse shape discrimination (PSD). Among the inorganic and organic detector choices, recently developed plastic scintillators can be fabricated in large sizes at low cost and show good neutron detection efficiency in combination with excellent neutron/gamma PSD. Unfortunately, these plastic scintillator have low density and effective Z limiting gamma-ray detection to gross counting. In this paper we report on the characterization of metal-loaded plastic scintillators that provide gamma-ray spectroscopy as well as fast neutron detection, whereby discrimination between gamma-rays and neutrons is accomplished using pulse shape analysis. In particular, we report on the investigations of tin-, bismuth-, and lead-loaded plastic scintillators for nuclear non-proliferation.

The scintillation properties of a novel plastic scintillator loaded with an organolead compound are presented. Under X-ray and gamma-ray excitation, emission is observed peaking at 435nm. The scintillation light output is 9000ph/MeV. An energy resolution (full width at half maximum over the peak position) of about 16% was observed for the 662keV full absorption peak. Excellent pulse shape discrimination between neutrons and gamma-rays with a Figure of Merit of 2.6 at 1MeVee was observed.

Avalanche photodiodes (APD) manufactured at RMD are fabricated using deep diffusion processes, resulting in a thick reach-through APD with excellent performance characteristics. These include a high quantum efficiency (>50% for visible photons) and low excess noise (F similar to 2). Due to the structure of the APD, the devices have very low junction capacitance (similar to 0.7pF/mm(2)). These devices have been made as squares or hexagons on the order of 2-4" dimensionally and require >1000 V for operation. Due to the high operating bias, studies on the Geiger behavior were dismissed. The low capacitance is conducive to developing large-area devices, and the large drift region allows for charge steering toward the high breakdown field region. These results provide initial data on the performance characteristics of RMD's APDs when operated in Geiger mode. Due to the thickness of these devices, they provide a high gain-bandwidth product for near IR single photon counting. A small area (similar to 4 mm(2)) APD was biased beyond the reverse bias breakdown voltage (similar to 700 V at -50 C), where the device showed typical Geiger-mode behavior with a low dark count rate (<54 kHz at 1700 V at an excess bias of 3 V). The data indicates a uniform response over the diode region, yet due to the large dark currents, the device was only operated to 5 V in excess bias beyond the breakdown voltage. The Geiger probability at 5V excess bias was measured as 3%, which is consistent with simulations that suggest an excess bias of similar to 300 V is required for 100% Geiger probability.

In this paper we review the physics and performance of silicon detectors passivated with wafer-scale molecular beam epitaxy (MBE) and atomic layer deposition (ALD). MBE growth of a two-dimensional (2D) doping superlattice on backside-illuminated (BSI) detectors provides nearly perfect protection from interface traps, even at trap densities in excess of 10(14) cm(-2). Superlattice-doped, BSI CMOS imaging detectors show no measurable degradation of quantum efficiency or dark current from long-term exposure to pulsed DUV lasers. Wafer-scale superlattice-doping has been used to passivate CMOS and CCD imaging arrays, fully-depleted CCDs and photodiodes, and large-area avalanche photodiodes. Superlattice-doped CCDs with ALD-grown antireflection coatings achieved world record quantum efficiency at deep and far ultraviolet wavelengths (100-300nm). Recently we have demonstrated solar-blind, superlattice doped avalanche photodiodes using integrated metal-dielectric coatings to achieve selective detection of ultraviolet light in the 200-250 nm spectral range with high out-of-band rejection.

We present an analysis of the signal properties of a position-sensitive solid-state photomultiplier (PS-SSPM) that has an integrated resistive network for position sensing. Attractive features of PS-SSPMs are their large area and ability to resolve small scintillator crystals. However, the large area leads to a high detector capacitance, and in order to achieve high spatial resolution a large network resistor value is required. These inevitably create a low-pass filter that drastically slows what would be a fast micro-cell discharge pulse. Significant changes in the signal shape of the PS-SSPM cathode output as a function of position are observed, which result in a position-dependent time delay when using traditional time pick-off methods such as leading edge discrimination and constant fraction discrimination. The timing resolution and time delay, as a function of position, were characterized for two different PS-SSPM designs, a continuous 10 mm ×10 mm PS-SSPM and a tiled 2 ×2 array of 5 mm ×5 mm PS-SSPMs. After time delay correction, the block timing resolution, measured with a 6 ×6 array of 1.3 ×1.3 ×20 mm 3 LSO crystals, was 8.6 ns and 8.5 ns, with the 10 mm PS-SSPM and 5 mm PS-SSPM respectively. The effect of crystal size on timing resolution was also studied, and contrary to expectation, a small improvement was measured when reducing the crystal size from 1.3 mm to 0.5 mm. Digital timing methods were studied and showed great promise for allowing accurate timing by implementation of a leading edge time pick-off. Position-dependent changes in signal shape on the anode side also are present, which complicates peak height data acquisition methods used for positioning. We studied the effect of trigger position on signal amplitude, flood histogram quality, and depth-of-interaction resolution in a dual-ended readout detector configuration. We conclude that detector timing and positioning can be significantly improved by implementation of digital timing methods and by accounting for changes in the shape of the signals from PS-SSPMs.

A TOC scintillator material, lanthanum yttrium oxide ((La,Y)2O3) has been investigated at RMD. The X-ray excited emission shows a broad band that peaks at ~ 415 nm, originating from the host lattice. Under gamma-ray excitation the emission decays with a fast time constant of ~ 17 ns, and multiple slower components. The temperature dependence of LYO was studied in the -30°C to +50°C range. The relative light output decreases with the increase in the temperature, whereas, the energy resolution was observed to be fairly constant. The scintillation light yield of the material estimated by a comparison with a BGO single crystal is ~21,000 photons/MeV. Energy resolution of 4.9% at 662keV (FWHM) was also measured. The composition shows good proportionality in the 60 keV to 1275 keV energy range, with only ~ 2% deviation from the linear response at 60 keV. The scintillation properties will be further improved by optimization of La concentration and optical quality of the ceramics. The material is not hygroscopic and scale up to large sizes is possible due to cubic structure of Y2O3. Overall, LYO seems to be a very promising material for gamma-ray spectroscopy.

He-3 tubes are the most popular thermal neutron detectors. They are easy to use, have good sensitivity for neutron detection, and are insensitive to gamma radiation. Due to low stockpiles of the He-3 gas, alternatives are being sought to replace these devices in many applications. One of the possible alternatives to these devices are scintillators incorporating isotopes with high cross-section for neutron capture (e. g. Li-6 or B-10). Cs2LiYCl(6): Ce (CLYC) is one of the scintillators that recently has been considered for neutron detection. This material offers good detection efficiency (similar to 80%), bright response (70,000 photons/neutron), high gamma ray equivalent energy of the neutron signal (>3MeV), and excellent separation between gamma and neutron radiation with pulse shape discrimination. A He-3 tube alternative based on a CLYC scintillator was constructed using a silicon photomultiplier (SiPM) for the optical readout. SiPMs are very compact optical detectors that are an alternative to usually bulky photomultiplier tubes. Constructed detector was characterized for its behavior across a temperature range of -20 degrees C to 50 degrees C.