R. Sia

Digital scintillation-based dosimeter-on-a-chip

A reliable, low-cost, real-time dosimeter is constructed from a scintillation crystal mounted to a CMOS solid-state photomultiplier. Determination of the minimum silicon area that can provide reliable dose information is important to minimize dosimeter cost, and allow pervasive deployment. The purpose of this paper is to examine the effect of errors from event statistics and temperature variations on the dose measured in the crystal and the calculated human equivalent dose calculated using principal component analysis (PCA). Measured spectra are written as a linear combination of the calibration data sets, or principal components, and weighting factors from the calibration data are used to calculate the human equivalent dose. Applying this method to data measured by a 1.2times1.2times 0.2-mm3 LYSO scintillator coupled to a 100-pixel SSPM allows a predicted dose sensitivity better than 1 muSv, with far less than 40% error in determination of the dose from several unknown sources outside the calibration set. The measured sensitivity is approximately 1/300 the radiation dose from natural background in one month, making possible use as a potential replacement for a monthly film badge. Statistical fluctuations, temperature-induced gain fluctuations, and number of calibration sources required are investigated with respect to the dose calculated using the PCA method.

Nuclear material detection techniques

Illicit nuclear materials represent a threat for the safety of the American citizens, and the detection and interdiction of a nuclear weapon is a national problem that has not been yet solved. Alleviating this threat represents an enormous challenge to current detection methods that have to be substantially improved to identify and discriminate threatening from benign incidents. Rugged, low-power and less-expensive radiation detectors and imagers are needed for large-scale wireless deployment. Detecting the gamma rays emitted by nuclear and fissionable materials, particularly special nuclear materials (SNM), is the most convenient way to identify and locate them. While there are detectors that have the necessary sensitivity, none are suitable to meet the present need, primarily because of the high occurrence of false alarms. The exploitation of neutron signatures represents a promising solution to detecting illicit nuclear materials. This work presents the development of several detector configurations such as a mobile active interrogation system based on a compact RF-Plasma neutron generator developed at LBNL and a fast neutron telescope that uses plastic scintillating-fibers developed at the University of New Hampshire. A human-portable improved Solid-State Neutron Detector (SSND) intended to replace pressurized 3He-tubes will be also presented. The SSND uses an ultra-compact CMOS-SSPM (Solid-State Photomultiplier) detector, developed at Radiation Monitoring devices Inc., coupled to a neutron sensitive scintillator. The detector is very fast and can provide time and spectroscopy information over a wide energy range including fast neutrons.

Integrated signal processing of CMOS Geiger photodiode arrays

Geiger photodiode (GPD) pixels convert the analog photon intensity to a digital count rate and are the basic element in solid-state photomultiplier detectors that are an emerging technology with applications in a variety of nuclear detection and imaging topics. CMOS GPD pixels simplify the integration of signal-processing electronics to enhance the performance and provide a detector-on-a-chip platform. For example, actively quenching the CMOS GPD pixels improves the response time of the pixels to accommodate large event rates and it preserves the digital nature of the binary photon signal, which can simplify the readout electronics and reduce the power consumption of the optical detector. In this work, we describe and characterize the performance of GPD pixels, with integrated active quenching, and examine the effect of active quenching on the performance of the GPD pixel. We demonstrate the integration of on-chip memory and a parallel readout interface for an array of CMOS GPD pixels as progress toward an all digital detector on a chip.

Performance of the LiF-TEA ring imaging Cherenkov detector at CLEO

We describe the particle identification capability of the CLEO RICH system. This system consists of a 1 cm thick LiF radiator coupled to a photon detector that uses wire proportional chambers filled with a mixture of CH4 and TEA. We discuss the yield of photoelectrons observed per ring and the angular resolution. We show the efficiencies achieved for particle identification and the associated fake rates from data collected with both CLEO III and CLEO-c detectors. Finally we show examples of the particle separation ability which is excellent for both CLEO III and CLEO-c data.

Geiger photodiodes for diffuse optical correlation tomography

Based on CMOS Geiger photodiode (GPD) pixels developed at RMD Inc. and fabricated with MOSIS consortium, we present a detector design that is capable of providing highspeed and single optical photon sensitivity in the near infrared region. The integration of the electronic reset with these CMOS pixels enables their use in a cost-effective large imaging array to provide a substantial increase in the signal-to-noise ratio and facilitate the high-speed, pixel-level signal processing required for photon-counting Diffuse Correlation Tomography (DCT). DCT is an imaging technique in progress that promises to provide a method for routine, non-invasive cancer screening and treatment by imaging blood flow, tissue oxygenation, and the distinct vasculature associated with the angiogenesis of cancerous growth using non-ionizing radiation. In this work, we present results of the design, fabrication and characterization of the CMOS Geiger pixels and their associated integrated reset circuits for DCT measurements.

Front end electronics and readout system for a gas radiator ring imaging Cherenkov detector using multi-anode photomultiplier tubes

We describe the design and performance of a novel custom made front end ASICs and their associated data acquisition (DAQ) system that we developed to process charge signals from an array of 53 Hamamatsu multi-anode photomultiplier tubes (MAPMTs) used as photon detectors for a ring imaging Cherenkov (RICH) detector. This system was tested as part of a gas radiator RICH prototype in the test beam facility at Fermilab. The VA MAPMT ASIC has 64 readout channels with built-in discriminator and parallel binary readout; features low noise, high dynamic range and is suitable for data driven architecture. We characterized a second iteration of this design that features higher dynamic range and optimum performance for large signals in our electronics laboratory test-setup

Neutron detectors based on CMOS solid state photomultipliers

CMOS solid-state photomultipliers (CMOS-SSPM) are new, potentially very inexpensive, photodetectors that have the promise of supplanting photomultiplier tubes and standard photodiodes for many nuclear radiation detection measurements using scintillator crystals. The compact size and very high gain make SSPMs attractive for use in applications where photomultiplier tubes cannot be used and standard photodiodes have insufficient sensitivity. In this effort, the use of SSPMs was investigated for the detection of neutrons with the goal of designing a detector for portable systems that has the capability of discriminating neutrons from gamma rays. The neutron scintillation signatures were measured using boron-loaded plastic scintillators. Our detector concept design incorporates a dual-scintillator design with both a neutrons sensitive organic scintillator (a boron-loaded gel) and a gamma ray sensitive inorganic scintillator (LYSO). Using this design, the gamma ray signal is suppressed and the neutron events are clearly resolved. The design was modeled to optimize the detection efficiency for both thermal and energetic neutrons. In addition, the detection of thermal neutrons in the presence of gamma rays was examined using the SSPM coupled to Cs2LiYCl6:Ce scintillator (CLYC).

Comparison of D{yields}K{sub S}{sup 0}{pi} and D{yields}K{sub L}{sup 0}{pi} Decay Rates

We present measurements of D{yields}K{sub S}{sup 0}{pi} and D{yields}K{sub L}{sup 0}{pi} branching fractions using 281 pb{sup -1} of {psi}(3770) data at the CLEO-c experiment. We find that B(D{sup 0}{yields}K{sub S}{sup 0}{pi}{sup 0}) is larger than B(D{sup 0}{yields}K{sub L}{sup 0}{pi}{sup 0}), with an asymmetry of R(D{sup 0})=0.108{+-}0.025{+-}0.024. For B(D{sup +}{yields}K{sub S}{sup 0}{pi}{sup +}) and B(D{sup +}{yields}K{sub L}{sup 0}{pi}{sup +}), we observe no measurable difference; the asymmetry is R(D{sup +})=0.022{+-}0.016{+-}0.018. The D{sup 0} asymmetry is consistent with the value based on the U-spin prediction A(D{sup 0}{yields}K{sup 0}{pi}{sup 0})/A(D{sup 0}{yields}K{sup 0}{pi}{sup 0})=-tan{sup 2}{theta}{sub C}, where {theta}{sub C} is the Cabibbo angle.

Measurement of the Decay Constant f{sub D{sub s}{sup +}} Using D{sub s}{sup +}{yields}l{sup +}{nu}

We measure the decay constant f{sub D{sub s}{sup +}} using the D{sub s}{sup +}{yields}l{sup +}{nu} channel, where the l{sup +} designates either a {mu}{sup +} or a {tau}{sup +}, when the {tau}{sup +}{yields}{pi}{sup +}{nu}. Using both measurements we find f{sub D{sub s}{sup +}}=274{+-}13{+-}7 MeV. Combining with our previous determination of f{sub D{sup +}}, we compute the ratio f{sub D{sub s}{sup +}}/f{sub D{sup +}}=1.23{+-}0.11{+-}0.04. We compare with theoretical estimates.

Evidence for the Decay D{sup 0}{yields}K{sup -}{pi}{sup +}{pi}{sup -}e{sup +}{nu}{sub e}

Using a 281 pb{sup -1} data sample collected at the {psi}(3770) with the CLEO-c detector, we present the first absolute branching fraction measurement of the decay D{sup 0}{yields}K{sup -}{pi}{sup +}{pi}{sup -}e{sup +}{nu}{sub e} at a statistical significance of about 4.0 standard deviations. We find 10 candidates consistent with the decay D{sup 0}{yields}K{sup -}{pi}{sup +}{pi}{sup -}e{sup +}{nu}{sub e}. The probability that a background fluctuation accounts for this signal is less than 4.1x10{sup -5}. We find B(D{sup 0}{yields}K{sup -}{pi}{sup +}{pi}{sup -}e{sup +}{nu}{sub e})=[2.8{sub -1.1}{sup +1.4}(stat){+-}0.3(syst)]x10 = {sup -4}. By restricting the invariant mass of the hadronic system to be consistent with K{sub 1}(1270), we obtain the product of branching fractions B(D{sup 0}{yields}K{sub 1}{sup -}(1270)e{sup +}{nu}{sub e})xB(K{sub 1}{sup -}(1270){yields}K{sup -}{pi}{sup +}{pi}{sup -})=[2.5{sub -1.0} = {sup +1.3}(stat){+-}0.2(syst)]x10{sup -4}. Using B(K{sub 1}{sup -}(1270){yields}K{sup -}{pi}{sup +}{pi}{sup -})=(33{+-}3)%, we obtain B(D{sup 0}{yields}K{sub 1}{sup -}(1270)e{sup +}{nu}{sub e})=[7.6{sub -3.0}{sup +4.1}(stat){+-}0.6(syst){+-}0.7] = x10{sup -4}. The last error accounts for the uncertainties in the measured K{sub 1}{sup -}(1270){yields}K{sup -}{pi}{sup +}{pi}{sup -} branching fractions.