Multichannel Scaling Research Articles

Focus on photonics, spectrometry, and spectroscopy

Focus on photonics, spectrometry, and spectroscopy

Reactive oxygen species in photodynamic therapy

Photosensitizer-mediated production of reactive oxygen species (ROS) plays a key role in photodynamic therapy (PDT). Reactive oxygen species mainly includes singlet oxygen, hydrogen peroxide, hydroxyl radical, superoxide anion radical and so on, among which singlet oxygen is the most important reactive oxygen species. In this paper, we firstly introduce the basic property of reactive oxygen species, generation and elimination of endogenous reactive oxygen species and generation mechanism of exogenous reactive oxygen species based on light, oxygen and photosensitizer. Next, we focus on the photosensitizers used to generate reactive oxygen species, factors that affect the yield of reactive oxygen species, and methods to increase the reactive oxygen species concentration at the tumor site. There are many factors that can affect the reactive oxygen species concentration at the tumor site, mainly among which are the singlet oxygen yield of the photosensitizer, the targeting of the photosensitizer, the oxygen concentration, and the illumination frequency. To achieve a good PDT effect, many photosensitizers or their nanoparticles with high singlet oxygen generation and good targeting ability are synthesized. Perfluorocarbon is used to deliver oxygen to overcome oxygen deficiency. Upconversion nanoparticles and two-photon absorption are very useful to solve the problem of weak penetration of short-wavelength light. New PDT methods are also introduced in the text, such as PDT combined photothermal therapy or chemotherapy. Then, we summarized various methods and technologies for reactive oxygen species detection, including direct detection of phosphorescence spectrophotometry, fluorescent probes and chemical probes for indirect detection, electron spin resonance, and positron emission tomography. The direct phosphorescence method mainly detects singlet oxygen based on the 1270 nm phosphorescence emission when singlet oxygen returns to the ground state. The first method to enhance the 1270 nm phosphor signal is to use a NIR photomultiplier tube (PMT) or an InGaAs linear array in combination with scanning of the excitation laser beam, and the second one is based on the use of a NIR camera with a filter. Because the lifetime of singlet oxygen is very short, time resolution is especially important. There are basically three main photon counting techniques: gated photon counting (GPC), multichannel scaling (MCS), and time-correlated single photon counting (TCSPC). In addition, singlet oxygen-sensitized delayed fluorescence (SOSDF) can also be used to detect singlet oxygen. Various new types of probes can specifically detect different types of reactive oxygen species, for example, 9, 10-anthracenedipropionic acid and MitoSOX can be used to detect singlet oxygen and superoxide anion in living cells respectively. The fluorescent probe itself does not have fluorescence, but reacts with reactive oxygen species to form an inner oxide, and emits strong fluorescence under the excitation of a certain wavelength of light. The difference of chemical probe is that it does not require light excitation because it can emit light spontaneously after reacted with reactive oxygen species. Electrons spin resonance (ESR) and positron emission tomography (PET) are also available to detect reactive oxygen species by using a probe. Finally, we discussed the mechanism of reactive oxygen species killing tumor cells, mainly in the following three aspects: (1) direct toxicity to tumor cells and induce their necrosis, apoptosis or autophagy; (2) damage on the tumor capillary endothelial cells and destruction of the microvasculature; (3) activation of an acute inflammatory response in host defense mechanisms. The effect of reactive oxygen species on the immune system and the apoptotic pathway of tumor cells from genes, proteins to the cell level were described in detail.

A newly designed multichannel scaling system: Validated by Feynman-α experiment in EHWZPR

In this work, an embedded multi-input multi-million-channel MCS in a newly design is constructed for multi-detector experimental research applications. Important characteristics of the system are possible to be tuned based on experimental case studies utilizing the reprogrammable nature of the silicon. By means of differentiation of the integrated counts registered in memory, this system is featured as a zero channel advance time measuring tool ideal for experiments on time correlated random processes. Using this equipment, Feynman-α experiment is performed in Esfahan Heavy Water Zero Power Reactor (EHWZPR) utilizing three different in-core neutron detectors. One million channel data is collected by the system in 5ms gate time from each neutron detector simultaneously. As heavy water moderated reactors are significantly slow systems, a huge number of data channels is required to be collected. Then, by making in use of bunching method, the data is analyzed and prompt neutron decay constant of the system is estimated for each neutron detector positioned in the core. The results are compared with the information provided by endogenous pulsed neutron source experiment and a good agreement is seen within the statistical uncertainties of the results. This equipment makes further research in depth possible in a range of stochastic experiments in nuclear physics such as cross correlation analysis of multi-detector experiments.

Silicon avalanche photodiode linear-array detector with multichannel scaling system for pulsed synchrotron X-ray experiments

We developed an X-ray detector system using a 64-pixel silicon avalanche photodiode (Si-APD) linear array and fast pulse-counting electronics for multichannel scaling. The Si-APD linear array consists of 64 pixels each 100 × 200 μ m2 in size, with a pixel pitch of 150 μ m and depletion depth of 10 μ m. The fast electronics, consisting of an ultrafast application-specific integrated circuit and field-programmable gate arrays, can record both the position and timing of X-rays arriving at each pixel of the linear array with 1 ns pulse-pair resolution. The count distribution was measured using 14.4 keV synchrotron X-rays for nuclear resonant forward scattering experiments on 57Fe, and the spatial resolution was improved by inclining the detector. We also successfully measured amorphous alloy Fe78Si9B13 during heating.

Nuclear resonant scattering measurements on (57)Fe by multichannel scaling with a 64-pixel silicon avalanche photodiode linear-array detector.

We developed a silicon avalanche photodiode (Si-APD) linear-array detector for use in nuclear resonant scattering experiments using synchrotron X-rays. The Si-APD linear array consists of 64 pixels (pixel size: 100 × 200 μm(2)) with a pixel pitch of 150 μm and depletion depth of 10 μm. An ultrafast frontend circuit allows the X-ray detector to obtain a high output rate of >10(7) cps per pixel. High-performance integrated circuits achieve multichannel scaling over 1024 continuous time bins with a 1 ns resolution for each pixel without dead time. The multichannel scaling method enabled us to record a time spectrum of the 14.4 keV nuclear radiation at each pixel with a time resolution of 1.4 ns (FWHM). This method was successfully applied to nuclear forward scattering and nuclear small-angle scattering on (57)Fe.

Use of delayed gamma rays for active non-destructive assay of 235U irradiated by pulsed neutron source (plasma focus)

A pulsed neutron source based on plasma focus device has been used for active interrogation and assay of 235U by monitoring its delayed high energy γ-rays. The method involves irradiation of fissile material by thermal neutrons obtained after moderation of a burst of neutrons emitted upon fusion of deuterium in plasma focus (PF) device. The delayed gamma rays emitted from the fissile material as a consequence of induced fission were detected by a large volume sodium iodide (NaI(Tl)) detector. The detector is coupled to a data acquisition system of 2k input size with 2k ADC conversion gain. Counting was carried out in pulse height analysis mode for time integrated counts up to 100s while the temporal profile of delayed gamma has been obtained by counting in multichannel scaling mode with dwell time of 50ms. To avoid the effect of passive (natural) and active (from surrounding materials) backgrounds, counts have been acquired for gamma energy between 3 and 10MeV. The lower limit of detection of 235U in the oxide samples with this set-up is estimated to be 14mg.

A straightforward experimental method to evaluate the Lamb–Mössbauer factor of a 57Co/Rh source

In analyzing Mössbauer spectra by means of the integral transmission function, a correct evaluation of the recoilless fs factor of the source at the position of the sample is needed. A novel method to evaluate fs for a 57Co source is proposed. The method uses the standard transmission experimental set up and it does not need further measurements but the ones that are mandatory in order to center the Mössbauer line and to calibrate the Mössbauer transducer. Firstly, the background counts are evaluated by collecting a standard Multi Channel Scaling (MCS) spectrum of a tick metal iron foil absorber and two Pulse Height Analysis (PHA) spectra with the same life-time and setting the maximum velocity of the transducer at the same value of the MCS spectrum. Secondly, fs is evaluated by fitting the collected MCS spectrum throughout the integral transmission approach. A test of the suitability of the technique is presented, too.

Non-destructive assay of fissile materials through active neutron interrogation technique using pulsed neutron (plasma focus) device

Pulsed neutrons emitted from a plasma focus (PF) device have been used for the first time for the non-destructive assay of 235U content in different chemical forms (oxide and metal). The PF device generates (1.2±0.3)×109 D–D fusion neutrons per shot with a pulse width of 46±5ns. The method involves the measurement of delayed neutrons from an irradiated sample 50ms after exposure to the neutron pulse for a time of about 100s in the multichannel scaling (MCS) mode. The calibration of the active interrogation delayed neutron counter (AIDNEC) system was carried out by irradiating U3O8 samples of varying amounts (0.1–40g) containing enriched 235U (14.8%) in the device. The delayed neutrons were monitored using a bank of six 3He detectors. The sensitivity of the system was found to be about 100counts/s/g over the accumulation time of 25s per neutron pulse of ∼109. The detection limit of the system is estimated to be 18mg of 235U. The system can be suitably modified for applications toward non-destructive assay of fissile content in waste packets.

Digitally synthesized high purity, high-voltage radio frequency drive electronics for mass spectrometry

Reported herein is development of a quadrupole mass spectrometer controller (MSC) with integrated radio frequency (rf) power supply and mass spectrometer drive electronics. Advances have been made in terms of the physical size and power consumption of the MSC, while simultaneously making improvements in frequency stability, total harmonic distortion, and spectral purity. The rf power supply portion of the MSC is based on a series-resonant LC tank, where the capacitive load is the mass spectrometer itself, and the inductor is a solenoid or toroid, with various core materials. The MSC drive electronics is based on a field programmable gate array (FPGA), with serial peripheral interface for analog-to-digital and digital-to-analog converter support, and RS232/RS422 communications interfaces. The MSC offers spectral quality comparable to, or exceeding, that of conventional rf power supplies used in commercially available mass spectrometers; and as well an inherent flexibility, via the FPGA implementation, for a variety of tasks that includes proportional-integral derivative closed-loop feedback and control of rf, rf amplitude, and mass spectrometer sensitivity. Also provided are dc offsets and resonant dipole excitation for mass selective accumulation in applications involving quadrupole ion traps; rf phase locking and phase shifting for external loading of a quadrupole ion trap; and multichannel scaling of acquired mass spectra. The functionality of the MSC is task specific, and is easily modified by simply loading FPGA registers or reprogramming FPGA firmware.

Improved analysis for matrix effect correction in LLW neutronic assay

The matrix effect correction for the differential die-away (DDA) measurement is an improvement in the fissile material content determination. In low-level radioactive waste (LLW) packages examination, the most widely used methods are based on neutron flux monitoring with 3He tubes, associated to a “matrix interrogation source” (MIS) originally developed for passive neutron measurement and which determine an experimental detection efficiency. This paper describes two new approaches developed with the goal of increasing the accuracy of the matrix effect correction and reducing the measurement time, which is a major objective in the non destructive assay (NDA) of large number of waste packages. The first method is based on an active prompt neutron coincidence measurement using a new generation list mode data card, which is an alternative to the MIS. Monte Carlo simulations have been performed to determine the correction function parameters. An experimental agreement within 20% is obtained with a fissile sample localized at the centre of different matrices provided that the positioning effect remains negligible. Homogeneous distributions of the fissile material have also been simulated and lead to a deviation less than 15% for most of the cases. The second method exploits the effect of matrices on the total active signal. A simulated annealing algorithm, using a reference data base of multi-channel scaling (MCS) spectra, is performed to fit the raw signal. The construction of the MCS library involves a learning phase to define and acquire the DDA signals as representative as possible of the real measurement conditions. Most of the cases are within a 4% agreement interval with the expected experimental value.

Neutron activation experiments for bremsstrahlung characterization studies

Activation experiments were conducted to assess the bremsstrahlung continuum produced from the activation of the 7Li isotope and the subsequent short-lived 13 MeV beta decay of 8Li (T1/2 = 843 ms). The combination of the high energy beta-decay and the high atomic numbered metals used in piping for 7Li liquid metal coolants is a scenario in which bremsstrahlung production is a principal shielding concern. A series of fast pneumatic activation experiments have been performed to obtain the spectral distributions of bremsstrahlung gamma-rays transmitted through stainless steel shield samples. Detectors were used in both pulse-height and multichannel scaling analysis modes for energy spectra determination and half-life verification, respectively. Experimental results were utilized to validate the electron transport and bremsstrahlung production models used in the Monte Carlo MCNP code.

TUKAN-an 8K pulse height analyzer and multi-channel scaler with a PCI or a USB interface

In this paper we present two types of 8K-channel analyzers designed for spectroscopy and intensity versus time measurements. The first type (Tukan-8K-PCI) incorporates a PCI interface and is designed to be plugged into a PCI slot of a normal PC. The second type (Tukan-8K-USB) incorporates a USB interface. It is mounted in a separate screened box and can be powered either directly from the USB port or from an external dc source (wall adapter or battery). Each type of device may operate in either of two independent operational modes: Multi Channel Analysis (MCA) and Multi-Channel Scaling (MCS). The most crucial component for the MCA mode-the Peak Detect and Hold circuit-is featuring a novel architecture based on a diamond transistor. Its analog stage can accept analog pulses with rise times as short as 100 ns and has a differential linearity below 1% with sliding scale averaging over the full scale. The functionality includes automatic stop on a programmable count in the Region-Of-Interest (ROI) and on preset live- or real time. The MCS mode works at medium counting rates of up to 8 MHz. The dwell time, the number of channels and single or multi-sweep mode may be preset. Each of these parameters can also be controlled externally via four user configurable logical I/O lines. A single Altera FLEX 10KE30 FPGA provides all control functions and incorporates PCI interface. The USB interface is based on FTDI FIFO controller. Advanced and user-friendly software has been developed for the analyzer

Scaling Modules for the IHEP Experimental Setups

Multichannel scaling modules, which have a high response speed and meet the specific requirements of experiments conducted with the IHEP physical setups, are described. The scaling modules are made to SUMMA, MISS, and Euromechanics standards and use high-speed microcircuits of the 1500 family and programmable logic integrated circuits from Altera.

Development of MCTS technique for 3-PM liquid scintillation counting

We have developed a multi-channel time scaling method that is suitable for activity measurement of beta emitting nuclides by means of 3-PM Liquid Scintillation Counting, using non-extending dead times and linear amplifiers. Since it enables to obtain the accidental coincidences directly, the true values for both double and triple coincidences are determined by simply taking into account the correction due to dead times. The advantages of the method are demonstrated by studying the activity of 204Tl and 14C. The measured results were compared with those derived by using the mathematical formulae.

Development of a three-dimensional data acquisition method for standardization of beta-emitting nuclides

We have developed a three-dimensional data-acquisition system with which pulse heights from an array of detectors can be multi-scaled with dwell times as short as 31 ns. The main part of the system consists of three ADCs of SAR (Successive Approximation Register) type, a 32 MHz oscillation clock and DRAM (Dynamic Random Access Memory) of 192 Mbyte capacity. The clock time is determined by count the clock pulse generated by 28 bits synchronous counter. Both the pulse height and the time information are stored at an array of DRAM, of 40-bits width, 12-bits for pulse height and 28-bits for clock time. The technique is particularly suitable for experiments such as both double and triple coincidence distributions are required. Virtues of the method are demonstrated by measuring the activity of 14C with a 3-PM liquid scintillation counting system. The computer discrimination together with the MCTS (multi-channel time scaling) technique is applied for efficiency variation method in the analysis.

Subtractions of accidental coincidences and Compton scattered events by multi-channel time scaling technique in γ-ray spectrometry

The multi-channel time scaling (MCTS) technique is well suited to γ-ray spectrometry, especially for cases where both statistical and timing analysis of event distributions is required. In this paper the technique is applied to the subtraction of Compton scattered events in single γ-ray spectrums obtained using a Ge detector and NaI (Tl) gamma detector. The efficiency curve for a Ge detector was obtained with a standardized gamma emitting nuclide in the energy regions from 80 to 1300 keV by means of the Compton suppression setup. Virtues of the MCTS technique are demonstrated by estimating the photopeak intensities of γ-rays in the decay of 133Ba and 152Eu.

A single-board VME mössbauer-spectrometry module

A VME module is described to interface a mössbauer spectrometer to a computer system. It is used at the IRI mössbauer spectrometry laboratory to control 12 spectrometers. Six mössbauer modules, with additional dual ported memories, are housed in a VME-rack. Features: Generation of computer composed functions and digitizing of function-related signals, multi-channel scaling, pulse height analysis, and current integration as an optional detection technique. Functions representing a desired velocity pattern are digitally stored in the function memory. They are converted to analog using a 12-bits Digital to Analog Converter (DAC). The output of the DAC is the voltage reference for a mössbauer drive unit that drives a velocity transducer carrying a gamma radiation source. Multi-Channel Scaling (MCS) is used to measure a mössbauer spectrum. Internally a function time-base and a multi-scaler time-base are generated. A Pulse Height Analyses (PHA) facility, using a 12-bits Analog to Digital Converter (ADC), is implemented to measure the gamma spectrum of the radiation source. A mössbauer transition energy can be selected in a handsome way using this feature. An additional task of the ADC is digitizing function related signals, such as the velocity-feedback signal. If this signal is digitized, the velocity reference-function could be modified by software to correct a deviation in the source movement. For measurements with very strong gamma sources the Current Integration Technique (CIT) is implemented. Instead of a voltage to frequency-converter, formerly applied for this type of experiments, the ADC can be used for signal digitizing in this mode of operation.

Development of multichannel time scaling technique to analyse the half-life of 75mAs using correlation analysis

We report on the use of a multichannel time scaling technique suitable for determining the half-life of long-lived intermediate states by means of correlation counting. Use of the method is demonstrated by studying the decay of an isomer of at 304 keV excitation energy using a pressurized proportional counter and NaI(Tl) detection set-up. The measurement time was 9000 s. Eighteen values for electron capture detection efficiencies were obtained in the energy region 1.4-12 keV. We obtained eighteen sets of data for determining the fraction of correlation events, each set consisting of 52 counting distributions determined by scanning the clock-time of electron capture events with dwell times varying from 5 ms to 1500 ms. There are four sets acceptable for this work according to our criteria. The half-life of the 304 keV level was determined to be and is compared with earlier results.

Development of high speed multichannel scalar using line memories

A high speed multichannel scaling mode time analyzer (MCS) for time of flight (TOF) experiments was developed by using high speed serial access memories and a personal computer. The MCS was composed of two memory banks, run alternately for each trigger. The channel width of the MCS was selected from 50 ns to 200 ns (4 stage). The count per channel per trigger signal was one, but the dead time for channel advancing may approach zero. The MCS was tested with linear accelerator (linac)-TOF experiments. The results agreed satisfactorily with the design goal. It was confirmed that the high speed MCS runs normally. A small discrepancy at high energy channels between the time spectrum of the MCS and that of the time-to-pulse-height converter (TPHC)-multichannel pulse height analyzer (PHA) time analyzer was observed. One of the reasons for the discrepancy was the uncertainty of the MCS start time after the trigger signal by linac because of asynchronous crystal oscillations with the linac trigger signal.

A miniaturized ASIC-based multichannel scaler instrument

A miniaturized multichannel scaler instrument has been developed to address size and operational constraints for data acquisition in a portable laser-induced luminescence system. The multichannel scaling (MCS) function is implemented as a programmable application specific integrated circuit (ASIC) with standard interfaces for control and data-acquisition. The instrument is microcontroller-based with sufficient computing power for data manipulation and algorithmic processing. The unit includes electronics for laser control and amplification and pulse height discrimination of PMT pulses. Modification of the instrument should allow use in nuclear, chemical, and spectroscopy-related applications including Mossbauer experiments. Interfaces are incorporated allowing both computer-controlled and stand-alone operation. Implementation of the MCS function as an ASIC and comparison with conventional implementations are discussed. Full characterization of the MCS is presented including differential nonlinearity, bin dead time, and bandwidth measurements. >