Analog Pulse Shape Discrimination Based on Time Duration and Pulse Height

Pulse shape discrimination is a name of a group of techniques used to detect and distinguish between different types of radiation interactions. Analog pulse shape discrimination methods can be more suitable than digital methods, for high-speed scintillators both from rate and power consumption perspectives. Common analog discrimination methods are based on pulse-height and pulse-energy discrimination techniques. Other techniques rely on the time difference in the pulse width such as the ZeroCrossing methods. Neither of the above combine both amplitude and time methods. We present a novel analog pulse shape discrimination topology that combines both height and time domain. The topology is based on discrimination according to the pulse duration in time combined with compensation function of the pulse height. Amplitude of the pulse is used as a restraining factor. Subsequently, our topology correctly identifies fast pulses that are prolonged in time due to their high amplitude. The topology yields superior discrimination capabilities, under degraded light collection conditions, with an uncertainty gap smaller than 1 ns in pulse width. The ability to control both the time and the amplitude parameters individually, provides tailored adjustment for various detectors and pulse shape discrimination applications

Improving Activity Estimation in Passive Gamma Scanning for Radioactive Waste Drums

A method to improve radioactive waste drum activity estimation in Segmented Gamma Scanning (SGS) systems was developed for homogenous content. We describe a method to quantify the activity of spatially distributed gamma-emitting isotopes (‘hot spots’) in homogenous content waste drums without the use of a collimator. Instead of averaging all the detector's readings we treat it as many different spatial samples as if we have multiple detectors surrounding the waste drum ("virtual detectors"). From these readings, we form a general linear model. Next, we derive the Maximum Likelihood Estimator (MLE) for the multiple sources position and activity. We solve this hyper-dimensional search problem using an Alternating Projections (AP) technique which transforms the problem into a simpler one-dimensional maximization problem. We tested this method using a mathematical simulation with a various number of sources, at random activities and positions for several energy bands. The preliminary results are consistent and show large improvement of the accuracy with comparison to industrial SGS systems and the same accuracy as new methods which exploits the spatial samples. Furthermore, since this method eliminates the need for heavy led collimator, none of the sources is blocked for the whole measurement period, which provides increased count rates and decreases the total measurement time

Improving Activity Estimation in Passive Gamma Scanning for Radioactive Waste Drums

A method to improve radioactive waste drum activity estimation in Segmented Gamma Scanning (SGS) systems was developed for homogenous content. We describe a method to quantify the activity of spatially distributed gamma-emitting isotopes (‘hot spots’) in homogenous content waste drums without the use of a collimator. Instead of averaging all the detector's readings we treat it as many different spatial samples as if we have multiple detectors surrounding the waste drum ("virtual detectors"). From these readings, we form a general linear model. Next, we derive the Maximum Likelihood Estimator (MLE) for the multiple sources position and activity. We solve this hyper-dimensional search problem using an Alternating Projections (AP) technique which transforms the problem into a simpler one-dimensional maximization problem. We tested this method using a mathematical simulation with a various number of sources, at random activities and positions for several energy bands. The preliminary results are consistent and show large improvement of the accuracy with comparison to industrial SGS systems and the same accuracy as new methods which exploits the spatial samples. Furthermore, since this method eliminates the need for heavy led collimator, none of the sources is blocked for the whole measurement period, which provides increased count rates and decreases the total measurement time

Design of 4π Directional Radiation Detector based on Compton Scattering Effect

Obtaining directional information is required in many applications such as nuclear homeland security, contamination mapping after a nuclear incident and radiological events, or during the decontamination work. However, many directional radiation detectors are based on directional shielding, made of lead or tungsten collimators, introducing two main drawbacks. The first is the size and weight, making those detectors too heavy and irrelevant for utilization in handheld devices, drone mapping, or space applications. The second drawback is the limited field of view, which requires multiple detectors to cover the whole required field of view or machinery to rotate the narrow field of view detector. We propose a novel 4π directional detector based on a segmented hollow cubic detector, which uses the Compton effect interactions with no heavy collimators. The symmetrical cubical design provides both higher efficiency and 4π detection ability. Instead of traditional two types of detectors (scatterer and absorber) structure, we use the same type of detector, based on GAGG(Ce) scintillator coupled to silicon photomultiplier. Additional advantage of the proposed detector obtained by locating the photon sensors inside the detector, behind the scintillators, which improves the radiation hardness required for space applications. Furthermore, such arrangement flattens the temperature variation across the detector, providing better gain stability. The main advantage of the proposed detector is the ability of 4pi radiation detection for high energy gamma-rays without the use of heavy collimators

Stikstofbemesting bij andijvie : startgiften en bijbemesting

Er is onderzocht of bij de teelt van andijvie er een verschil in opbrengsteffect was bij het geven van een stikstofstartgift of -bemesting 3 weken na planten

Spectral Enhancement of a SiPM Array-Based Radiation Detector

Silicon Photomultipliers (SiPMs) have many advantages when used in radiation detectors. Low bias voltage, compactness and immunity to electromagnetic interference are among their prominent benefits. However, due to their small size, usually an array of SiPM components is required in order to cover the coupling surface area of a scintillator. Since the SiPM is a semiconductor, biased in a reversed voltage, gain variation and strong temperature dependence are introduced. As a result, SiPM-based detectors, particularly an array of SiPMs, undergo spectral signal to noise ratio reduction. This work studies the effect of the SiPM breakdown voltage variation on the obtained energy spectrum and proposes an electronic approach to overcome this technological drawback. This developed technology provides an adequate temperature-dependent, commonly distributed high bias voltage and an individual offset-voltage fine tuning that enables adjustment of all the SiPM components to their optimum operating points. Powerwise it is beneficial to operate SiPM at lower voltages, where undesirable gain variation is more dominant. The proposed solution enables working at lower bias voltages, which provides lower power consumption and better radiation hardness, while yielding an enhanced spectrum resolution. The proposed electronic approach enhances the obtained spectra, reducing the noise threshold by 16 % when working at 1 V overvoltage. Hence provides an enhanced signal to noise ratio over the traditional biasing methods