EP3224652A1

EP3224652A1 - Scintillation detector with a high count rate

Info

Publication number: EP3224652A1
Application number: EP15785083.5A
Authority: EP
Inventors: Sebastian Jaksch; Henrich Frielinghaus; Ralf Engels; Günter KEMMERLING; Kalliopi KANAKI; Richard HALL-WILTON; Sylvain DÉSERT; Codin GHEORGHE
Original assignee: Forschungszentrum Juelich GmbH; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA; Integrated Detector Electronics As; Legal Division European Spallation Source Eric
Current assignee: Integrated Detector Electronics As; Legal Division European Spallation Source Eric; Forschungszentrum Juelich GmbH; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2014-11-28
Filing date: 2015-10-20
Publication date: 2017-10-04
Also published as: US10451750B2; CN107003418A; DE102014224449A1; WO2016083021A1; US20170329027A1; JP2018505421A; JP6733962B2

Abstract

The invention relates to a scintillation detector with which high count rates and/or high resolutions can be achieved. The scintillator of the claimed scintillation detector is formed from pixels (2) separated from one another by intermediate spaces (4). Alternatively, or additionally, the surface of said scintillator is divided, by grooves, into pixels (2). Such a structure allows not just a particularly high resolution; when using multiple modules it also allows high count rates in the range of approximately 20 MHz.

Description

Scintillation detector with high count rate

The invention relates to a scintillation detector, in particular for neutrons.

A scintillation detector is a scintillation-based measuring device for determining the energy, intensity and position of ionizing radiation. In the scintillator of a scintillation detector, light pulses are generated by incident ionizing radiation, the number of which depends on the energy of the incident radiation. These very weak flashes of light release electrons from a photocathode behind a mounted photomultiplier. These electrons are multiplied by collisions at the electrodes in the photomultiplier. At the anode then a current pulse can be removed, the amplitude of which depends on the energy of the incident radiation. Instead of a photomultiplier, a photodiode can also be used.

A scintillation detector can be used to measure alpha, beta, gamma or neutron radiation, depending on the scintillator. Thallium-doped sodium iodide, lanthanum chloride or cesium iodide are suitable as scintillators, for example. A scintillation detector for neutrons with a scintillator comprising ⁶ Li is known from document EP 2631676 A1.

A neutron scintillation detector with a one square meter scintillator surface is currently limited to a count rate of a few hundred kHz to about 1 MHz. In addition, the achievable resolution, minimal to about 8 mm in each direction, associated with a high calculation effort during the measurement, since this resolution is possible only by interpolation on the Anger principle. The maintenance and repair of such a scintillation detector are relatively expensive. Achievable geometries are relatively limited. In the area of a primary beam scintillation detectors must be protected by a shield.

Alternatively, gas detectors can be used for the detection of neutrons. Counting rates of 1 to 1.5 MHz are reliably achievable. As a gas is usually ³ He used, but is increasingly limited available.

It is an object of the invention to provide a scintillation detector, with the large count rates and high resolutions are possible. A scintillation detector comprises the features of claim 1 for achieving the object. Advantageous embodiments emerge from the subclaims.

The scintillator of the scintillation detector according to the invention is formed of a plurality of pixels separated by spaces. Alternatively or additionally, the surface of the scintillator is divided into pixels by grooves. Such a structure not only allows a particularly high resolution. In addition, when using multiple detector modules high count rates in the range of several 20 MHz are possible.

The grooves and / or the interspaces between the individual scintillator pixels are preferably filled with reflection material for the light to be detected in order to be able to achieve the object of the invention in a further improved manner by an optical separation of the individual pixels achieved thereby. Crosstalk can be avoided as advantageous. Barium sulfate, for example, serve as a reflection material to further achieve the object of the invention to improve. For example, using a binder, the reflection material may be attached.

Instead of a reflection material, an absorber material may be used for the light to be detected in order to avoid crosstalk. A reflector, however, provides for a higher sensitivity and is therefore to be preferred.

It is possible to realize pixel sizes which are up to 8 mm, preferably up to 6 mm, more preferably up to 3 mm long, and / or which are up to 8 mm, preferably 6 mm, more preferably up to 3 mm, wide. The same applies to the pixelation of the scintillation or converter material by grooves.

The pixels of the scintillator preferably contain ⁶ Li in order to be able to manufacture and detect neutrons. Alternatively, ¹⁰ B or another neutron converter may be provided. Various scintillation materials are possible. It can also be chosen between different established materials.

In order to be able to read out in a spatially resolving manner and with a high counting rate, a multi-anode photomultiplier has proven suitable. The multi-anode photomultiplier converts light flashes generated by the scintillator into electrical signals. One However, multi-anode photomultipliers can also be replaced by an adequate light detection unit.

The size of a pixel of the scintillator advantageously corresponds to the size of a subsequently arranged anode of the photosensitive surface, here photomultiplier. The same applies to other light-reading units. This ensures that the flashes of light that are generated in a pixel, almost completely reach an opposite anode of the photomultiplier described here or a corresponding Lichtausleseeinheit so as to detect high count rate and high spatial resolution can. The pixels of the light extraction unit are therefore in one embodiment up to 8 mm, preferably up to 6 mm, more preferably up to 3 mm, long and / or up to 8 mm, preferably up to 6 mm, more preferably up to 3 mm, wide ,

The pixels of the light extraction unit are preferably at least 3 mm long and / or at least 3 mm wide in order not to have to operate an excessively high technical production cost.

The scintillation detector consists in one embodiment of a plurality of modules. Each module includes its own scintillator, its own light reading unit and its own readout electronics. An exchange of individual modules is possible and minimizes maintenance and repair costs. A single module advantageously has a footprint of not more than 52 to 52 mm ² .

Further advantages and refinements which enable a further improved counting rate and / or high spatial resolution will become apparent from the following description.

In addition to a light reading unit for converting the light into electrical signals, the scintillation detector comprises amplification and digitization of the signals of the light reading unit via integrated electronic components and a fast programmable logic module for the time-resolved registration of logical pulses corresponding to the neutrons.

For example, ⁶ Li-containing scintillator pixels are transparent. For example, glass which has been doped with ⁶ Li and which is referred to below as Li glass is used. With neutron capture, blue light can be emitted and an absorption efficiency of about 98% at a neutron wavelength of 5 Å is possible.

A multi-anode photomultiplier, for example, has in its design relative to the entire surface facing the scintillator an active surface for light detection of approximately 89%, which is separated by individual anode pixels of size 5.8 × 5.8 mm ² at a distance of 6.08 / 6.26 mm (inside / outside) or 2.8 x 2.8 mm ² at a distance of 3.04 / 3.22 mm (inside / outside). The same applies to other light-reading units.

Integrated electronic components perform amplification and noise filtering of the individual signals of the light reading unit.

In one embodiment, the integrated electronic components each comprise a comparator for the individual signals, which generates a logical output signal over an adjustable threshold.

The integrated electronic components advantageously comprise an analog-to-digital converter, with which the generated amount of charge of an anode signal can be measured.

A programmable logic module is advantageously present, which can make an adjustment of the measurement modes and the comparator thresholds of the integrated electronic modules.

The programmable logic device can advantageously register the logic signals of the integrated electronic components and sum them up in internal memories in time.

The programmable logic device can advantageously register the data of the analog-to-digital converter and add up in internal memories for each channel of the size accordingly.

The programmable logic module advantageously has an external interface for accessing or transporting the data registered in internal memories.

The detector has in the downstream electronics so in particular a programmable logic device with internal memory areas, the diverse Tasks takes over. It performs the adjustment of the measurement modes and the comparator thresholds of the integrated electronic components and registers both the logical comparator signals, which are summed up in internal memory locations in time, as well as the data of the analog-to-digital converter, which is also stored in internal memory for each channel Size to be summed up accordingly. In addition, it has an external interface for accessing or transporting the data registered in internal memories so that they can be displayed and analyzed by a computer with a monitor and / or written to a file for later evaluation.

Thus, a modular and scalable multi-channel thermal neutron detector is described that distinguishes neutrons and gamma radiation by setting a comparator threshold to the level of the generated signals.

In particular, special light reading units, e.g. Multi-anode photomultipliers (commercially available, for example, commercially available under the designation H8500, H9500) which, in an extremely dense package, have many single light detection channels with small area and almost borderless transition to adjacent channels. As a result, both a relatively high resolution and a high active area for light detection are realized, which can not be achieved with single-channel photomultipliers. The high active surface for light detection is particularly advantageous, since it determines the amount of light detected and thus the important distinction between neutrons and gamma radiation. The active area is then limited only by the, for example, 1, 5 mm wide outer edge of the preferably used multi-anode photomultipliers, so that, measured on the total area, the proportion of active area is 89%.

In the detector, these properties of the multi-anode photomultipliers are exploited in a corresponding embodiment in order to use the individual channels as separate detectors for thermal neutrons. The achieved resolution of, for example, 6 mm or 3 mm is suitable for many applications in neutron scattering. As detection material, mainly ⁶ Li-containing scintillator pixels are used, which generate light with neutron capture light with a very low cooldown (eg ⁶ Li glass). The size of these scintillator pixels is dimensioned such that they cover nearly one channel of the multi-anode photomultipliers in terms of area. It only becomes one small gap between adjacent pixels filled with optical reflector material. This is intended to largely avoid disturbing crosstalk of the generated light to neighboring channels, so that only the channel made generates a significant electrical signal. In a sandwich production of Szintillationsmaterial and substrate, in which only the scintillation material is pixelated by grooves, also a crosstalk should be suppressed by reflection in the substrate. This is achieved either by a lower refractive index of the carrier material and thus resulting total internal reflection or a reflective adhesive or absorption layer. A combination of both measures is possible.

The processing of the electrical signals can be made separate and relatively simple with the aim of making a distinction between neutrons and gamma radiation by the height of the signal. As a first step, amplification and noise filtering of the very small electrical signal are suitable in order to improve the precision in pulse height determination. Subsequently, the signal is fed to a comparator, in which an adjustable threshold is used to distinguish between neutrons and gamma radiation. In the case of a neutron event, the comparator generates a logic pulse. To set the comparator threshold, an analog-to-digital converter is used, with which the generated pulse heights can be measured. A numerical representation of the pulse heights in a histogram shows the value of the required threshold. Since the analog-to-digital converter is used only for adjustment purposes, a solution can be used for the detector by multiplexing the channels to the converter.

In order to ensure a modularity and scalability of the detector in one embodiment, the (in accordance erected horizontal and vertical) expansion of the signal processing, ie the base area, the size front surface of the light reading unit eg multi-anode photomultiplier does not. Therefore, a compact solution is used via integrated electronic components. A single module then has, for example, a footprint of 52 × 52 mm ² . A scintillation detector may then comprise a plurality of such modules. The maintenance is kept so low. In case of repair, a defective module can be easily replaced. A module becomes a unit understood, which can be used as a scintillation detector, both in combination with other modules as well as independent of other modules.

The achievable count rates with this detector are essentially determined by the cooldown of the scintillator, the response time, ie the response time, the light readout unit such. limits the maximum anode current of the multi-anode photomultiplier and the time constant in the amplification and noise filtering of the electrical signals. The maximum anode current is fixed by the special multi-anode photomultipliers, but by suitable choice of the scintillator and the associated time constant in the signal processing and in particular by the high segmentation of the detector described here, based on the area, very high count rates can be achieved , The active area for neutron detection can be determined by the edge of the light reading unit here: multi-anode photomultiplier and the spaces between the scintillator pixels. This results in a proportion of the active detection area for neutrons of approximately 85% of the total area, which, combined with the absorption of the scintillator, allows a detection efficiency of more than 80% for thermal neutrons at 5 Å. At the same time, the modular design of the detector allows use in a scalable array for large areas where the characteristics scale equally with the area.

The following advantages can thus be realized by the detector according to the invention.

Via pixelization of the scintillator, single-channel processing in the detection of neutrons with e.g. Multianoden Photomultipliern be realized.

• The electronic processing of the channels can be made independent and relatively simple.

• By using space-saving, integrated components, the dimension of the electronics can be limited to the surface of the light-extraction unit.

• At the same time, high spatial resolution, high count rates and high detection efficiencies can be achieved, which can not be achieved with single-channel photomultipliers. • A detector can be composed of modules to create a large-area detector. The advantageous properties are then scaled according to the area.

The scintillator may comprise a substrate or support in the form of a glass pane, which is preferably continuous. In contrast, pixels of the scintillator, for example made of Li glass, may be separate from each other and have gaps between the pixels filled with reflector material (e.g., barium sulfate) for optical separation.

In particular, the substrate and the pixels are attached to each other by an adhesive layer. Commercially available optical adhesives or gels are suitable for this purpose.

An additional adhesive layer may be present between the pixels and the photomultiplier or the light extraction unit. This should have the highest possible transparency for light.

The scintillation detector is to be created in particular for the detection of neutrons. By selecting the material of the scintillator this can also be set up for the detection of another radiation.

The invention will be explained in more detail below with reference to an exemplary embodiment.

Show it

FIG. 1 shows a scintillation detector in a sectional view;

FIG. 2: scintillator seen in plan view;

FIG. 3: Scintillator with a carrier whose refractive index is greater than that

Refractive index of the scintillation material;

FIG. 4: scintillator with a carrier whose refractive index is smaller than that

Refractive index of the scintillation material.

FIG. 1 illustrates a scintillation detector according to the invention in a lateral sectional view. The scintillation detector comprises, as a scintillating material support, a glass sheet 1 on which Li-glass pixels 2 having an area of 6 mm × 6 mm are attached through an adhesive layer 3. The scintillation material consisting of pixels 2 have a distance or gap of 100 μηη. The spaces between the pixels 2 are filled with barium sulfate 4. An adhesive layer 5 attaches a multi-anode photomultiplier 6 to the pixels 2.

About post connector 7 of the Multianodenphotomultipliers 6 and a frame 8 is followed by an evaluation 9 and connected to the Multianodenphotomultiplier 6.

The carrier material, that is to say the glass pane 1, has a lower refractive index than the scintillation material, that is to say the pixels 2, in order to further improve the prevention of crosstalk.

During operation, neutrons hit the scintillation detector as indicated by the arrow 10.

The behind the scintillator with the components 1, 2, 3, 4 arranged further components of the detector, so the photomultiplier 6 and the transmitter 9 are as shown in Figure 1 not laterally opposite the scintillator out to allow a modular design suitable. Seen in plan view of the glass pane 1 so that the base surface of the transmitter and the front surface of the multi-anode photomultiplier does not exceed the glass surface 1.

FIG. 2 shows the scintillator seen in a view of the pixels 2, which have an area of 6 mm × 6 mm.

FIGS. 3 and 4 each show a scintillator with a pixel 2 in which a flash of light has been produced due to a neutron incidence. Starting from the area 1 1, the light propagates according to the arrow. In the case of FIG. 3, the refractive index of the glass substrate 1 is greater than the refractive index of the pixels 2. In the case of FIG. 4, the refractive index of the glass substrate 1 is smaller than the refractive index of the pixels 2. In the case of FIG by refraction and reflection take place an undesirable crosstalk. This is avoided in the case of FIG. If the refractive index of the Li-glass 2 is lower than that of the carrier glass 1, as shown in FIG. 3, then the adhesive layer 3 has no appreciable influence on the reflection behavior of the light.

In this case, by refraction, light radiated from the scintillation process in the Li glass 2 in the direction of the substrate glass 1 can penetrate into the adjacent pixels 2. This allows the pixels to cross-talk with each other, resulting in poorer spatial resolution as well as higher noise.

If the refractive index of the Li-glass 2 according to FIG. 4 is higher than that of the carrier glass 1, then the adhesive layer 3 again has no appreciable influence on the reflection behavior of the light. In this case, as shown in FIG. 4, a total internal reflection takes place so that no crosstalk between the pixels 2 takes place.

However, the adhesive 3 may alternatively or additionally be selected such that this light, which is scattered towards the rear in the direction of the glass pane 1, absorbs and / or reflects light. This also prevents crosstalk.

Claims

Claims:

1 . Scintillation detector with a scintillator, a light reading unit, in particular a photomultiplier (6), and an evaluation (9), characterized in that the scintillator of pixels (2), which are separated by gaps (4), and / or Surface is pixelated by grooves.

2. scintillation detector according to claim 1, characterized in that the grooves and / or the interstices (4) are filled with reflection material for the light to be detected.

3. scintillation detector according to the preceding claim, characterized in that the reflection material consists of barium sulfate.

4. scintillation detector according to any one of the preceding claims, characterized in that the space between the pixels (2) generated by the gap (4) is at least 100 μηη and / or the grooves are at least 100 μηη wide.

5. Scintillation detector according to one of the preceding claims, characterized in that the pixels (2) are up to 6 mm, preferably up to 3 mm long and / or up to 6 mm, preferably up to 3 mm wide and / or that the pixels (2) are at least 3 mm long and / or at least 3 mm wide.

6. Scintillation detector according to one of the preceding claims, characterized in that the pixels (2) contain ⁶ Li.

A scintillation detector according to any one of the preceding claims, wherein the scintillator comprises a carrier (1) for the scintillation material (2) which generates light flashes by incident radiation having a lower refractive index than the scintillation material (2).

A scintillation detector according to any one of the preceding claims, wherein the scintillator comprises a support (1) for the scintillation material (2) which generates light flashes by incident radiation, and a light absorbing and between the support (1) and the scintillation material (2) / or light-reflecting adhesive layer (3) is introduced.

9. Scintillation detector according to one of the preceding claims, characterized in that pixels of the light extraction unit, in particular the anodes of a multi-anode photomultiplier, up to 6 mm, preferably up to 3 mm, long and / or up to 6 mm, preferably up to 3 mm , are wide and / or that the pixels of the light extraction unit, in particular the anodes of a multi-anode photomultiplier, are preferably at least 3 mm long and / or at least 3 mm wide.

10. Scintillation detector according to one of the preceding claims, characterized in that the base surface of the evaluation electronics does not exceed the size of the front surface of the light readout unit (multi-anode photomultipliers).

1 1. Scintillation detector according to the preceding claim, characterized in that the scintillation detector consists of a plurality of modules.

12. Scintillation detector according to one of the preceding claims, characterized in that the transmitter comprises one or more integrated electronic components, which perform amplification and noise filtering of the individual signals of the pixels of a light readout unit (multi-anode photomultipliers).

13. Scintillation detector according to one of the preceding claims, characterized in that the transmitter has a programmable logic module with internal memory areas, which performs a plurality of tasks and in particular an adjustment of the measurement modes and / or comparator thresholds of integrated electronic components and registration of logical comparator signals, which are summed up in internal memory locations in time, as well as data from an analog-to-digital converter, which are also summed up in internal memories.