RU2087923C1 - Position-sensing neutron detector - Google Patents

Abstract

FIELD: neutron detectors. SUBSTANCE: detector has quartz tube filled with liquid scintillator and two photoelectronic multipliers placed on ends of tube and having direct contact with scintillator. Expansion chamber is placed above quartz tube for metered pressure release in case of scintillator expansion. Knock-down design of packing between quartz tube and photoelectronic multipliers provides for easy replacement of detector components. Supply voltage dividers of multipliers are brought to anode-signal minimum time spread mode of operation. Spectrometric signal is picked off final dinode of photoelectronic multiplier and brought out through inverter-repeater circuit. Two time signals (multiplier anodes) and two spectrometric signals (multiplier dinodes) are simultaneously picked off detector. Detector can be used at a time for neutron spectrometry by transit time, measurement of neutron escape angle, and signal separation from neutrons and gamma-quanta. EFFECT: enlarged functional capabilities. 1 dwg

Description

 The invention relates to techniques for detecting neutrons, and more specifically to devices for spectrometry of neutrons by time of flight and to determine the angle of departure of neutrons, and is intended for use in nuclear physics experiments.

 The device described in 1 is known. It consists of a quartz tube 55 cm long and 3.8 cm in diameter, filled with a liquid scintillator, and two photomultiplier tubes (PMTs) of the GDB-49 type. The tube has quartz windows at the ends to which the PMTs are pressed at the optical contact.

 The disadvantages of this device are the significant attenuation (absorption and reflection) of the light collected on the PMT in the quartz window-optical lubricant-PMT connection, as well as the absence of an expansion chamber for dosed pressure relief during scintillator expansion, which does not allow the indicated detector to be placed vertically (the detector is located only in horizontal plane).

 The closest in technical essence to the claimed detector is the device selected as a prototype, described in 2 The prototype consists of a quartz container 100 cm long, rectangular section 11.5 * 6 cm, filled with a NE-213 liquid scintillator, and two photomultipliers of the RCA 8854 type located at the ends of the container.

The disadvantages of this device are
the connection of the PMT and the quartz container, since the PMTs are glued to the ends of the quartz container with the special composition AV 138 and HV 998 (Germany), therefore this connection is not collapsible even if one of the structural elements fails (for example, a PMT, the cost of which is high $ 2000 ) the detector is not suitable for work and there is no possibility of replacing a structural element;
PMT supply voltage dividers, since devices 1,2 use standard (specified in the passport by the manufacturer manufacturer) power supply dividers, which leads to the fact that PMTs do not work in the optimal time and spectrometric modes that can be achieved with a PMT of this sample;
incomplete information retrieval from the device, since in the device 1 the dynode signals are not removed from the PMT, and in the device 2 the dynode signals are summed up and not used individually, which reduces the amount of information taken, and, therefore, the device’s capabilities.

 The objective of the invention is to develop a device devoid of the disadvantages of the above, which can be used simultaneously for neutron spectrometry by time of flight; determination of the neutron emission angle (positional sensitivity of the detector); separation of the signal from neutrons and gamma rays.

 The drawing shows a schematic position-sensitive neutron detector.

 According to the invention, the device (position-sensitive neutron detector) consists of a quartz tube 1 with a length of 100 cm with an outer diameter of 6 cm (wall thickness 2.5 mm) and two photomultipliers (PMT type 30 with a photocathode diameter of 5 cm) 2. The quartz tube is filled with liquid scintillator 3. ZhS-13 type scintillator based on α-methyl-naphthalene with separation of neutrons and gamma quanta. The photomultipliers are immersed directly in the liquid scintillator to avoid light attenuation at the ends of the quartz tube. PMTs are located at the ends of a quartz tube. Between the quartz tube and the PMT, a collapsible seal 4 is installed, made using 2-sided flanges 5 and a rubber-like plastic 6 resistant to liquid hydrocarbons located between the flanges. Such a collapsible connection, in contrast to the prototype, allows you to quickly replace structural elements (for example, PMTs) when they fail, which makes an expensive detector suitable for operation for a long time. The expansion chamber 7, located above the quartz tube, has a Teflon plug 8 with a plastic seal 9 inside it, as well as a capillary valve 10 for dosed pressure relief during expansion of the scintillator. This design of the expansion chamber allows both horizontal and vertical location of the detector, which is important for conducting physical experiments on the registration of neutrons in different reaction planes. The photocathode and the first PMT dynodes are protected by permaloy cylinder 11. To protect from light, the detector is placed in an iron casing (10 * 10 * 160 cm, wall thickness 0.8 mm) 12. The casing also contains power supply voltage dividers 13 PMTs and an inverter-repeater 14 for removing the spectrometric signal from the last PMT dynode.

 PMT supply voltage dividers, in contrast to the prototype, are in the mode of minimum time spread of the anode signal. The mode is achieved by selecting the resistances of the divider between the cathode, the first and second focusing electrodes of the PMT. The latter result in obtaining the best time resolution for the PMT of this sample. The time resolution of the electronic path containing two PMTs and electronics (shapers with a tracking threshold, time-to-digital converters) was 1.4 ns. The addition of damping resistances at the last PMT dynodes made it possible to remove spurious oscillations of the PMT anode signal, which eliminated false alarms of the electronics at low detection thresholds. The spectrometric signal is taken from the last PMT dynode and output through the inverter-repeater circuit. The signal, in contrast to the prototype, has a negative polarity, which allows the use of the same type of electronics to service both dynode and anode signals (anode signals have a negative polarity).

 The detector operates as follows. When a neutron enters a liquid scintillator and collides with hydrogen or carbon nuclei, the resulting radiation causes the scintillator to glow, which is detected by a PMT. Two time signals (PMT anodes) and two spectrometric signals (PMT diodes) are simultaneously taken from the detector. The individual removal of all signals from the detector leads to additional information, and, consequently, to improved characteristics of the neutron spectrometry device and to determine the position of the neutron entering the detector, since information on the position of the neutron entering the detector is obtained from the difference between the times of light arrival to two PMTs with both ends of the detector, and the ratio of the amplitudes of the dynode signals gives additional information about the position. Neutron spectrometry is carried out by the time of flight of the neutron to the detector, and the sum of the amplitudes of the dynode signals determines the proton recoil energy and, therefore, provides additional information about the neutron energy.

 The quality of a position-sensitive neutron detector is determined by the following characteristics: time resolution, position resolution, registration efficiency, separating ability of neutrons and gamma quanta, energy detection threshold.

Detector Features:
time resolution (together with electronics) 1.4 ns;
positional resolution with a length of 100 cm 10 cm;
energy threshold of neutron registration 0.5 MeV;
neutron detection efficiency at an average neutron energy in the fission spectrum of 40%
Separating power of neutrons and gamma rays> 100.

The detector is also characterized by:
reliability in work (> 1000 hours of work), low cost (compared with the prototype), the ability to quickly replace structural elements.

Claims (1)

 A position-sensitive neutron detector, consisting of a quartz tube filled with a liquid scintillator, and two photoelectronic multipliers located at the ends of the device placed in an iron casing, characterized in that the photoelectronic multipliers have direct contact with the scintillator, and between the quartz tube and the photoelectron multiplier installed collapsible seal made using double-sided flanges and a rubber-like liquid-resistant plastic hydrocarbon located flanges, and the expansion chamber located above the quartz tube has a Teflon plug with a plastic seal inside it, as well as a capillary valve to relieve pressure when the scintillator expands, and the voltage dividers of the photomultiplier tubes provide a mode of minimum time spread of the anode signal and contain damping resistance at the last dynodes of the photomultiplier tubes, and the spectrometric signal taken from the last dynode of the photomultiplier tube den through the inverter follower circuit, and has a negative polarity.