Position-sensitive Neutron Detector Research Articles

LET, a cold neutron multi-disk chopper spectrometer at ISIS

LET is a new multi-chopper direct geometry cold neutron spectrometer, recently installed on target station 2 (TS2) at the ISIS spallation neutron source. The characteristics of the primary spectrometer are a 25 m straight super-mirror guide viewing the new highly efficient coupled solid methane moderator system. This combination yields a high incident flux of neutrons with a wide dynamic range of 0.6–80 meV. LET employs a novel flux compression guide design which in combination with two 300 Hz counter rotating choppers produces fine energy resolutions of ≥ 0.8 % δ E / Ei , to be realised with very little flux sacrifice compared to conventional methods. The multi-chopper system is designed to make full use of the long 100 ms time frames of TS2, allowing the user to make multiple measurements within a single frame. The secondary spectrometer is characterised by a wide area position sensitive 3He multidetector with π steradians of nearly gapless coverage over the angular range from −40° to +140° in the horizontal plane and ±30° in the vertical plane. The multidetector utilises the worlds first 4 m position sensitive 3He neutron detector tubes. LET has been designed specifically to allow the use of polarised neutrons allowing the user to exploit full XYZ neutron polarisation analysis. In addition a new 9 T magnet has been designed for LET allowing the use of large samples of 25 mm×25 mm with a 30° vertical opening to make use of the large multidetector.

Imaging of a spatial distribution of preferred orientation of crystallites by pulsed neutron Bragg edge transmission

A pulsed neutron transmission coupled with a two-dimensional position sensitive neutron detector gives a time-of-flight spectrum at each pixel of the detector, which depends on the total cross-sections of materials. In order to extract quantitative information of the preferred orientation included in the Bragg scattering total cross-section data, a spectral analysis software for the 2D imaging has been developed, and the transmission data of an unbent iron plate were analyzed. The 2D images with respect to the preferred orientation were successfully obtained, and the effectiveness of spectroscopic neutron transmission imaging was indicated.

Development of material evaluation method by using a pulsed neutron transmission with pixel type detectors

A spectroscopic neutron imaging is attractive in the research field of energy-selective neutron radiography. Imaging using the time-of-flight (TOF) method at a pulsed neutron source is very suitable for such spectroscopic measurements. We developed new two-dimensional position sensitive neutron detectors (2D-PSNDs) aiming at high detection efficiency, high counting rate and high time resolution which are the most important 2D-PSND performances for the spectroscopic imaging. These detectors consist of independent 6Li-glass (Ce) scintillator pixels, and have been used in various pulsed neutron transmission experiments. As a result, we have succeeded in developing various new imaging techniques; crystallographic, nuclide-selective and thermographic imaging.

A gas mixture regeneration system for a position-sensitive thermal neutron detector with a 3He-based gas converter

A gas mixture regeneration system is designed for a two-dimensional position-sensitive thermal neutron detector based on a multiwire proportional chamber with a 3He-based converter. The basic characteristics of the system are given, and processing steps aimed at decreasing the gas liberation from the detector structure are described. The influence of the electronegative impurity accumulation on the detector characteristics and operation of the gas regeneration system are studied. The system is designed on request of the Laboratory of Neutron Physics, JINR (Dubna), for modernizing the ДH-2 diffractometer operating on beams of the ИБP-2 reactor.

A Monte Carlo simulation comparing hydrocarbons as stopping gases for position sensitive neutron detectors

Various neutron detectors are being developed for the next generation user facilities, which incorporate new as well as existing approaches for the detection of thermal neutrons. Improvements in neutron detector efficiency, detector size and position resolution have occurred over the last three decades and further advances are expected in the next ten years. Since gas detectors are expected to continue in a key role for future thermal neutron experiments, it is advantageous to review some of the criteria for the choice of proton/triton stopping gases for gas-based detectors. Monte Carlo simulations, using the group of programs “Stopping and Range of Ions in Matter”, have been run to determine key performance characteristics for neutron detectors which utilize the reaction 3He(n,p)t. This paper will focus on investigating the use of three common hydrocarbons and CF 4 as stopping gases for thermal neutron detectors. A discussion of these gases will include their behavior in terms of proton and triton range, ion distribution and straggle.

Pulsed neutron imaging using resonance transmission spectroscopy

We are developing the energy-selective neutron radiography and tomography technique by using the pulsed neutron source and the time-of-flight (TOF) spectroscopy. Neutron resonance absorption spectroscopy with computer tomography, N-RAS/CT, can non-destructively give the tomographic image indicating material information such as nuclide, density and temperature inside the object. The primary N-RAS/CT was performed by detecting prompt γ-rays emitted from nuclei absorbing neutrons as a function of neutron TOF. In this case, position dependent data need to be obtained by scanning the object with a moving slit. On the other hand, in this paper, we propose a new N-RAS/CT method using neutron transmission spectroscopy combined with 2-dimensional position sensitive neutron detector (2d-PSND), which is applicable to TOF measurement. The greatest feature of this method is shorter measurement time than the previous one because 2d-PSND can obtain spatial information at once. For this reason, we carried out the new N-RAS/CT experiment to examine its feasibility at the pulsed neutron facility based on the small accelerator.

Evaluation of the performance of a fibre-coded neutron detector with a ZnS/ 10B 2O 3 ceramic scintillator

The detection performance of a fibre-coded linear position-sensitive neutron detector equipped with a ZnS/ 10B 2O 3 ceramic scintillator has been evaluated. The neutron detection efficiency of this detector at 1 Å was 1.2-fold higher than that of a similar detector based on a ZnS/ 6LiF scintillator. The two detectors exhibited similar gamma sensitivities.

Performance studies on high pressure 1-D position sensitive neutron detectors

The powder diffractometer and Hi-Q diffractometer at Dhruva reactor make use of five identical 1-D position sensitive detectors (PSDs) to scan scattering angles in the range 3° to 140°. In order to improve the overall throughput of these spectrometers, it is planned to install a bank of 15 high-efficiency and high-resolution PSDs arranged in three layers with five PSDs in each layer. With each high pressure PSD (3He 10 bar + Kr 2 bar) showing the efficiency gain of 1.8 at 1.2 A, detector bank is expected to show overall gain of 5.5 times the present detection efficiency and reduction in data collection time by equivalent factor. The 1-D PSDs are developed in batches of five, and are characterized so that all PSDs operate at uniform parameters such as position resolution, uniformity of efficiency and linearity of response. Position spectrum indicates the differential position resolution to be ∼1 mm and integral position resolution to be 3–4 mm. Broadening of position spectrum at the extreme end of sensitive length of PSD is analysed using fine shift of the beam. Dependence of position resolution and dynamic range of output pulse on the input impedance of pre-amplifier is also presented.

Modern trends in the development of position sensitive neutron detectors for condensed matter research

Different types of neutron scattering experiment for the study of condensed matter properties pose specific and often contradictory requirements for detector characteristics. There is no single type of detector which satisfies all the criteria. Therefore, compromise is inevitable and some of the characteristics are trade off in favour of others. Present report gives an overview of detector systems presently operating at the leading neutron scattering facilities as well as some development work around the globe.

Development of curved position-sensitive neutron detectors for FCD at HANARO

Development of curved position-sensitive neutron detectors for FCD at HANARO

Low-Frequency Noise of Resistively Coupled Charge Amplifiers

In resistive wire position sensitive neutron detector systems two charge sensitive preamp inputs are connected via the tube impedance. Due to this coupling the output noise increases significantly. This work investigates the behavior of that kind of coupling induced noise using a technique called "noise gain calculation". The output noise correlation is analyzed analytically. Attained results are cross checked via simulations and measurements. Conclusions are drawn to better understand system resolution estimation for coupled preamplifier designs.

Charge equalizing and error estimation in position sensitive neutron detectors

The conventional design of detector electronics for resistive wire position sensitive neutron detectors (PSD) using of-the-shelf charge sensitive preamplifiers and gauss-pulse shaping devices causes uncertainty in spatial position and resolution due to charge equalization between both ends of the resistive PSD. This paper describes in detail charge equalization effects and their drawbacks for a PSD system design. Error estimations for a conventional design are given. Attained results should help to better understand PSD electronics design and to provide data for system optimization.

On studies of 3He and isobutane mixture as neutron proportional counter gas

The performance of neutron detectors filled with 3He+iC 4H 10 (isobutane) gas mixtures has been studied and compared with the performance of detectors filled with 3He+Kr gas mixtures. The investigations are made to determine suitable concentration of isobutane in the gas mixture to design neutron proportional counters and linear position sensitive neutron detectors (1-D PSDs). Energy resolution, range of proportionality, plateau and gas gain characteristics are studied for various gas mixtures of 3He and isobutane. The values for various gas constants are determined by fitting the gas gains to Diethorn and Bateman's equations and their variation with isobutane concentration in the fill gas mixture is studied.

Development of a position sensitive neutron detector with high efficiency and energy resolution for use at high-flux beam sources

We are developing a high-efficiency neutron detector with 1 cm position resolution and coarse energy resolution for use at high-flux neutron source facilities currently proposed or under construction. The detector concept integrates a segmented 3He ionization chamber with the position sensitive, charged particle collection methods of a MicroMegas detector. Neutron absorption on the helium produces protons and tritons that ionize the fill gas. The charge is amplified in the field region around a wire mesh and subsequently detected in current mode by wire strips mounted on a substrate. One module consisting of a high-voltage plate, a field-shaping high-voltage plate, a grid and wire strips defines a detection region. For 100 % efficiency, detector modules are consecutively placed along the beam axis. Analysis over several regions with alternating wire strip orientation provides a two-dimensional beam profile. By using 3He, a 1/v absorption gas, each axial region captures neutrons of a different energy range, providing an energy-sensitive detection scheme especially useful at continuous beam sources.

Investigation of the Neutron Quantum States in the Earth's Gravitational Field.

We studied the neutron quantum states in the potential well formed by the Earth's gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in two lowest quantum states correspond to their expectations with an accuracy of ≈25 %. The spatial density distribution in a standing neutron wave above a mirror was measured for a set of a few lowest quantum states. A position-sensitive neutron detector with an extra high spatial resolution of 1 μm to 2 μm was developed and tested for this particular task. Although this experiment was not designed or optimized to search for an additional short-range force, nevertheless it allowed us to slightly improve the published boundary in the nanometer range of characteristic distances. We studied systematical uncertainties in the chosen "flow-through" method as well as the feasibility to improve further the accuracy in this experiment.

Study of the neutron quantum states in the gravity field

We have studied neutron quantum states in the potential well formed by the earth's gravitational field and a horizontal mirror. The estimated characteristic sizes of the neutron wave functions in the two lowest quantum states correspond to expectations with an experimental accuracy. A position-sensitive neutron detector with an extra-high spatial resolution of ~2 microns was developed and tested for this particular experiment, to be used to measure the spatial density distribution in a standing neutron wave above a mirror for a set of some of the lowest quantum states. The present experiment can be used to set an upper limit for an additional short-range fundamental force. We studied methodological uncertainties as well as the feasibility of improving further the accuracy of this experiment.

傾斜線式読取法による中性子位置検出器の位置分解能

傾斜線式読取法による中性子位置検出器の, 位置分解能を調べた。この検出器では, 比例計数管の陽極芯線に沿って傾斜した2本の位置読取線を張ってある。幅約1mmの固体相のホウ素とチッ化ホウ素を中性子転換物質として使い, 計数ガス (PRガス) の圧力は1.00気圧から1.44気圧である。検出粒子の (位置) : (エネルギー) 2次元スペクトルには中性子転換物質線に対応する明瞭な分布が現われた。このデータから検出粒子の位置スペクトルを求め, 粒子のエネルギーや計数ガスの圧力と位置分解能の関係を調べた。計数ガス圧1.44気圧の時, 低エネルギー粒子に対する半値幅位置分解能は約2mmになった。

Current Status of Position-Sensitive Neutron Detectors for Pulsed Neutron Sources

Nowadays, neutron detectors draw many attentions since new intense spallation neutron sources and new neutron optics are being realized. Conventional neutron detectors suffer from their poor count rate characteristics, position resolutions, and energy resolutions, etc. Since those properties are related one another in a complicated way, better design of the neutron detector engineering is required. Also, people anticipate new innovative technologies to overcome the current limitation of the detector performance. Future trends for neutron detectors are introduced in this paper.

A gas proportional scintillator counter for thermal neutrons instrumentation

A gaseous scintillation detector consisting of a 3He+CF4 filled MSGC detector coupled with an optical readout has been investigated for an application for high-resolution and high counting rate position-sensitive neutron detector. Measurements of the photons' emission as a function of the gas mixture have been carried out indicating that filling the detector with 3He+CF4 is a very good choice also from the point of view of optical readout and not only for charge readout. The light yield has been systematically measured as a function of the CF4 concentration and operating voltages. We also studied the emission of primary light, rather strong in CF4 mixtures, which allows the observation of the light signal even in the absence of high voltage on the electrodes. Finally, some measurements of the position resolution will be presented.

Low efficiency 2-dimensional position-sensitive neutron detector for beam profile measurement

A gas-filled position-sensitive wire detector has been developed for monitoring thermal neutron beams with flux up to 10 7 n/cm 2/s over an area ≈80 cm 2. It is filled with CF 4(4 atm) and a small quantity of 3He, has 1.2 mm spatial resolution, 0.1% efficiency (at 0.18 nm) and can achieve a count rate of 350 kHz. Experiments at the 30 MW HANARO reactor showed that the fabricated PSD is a very useful and convenient tool for adjusting neutron monochromators, especially focusing monochromators, and for monitoring monochromatic beams. It can be used for various neutron optics experiments.