Neutron detection - Knowledge (XXG)

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example would be a common planar Si diode coated with either B or LiF. This type of detector was first proposed by Babcock et al. The concept is straightforward. A neutron is absorbed in the reactive film and spontaneously emits energetic reaction products. A reaction product may reach the semiconductor surface, and upon entering the semiconductor produces electron-hole pairs. Under a reverse bias voltage, these electrons and holes are drifted through the diode to produce an induced current, usually integrated in pulse mode to form a voltage output. The maximum intrinsic efficiency for single-coated devices is approximately 5% for thermal neutrons (0.0259 eV), and the design and operation are thoroughly described in the literature. The neutron detection efficiency limitation is a consequence of reaction-product self-absorption. For instance, the range in a boron film of 1.47 MeV α particles from the B(n,α) Li reaction is approximately 4.5 microns, and the range in LiF of 2.7 MeV tritons from the B(n,α) Li reaction is approximately 28 microns. Reaction products originating at distances further from the film/semiconductor interface can not reach the semiconductor surface, and consequently will not contribute to neutron detection. Devices coated with natural Gd have also been explored, mainly because of its large thermal neutron microscopic cross section of 49,000 barns. However, the Gd(n,γ) reaction products of interest are mainly low energy conversion electrons, mostly grouped around 70 keV. Consequently, discrimination between neutron induced events and gamma-ray events (mainly producing Compton scattered electrons) is difficult for Gd-coated semiconductor diodes. A compensated pixel design sought to remedy the problem. Overall, devices coated with either B or LiF are preferred mainly because the energetic charged-particle reaction products are much easier to discriminate from background radiations.

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interact with the glass matrix to produce ionization, which transfers energy to Ce ions and results in the emission of photons with wavelength 390 nm – 600 nm as the excited state Ce ions return to the ground state. The event results in a flash of light of several thousand photons for each neutron absorbed. A portion of the scintillation light propagates through the glass fiber, which acts as a waveguide. The fibers ends are optically coupled to a pair of photomultiplier tubes (PMTs) to detect photon bursts. The detectors can be used to detect both neutrons and gamma rays, which are typically distinguished using pulse-height discrimination. Substantial effort and progress in reducing fiber detector sensitivity to gamma radiation has been made. Original detectors suffered from false neutrons in a 0.02 mR gamma field. Design, process, and algorithm improvements now enable operation in gamma fields up to 20 mR/h (Co).

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are designed for use as gamma-ray spectrometers and, hence, are intrinsically sensitive to the gamma-ray background. With adequate energy resolution, pulse height discrimination can be used to separate the prompt gamma-ray emissions from neutron interactions. However, the effective neutron detection efficiency is compromised because of the relatively small Compton ratio. In other words, the majority of events add to the Compton continuum rather than to the full energy peak, thus, making discrimination between neutrons and background gamma rays difficult. Also, both natural Cd and Hg have relatively large thermal-neutron (n,γ) cross sections of 2444 b and 369.8 b, respectively. Consequently, most thermal neutrons are absorbed near the detector surface so that nearly half of the prompt gamma rays are emitted in directions away from the detector bulk and, thus, produce poor gamma-ray reabsorption or interaction efficiency.

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capability to distinguish between neutrons and gammas is excellent in noble gas based 4-He detectors due to their low electron density and excellent pulse shape discrimination property. In fact, inorganic scintillators such as zinc sulfide has been shown to exhibit large differences in their decay times for protons and electrons; a feature that has been exploited by combining the inorganic crystal with a neutron converter (such as polymethyl methacrylate) in the Micro-Layered Fast-Neutron Detector. Such detection systems are capable of selectively detecting only fast neutrons in a mixed neutron-gamma radiation field without requiring any additional discrimination techniques such as pulse shape discrimination.

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crystals have been reported. Finally, traditional semiconductor materials with neutron reactive dopants have been investigated, namely, Si(Li) detectors. Neutrons interact with the lithium dopant in the material and produce energetic reaction products. However, the dopant concentration is relatively low in Li drifted Si detectors (or other doped semiconductors), typically less than 10 cm. For a degenerate concentration of Li on the order of 10 cm, a 5-cm thick block of natural Si(Li) would have less than 1% thermal-neutron detection efficiency, while a 5-cm thick block of a Si(Li) detector would have only 4.6% thermal-neutron detection efficiency.

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greater than 30% thermal neutron detection efficiency. Although MSNDs can operate on the built-in potential (zero applied voltage), they perform best when 2-3 volts are applied. There are several groups now working on MSND variations. The most successful types are the variety backfilled with LiF material. MSNDs are now manufactured and sold commercially by Radiation Detection Technologies, Inc. Advanced experimental versions of double-sided MSNDs with opposing microstructures on both sides of a semiconductor wafer have been reported with over 65% thermal neutron detection efficiency, and are theoretically capable of over 70% efficiency.

1236:(ADC). The total deposited charge is a direct measure of the energy of the ionizing particle (neutron or photon) entering the neutron detector. This signal integration technique is an established method for measuring ionization in the detector in nuclear physics. The ADC has a higher dead time than the oscilloscope, which has limited memory and needs to transfer events quickly to the ADC. Thus, the ADC samples out approximately one in every 30 events from the oscilloscope for analysis. Since the typical event rate is around 10 neutrons every second, this sampling will still accumulate thousands of events every second. 817:

in a variety of applications. Further, they do not rely on He or any raw material that has limited availability, nor do they contain toxic or regulated materials. Their performance matches or exceeds that of He tubes for gross neutron counting due to the higher density of neutron absorbing species in the solid glass compared to high-pressure gaseous He. Even though the thermal neutron cross section of Li is low compared to He (940 barns vs. 5330 barns), the atom density of Li in the fiber is fifty times greater, resulting in an advantage in effective capture density ratio of approximately 10:1.

771:) enriched to 96% boron-10 (natural boron is 20% B, 80% B). Boron trifluoride is highly toxic. The sensitivity of this detector is around 35-40 CPS/nv (counts per second per neutron flux) whereas that of Boron lined is about 4 CPS/nv. This is because in Boron lined, n reacts with Boron and hence produce ion pairs inside the layer. Hence charged particles produced (Alpha and Li) they lose some of their energy inside that layer. Low energy charged particles are unable to reach the Ionization chamber's gas environment. Hence, the number of ionizations produced in gas is also lower. 1329:

Scintillation detectors were invented in 1903 by Crookes but were not very efficient until the PMT (photomultiplier tube) was developed by Curran and Baker in 1944. The PMT gives a reliable and efficient method of detection since it can multiply the initial signal of a single scintillation photon hitting the PMT face millions of times into a measurable electrical pulse. Even so, scintillator detector design has room for improvement as do other options for neutron detection besides scintillation.

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capabilities as 3He or CLYC or CLLB detectors at a lower cost.Li (95% enriched) co-doping introduces efficient thermal neutron detection to the most established gamma-ray scintillator while retaining the favorable scintillation properties of standard NaI(Tl). NaIL can provide large volume, single material detectors for both gammas and neutrons at a low price per volume.

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is well-centered. This fact can be used to identify incoming neutrons and to count the total rate of incoming neutrons. The steps leading to this separation (those that are usually performed at leading national laboratories, Jefferson Lab specifically among them) are gated pulse extraction and plotting-the-difference.

1131:, plastic, thermo-coal, etc. Thus, photons cause major interference in neutron detection, since it is uncertain if neutrons or photons are being detected by the neutron detector. Both register similar energies after scattering into the detector from the target or ambient light, and are thus hard to distinguish. 1279:

same tail-energy value. In this case, plotted points are simply made denser with more overlapping dots on the two-dimensional plot, and can thus be used to eyeball the number of events corresponding to each energy-deposition. A considerable random fraction (1/30) of all events is plotted on the graph.

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McGregor, D.S.; Klann, R.T.; Sanders, J.D.; Lindsay, J.T.; Linden, K.J.; Gersch, H.K.; De Lurgio, P.M.; Fink, C.L.; Ariesanti, E. (2002). James, Ralph B; Franks, Larry A; Burger, Arnold; Westbrook, Edwin M; Durst, Roger D (eds.). "Recent Results From Thin-Film-Coated Semiconductor Neutron Detectors".

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in continuous time (having a stream of "1" and "0" pulses as one input and the current signal as the other), the tail portion of every current pulse signal is extracted. This gated discrimination method is used on a regular basis on liquid scintillators. The gated delay unit is precisely to this end,

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The ADC sends its data to a DAQ unit that sorts the data in presentable form for analysis. The key to further analysis lies in the difference between the shape of the photon ionization-current pulse and that of the neutron. The photon pulse is longer at the ends (or "tails") whereas the neutron pulse

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Semiconductor detectors in which one of more constituent atoms are neutron reactive are called bulk semiconductor neutron detectors. Bulk solid-state neutron detectors can be divided into two basic categories: those that rely on the detection of charged-particle reaction products and those that rely

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There are two basic types of semiconductor neutron detectors, the first being electron devices coated with a neutron reactive material and the second being a semiconductor being partly composed of neutron reactive material. The most successful of these configurations is the coated device type, and an

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If the detector lies in a region of high beam activity, it is hit continuously by neutrons and background noise at overwhelmingly high rates. This obfuscates collected data, since there is extreme overlap in measurement, and separate events are not easily distinguished from each other. Thus, part of

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have been successfully used as neutron detectors. These detectors rely upon the prompt gamma-ray emissions from the Cd(n, γ)Cd reaction (producing 558.6 keV and 651.3 keV gamma rays) and the Hg(n, γ) Hg reaction (producing 368.1 keV and 661.1 keV gamma rays). However, these semiconductor materials

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The scintillating glass fibers work by incorporating Li and Ce into the glass bulk composition. The Li has a high cross-section for thermal neutron absorption through the Li(n,α) reaction. Neutron absorption produces a tritium ion, an alpha particle, and kinetic energy. The alpha particle and triton

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Helium-3 is an effective neutron detector material because it reacts by absorbing thermal neutrons, producing a H and H ion. Its sensitivity to gamma rays is negligible, providing a very useful neutron detector. Unfortunately the supply of He is limited to production as a byproduct from the decay of

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Further refinements are usually necessary to differentiate the neutron signal from the effects of other types of radiation. Since the energy of a thermal neutron is relatively low, charged particle reactions are discrete (i.e., essentially monoenergetic and lie within a narrow bandwidth of energies)

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The effectiveness of any detection analysis can be seen by its ability to accurately count and separate the number of neutrons and photons striking the detector. Also, the effectiveness of the second and third steps reveals whether event rates in the experiment are manageable. If clear plots can be

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In this step lies the crucial point of the analysis: the extracted ionization values are plotted. Specifically, the graph plots energy deposition in the tail against energy deposition in the entire signal for a range of neutron energies. Typically, for a given energy, there are many events with the

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Fast neutrons are often detected by first moderating (slowing) them to thermal energies. However, during that process the information on the original energy of the neutron, its direction of travel, and the time of emission is lost. For many applications, the detection of "fast" neutrons that retain

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C. These boron-based films are often grown upon n-type Si substrates, which can form a p–n junction with the Si and, therefore, produce a coated Si diode as described at the beginning of this section. Consequently, the neutron response from the device can be easily mistaken as a bulk response when

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The MSND device configuration was first proposed by Muminov and Tsvang, and later by Schelten et al. It was years later when the first working example of a MSND was fabricated and demonstrated , then having only 3.3% thermal neutron detection efficiency. Since that initial work, MSNDs have achieved

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The low efficiency of coated planar diodes led to the development of microstructured semiconductor neutron detectors (MSND). These detectors have microscopic structures etched into a semiconductor substrate, subsequently formed into a pin style diode. The microstructures are backfilled with neutron

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has the advantage over other materials that the number of optical photons produced per neutron capture is around 30.000 which is 5 times higher than for example in neutron-sensitive scintillating glass fibers. This property makes neutron photon discrimination easier. Due to its high Li density this

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is a neutron sensitive inorganic scintillator crystal which like neutron-sensitive scintillating glass fiber detectors makes use of neutron capture by Li. Unlike scintillating glass fiber detectors however the Li is part of the crystalline structure of the scintillator giving it a naturally high Li

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The scintillating fiber detectors have excellent sensitivity, they are rugged, and have fast timing (~60 ns) so that a large dynamic range in counting rates is possible. The detectors have the advantage that they can be formed into any desired shape, and can be made very large or very small for use

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Although sometimes facilitated by higher incoming neutron energies, neutron detection is generally a difficult task, for all the reasons stated earlier. Thus, better scintillator design is also in the foreground and has been the topic of pursuit ever since the invention of scintillation detectors.

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It is important here to observe precisely those variables that matter, since there may be false indicators along the way. For example, ionization currents might get periodic high surges, which do not imply high rates but just high energy depositions for stray events. These surges will be tabulated

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If the tail size extracted is a fixed proportion of the total pulse, then there will be two lines on the plot, having different slopes. The line with the greater slope will correspond to photon events and the line with the lesser slope to neutron events. This is precisely because the photon energy

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The oscilloscope registers a current pulse with every event. The pulse is merely the ionization current in the detector caused by this event plotted against time. The total energy of the incident particle can be found by integrating this current pulse with respect to time to yield the total charge

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Sodium Iodide crystal co-doped with Thallium and Lithium a.k.a. NaIL has the ability to detect Gamma radiation and Thermal Neutrons in a single crystal with exceptional Pulse-shape Discrimination.The use of low Li concentrations in NaIL and large thicknesses can achieve the same neutron detection

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in 1987 and major advances were made in the late 1980s and early 1990s at Pacific Northwest National Laboratory where it was developed as a classified technology. It was declassified in 1994 and first licensed by Oxford Instruments in 1997, followed by a transfer to Nucsafe in 1999. The fiber and

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Detection of fast neutrons poses a range of special problems. A directional fast-neutron detector has been developed using multiple proton recoils in separated planes of plastic scintillator material. The paths of the recoil nuclei created by neutron collision are recorded; determination of the

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Li-containing semiconductors, categorized as Nowotny–Juza compounds, have also been investigated as bulk neutron detectors. The Nowotny–Juza compound LiZnAs has been demonstrated as a neutron detector; however, the material is difficult and expensive to synthesize, and only small semiconductor

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Typical fast neutron detectors are liquid scintillators, 4-He based noble gas detectors and plastic detectors. Fast neutron detectors differentiate themselves from one another by their (1) capability of neutron/gamma discrimination (through pulse shape discrimination) and (2) sensitivity. The

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BN can be formed as either simple hexagonal, cubic (zincblende) or wurtzite crystals, depending on the growth temperature, and it is usually grown by thin film methods. It is the simple hexagonal form of BN that has been most studied as a neutron detector. Thin film chemical vapor deposition

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Detection rates can be kept low in many ways. Sampling of events can be used to choose only a few events for analysis. If the rates are so high that one event cannot be distinguished from another, physical experimental parameters (shielding, detector-target distance, solid-angle, etc.) can be

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reactions. Neutrons collide with the nuclei of atoms in the detector, transferring energy to those nuclei and creating ions, which are detected. Since the maximum transfer of energy occurs when the mass of the atom with which the neutron collides is comparable to the neutron mass, hydrogenous

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in this unit, implying that no matter how fast particles are coming in, it is very unlikely for this unit to fail to count an event (e.g. incoming particle). The low dead time is due to sophisticated electronics in this unit, which take little time to recover from the relatively easy task of

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Boron-based semiconductors in cubic form are difficult to grow as bulk crystals, mainly because they require high temperatures and high pressure for synthesis. BP and Bas can decompose into undesirable crystal structures (cubic to icosahedral form) unless synthesized under high pressure.

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reactive material, usually LiF, although B has been used. The increased semiconductor surface area adjacent to the reactive material and the increased probability that a reaction product will enter the semiconductor greatly increase the intrinsic neutron detection efficiency.

1083:, in which the neutrons are produced by spallation reaction, and the traditional research reactor facilities in which neutrons are produced during fission of uranium isotopes. Noteworthy among the various neutron detection experiments is the trademark experiment of the 2896:

Ochs, T.R.; Bellinger, S.L.; Fronk, R.G.; Henson, L.C.; Huddleston, D.E.; Lyric, Z.I.; Shultis, J.K.; Smith C.T.; Sobering, T.J.; McGregor, D.S. (2017). "Present Status of the Microstructured Semiconductor Neutron Detector-Based Direct Helium-3 Replacement".

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Activation samples may be placed in a neutron field to characterize the energy spectrum and intensity of the neutrons. Activation reactions that have differing energy thresholds can be used including Fe(n,p) Mn, Al(n,α)Na, Nb(n,2n) Nb, & Si(n,p)Al.

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obtained in the above steps, allowing for easy neutron-photon separation, the detection can be termed effective and the rates manageable. On the other hand, smudging and indistinguishability of data points will not allow for easy separation of events.

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C also forms icosahedral units in a rhombohedral crystal structure, an undesirable transformation because the icosahedral structure has relatively poor charge collection properties which make these icosahedral forms unsuitable for neutron detection.

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less, as mentioned above. This means that is it highly unlikely for there to be two particles generating one current pulse. The current pulses last 50 ns each, and start to register the next event after a gap from the previous event.

1223:. The scaler unit is merely used to count the number of incoming particles or events. It does so by incrementing its tally of particles every time it detects a surge in the detector signal from the zero-point. There is very little 2402:

McGregor, D.S.; Hammig, M.D.; Yang Y-H.; Gersch, H.K.; Klann, R.T. (2003). "Design Considerations for Thin Film Coated Semiconductor Thermal Neutron Detectors – I: Basics Regarding Alpha Particle Emitting Neutron Reactive Films".

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The bulk materials that rely upon charged-particle emissions are based on boron and lithium containing semiconductors. In the search for bulk semiconductor neutron detectors, the boron-based materials, such as BP, BAs, BN, and

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Seymour, R.; Crawford, T.; et al. (2001). "Portal, freight and vehicle monitor performance using scintillating glass fiber detectors for the detection of plutonium in the Illicit Trafficking Radiation Assessment Program".

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After extracting the tail, the usual current integration is carried out on both the tail section and the complete signal. This yields two ionization values for each event, which are stored in the event table in the DAQ system.

3438:; J. L. Dolan; E. C. Miller; M. Flaska; S. D. Clarke; A. Enqvist; P. Peerani; M. A. Smith-Nelson; E. Padovani; J. B. Czirr; L. B. Rees (2011). "Evaluation of New and Existing Organic Scintillators for Fast Neutron Detection". 786:

gas-filled proportional detectors, with the exception that the walls are coated with B. In this design, since the reaction takes place on the surface, only one of the two particles will escape into the proportional counter.

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Kawaguchi, N.; Yanagida, T.; Yokota, Y.; Watanabe, K.; Kamada, K.; Fukuda, K.; Suyama, T.; Yoshikawa, A. (2009). "Study of crystal growth and scintillation properties as a neutron detector of 2-inch diameter eu doped

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Neutrons are neutral and thus do not respond to electric fields. This makes it hard to direct their course towards a detector to facilitate detection. Neutrons also do not ionize atoms except by direct collision, so

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Charge: Neutrons are neutral particles and do not ionize directly; hence they are harder than charged particles to detect directly. Further, their paths of motion are only weakly affected by electric and magnetic

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Fronk, R.G.; Bellinger, S.L.; Henson, L.C.; Huddleston, D.E.; Ochs, T.R.; Sobering, T.J.; McGregor, D.S. (2015). "High-Efficiency Microstructured Semiconductor Neutron Detectors for Direct Helium-3 Replacement".

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registering a logical high every time an event occurs. The trigger unit coordinates all the electronics of the system and gives a logical high to these units when the whole setup is ready to record an event run.

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Cerny, J. C., Dolemal, Z., Ivanov, M. P., Kuzmin, E. P., Svejda, J., Wilhelm, I. (2003). "Study of neutron response and n–γ discrimination by charge comparison method for small liquid scintillation detector".

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Bliss, M.; Craig R. A.; Reeder P. L. (1994). "The Physics and Structure-property Relationships of Scintillator Materials: Effect of Thermal History and Chemistry on the Light Output of Scintillating Glasses".

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Seymour, R. S.; Richardson B.; Morichi M.; Bliss M.; Craig R. A.; Sunberg D. S. (2000). "Scintillating-glass-fiber neutron sensors, their application and performance for plutonium detection and monitoring".

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Bliss, M.; Brodzinski R. L.; Craig R. A.; Geelhood B. D.; Knopf M. A.; Miley H. S.; Perkins R. W.; Reeder P. L.; Sunberg D. S.; Warner R. A.; Wogman N. A. (1995). Johnson, C. Bruce; Fenyves, Ervin J (eds.).

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Scintillating Li glass for neutron detection was first reported in the scientific literature in 1957 and key advances were made in the 1960s and 1970s. Scintillating fiber was demonstrated by Atkinson M.

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Doan, T.C.; Majety, S.; Grenadier, S.; Li, J.; Lin, J.Y.; Jiang, H.X. (2015). "Hexagonal Boron Nitride Thin Film Thermal Neutron Detectors with High Energy Resolution of the Reaction Products".

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Atomic and subatomic particles are detected by the signature they produce through interaction with their surroundings. The interactions result from the particles' fundamental characteristics.

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Uher, J.; Jakubek, J.; Kenney, C.; Kohout, Z.; Linhart, V.; Parker, S.; Petersson, S.; Pospisil, S.; Thungstrom, G. (2007). "Characterization of 3D Thermal Neutron Semiconductor Detectors".

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and detector shielding. Detection software consists of analysis tools that perform tasks such as graphical analysis to measure the number and energies of neutrons striking the detector.

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McGregor, D.S.; Klann, R.T.; Gersch, H.K.; Ariesanti, E.; Sanders, J.D.; Van Der Elzen, B. (2002). "New Surface Morphology for Low Stress Thin-Film-Coated Thermal Neutron Detectors".

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McGregor, D.S.; Klann, R.T.; Gersch, H.K.; Ariesanti, E.; Sanders, J.D.; Van Der Elzen, B. (2001). "New Surface Morphology for Low Stress Thin-Film-Coated Thermal Neutron Detectors".

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deposition current, plotted against time, leaves a longer "tail" than does the neutron deposition plot, giving the photon tail more proportion of the total energy than neutron tails.

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Vradii, A.G.; Krapivin, M.I.; Maslova, L.V.; Matveev, O.A.; Khusainov, A.Kh.; Shashurin, V.K. (1977). "Possibilities of Recording Thermal Neutrons with Cadmium Telluride Detectors".

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density. A doping agent is added to provide the crystal with its scintillating properties, two common doping agents are trivalent cerium and divalent europium. Europium doped LiCaAlF

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Experiments that make use of this science include scattering experiments in which neutrons directed and then scattered from a sample are to be detected. Facilities include the

360:. There are two key aspects to effective neutron detection: hardware and software. Detection hardware refers to the kind of neutron detector used (the most common today is the 3988: 1308:

One might ask how experimenters can be sure that every current pulse in the oscilloscope corresponds to exactly one event. This is true because the pulse lasts about 50

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tritium (which has a 12.3 year half-life); tritium is produced either as part of weapons programs as a booster for nuclear weapons or as a byproduct of reactor operation.

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Absorptive reactions with prompt reactions - low energy neutrons are typically detected indirectly through absorption reactions. Typical absorber materials used have high

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Schelten, J.; Balzhauser, M.; Hongesberg, F.; Engels, R.; Reinartz, R. (1997). "A New Neutron Detector Development Based on Silicon Semiconductor and LiF Converter".

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and now termed the "EMC experiment." The same experiment is performed today with more sophisticated equipment to obtain more definite results related to the original

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on the detection of prompt capture gamma rays. In general, this type of neutron detector is difficult to make reliably and presently are not commercially available.

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Yousuke, I.; Daiki, S.; Hirohiko, K.; Nobuhiro, S.; Kenji, I. (2000). "Deterioration of pulse-shape discrimination in liquid organic scintillator at high energies".

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Cecil, R. A., Anderson, B. D., Madey, R. (1979). "Improved Predictions of Neutron Detection Efficiency for Hydrocarbon Scintillators from 1 MeV to about 300 MeV".

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van Eijk, C. W. E.; de Haas, J. T. M.; Dorenbos, P.; Kramer, K. W.; Gudel, H. U. (2005). "Development of Elpasolite and Monoclinic Thermal Neutron Scintillators".

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producing an excited nucleus, or absorption with transmutation of the resulting nucleus. Most detection approaches rely on detecting the various reaction products.

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Miyanaga, N.; Ohba, N.; Fujimoto, K. (1997). "Fiber scintillator/streak camera detector for burn history measurement in inertial confinement fusion experiment".

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In this setup, the incoming particles, comprising neutrons and photons, strike the neutron detector; this is typically a scintillation detector consisting of

364:) and to the electronics used in the detection setup. Further, the hardware setup also defines key experimental parameters, such as source-detector distance, 3403:

Stromswold, D.C.; AJ Peurrung; RR Hansen; PL Reeder (1999). "Direct Fast-Neutron Detection. PNNL-13068, Pacific Northwest National Laboratory, Richland, WA".

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Caruso, A.N.; Dowben, P.A.; Balkir, N.; Schemm, N.; Osberg, K.; Fairchild, R.W.; Flores, O.B.; Balaz, S.; Harken, A.D.; Robertson, B.W.; Brand, J.I. (2006).

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energy and momentum of two recoil nuclei allow calculation of the direction of travel and energy of the neutron that underwent elastic scattering with them.

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Figure 1 shows the typical main components of the setup of a neutron detection unit. In principle, the diagram shows the setup as it would be in any modern

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makes it less suitable for measurements in high radiation environments, the Ce doped variant has a shorter decay time but suffers from a lower light-yield.

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the challenge lies in keeping detection rates as low as possible and in designing a detector that can keep up with the high rates to yield coherent data.

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Materials science: Elastic and inelastic neutron scattering enables experimentalists to characterize the morphology of materials from scales ranging from

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Vanier, P. E.; Forman, L.; Dioszegi, I.; Salwen, C.; Ghosh, V. J. (2007). "Calibration and testing of a large-area fast-neutron directional detector".

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Ghosh, P.; D. M. Nichols; W. Fu; J. A. Roberts; D. S. McGregor (2019). "Gamma-Ray Rejection of the SiPM-coupled Micro-Layered Fast-Neutron Detector".

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Figure 2: Expected plot of tail energy against energy in the complete pulse plotted for all event energies. Dots represent number densities of events.

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may have dozens of neutron detectors, one per fuel assembly. Most neutron detectors used in thermal-spectrum nuclear reactors are optimized to detect

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Abel, K. H.; Arthur R. J.; Bliss M.; Brite D. W.; et al. (1993). "Performance and Applications of Scintillating-Glass-Fiber Neutron Sensors".

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and makes a delayed copy of the original signal in such a way that its tail section is seen alongside its main section on the oscilloscope screen.

458:(about 14 minutes, 46 seconds). Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as 258: 3838:

Jastaniah, S. D., Sellin, P. J. (2003). "Digital techniques for n–γ pulse shape discrimination capture-gated neutron spectroscopy using liquid".

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Popisil, S.; Sopko, B.; Havrankova, E.; Janout, Z.; Konicek, J.; Macha, I.; Pavlu, J. (1993). "Si Diode as a Small Detector of Slow Neutrons".

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Lewis, J.M.; R. P. Kelley; D. Murer; K. A. Jordan (2014). "Fission signal detection using helium-4 gas fast neutron scintillation detectors".

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McGregor, D.S.; Bellinger, S.L.; Fronk, R.G.; Henson, L.C.; Huddleston, D.E.; Ochs, T.R.; Shultis, J.K.; Sobering, T.J.; Taylor, R.D. (2015).

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Whereas In BF3 gas filled, N reacts with B in gas and fully energetic Alpha and Li are able to produce more ionizations and give more pulses.

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it is actually a coated diode response. To date, there is sparse evidence of boron-based semiconductors producing intrinsic neutron signals.

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Neutron detection in an experimental environment is not an easy science. The major challenges faced by modern-day neutron detection include

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of which can be detected by a number of means. Commonly used reactions include He(n,p) H, Li(n,t) He, B(n,α) Li and the fission of uranium.

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Li co-doped NaI:Tl (NaIL) − A Large Volume Neutron-Gamma Scintillator with Exceptional Pulse Shape Discrimination 2017 IEEE Presentation.

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Proceedings of the Institute of Nuclear Materials Management 52nd Annual Meeting on CD-ROM, Palm Desert, California, USA. July 17 – 22

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Kole, M.; et al. (2013). "A Balloon-borne Measurement of High Latitude Atmospheric Neutrons Using a LiCAF Neutron Detector".

673:

Elastic scattering reactions (also referred to as proton-recoil) - High energy neutrons are typically detected indirectly through

3126:

Domnich, V.; Reynaud, S.; Haber, R.A.; Chowalla, M. (2011). "Boron Carbide: Structure, Properties, and Stability Under Stress".

735:

while other reactions such as gamma reactions will span a broad energy range, it is possible to discriminate among the sources.

3931:"Analysis of neutron and photon detection position for the calibration of plastic (BC-420) and liquid (BC-501) scintillators" 3662: 2847: 1064: 440: 322: 116: 94: 3026: 1714:

Spowart, A. R. (1976). "Neutron Scintillating Glasses .1. Activation By External Charged-Particles And Thermal-Neutrons".

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Scintillation neutron detectors include liquid organic scintillators, crystals, plastics, glass and scintillation fibers.

582:

produced by neutron decay are detectable, the decay rate is too low to serve as the basis for a practical detector system.

300: 3155:"Device Fabrication, Characterization, and Thermal Neutron Detection Response of LiZnP and LiZnAs Semiconducting Devices" 2555: 2383:

Babcock, R.V.; Davis, R.E.; Ruby, S.L.; Sun, K.H.; Wolley, E.D. (1959). "Coated Semiconductor is Tiny Neutron Detector".

286: 111: 1219:

The detection signal from the neutron detector is connected to the scaler unit, gated delay unit, trigger unit and the

4050: 1366: 1350: 1344: 1233: 1154: 1084: 956:

Neutron detection is used for varying purposes. Each application has different requirements for the detection system.

154: 2253:

Large Format Li Co-doped NaI:Tl Scintilation Detector for Gamma-ray and Neutron Dual Detection, 2017 Technical Paper.

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Seymour, R. S.; Craig R. A.; Bliss M.; Richardson B.; Hull C. D.; Barnett D. S. (1998). Robertson, David E. (ed.).

310: 1644:

Egelstaff, P. A.; et al. (1957). "Glass Scintillators For Prompt Detection Of Intermediate Energy Neutrons".

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has been used for neutron detection at high altitudes on balloon missions. The long decay time of Eu doped LiCaAlF

1068: 252: 240: 3153:

Montag, B.W.; Reichenberger, M.A.; Edwards, N.; Ugorwoski, P.B.; Sunder, M.; Weeks, J.; McGregor, D.S. (2016).

2003:"Performance of a neutron-sensitive scintillating glass-fiber panel for portal, freight and vehicle monitoring" 1035: 274: 3686:

John F. Beacom & Mark R. Vagins (2004). "Antineutrino Spectroscopy with Large Water Čerenkov Detectors".

2940:

Ananthanarayanan, K.P.; Gielisse, P.J.; Choudry, A. (1974). "Boron Compounds for Thermal Neutron Detection".

3688: 1305:

and viewed with cynicism if unjustifiable, especially since there is so much background noise in the setup.

1170: 1080: 1076: 616: 596: 418: 294: 727:(i.e., neutrons that have slowed to equilibrium with their surroundings), they are typically surrounded by 3056:

McGregor, D.S.; Unruh, T.; McNeil, W.J. (2008). "Thermal Neutron Detection with Pyrolytic Boron Nitride".

2518: 1369:– position sensitive neutron detectors are developed using technologies of the microchannel plate detector 1205: 1198: 168: 126: 1460: 4017: 3972: 3869: 3818: 3408: 2107: 965: 704: 361: 104: 63: 2099: 1679:

Bollinger, L. M.; Thomas, G. E.; Ginther, R. J. (1962). "Neutron Detection With Glass Scintillators".

1574:

Bollinger, L. M.; Thomas, G. E.; Ginther, R. J. (1962). "Neutron Detection With Glass Scintillators".

979:. For example, the detected neutron rate from a plasma can give information about the ion temperature. 3997: 3944: 3849: 3798: 3707: 3501: 3462: 3320: 3281: 3246: 3166: 3100: 3065: 2999: 2949: 2906: 2859: 2820: 2757: 2722: 2687: 2619: 2570: 2482: 2447: 2412: 2338: 2227: 2196: 2147: 2050: 1967: 1900: 1864: 1802: 1762: 1723: 1688: 1653: 1618: 1583: 1562: 1005: 976: 692: 667: 411: 173: 3488:

Ghosh, P.; W. Fu; M. J. Harrison; P. K. Doyle; N. S. Edwards; J. A. Roberts; D. S. McGregor (2018).

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tube (PMT), and will be connected to a data acquisition (DAQ) system to register detection details.

2975:

Kumashiro, Y.; Okada, Y.; Misawa, S.; Koshiro, T. (1987). "The Preparation of BP Single Crystals".

1132: 1060: 1047: 436:, techniques for detection of the magnetic moment are too insensitive to use for neutron detection. 89: 45: 1320:

events every second. This number is much higher than the actual typical rate, which is usually an

964:, neutron detectors provide an important measure of power in nuclear power and research reactors. 3960: 3788: 3731: 3697: 3603: 3560: 3519: 3385: 3344: 3211: 2922: 2664: 2536: 2311: 2186: 2163: 2066: 2022: 1983: 1818: 1545: 1499: 1321: 1135:

detection can also be used to discriminate real neutron events from photons and other radiation.

674: 407: 230: 164: 149: 80: 71: 67: 2990:

Emin, D.; Aselage, T.L. (2005). "A Proposed Boron-Carbide-Based Solid-State Neutron Detector".

2647:

Muminov, R.A.; Tsvang, L.D. (1987). "High-Efficiency Semiconductor Thermal-Neutron Detectors".

1428: 838:

material is suitable for producing light weight compact neutron detectors, as a result LiCaAlF

630:

or similar reaction, producing reaction products that then decay at some later time, releasing

3915: 3894: 3723: 3668: 3658: 3634: 3593: 3550: 3375: 3336: 2303: 2100:"Alternative Neutron Detector Technologies for Homeland Security PIET-43741-TM-840 PNNL-18471" 1535: 1489: 1432: 983: 764: 739: 728: 212: 206: 131: 58: 54: 3490:"A high-efficiency, low-Ĉerenkov Micro-Layered Fast-Neutron Detector for the TREAT hodoscope" 2286:

Caruso, A.N. (2010). "The Physics of Solid-State Neutron Detector Materials and Geometries".

4045: 4005: 3952: 3857: 3806: 3715: 3626: 3585: 3542: 3509: 3470: 3367: 3328: 3289: 3254: 3203: 3174: 3135: 3108: 3073: 3038: 3007: 2957: 2914: 2867: 2828: 2793: 2765: 2730: 2695: 2656: 2627: 2586: 2578: 2528: 2490: 2455: 2420: 2346: 2295: 2235: 2155: 2058: 2014: 1975: 1939: 1927: 1908: 1872: 1852: 1810: 1770: 1731: 1696: 1661: 1626: 1591: 1527: 1481: 1420: 1190: 1104: 1009: 430: 198: 3930: 3579: 3308: 1363:– position sensitive neutron detectors are developed using technologies of the Anger camera 1119:, which aren't easily eliminated by physical barriers. The other sources of noise, such as 591:

As a result of these properties, detection of neutrons fall into several major categories:

3421: 3229:

McGregor, D.S.; Lindsay, J.T.; Olsen, R.W. (1996). "Thermal Neutron Detection with Cadmium

2438:

Rauch, H.; Grass, F.; Feigl, B. (1967). "Ein Neuartiger Detektor fur Langsame Neutronen".

2120: 1213: 1166: 1028: 1020: 969: 763:

As elemental boron is not gaseous, neutron detectors containing boron may alternately use

724: 623: 403:

is not directly detectable, but does influence reactions through which it can be detected.

2299: 960:

Reactor instrumentation: Since reactor power is essentially linearly proportional to the

4001: 3948: 3853: 3802: 3711: 3546: 3505: 3466: 3324: 3285: 3250: 3170: 3104: 3069: 3003: 2953: 2910: 2863: 2824: 2761: 2726: 2691: 2623: 2608:"Development of Compact High Efficiency Microstructured Semiconductor Neutron Detectors" 2574: 2486: 2451: 2416: 2342: 2231: 2200: 2151: 2054: 1971: 1904: 1868: 1806: 1766: 1727: 1692: 1657: 1622: 1587: 1253:

Ionization current signals are all pulses with a local peak in between. Using a logical

707:

allows the detector to respond to neutrons. Nuclides commonly used for this purpose are

30: 1120: 1001: 990: 975:

Plasma physics: Neutron detection is used in fusion plasma physics experiments such as

194: 3272:

Beyerle, A.G.; Hull, K.L. (1987). "Neutron Detection with Mercuric Iodide Detectors".

3258: 2699: 2632: 2607: 2424: 4039: 4009: 3964: 3901: 3564: 3523: 3293: 3139: 2961: 2668: 2494: 2459: 2350: 2026: 1912: 1822: 1774: 1735: 1700: 1665: 1595: 1503: 1421: 1355: 1338: 1124: 1043: 631: 447: 399: 3735: 3607: 3389: 3348: 3215: 2926: 2540: 2167: 2070: 1987: 1050:, yielding neutrons. Neutrons detectors can be used for monitor for SNM in commerce. 2582: 2315: 2214:

Iwanowska, J.; et al. (2011). "Thermal neutron detection with Ce doped LiCaAlF

1549: 1360: 1220: 1165:

Detectors relying on neutron absorption are generally more sensitive to low-energy

961: 50: 3719: 3621:

Frenje, J. (1996), "The MPR Neutron Diagnostic at Jet — an ITER Prototype Study",

1173:, on the other hand, have trouble registering the impacts of low-energy neutrons. 304: 3630: 3589: 3371: 1531: 1039: 720: 622:

Activation processes - Neutrons may be detected by reacting with absorbers in a

612: 443:, which has not yet been detected. Hence it is not a viable detection signature. 365: 216: 3956: 3861: 3810: 3514: 3489: 3179: 3154: 3112: 3077: 3042: 2832: 2797: 2329:

Rose, A. (1967). "Sputtered Boron Films on Silicon Surface Barrier Detectors".

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manipulated to give the lowest rates possible and thus distinguishable events.

982:

Particle physics: Neutron detection has been proposed as a method of enhancing

782:

Alternately, boron-lined gas-filled proportional counters react similarly to BF

3435: 2848:"6:1 Aspect Ratio Silicon Pillar Based Thermal Neutron Detector Filled with B" 2062: 1979: 1309: 1092: 1024: 994: 696: 627: 459: 202: 3895:"Neutron Tagged Bound Proton Structure to Probe the Origin of the EMC Effect" 2918: 2846:

Nikolic, R.J.; Conway, A.M.; Reinhart, C.E.; Graff, R.T.; Wang, T.F. (2008).

1928:"Relationship Between Microstructure and Efficiency of Scintillating Glasses" 1115:

The main components of background noise in neutron detection are high-energy

3672: 3539:

2019 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)

3332: 2769: 2734: 1347:– A field portable neutron spectrometer based on the Bonner Sphere Principle 1224: 1209: 809:

fiber detectors are now manufactured and sold commercially by Nucsafe, Inc.

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2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149)

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1876: 1791:"Glass-fiber-based neutron detectors for high- and low-flux environments" 1254: 1012:. Neutron detectors used for radiation safety must take into account the 875:

Basic design of a microstructured semiconductor neutron detector (MSND).

708: 695:

can be adapted to detect neutrons. While neutrons do not typically cause

655: 615:. Each of these reacts by emission of high energy ionized particles, the 608: 600: 357: 3793: 1751:"Initial Tests Of A High-Resolution Scintillating Fiber (Scifi) Tracker" 1232:

deposited at the end of the PMT. This integration is carried out in the

3702: 3207: 2660: 700: 663: 659: 647: 353: 22: 3474: 3011: 2871: 2591: 2532: 2134:

Yanagida, T.; et al. (2011). "Europium and Sodium Codoped LiCaAlF

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Abel, K. H.; Arthur R. J.; Bliss M.; Brite D. W.; et al. (1994).

1814: 1630: 1169:, and are orders of magnitude less sensitive to high-energy neutrons. 1107:, high detection rates, neutron neutrality, and low neutron energies. 3340: 3027:"The All Boron Carbide Diode Neutron Detector: Comparison and Theory" 1838:

Proceedings of the SCIFI 93 Workshop on Scintillating Fiber Detectors

1116: 639: 439:

Electric dipole moment: The neutron is predicted to have only a tiny

278: 264: 1750: 2556:"Present Status of Microstructured Semiconductor Neutron Detectors" 4031:

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2191: 1269: 1180: 870: 716: 446:

Decay: Outside the nucleus, free neutrons are unstable and have a

1427:(2nd ed.). Washington, D.C.: Taylor & Francis. pp. 731:

to reduce their energy and increase the likelihood of detection.

2715:

IEEE Nucl Sci. Symp. Conf. Rec., San Diego, California, Nov. 4-9

1181: 1128: 1088: 1000:

Radiation safety: Neutron radiation is a hazard associated with

651: 643: 1524:

2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC)

1451:

Materials with a high hydrogen content such as water or plastic

917:

Prompt gamma-ray emitting semiconductors, such as CdTe, and HgI

892:

C, have been investigated more than other potential materials.

2977:

Proc. Tenth International Conference Chemical Vapor Deposition

1099:

Challenges in neutron detection in an experimental environment

1019:

Cosmic ray detection: Secondary neutrons are one component of

3494:

Nuclear Instruments and Methods in Physics Research Section A

1016:(i.e., the way damage caused by neutrons varies with energy). 406:

Reactions: Neutrons react with a number of materials through

2884: 1127:, can be eliminated by various shielding materials, such as 678:

materials are often the preferred medium for such detectors.

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Pozzi, S. A., Mullens, J. A., and Mihalczo, J. T. (2003).

3623:

Diagnostics for Experimental Thermonuclear Fusion Reactors

2098:

Van Ginhoven, R. M.; Kouzes R. T.; Stephens D. L. (2009).

2083: 905:

methods are usually employed to produce BP, BAs, BN, or B

738:

As a class, gas ionization detectors measure the number (

1031:, are employed to monitor variations in cosmic ray flux. 3754:

Techniques for Nuclear and Particle Physics Experiments

3657:(2nd ed.). Cambridge: Cambridge University Press. 2554:

McGregor, D.S.; Bellinger, S.L.; Shultis, J.K. (2013).

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723:. Since these materials are most likely to react with 3936: