Characterization of prototype perforated semiconductor neutron detectors

Semiconductor detectors whose surfaces are coated with neutron-reactive material can be made to detect thermal neutrons, but with efficiencies only of a few percent. However, perforating the semiconductor material, filling the perforations with neutron-reactive material, and then coating the detector surface can lead to neutron detectors of much higher thermal neutron detection efficiencies, perhaps approaching or exceeding 50%. Several perforated semiconductor neutron detectors have been constructed, both for dosimetry and for position-sensitive neutron detection. The characterization of prototype devices based on these detectors is described.     

Perforated diode neutron detector modules fabricated from high-purity silicon

Compact neutron detectors are being designed and tested for use as low-power real-time personnel dosimeters. The neutron detectors are pin diodes that are mass produced from high-purity Si wafers. Each detector has thousands of circular perforations etched vertically into the device. The perforations are backfilled with ⁶LiF to make the pin diodes sensitive to thermal neutrons. The prototype devices deliver 4.7% thermal neutron detection efficiency while operating on only 15 V, showing a 9% increase in efficiency over identical planar devices.     

The epithermal neutron flux distribution in a nuclear reactor and its effect on epithermal neutron activation analysis

The shape of the epithermal neutron energy distribution has been determined in two irradiation positions of the University of London CONSORT II reactor. The method applied involves cadmium ratio measurements using a series of resonance detectors. Principles of the method and some considerations relative to epithermal neutron activation analysis in connection with the deviation of the epithermal neutron flux distribution from the 1/E law are given.     

Shielding optimization in an in vivo activation analysis setup

A neutron irradiation setup for in vivo activation analysis was characterized to optimize its spectrum measurements. In order to have a reliable spectrum, some shields and filters were defined to eliminate as much background possible. Since there were different types of background sources, different states were studied and necessary shields were employed to optimize the spectrum. To use a neutron shield, boron carbide layers (3 cm) around 3 × 3 in. sodium iodine detectors were employed. To prevent γ-ray background, bismuth (2 cm) is used under the detectors.     

Characterizing the radiation response of Cherenkov glass detectors with isotopic sources

Cherenkov detectors are widely used for particle identification and threshold detectors in high-energy physics. Glass Cherenkov detectors that are sensitive to beta emissions originating from neutron activation have been demonstrated recently as a potential replacement for activation foils. In this work, we set the groundwork to evaluate large Cherenkov glass detectors for sensitivity to MeV photons through first understanding the measured response of small Cherenkov glass detectors to isotopic gamma-ray sources. Counting and pulse height measurements are acquired with reflected glass Cherenkov detectors read out with a photomultiplier tube. Simulation was used to inform our understanding of the measured results. This simulation included radioactive source decay, radiation interaction, Cherenkov light generation, optical ray tracing, and photoelectron production. Implications for the use of Cherenkov glass detectors to measure low energy gamma-ray response are discussed.     

U determination in environmental samples by delayed neutron activation analysis in Korea

A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 10¹³ n cm⁻² s⁻¹. The delayed neutron counting system is composed of 18 ³He detectors which are divided into three groups with six detectors and the collected signals of each group are processed to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination of uranium mass fraction in the collected environmental samples.     

Dosimetry of fast neutrons in 1W nuclear reactor with plastic nuclear-track detectors

A nuclear reactor at Kinki University is operated at the maximum of 1W. It produces fission neutrons as much as gamma-rays. To facilitate its use for neutron radiobiology, fast neutrons inside the reactor were measured with nuclear-track detectors TS 16 N and a pair of ion chambers. The angular dependence of TS 16 N response, an anisotropy of fast neutron fluxes in the reactor and misuse of the kerma factor assumed for radiation protection business are the major causes of discrepancy is measured doses by the two methods. Correction factors for the three causes are proposed. After correction, neutron doses estimated with TS 16 N and chambers agree within 5%. The dose-rate at the reactor's center is about 20 tissue-cGy/h. This is the first in situ dosimetry of fast neutrons in a reactor with track detectors attached to biologic samples. Our routine usage has demonstrated that, if used with caution, TS 16 N elements are handy, reliable monitors for fast neutron dosimetry as they are insensitive to contaminated gamma-rays and small enough to be attached to biologic samples.     

Development of a neutron beam line and detector system for multiple prompt gamma-ray analysis

A neutron beam line for multiple prompt gamma-ray analysis was constructed at the Japan Atomic Energy Agency. A detector system for the MPGA was constructed at the C2-3-2 beam line in January 2005. It comprised eight (upgraded in March 2007) clover Ge detectors with a BGO Compton suppressor. High efficiency detector system provides an advantage in terms of the detection limit of MPGA when compared to the result of PGA. The supermirror neutron bender was improved and a supermirror neutron guide was installed upstream of the sample position.     

A program for complete quantitative neutron activation analysis using Ge(Li) detector gamma spectrometry and a small computer

It is shown that the large sophisticated programs designed for big computers can be efficiently used on medium scale machines for complete quantitative neutron activation analysis with Ge(Li) detectors.     

The effect of scintillator materials on the fast neutron multiplicity measurement

Journal of Radioanalytical and Nuclear Chemistry - To analyze the effect of scintillator detectors on the fast neutron multiplicity, this paper uses Geant4 and Matlab to simulate and study three...     

Non-carbon-based compact shadow shielding for 14 MeV neutrons

We are developing a scanning spectroscopy system to measure prompt gammas-rays induced by inelastic neutron scattering and thermal neutron capture to non-invasively analyze soil in situ. Using a radiation source, a 14 MeV (d,t) neutron generator (NG), in a close proximity to the detection system without any precautions will flood and saturate the detectors with direct radiation. Therefore, we devized and partially optimized a shadow shielding sited between the source and the detection system; we discuss our experimental results and basic Monte Carlo calculations.     

Scintillating-Glass-Fiber Neutron Sensors, their Application and Performance for Plutonium Detection and Monitoring

Most neutron detection sensors presently employ ³He gas-filled detectors. Despite their excellent performance and widespread use, there are significant limitations to this technology. A significant alternative neutron sensor utilizing neutron-active material incorporated into a glass scintillator is presented that offers novel commercial sensors not possible or practical with gas tube technology. The scintillating optical fiber permits sensors with a multitude of sizes ranging from devices of a single fiber of 150µm to sensors with tens of thousands of fibers with areas as large as 5 m² depending on the neutron flux to be measured. A second significant advantage is the use of high-speed electronics that allow a greater dynamic range, not possible with gas detectors. These sensors are flexible, conformable and less sensitive to vibration that optimizes the source-to-detector geometry and provides robust performance in field applications. The glass-fibers are sensitive to both gamma-rays and neutrons. However, the coincidence electronics are optimized for neutron to gamma-ray discrimination allowing very sensitive measurements with a low false-alarm rate. Applications include SNM surveillance, material control and accountability (MC&A), safeguard inspections, Pu health physics/bioassay and environmental characterization.     

Determination of total oxygen in standard rocks by cyclic activation analysis using a 14 MeV neutron generator

Total oxygen, in fourteen rock standards and three ores, was determined with an experimental set up employing cyclic activation analysis using a 14 MeV neutron generator gamma-spectroscopy and NaI(T1) detectors.     

A combined set of automatic and interactive programs for instrumental neutron activation analysis

A set of several automatic and interactive computer programs for instrumental neutron activation analysis is discussed. The system allows fast and precise evaluation of data obtained from counting samples on a large number of different Ge(Li) detectors.     

A method for bulk hydrogen analysis based on transmission and back scattering of fast neutrons

A method was proposed for bulk hydrogen analysis. It is based on simultaneous detection of transmitted fast neutrons and back scattered thermal neutrons from the investigated samples by ³He detectors. The fast neutron beams were obtained from ²⁵²Cf and Pu–Be neutron sources. The experimental set-up as well as samples preparation were described. Incident thermal neutrons beams obtained from either ²⁵²Cf or Pu–Be sources, were used to investigate the samples by neutron backscattering. The results obtained from transmission and backscattering of fast neutrons were compared and discussed. The advantage and capabilities of the proposed method were presented. The results obtained using fast neutron beams are more sensitive than those obtained using thermal neutron beams. Validation procedures were proposed to credit the results.     

Design and evaluation of a TNA explosive-detection system to screen carry-on luggage

Thermal neutron analysis (TNA) technology has been used for the non-destructive detection of explosives. The system uses a relatively weak ²⁵²Cf neutron source (1.03·10⁷ n/s) and two 3"×3" NaI(Tl) detectors. The presence of explosives is confirmed via detection of the 10.83 MeV prompt gamma-ray associated with nitrogen decay. The MCNP4A code was used to simulate the neutron and gamma transport through the system. The thermal neutron flux in the activation position was measured using gold and indium foils. The measured thermal neutron flux was lower, by not more than 9.5%, than that of simulation. In this report the results of the preliminary tests on the system are described.     

Use of bubble detectors in personal neutron dosimetry

ICRP 60 recommendation require to improve the lowest limit of detection (LLD) of an individual neutron dosimeter by a factor estimated up to about five. Bubble neutron detectors could fulfill such conditions, the LLD of systems already available is claimed to be well below 10 Sv. We have tried to test them at different neutron sources. The results obtained are presented.Work partially supported through EC Project F13P-CT93-0072.     

Measurements of fast neutrons above ground and in 47 m depth with a <Superscript>3</Superscript>He proportional counter

Neutrons contribute to the background of low radioactivity measurements, especially with detectors in large lead shields above ground, and to a lower extent in underground laboratories of medium depth. We measured the natural neutron flux in the energy region of fission by commercial ³He filled proportional counters at different places above ground and in an underground laboratory, which is covered by 47 m of rock, and demonstrated the drastic reduction of the neutron flux in the underground and the influence of the materials of the environment.     

Property of TS-16N solid state nuclear track detectors as an imaging medium for macroautoradiography of alpha-emitters in biological specimens

Feasibility of TS-16N solid state nuclear track detectors for an imaging medium of rapid autoradiography of alpha-emitters is described. Though a little longer etching time was required, the contrast of autoradiographic image on this detector proved to be superior to CR-39 detectors whose property for macroautoradiography was previously reported by the authors. The resolutions of these two different type detectors were almost equivalent to each other. The autoradiography taken by way of trial proved that this detector could be used to study metabolism and dosimetry of internally deposited alpha-emitters. With further study, the inherent properties of this detector such as low background or high sensitivity should extend the field of track etch imaging technique such as fast neutron radiography.