Lithium Glass Scintillator Research Articles

Detection of fusion alphas from D2-T2 gas targets

Detectors for recording alphas from fusions in D2–T2 gas targets require protection against diffusion of tritium into the detector medium. Tests have been carried out on surface barrier detectors to determine the feasibility of using thin coatings of oxide and metal for this purpose. The results show that a layer of 0.5 μm aluminium oxide plus 0.2 μm gold provides effective protection for at least 280 h, without impairing the transmission of 2 MeV alphas into the detector. Tests of an alternative detector, a phoswich of thin film plastic and lithium-glass scintillators, are also described.

Analysis and measured integral data on an experimental lithium module at the LOTUS neutronics facility

Abstract In-system foil activation rates and tritium production rates were measured in an experimental lithium module (ELM), which has a 60 cm thick pseudo-cylindrical lithium metal region, at the fusion blanket neutronics facility LOTUS. Sets of two foils each made of Zr and In were irradiated at multiple locations in the central rod to measure 90Zr(n, 2n)89m + gZr and 115In(n, n′)115mIn reaction rates. Tritium measurements were done using two techniques: off-line liquid scintillation technique of Dierckx and on-line lithium glass scintillation technique, the latter technique providing only T6 (tritium from 6Li). These measurements have been analyzed both by two-dimensional and three-dimensional transport codes DORT and MCNP respectively. Though computed results broadly reproduce spatial profiles (along the central rod) of the measured quantities, differences as large as 30% are found.

Edge effect of thin lithium-glass scintillators

The edge effect of thin lithium-glass scintillators — the distortion of the pulse height spectrum at the low energy side of the thermal peak due to the partial energy deposition of the alpha particle and/or the triton — was examined. The pulse height spectra of scintillators of various thicknesses were measured for thermal neutrons. It was revealed that the “tail-to-total ratio” is 10.8, 4.4, 2.7, 2.0 and 1.5% for 0.1, 0.3, 0.6, 1.0 and 2.0 mm thick scintillators, respectively. A Monte Carlo simulation of the pulse height spectra was also made. The results of the simulation explained well the measured ones. The neutron energy dependence on the value of the “tail-to-total ratio” was examined by this Monte Carlo code and it was shown that the dependence is very small for a 0.3 mm thickness scintillator.

Thermal flux perturbation of lithium-glass scintillator

Experimental and calculational investigations were made on thermal flux perturbation of 6Li-enriched lithium-glass scintillators placed in a graphite pile. The (n, α) reaction rates were measured for the various glass scintillators for four different thicknesses and three different 6Li contents. It was shown that the decrease of the reaction rate due to the flux perturbation is 66% for 1 mm thick, 6.3% 6Li content glass, and 3% for 0.1 mm thick, 1.0% 6Li content glass. A calculation of the flux perturbation was performed by the modified Skyrme theory and close agreement with the measurement was obtained. The self-shielding effect was also calculated by a Monte Carlo method, and its dependence on energy was discussed.

Characteristics of the scintillation responses of small lithium glass detectors to electron excitation

The response characteristics of lithium glass scintillators to electron excitation have been determined for a range of electron energies, lithium concentrations and lithium enrichments. The characteristics determined were the absolute scintillation efficiency and intrinsic resolution. These measurements form part of a study on the possible use of such glasses for the determination of the tritium breeding in fusion reactor blanket experiments. The measurements were undertaken to investigate the effects of the gamma background on the signals arising from the tritium production reactions induced within the glass scintillators. Criteria for the selection of glasses most suitable for tritium breeding are discussed in terms of their measured characteristics.

Light conversion efficiency of small lithium scintillators for electrons, protons, deuterons and alpha particles

The absolute responses of thin, cerium-activated lithium glass scintillators to electrons, protons, deuterons and alpha particles have been measured as a function of their kinetic energy (0.3–2.7 MeV), lithium concentration (2.4–8.3 wt.%) and lithium enrichment (95 wt.% 6Li to 99.99 wt.% 7Li) in the glass. Absolute calibration of the scintillation energy was derived from measurements of the energy resolution of the observed pulse height spectrum.

An on-line method for tritium production measurement with a pair of lithium-glass scintillators

A highly sensitive on-line method for measuring the tritium production rate (TPR) of 6Li with the use of a pair of small-sized 6Li- and 7Li-glass scintillators (10 mm diameter by 3 mm thickness each) is presented. In this method, the TPR of 6Li is measured by using the difference between the response of 6Li-glass and that of 7Li-glass scintillator in a mixed neutron-gamma radiation field. The difference in the gamma-ray detection efficiency between the two scintillators and that in the gain between the two detectors is taken into account. This method was applied to the measurement of the TPR distribution in an assembly simulating a fusion blanket. The results were compared with those of the liquid scintillation method. It is shown that the present method is successful for the TPR measurement.

Tritium Production Measurements by the Lithium-Glass Scintillator Method

As a part of the Phase I of JAERI/USDOE collaborative program on fusion blanket neutronics, the effect of constituents of the fusion blanket on tritium production rate distribution was examined experimentally by the Lithium-glass scintillator method. The self-shielding factor of the Lithium-glass scintillator was estimated by an experiment as well as a calculational method. The Li-glass method has shown excellent performance and reliability in the parametric measurement of the tritium production rate distribution.

The preparation and properties of cerium-activated lithium glass scintillators

We report the preparation of cerium activated lithium glass scintillators for thermal neutron detection and their properties. The technological requirements and appropriate compositions are proposed, by which high detection efficiency of lithium glass scintillators for thermal neutrons can be obtained. When used as neutron detectors, the 6Li glass ST-602 affords excellent pulse height discrimination against gamma radiation, particularly in the case of thin 6Li glass.

Neutron detection efficiency of a thick lithium glass detector

The neutron detection efficiency of a 9.55 mm thick NE-912 lithium glass scintillator has been determined for the energy range from 25 keV to 2 MeV. It was measured relative to a thin, 0.835 mm thick NE-908 glass, which was determined by Monte Carlo calculations. The measured efficiency curve shows the marked effect of the 16O resonance at 442 keV, and a strong increase with energy for En> 1.2 MeV, due to (n,n′γ) reactions.

Amm242fission cross section

The neutron-induced fission cross section of $^{242}\mathrm{Am}^{m}$ has been measured over the energy region from ${10}^{\ensuremath{-}3}$ eV to \ensuremath{\sim}20 MeV in a series of experiments utilizing a linac-produced "white" neutron source and a monoenergetic source of 14.1 MeV neutrons. The cross section was measured relative to that of $^{235}\mathrm{U}$ in the thermal (0.001 to \ensuremath{\sim}3 eV) and high energy (1 keV to \ensuremath{\sim}20 MeV) regions and normalized to the ENDF/B-V $^{235}\mathrm{U}(\mathrm{n},f)$ evaluated cross section. In the resonance energy region (0.5 eV to 10 keV) the neutron flux was measured using thin lithium glass scintillators and the relative cross section thus obtained was normalized to the thermal energy measurement. This procedure allowed a consistency check between the thermal and high energy data. The cross section data have a statistical accuracy of \ensuremath{\sim}0.5% at thermal energies and in the 1-MeV energy region, and a systematic uncertainty of \ensuremath{\sim}5%. We confirmed that $^{242}\mathrm{Am}^{m}$ has the largest thermal fission cross section known with a 2200 m/sec value of 6328 b. Results of a Breit-Wigner sum-of-single-levels analysis of 48 fission resonances up to 20 eV are presented and the connection of these resonance properties to the large thermal cross section is discussed. Our measurements are compared with previously reported results.

Monte Carlo calculation of energy response functions for a lithium glass scintillator for neutrons between 1 and 6 MeV

Energy response functions have been calculated for a cylinder of NE905 lithum glass scintillator which was 44 mm in diameter and 25 mm long. The calculations were performed by the Monte Carlo method in the neutron energy range 1–6 MeV. The neutron detection efficiency, as a function of discriminator setting, has been derived from the response functions and has been compared with experimental measurements. Reasons are given for the increase in efficiency above 2 MeV.

The resolution of a position-sensitive scintillation detector for neutrons

The space distribution of neutron interactions in a lithium-glass scintillator is measured by means of a method which uses the relative pulse amplitudes from two photomultipliers as position indicators. Digital linearization and background discrimination are done during the storage process in an on-line computer. The system gives a resolution of (5.4±0.4)%.

Measurements of the6Li(n, α) T cross section in the keV energy range

The6Li(n, α) cross section was measured in the 90–1500 keV energy range with uncertainties of 3–5%. A lithium glass scintillation detector was used for the measurement of the (n, α)-reaction rate. Flat response neutron detectors were used to monitor the neutron flux. A calibrated vanadium bath was employed to obtain absolute values. The results were analysed in terms of the single-level multi-channelR-matrix theory.

Secondary electron detector, with an extended life, for use in a scanning electron microscope

The plastic scintillator tip used as the secondary electron detector of a scanning microscope has a limited working life particularly with high electron beam currents. A detector with an extended life and capable of working up to beam currents of 3*10-6 A has been made by replacing the plastic scintillator tip with one made of a lithium glass scintillator.

Effects of elastic scattering on the low energy neutron detection efficiency of a lithium glass and boron-loaded liquid scintillator

The neutron detection efficiencies of a lithium glass and a boron-loaded liquid scintillation detector were calibrated over the energy range from thermal to 8 keV. The calibrations were based on the measurement of a known spectrum from the low power experimental reactor facility MOATA and detailed three-dimensional Monte Carlo calculations. For both detectors good agreement was obtained between their measured and calculated efficiencies. Elastic scattering within the lithium glass produced an enhancement of the detection efficiency in the epithermal region and this enhancement increased with energy. A significant distortion of the measured spectrum arose from the scattering of neutrons into the detectors by the surrounding shielding materials.

Étude de la diffusion multiple des neutrons dans les scintillateurs chargés en 6Li couples À la photocathode du PM associé

A Monte Carlo method is used to study the multiple scattering of neutrons in 6Li scintillators. The back-scattering by the photocathode of the photomultiplier is taken into account. The nuclear processes considered are absorption by the (n, α) reaction and inelastic scattering. For heavy nuclei the scattering is assumed to be isotropic in the center of mass system while for light nuclei published values of the angular distributions are employed. Three cases are considered: 1. 1. A collimated beam of monoenergetic neutrons incident normally on a lithium glass scintillator type NE 905. 2. 2. The same scintillator irradiated by neutrons from the p(T,n) 3He reaction with energy selection by means of the associated particle technique. The angular distribution and energy spectrum of the neutrons incident on the scintillator are altered by the multiple scattering of the 3He particles in the target. 3. 3. A collimated beam of monoenergetic neutrons incident normally on a I 6Li Harshaw type crystal enclosed in a protective capsule. The multiple scattering correction curves make it apparent which portion of the effect is due to what may be properly said to be multiple scattering and which portion is actually due to the effects of geometry.

Calibration and use of a 5-inch diameter lithium glass detector

A 5 in-diam. by 0.5 in-thick lithium glass scintillator has been calibrated from 50 eV to 8 MeV neutron energy using the 10B(n,α) and H(n,p) cross sections as standards. Monte Carlo calculations of the detector efficiency have been made and found to agree with observed values below 250 keV and to disagree above that energy. The scintillator efficiency has been found to increase at energies above 1 MeV due to detection of gamma rays from inelastic neutron scattering. The detector has been used to measure neutron spectra at intermediate energies by the time-of-flight technique. A systematic method is presented for removing background gamma rays that does not require the use of a depleted lithium glass scintillator or the use of pulse shape discrimination.

The use of vanadium scattering to intercalibrate an array of thermal neutron detectors

32 Lithium-glass scintillation detectors are intercalibrated by scattering thermal neutrons nearly isotropically using various vanadium samples. The experimental problems of the method are discussed and the results compared with those calculated from theory.

Improvements in thermal neutron scintillation detectors for time-of-flight studies

Scintillation methods of detecting thermal neutrons are reviewed and ways of preparing and using the organic borate/zincsulphide scintillator are described which lead to a marked improvement in efficiency. In particular, a method of pulse-shape discrimination is described, based on a pronounced difference in pulse sha[es from ZnS(Ag) excited by alpha-particles and electrons. Methods of measuring detector efficiency or neutron flux are reviewed and a simple method is shown to be satisfactory to 1 2 % accuracy. Using these techniques a thermal neutron efficiency of 42% is observed in the presence of 5mR/h gamma radiation, or 52% in the absence of gamma background. Some tests have been carried out on lithium glass scintillators showing that with small area detectors in applications where the gamma background is low, high efficiencies can be achieved, but where gamma backgrounds are high the zincsulphide type is preferable.