Small Scintillation Detector Research Articles

First Results of the CREDO-Maze Cosmic Ray Project

The CREDO-Maze project is the concept for a network of stations recording local, extensive cosmic ray air showers. Each station consists of four small scintillation detectors and a control unit that monitors the cosmic ray flux 24 h a day and transmits the results to the central server. The modular design of each array allows the results to be used in educational classes on nuclear radiation, relativistic physics, and particle physics and as a teaching aid in regular school classrooms and more. As an example, we present here some preliminary results from the CREDO-Maze muon telescope missions to the Arctic and down into a deep salt mine, as well as the first shower-particle correlation measurements from a table-top experiment at Walailak University. These experiments show that the different geometric configurations of the CREDO-Maze detector set can be used for projects beyond the scope of the secondary school curriculum, and they can form the basis of student theses and dissertations at universities.

Advantages of Gamma-Radiometric and Spectrometric Low-Altitude Geophysical Surveys by Unmanned Aerial Systems with Small Scintillation Detectors

Unmanned aerial systems (UAS) for airborne gamma-ray surveys in radioecological and geological research are being increasingly used, since they provide radiation safety for personnel and high survey performance. Improvement of detection modules is one of the main directions in which UAS-gamma is developing. Semiconductor detectors are used increasingly as they have a small mass and are convenient for light unmanned aerial vehicles (UAVs). Simultaneously, in our opinion, the potential of traditional scintillation detectors is not exhausted because they are cheaper and more affordable. Radiometric and spectrometric detection modules based on scintillation detectors can even be created at home. The main disadvantage of scintillation detectors is the need for large crystals with significant mass to obtain high data quality. Traditional aerial gamma surveys with operated aircraft systems use scintillation detectors with a volume of tens or hundreds of litres. In this paper, we present the comparison result of radiometric and spectrometric surveys with small volume detectors made at different altitudes and ground surveys. We prove that with properly designed and applied ultralight UAS for aerial gamma spectrometry it is possible to obtain high-quality and informative data.

Combining Cherenkov and scintillation detector observations with simulations to deduce the nature of high-energy radiation excesses during thunderstorms

We present co-observations of three strong count-rate enhancements associated with thunderstorms observed over 17 April 2015 to 23 September 2015 by the High Altitude Water Cherenkov (HAWC) array, and a suite of small scintillation detectors comprising the Gamma-ray Observations During Overhead Thunderstorms (GODOT) instrument. Because the HAWC array is most sensitive to ionizing radiation at high energies ($g100\text{ }\text{ }\mathrm{MeV}$), and the small scintillation detectors are most sensitive to ionizing radiation at low energies ($3--20\text{ }\text{ }\mathrm{MeV}$), we investigate using the ratio of these detector counting rates variations to infer spectral characteristics of these enhancements, and understand the physics behind these thunderstorm accelerator mechanisms. We consider two extreme mechanisms that can produce these enhancements: a point source of relativistic runaway electron avalanches (RREA), and modification of the background cosmic-ray spectrum (MOS) from an electric field profile that is everywhere below the RREA threshold. We simulate the responses of HAWC and the GODOT $12.7\text{ }\text{ }\mathrm{cm}\ifmmode\times\else\texttimes\fi{}\ensuremath{\oslash}12.7\text{ }\text{ }\mathrm{cm}$ NaI(Tl) scintillator and show that their ratio can discern between the two models, and that the observed thunderstorm rate enhancements are incompatible with the spectra from a point source of RREA, but consistent with our model of MOS for thunderstorm potentials within the range of $\ensuremath{-}250$ to 250 MV.

Energy dependent response of plastic scintillation detectors to photon radiation of low to medium energy.

Plastic scintillation detectors are promising candidates for the dosimetry of low- to medium-energy photons but quantitative knowledge of their energy response is a prerequisite for their correct use. The purpose of this study was to characterize the energy dependent response of small scintillation detectors (active volume <1 mm(3)) made from the commonly used plastic scintillator BC400. Different detectors made from BC400 were calibrated at a number of radiation qualities ranging from 10 to 280 kV and at a (60)Co beam. All calibrations were performed at the Physikalisch-Technische Bundesanstalt, the National Metrology Institute of Germany. The energy response in terms of air kerma, dose to water, and dose to the scintillator was determined. Conversion factors from air kerma to dose to water and to dose to the scintillator were derived from Monte Carlo simulations. In order to quantitatively describe the energy dependence, a semiempirical model known as unimolecular quenching or Birks' formula was fitted to the data and from this the response to secondary electrons generated within the scintillator material BC400 was derived. The detector energy response in terms of air kerma differs for different scintillator sizes and different detector casings. It is therefore necessary to take attenuation within the scintillator and in the casing into account when deriving the response in terms of dose to water from a calibration in terms of air kerma. The measured energy response in terms of dose to water for BC400 cannot be reproduced by the ratio of mean mass energy-absorption coefficients for polyvinyl toluene to water but shows evidence of quenching. The quenching parameter kB in Birks' formula was determined to be kB = (12.3 ± 0.9) mg MeV(-1) cm(-2). The energy response was quantified relative to the response to (60)Co which is the common radiation quality for the calibration of therapy dosemeters. The observed energy dependence could be well explained with the assumption of ionization quenching as described by Birks' formula. Plastic scintillation detectors should be calibrated at the same radiation quality that they will be used at and changes of the spectrum within the application need to be considered. The authors results can be used to evaluate the range of validity of a given calibration.

Time correlation measurements from extensive air showers detected by the EEE telescopes

Time correlated events due to cosmic muons from extensive air showers have been detected by means of telescope pairs of the EEE (Extreme Energy Events) Project array. The coincidence rate, properly normalized for detector acceptance, efficiency and altitude location, has been extracted as a function of the relative distance between the telescopes. The results have been also compared with additional measurements carried out by small scintillator detectors at various distances.

Energy resolution of small scintillation detectors with SiPM light readout

The development of silicon photomultipliers (SiPMs) with a large number of APD cells and improved linearity of the pulse height response prompted interest in their application to gamma spectrometry with scintillators. Hamamatsu MPPC sensors equipped with 3600 and 14400 APD cells were chosen in our study because of their well pronounced single photoelectron spectra, which allowed us to precisely measure the photoelectron numbers (PHE) or fired APD cells and then to discuss, in a quantitative manner, the obtainable energy resolution. The studied detectors were first characterized in direct detection of laser light pulses and then in gamma spectroscopy with LFS and CsI:Tl crystals. In the study with the laser light pulses the linearity of the MPPC response versus a light pulse intensity monitored with PMT was measured. Two different methods were used for an evaluation of the MPPC response expressed in the number of photoelectrons (PHE) generated by light illumination. The direct method (PHEdir), based on the comparison of the light peak position to that of the single photoelectron peak, determined the upper limit of the PHE. The lower limit of the PHE was derived from an analysis of the measured pulse height resolution under the assumption of Poisson statistics and MPPC excess noise factor (ENF) of 1. Furthermore, the ENF of the MPPC is discussed with respect to the contributions of device dead time, optical cross-talk and after-pulses to the results obtained. In the scintillation tests, measurements of energy resolution and non-proportionality of the light yield were performed with LFS and CsI:Tl crystals, and both types of 3 × 3 mm MPPC detectors were used for light readout. The results are discussed in a quantitative manner based on the measured PHE.

Detection of extensive cosmic air showers by small scintillation detectors with wavelength-shifting fibres

A set of three small scintillation detectors was employed to measure correlated events due to the passage of cosmic muons originating from extensive air showers. The coincidence rate between (any) two detectors was extracted as a function of their relative distance. The difference between the arrival times in three non-aligned detectors was used to reconstruct the orientation of the shower axis.

Development of a small scintillation detector with an optical fiber for fast neutrons

To investigate the characteristics of a reactor and a neutron generator, a small scintillation detector with an optical fiber with ThO(2) has been developed to measure fast neutrons. However, experimental facilities where (232)Th can be used are limited by regulations, and S/N ratio is low because the background counts of this detector are increase by alpha decay of (232)Th. The purpose of this study is to develop a new optical fiber detector for measuring fast neutrons that does not use nuclear material such as (232)Th. From the measured and calculated results, the new optical fiber detector which uses ZnS(Ag) as a converter material together with a scintillator have the highest detection efficiency among several developed detectors. It is applied for the measurement of reaction rates generated from fast neutrons; furthermore, the absolute detection efficiency of this detector was obtained experimentally.

Possibility of increasing the accuracy and efficiency of continuous nuclear-physical measurements

In general, the useful (target) information in a recorded energy distribu,ion of the radiation can be present in several energy intervals of the spectrum of the radiation. The working intervals of the measurements are usually sections of the spectrum where useful information is present in a "pure" form or together with noise (background). The noise can be determined (known) and taken into account when the results are processed. So, in the case of -/-testing of rocks for the content of natural radioactive elements, -/-rays with energy greater than 250-300 keV are recorded, whose flux density is directly proportional to the mass fraction of radioactive elements in the rocks, since it is represented mainly by the primary and singlyscattered radiation of the elements. The radiation flux density in the low-energy range of the spectrum of natural -/-radiation (20-250 keV, mainly multiply-scattered radiation) also depends on the mass fraction of radioactive elements in the rocks, but this dependence is parametrically related with the effective atomic number of the emitting--absorbing medium in the region of the detector, whose uncontrollable variations over the well shaft can lead to a large error in the determination of the mass fraction of the radioactive elements. At the same time, the flux density of useful (relative to the mass fraction) information in the interval 20-250 keV is much higher than in the interval above 250 keV, especially when the radiation is detected with small scintillation detectors which possess a high sensivity to the low-energy part of the radiation spectrum. This information would greatly decrease the statistical errors in determining the natural radioactive elements, as happens in measurements of the total radiation specmam in media with constant effective atomic number. On this basis, the problem of statistical grouping of the useful information in the signal fluxes in detection of ionizing particles can be formulated in the most general form as follows. Useful information is present in two statistically independent signal fluxes (in two nonoverlapping intervals of the radiation spectrum). In the first signal flux (conventionally, the main flux)

Diagnostics of alpha particles and their effects (abstract)

The pending approach of significant alpha particle populations in D-T plasmas in TFTR and JET and in the burning plasma devices, CIT and ITER, has led to detailed study of the measurement of the alpha particles both directly and through their potential effects on the plasma. The possible diagnostics of alpha particles, previously reviewed, for example, by Zweben [S. J. Zweben, Rev. Sci. Instrum. 57, 1723 (1986)], for use on such devices have been narrowed down to a relatively small number of possibilities. Small scintillator detectors at the wall have proven very effective in detecting the escaping T and p fusion products from the D-D reaction and hence mocking-up the relevant studies of loss required by ITER. Development of high-power pulsed microwave scattering systems for investigating the fast confined alphas is in progress for TFTR and JET. Selection of the right frequency and mode will be needed for CIT and ITER but this technique has the major advantage of being able to conform to readily available access. The use of a carbon impurity pellet to provide a suitably dense ablation target cloud so that the spectra of the emitted helium light will provide data on the energy distribution of these fast alphas is also being developed. For the slowing-down group (Eα≤500 keV), charge exchange recombination spectroscopy using a source beam of neutrals is the most probable diagnostic but it becomes limited by the penetration of the beams. But, in addition to the direct measurement of the alphas, or of the neutrons, to give information on their source profile and time behavior, they significantly heat the plasma and also, potentially, lead to new instability modes which could lead to enhanced loss of themselves or of the plasma. These instabilities have been extensively analyzed recently so that methods for identifying their presence can now be evaluated. These diagnostics, and some aspects of their implementation on TFTR, CIT, and ITER will be described. This work was supported by U.S. DOE contract No. DE-AC02-76-CHO-3073.

The Location of Urinary Calculi Using Radionuclide Imaging

Summary— A method of in vivolabeling urinary calculi with 99mTc-methylene diphosphonate is described. This enables a radionuclide image of the stones to be produced and permits their location at operation by means of a small scintillation detector. The degree of uptake of the radiopharmaceutical on renal stones appears to depend on a number of factors, particularly the chemical composition of the stones.

The location of urinary calculi using radionuclide imaging.

Summary— A method of in vivolabeling urinary calculi with 99mTc‐methylene diphosphonate is described. This enables a radionuclide image of the stones to be produced and permits their location at operation by means of a small scintillation detector. The degree of uptake of the radiopharmaceutical on renal stones appears to depend on a number of factors, particularly the chemical composition of the stones.

Letter: Gain instability of scintillation detectors and consequences for dynamic tracer studies.

In measurement systems for regional blood-flow studies, based on the clearance process of an injected radioactive tracer, small scintillation detectors are widely used (Jaffe, McHenry and Goldberg, 1970). In applying commercially available mini-probes, we met serious problems with regard to instability. Our experience may be of interest to other users.