Radioactive contamination of ZnWO4 crystal scintillators

The radioactive contamination of ZnWO4 crystal scintillators has been measured deep underground at the Gran Sasso National Laboratory (LNGS) of the INFN in Italy with a total exposure 3197 kg x h. Monte Carlo simulation, time-amplitude and pulse-shape analyses of the data have been applied to estimate the radioactive contamination of the ZnWO4 samples. One of the ZnWO4 crystals has also been tested by ultra-low background gamma spectrometry. The radioactive contaminations of the ZnWO4 samples do not exceed 0.002 -- 0.8 mBq/kg (depending on the radionuclide), the total alpha activity is in the range: 0.2 - 2 mBq/kg. Particular radioactivity, beta active 65Zn and alpha active 180W, has been detected. The effect of the re-crystallization on the radiopurity of the ZnWO4 crystal has been studied. The radioactive contamination of samples of the ceramic details of the set-ups used in the crystals growth has been checked by low background gamma spectrometry. A project scheme on further improvement of the radiopurity level of the ZnWO4 crystal scintillators is briefly addressed.Comment: 15 pages, 8 figures, 6 tables, submitted for publicatio

Построение минимаксных ансамблей апериодических кодов Голда

Introduction. Signals constructed on the basis of ensembles of code sequences are widely used in digital communication systems. During development of such systems, the most attention is paid to analysis, synthesis and implementation of periodic signal ensembles. Theoretic methods for synthesis of periodic signal ensembles are developed and are in use. Considerably fewer results are received regarding construction of aperiodic signal ensembles with given properties. Theoretical methods for synthesis of such ensembles are practically nonexistent.Aim. To construct aperiodic Gold code ensembles with the best ratios of code length to ensemble volume among the most known binary codes.Materials and methods. Methods of directed search and discrete choice of the best ensemble based on unconditional preference criteria are used.Results. Full and truncated aperiodic Gold code ensembles with given length and ensemble volume were constructed. Parameters and shape of auto- and mutual correlation functions were shown for a number of constructed ensembles. Comparison of the paper results with known results for periodic Gold code ensembles has been conducted regarding growth of minimax correlation function values depending on code length and ensemble volume.Conclusion. The developed algorithms, unlike the known ones, make it possible to form both complete ensembles and ensembles taking into account the limitation of their volume. In addition, the algorithms can be extended to the tasks of forming ensembles from other families, for example, assembled from code sequences belonging to different families.Введение. В системах цифровой связи широко применяются сигналы, построенные на основе ансамблей кодовых последовательностей. При разработке этих систем наибольшее внимание уделяется анализу, синтезу и реализации ансамблей периодических сигналов. Разработаны и используются теоретические методики синтеза ансамблей периодических сигналов. Значительно меньше результатов получено в области построения ансамблей апериодических сигналов с заданными корреляционными свойствами. Теоретические методики синтеза таких ансамблей сигналов практически отсутствуют.Цель работы. Построение минимаксных ансамблей апериодических кодов Голда, которые обладают одним из лучших среди известных бинарных кодов соотношением длины кодов и объема ансамбля.Материалы и методы. Для построения минимаксного ансамбля используются направленный перебор и метод дискретного выбора лучшего ансамбля на основе безусловного критерия предпочтения.Результаты. В статье описан алгоритм формирования полных и неполных минимаксных ансамблей апериодических кодов Голда с заданными длиной и объемом ансамбля. Приведены параметры и вид авто- и взаимнокорреляционных функций для ряда полученных ансамблей. Выполнено сравнение результатов статьи с известными результатами для ансамблей периодических кодов Голда в части роста минимаксных значений корреляционных функций в зависимости от длины кодов и объема ансамблей.Заключение. Разработанные алгоритмы, в отличие от известных, позволяют конструировать как полные ансамбли, так и ансамбли, учитывающие ограничение их объема. Кроме того, данные алгоритмы могут быть распространены на задачи построения ансамблей из других семейств, например, собранных из кодовых последовательностей, принадлежащих различным семействам

Formation of Minimax Ensembles of Aperiodic Gold Codes

Introduction. Signals constructed on the basis of ensembles of code sequences are widely used in digital communication systems. During development of such systems, the most attention is paid to analysis, synthesis and implementation of periodic signal ensembles. Theoretic methods for synthesis of periodic signal ensembles are developed and are in use. Considerably fewer results are received regarding construction of aperiodic signal ensembles with given properties. Theoretical methods for synthesis of such ensembles are practically nonexistent.Aim. To construct aperiodic Gold code ensembles with the best ratios of code length to ensemble volume among the most known binary codes.Materials and methods. Methods of directed search and discrete choice of the best ensemble based on unconditional preference criteria are used.Results. Full and truncated aperiodic Gold code ensembles with given length and ensemble volume were constructed. Parameters and shape of auto- and mutual correlation functions were shown for a number of constructed ensembles. Comparison of the paper results with known results for periodic Gold code ensembles has been conducted regarding growth of minimax correlation function values depending on code length and ensemble volume.Conclusion. The developed algorithms, unlike the known ones, make it possible to form both complete ensembles and ensembles taking into account the limitation of their volume. In addition, the algorithms can be extended to the tasks of forming ensembles from other families, for example, assembled from code sequences belonging to different families

Research and Development of ZnBO4ZnBO_{4} (B = W, Mo) Crystal Scintillators for Dark Matter and Double Beta Decay Searching

Oxide crystal scintillators play a considerable role in fundamental and applied researches. However, working out of new generation of high-sensitivity equipment and new methods of research puts higher requirements. The $ZnBO_{4}$ (B = W, Mo) crystals were grown from charge in platinum crucibles with high frequency heating, using the Czochralski method. The raw powder with optimum composition was prepared by solid phase high temperature synthesis using ZnO and $BO_{3}$ (B = W, Mo) with 4-5N purity. Single crystals with sizes up to ∅ 50 × 100 mm were grown and scintillation elements of various sizes and shapes (cylinders, rectangular and hexahedron prisms) were produced. High spectrometric characteristics were obtained for $ZnWO_{4}:R$ = 8-10% under excitation by $\text{}^{137}Cs (E_{γ}$=662 keV), low radiation background (less than 0.2 mBq/kg) and low afterglow (0.002%, 20 ms after excitation). The obtained results demonstrate good prospects for $ZnWO_{4}$ and ZnMoO_{4} crystal scintillators for application in low-count rate experiments, searching for double beta decay processes, interaction with dark matter particles, and also studies of rare decay processes. The material has also a good potential for application in modern tomography, scintillation bolometers and for other major researches using scintillators

Drilling by Electromechanical Method on the Akademiya Nauk Glacier, Severnaya Zemlya Archipelago

In May 1999, drilling of a borehole through the entire ice strata (around 750 m) was initiated on the Akademiya Nauk glacier of Komsomolets Island, Severnaya Zemlya Archipelago. The Arctic and Antarctic Research Institute (AARI), St. Petersburg Mining Institute (SPMI) and Alfred Wegener Institute (AWI, Germany) take part in this venture. For undertaking drilling activities, a dismantling drilling complex was designed and manufactured at SPMI by request of AWI. It includes a drilling house, land drilling equipment and two sets of the electromechanical drill KEMS-127 that also allows drilling of subglacial mountain rocks. The core has a maximum length of 1.5 m and a diameter of 106 mm. Drilling started in spring of 1999 and 54 m was drilled. In April 2000, the borehole drilling was continued. Up to a depth of 109 m, a "dry" method was used. Then the borehole was filled with aviation kerosene TS-1. By the end of seasonal work (May 9, 2000), the borehole bottom reached a depth of 504.7 m. After the drilling was stopped, a complex of geophysical observations was carried out that included measurements of the borehole diameter, the axis deviation angle from the vertical, temperature at different depths and drilling fluid pressure. An analysis of the data obtained allows a conclusion about the reliability and stability of the drilling technology and equipment and developing recommendations to continue drilling that is planned to do during 2001 season

MgWO4-A new crystal scintillator

Magnesium tungstate (MgWO4) crystals of ~1 cm3 volume were obtained for the first time using a flux growth technique. The crystal was subjected to comprehensive characterisation that included room-temperature measurements of the transmittance, X-ray luminescence spectra, afterglow under X-ray excitation, relative photoelectron output, energy resolution, non-proportionality of scintillation response to γ-quanta, response to α-particles, and pulse shape for γ-quanta and α-particles. The light output and decay kinetics of MgWO4 were studied over the temperature range 7-305 K. Under X-ray excitation the crystal exhibits an intense luminescence band peaking at a wavelength of 470 nm; the intensity of afterglow after 20 ms is 0.035%. An energy resolution of 9.1% for 662 keV γ-quanta of 137Cs was measured with a small (≈0.9 g) sample of the MgWO4 crystal. The photoelectron output of the MgWO4 crystal scintillator is 35% that of CdWO4 and 27% that of NaI(Tl). The detector showed pulse-shape discrimination ability in measurements with α-particles and γ-quanta, which enabled us to assess the radioactive contamination of the scintillator. The results of these studies demonstrate the prospect of this material for a variety of scintillation applications, including rare event searches. © 2008 Elsevier B.V