Silicon detectors for γ-ray and β-spectroscopy

Large active volume Si(Li) detectors were successfully developed for γ-ray spectrometry at room temperature that show a sufficient efficiency and an energy resolution that is better than scintillation detectors. The higher efficiency of the proposed detectors with respect to normal silicon diodes is achieved by increasing the active volume. For this purpose special attention is given to the selection of the initial material which has to show homogeneous electro-physical parameters, low concentration of oxygen impurities and high structural perfection. The technique of using lithium ions is used as these drift into large depths and hence the profile of the impurity distribution is optimized

Lipid metabolic changes in an early divergent fungus govern the establishment of a mutualistic symbiosis with endobacteria.

The recent accumulation of newly discovered fungal-bacterial mutualisms challenges the paradigm that fungi and bacteria are natural antagonists. To understand the mechanisms that govern the establishment and maintenance over evolutionary time of mutualisms between fungi and bacteria, we studied a symbiosis of the fungus Rhizopus microsporus (Mucoromycotina) and its Burkholderia endobacteria. We found that nonhost R. microsporus, as well as other mucoralean fungi, interact antagonistically with endobacteria derived from the host and are not invaded by them. Comparison of gene expression profiles of host and nonhost fungi during interaction with endobacteria revealed dramatic changes in expression of lipid metabolic genes in the host. Analysis of the host lipidome confirmed that symbiosis establishment was accompanied by specific changes in the fungal lipid profile. Diacylglycerol kinase (DGK) activity was important for these lipid metabolic changes, as its inhibition altered the fungal lipid profile and caused a shift in the host-bacterial interaction into an antagonism. We conclude that adjustments in host lipid metabolism during symbiosis establishment, mediated by DGKs, are required for the mutualistic outcome of the Rhizopus-Burkholderia symbiosis. In addition, the neutral and phospholipid profiles of R. microsporus provide important insights into lipid metabolism in an understudied group of oleaginous Mucoromycotina. Lastly, our study revealed that the DGKs involved in the symbiosis form a previously uncharacterized clade of DGK domain proteins

Bacterial endosymbionts influence host sexuality and reveal reproductive genes of early divergent fungi.

Many heritable mutualisms, in which beneficial symbionts are transmitted vertically between host generations, originate as antagonisms with parasite dispersal constrained by the host. Only after the parasite gains control over its transmission is the symbiosis expected to transition from antagonism to mutualism. Here, we explore this prediction in the mutualism between the fungus Rhizopus microsporus (Rm, Mucoromycotina) and a beta-proteobacterium Burkholderia, which controls host asexual reproduction. We show that reproductive addiction of Rm to endobacteria extends to mating, and is mediated by the symbiont gaining transcriptional control of the fungal ras2 gene, which encodes a GTPase central to fungal reproductive development. We also discover candidate G-protein-coupled receptors for the perception of trisporic acids, mating pheromones unique to Mucoromycotina. Our results demonstrate that regulating host asexual proliferation and modifying its sexual reproduction are sufficient for the symbiont's control of its own transmission, needed for antagonism-to-mutualism transition in heritable symbioses. These properties establish the Rm-Burkholderia symbiosis as a powerful system for identifying reproductive genes in Mucoromycotina

Silicon detectors for gamma-ray and beta spectroscopy

Large active volume Si(Li) detectors were successfully developed for gamma-ray spectrometry at room temperature that show a sufficient efficiency and an energy resolution that is better than scintillation detectors. The higher efficiency of the proposed detectors with respect to normal silicon diodes is achieved by increasing the active volume. For this purpose special attention is given to the selection of the initial material which has to show homogeneous electrophysical parameters, low concentration of oxygen impurities and high structural perfection. The technique of using lithium ions is used as these drift into large depths and hence the profile of the impurity distribution is optimized

Radiation hardness of silicon detectors based on pre-irradiated silicon

Radiation hardness of planar detectors processed from pre-irradiated and thermo-annealed n-type FZ silicon substrates, and standard FZ as a reference, was studied. The high purity n-Si wafers with carrier concentration 4.8x1011 cm-3 were pre-irradiated in Kiev’s nuclear research reactor by fast neutrons to fluence of about 1016 neutrons/cm2 and thermo-annealed at a temperature of about 850 1C. Silicon diodes were fabricated from standard and pre-irradiated silicon substrates by IRST (Italy). All diodes were subsequently irradiated by fast neutrons at Kiev and Ljubljana nuclear reactors. The dependence of the effective doping concentration as a function of fluence (Neff = f(F)) was measured for reference and pre-irradiated diodes. Pre-irradiation of silicon improves the radiation hardness by decreasing the acceptor introduction rate (b), thus mitigating the depletion voltage (Vdep) increase. In particular, b in reference samples is about 0.017 cm-1, and for pre-irradiated samples is about 0.008 cm-1. Therefore, the method of preliminary irradiation can be useful to increase the radiation hardness of silicon devices to be used as sensors or detectors in harsh radiation environments

Radiation hardness of silicon detectors based on pre-irradiated silicon

Radiation hardness of planar detectors processed from pre-irradiated and thermo-annealed n-type FZ silicon substrates, and standard FZ as a reference, was studied. The high purity n-Si wafers with carrier concentration 4.8x1011 cm-3 were pre-irradiated in Kiev’s nuclear research reactor by fast neutrons to fluence of about 1016 neutrons/cm2 and thermo-annealed at a temperature of about 850 1C. Silicon diodes were fabricated from standard and pre-irradiated silicon substrates by IRST (Italy). All diodes were subsequently irradiated by fast neutrons at Kiev and Ljubljana nuclear reactors. The dependence of the effective doping concentration as a function of fluence (Neff = f(F)) was measured for reference and pre-irradiated diodes. Pre-irradiation of silicon improves the radiation hardness by decreasing the acceptor introduction rate (b), thus mitigating the depletion voltage (Vdep) increase. In particular, b in reference samples is about 0.017 cm-1, and for pre-irradiated samples is about 0.008 cm-1. Therefore, the method of preliminary irradiation can be useful to increase the radiation hardness of silicon devices to be used as sensors or detectors in harsh radiation environments