The proton light output function in electron-equivalent energy of various scintillators based on linear alkylbenzene (LAB) has been measured in the energy range from 1 MeV to 17.15 MeV for the first ...time. The measurement was performed at the Physikalisch–Technische Bundesanstalt (PTB) using a neutron beam with continuous energy distribution. The proton light output data is extracted from proton recoil spectra originating from neutron–proton scattering in the scintillator. The functional behavior of the proton light output is described successfully by Birks’ law with a Birks constant
kB
between (0.0094±0.0002) cm MeV
−1
and (0.0098±0.0003) cm MeV
−1
for the different LAB solutions. The constant
C
, parameterizing the quadratic term in the generalized Birks law, is consistent with zero for all investigated scintillators with an upper limit (95 % CL) of about 10
−7
cm
2
MeV
−2
. The resulting quenching factors are especially important for future planned supernova neutrino detection based on the elastic scattering of neutrinos on protons. The impact of proton quenching on the supernova event yield from neutrino–proton scattering is discussed.
We characterize the neutron output of a deuterium–deuterium plasma fusion neutron generator, model 35-DD-W-S, manufactured by NSD/Gradel-Fusion. The measured energy spectrum is found to be dominated ...by neutron peaks at 2.2 MeV and 2.7 MeV. A detailed GEANT4 simulation accurately reproduces the measured energy spectrum and confirms our understanding of the fusion process in this generator. Additionally, a contribution of 14.1MeV neutrons from deuterium–tritium fusion is found at a level of 3.5%, from tritium produced in previous deuterium–deuterium reactions. We have measured both the absolute neutron flux as well as its relative variation on the operational parameters of the generator. We find the flux to be proportional to voltage V3.32±0.14 and current I0.97±0.01. Further, we have measured the angular dependence of the neutron emission with respect to the polar angle. We conclude that it is well described by isotropic production of neutrons within the cathode field cage.
The goal of this study is to provide a benchmark for the use of Monte Carlo simulation when applied to coincidence summing corrections. The examples are based on simple geometries: two types of ...germanium detectors and four kinds of sources, to mimic eight typical measurement conditions. The coincidence corrective factors are computed for four radionuclides. The exercise input files and calculation results with practical recommendations are made available for new users on a dedicated webpage.
The argument that well-characterised quasi-monoenergetic neutron (QMN) sources reaching into the energy domain >20 MeV are needed is presented. A brief overview of the existing facilities is given, ...and a list of key factors that an ideal QMN source for dosimetry and spectrometry should offer is presented. The authors conclude that all of the six QMN facilities currently in existence worldwide operate in sub-optimal conditions for dosimetry. The only currently available QMN facility in Europe capable of operating at energies >40 MeV, TSL in Uppsala, Sweden, is threatened with shutdown in the immediate future. One facility, NFS at GANIL, France, is currently under construction. NFS could deliver QMN beams up to about 30 MeV. It is, however, so far not clear if and when NFS will be able to offer QMN beams or operate with only so-called white neutron beams. It is likely that by 2016, QMN beams with energies >40 MeV will be available only in South Africa and Japan, with none in Europe.
In ‘quantity‐languages’, such as Japanese or Finnish, sound duration is linguistically relevant. We showed that quantity‐language speakers were superior to speakers of a non‐quantity language in ...discriminating the duration of even non‐speech sounds. In contrast, there was no group difference in the discrimination of sound frequency. This result, obtained both by behavioural and neural indices at attentive and automatic levels of processing, indicates precise feature‐specific tuning of the auditory‐cortex functions by the mother tongue.
Studies of the actin-based motility of the intracellular pathogens Listeria monocytogenes and Shigella flexneri have provided important insight into the events occurring at the leading edges of ...motile cells. Like the bacteria Listeria and Shigella, vaccinia virus, a relative of the causative agent of smallpox, uses actin-based motility to spread between cells. In contrast to Listeria or Shigella, the actin-based motility of vaccinia is dependent on an unknown phosphotyrosine protein, but the underlying mechanism remains obscure. Here we show that phosphorylation of tyrosine 112 in the viral protein A36R by Src-family kinases is essential for the actin-based motility of vaccinia. Tyrosine phosphorylation of A36R results in a direct interaction with the adaptor protein Nck and the recruitment of the Ena/VASP family member N-WASP to the site of actin assembly. We also show that Nck and N-WASP are essential for the actin-based motility of vaccinia virus. We suggest that vaccinia virus spreads by mimicking the signalling pathways that are normally involved in actin polymerization at the plasma membrane.
During microtubule depolymerization, the central, juxtanuclear Golgi apparatus scatters to multiple peripheral sites. We have tested here whether such scattering is due to a fragmentation process and ...subsequent outward tracking of Golgi units or if peripheral Golgi elements reform through a novel recycling pathway. To mark the Golgi in HeLa cells, we stably expressed the Golgi stack enzyme N-acetylgalactosaminyltransferase-2 (GalNAc-T2) fused to the green fluorescent protein (GFP) or to an 11-amino acid epitope, VSV-G (VSV), and the trans/TGN enzyme β1,4-galactosyltransferase (GalT) fused to GFP. After nocodazole addition, time-lapse microscopy of Gal-NAc-T2-GFP and GalT-GFP revealed that scattered Golgi elements appeared abruptly and that no Golgi fragments tracked outward from the compact, juxtanuclear Golgi complex. Once formed, the scattered structures were relatively stable in fluorescence intensity for tens of minutes. During the entire process of dispersal, immunogold labeling for GalNAc-T2-VSV and GalT showed that these were continuously concentrated over stacked Golgi cisternae and tubulovesicular Golgi structures similar to untreated cells, suggesting that polarized Golgi stacks reform rapidly at scattered sites. In fluorescence recovery after photobleaching over a narrow (FRAP) or wide area (FRAP-W) experiments, peripheral Golgi stacks continuously exchanged resident proteins with each other through what appeared to be an ER intermediate. That Golgi enzymes cycle through the ER was confirmed by microinjecting the dominant-negative mutant of Sar1 ( Sar1 pdn) blocking ER export. Sar1 pdnwas either microinjected into untreated or nocodazole-treated cells in the presence of protein synthesis inhibitors. In both cases, this caused a gradual accumulation of GalNAc-T2-VSV in the ER. Few to no peripheral Golgi elements were seen in the nocodazole-treated cells microinjected with Sar1 pdn. In conclusion, we have shown that Golgi-resident glycosylation enzymes recycle through the ER and that this novel pathway is the likely explanation for the nocodazole-induced Golgi scattering observed in interphase cells.
Monoenergetic and white neutron beams with a maximum energy of 200 MeV are produced at the neutron beam facility of the iThemba Laboratory for Accelerator-Based Sciences (iTL) by (
p,
n) reactions on ...Li, Be and C targets. The iTL separated-sector cyclotron can accelerate protons from 25 MeV to 200 MeV. Time of flight (TOF) measurements can be carried out by increasing the time separation between proton bunches up to 500 ns with a beam pulse selector. In the present work, the methods of beam characterisation used at this facility are discussed. Comparisons with metrological standards are presented. Specific issues related to monitoring the neutron fields at different accelerator settings are analysed.
Solvent conditions are unexpectedly sufficient to drastically and reversibly slow down cells. In vitro on the molecular level, protein–solvent interactions drastically change in the presence of heavy ...water (D2O) and its stronger hydrogen bonds. Adding D2O to the cell medium of living cells increases the molecular intracellular viscosity. While cell morphology and phenotype remain unchanged, cellular dynamics transform into slow motion in a changeable manner. This is exemplified in the slowdown of cell proliferation and migration, which is caused by a reversible gelation of the cytoplasm. In analogy to the time–temperature superposition principle, where temperature is replaced by D2O, an increase in viscosity slows down the effective time. Actin networks, crucial structures in the cytoplasm, switch from a power‐law‐like viscoelastic to a more rubber‐like elastic behavior. The resulting intracellular resistance and dissipation impair cell movement. Since cells are highly adaptive non‐equilibrium systems, they usually respond irreversibly from a thermodynamic perspective. D2O induced changes, however, are fully reversible and their effects are independent of signaling as well as expression. The stronger hydrogen bonds lead to glass‐like, drawn‐out intramolecular dynamics, which may facilitate longer storage times of biological matter, for instance, during transport of organ transplants.
Heavy water (D2O) reversibly slows down cells, retards cell invasion, and drastically impacts cell mechanics possibly prolonging storage times for biological materials. Cellular dynamics transform into slow motion, which can be captured via the time–temperature superposition principle, where temperature is replaced by D2O. Induced changes are fully reversible and effects are independent of signaling/expression.
Three reference radiation fields for the purpose of radiation protection were characterised: (1) radiation field R-F, consisting of photons in the energy range of about 6 and 7 MeV and a small ...neutron contamination; (2) radiation field R-C, consisting of photons with energies of about 4.4 MeV and neutrons with energies up to 2.65 MeV; (3) radiation field R-CF, consisting of photons in the energy range of about 1 and 7 MeV and neutrons with energies about 1.5 MeV. The radiation fields R-F and R-C have previously been defined in the ISO standard 4037. Their neutron components, however, have never been described accurately in the past. The new radiation field R-CF is proposed for the first time. This radiation field can, e.g., be used to calibrate tissue-equivalent proportional counters instruments for measurements at flight altitudes.
PDF
