Scintillating fibres

This review first describes the basic working principles of scintillating fibres together with their most common readout techniques. It concentrates on plastic fibres, since they are better suited for application in High Energy Physics. The following section reviews fibre trackers and lead/scintillating calorimeters. Both detector devices are compared with competing techniques based on other media. The review continues with dose rates at the LHC-collider and discusses the radiation damage on scintillating fibres. The conclusion covers the progress achieved with the fibre technique and presents an outlook on future developments

Photoelectron backscattering from silicon anodes of hybrid photodetector tubes

The impact of photoelectron backscattering on spectral distributions measured with hybrid photodetector tubes has been calculated. The calculations are based on the backscattering coefficient mu , the average number of photoelectrons N/sub phel/ emitted from the photocathode, and on the distribution of the fractional photoelectron energy q absorbed in silicon during the backscattering process. We obtained the following results: the average number of absorbed (measured) photoelectrons N/sub meas/ in the silicon anode amounts to ~88% of the incident N/sub phel/. Photoelectron- and gamma-absorption peaks are broadened by a factor 1.043 due to backscattering. As an example, for photomultiplier tubes, this broadening can amount to an average factor of 1.18 due to statistic and gain fluctuations on the dynode chain. (15 refs)

Hybrid photon detectors

Hybrid photon detectors detect light via vacuum photocathodes and accelerate the emitted photoelectrons by an electric field towards inversely polarized silicon anodes, where they are absorbed, thus producing electron-hole pairs. These, in turn, are collected and generate electronic signals on their ohmic contacts. This review first describes the characteristic properties of the main components of hybrid photon detectors: light entrance windows, photocathodes, and silicon anodes. Then, essential relations describing the trajectories of photoelectrons in electric and magnetic fields and their backscattering from the silicon anodes are derived. Depending on their anode configurations, three families of hybrid photon detectors are presented: hybrid photomultiplier tubes with single anodes for photon counting with high sensitivity and for gamma spectroscopy; multi-anode photon detector tubes with anodes subdivided into square or hexagonal pads for position-sensitive photon detection; imaging silicon pixel array tubes with finely segmented anodes for photon-sensitive imaging devices. Some of the hybrid photon detectors’ applications and achievements in radiation detection are discussed and compared with competing devices such as photomultipliers, image intensifiers, photodiodes, silicon drift chambers, charge coupled devices, visible light photon counters, and photographic emulsions

Histone H3 tail positioning and acetylation by the c-Myb but not the v-Myb DNA-binding SANT domain

The c-Myb transcription factor coordinates proliferation and differentiation of hematopoietic precursor cells. Myb has three consecutive N-terminal SANT-type repeat domains (R1, R2, R3), two of which (R2, R3) form the DNA-binding domain (DBD). Three amino acid substitutions in R2 alter the way Myb regulates genes and determine the leukemogenicity of the retrovirally transduced v-Myb oncogene. The molecular mechanism of how these mutations unleash the leukemogenic potential of Myb is unknown. Here we demonstrate that the c-Myb-DBD binds to the N-terminal histone tails of H3 and H3.3. C-Myb binding facilitates histone tail acetylation, which is mandatory during activation of prevalent differentiation genes in conjunction with CCAAT enhancer-binding proteins (C/EBP). Leukemogenic mutations in v-Myb eliminate the interaction with H3 and acetylation of H3 tails and abolish activation of endogenous differentiation genes. In primary v-myb-transformed myeloblasts, pharmacologic enhancement of H3 acetylation restored activation of differentiation genes and induced cell differentiation. Our data link a novel chromatin function of c-Myb with lineage-specific expression of differentiation genes and relate the loss of this function with the leukemic conversion of Myb

X-ray detection with a scintillating YAP-window hybrid photomultiplier tube

A YAP(YAlO/sub 3/:Ce)-scintillating window, coated on its inner surface with an S20-photocathode, seals a cross-focusing hybrid photomultiplier tube (HPMT) equipped with a small p-i-n anode of 2-mm diameter. This new radiation detector separates X-ray lines down to about 2-keV peak energy from the HPMT noise. Its detection efficiency for high gamma energies depends on the YAP-window thickness and amounts to about 18% attenuation at 400-keV energy in the present version. Competitive radiation detectors like Si photodiodes and Si drift chambers are discussed and compared to our prototype, with particular attention given to their energy resolution and noise performance, which limits their active area considerably. (19 refs)

An ISPA-camera for gamma rays

With the recently developed ISPA (Imaging Silicon Pixel Array)-tube attached either to a planar YAlO3(Ce) (YAP) disc (1mm thick) or to a matrix of optically-separated YAP-crystals (5mm high, 0.6 x 0.6 mm2 cross-section) we achieved high spatial resolution of 57Co-122 keV photons. The vacuum-sealed ISPA-tube is only 4 cm long with 3.5 cm diameter and consists of a photocathode viewed at 3 cm distance by a silicon pixel chip, directly detecting the photoelectrons. The chip-anode consists of 1024 rectangular pixels with 75 µm x 500 µm edges, each bump-bonded to their individual front-end electronics. The total pixel array read-out time is 10 µs. The measured intrinsic spatial resolutions (FWHM) of this ISPA-camera are 700 µm (planar YAP) and 310 µm (YAP-matrix). Apart from its already demonstrated application for particle tracking with scintillating fibres, the ISPA-tube provides also an excellent tool in medicine, biology and chemistry

A HPMT based set-up to characterize scintillating crystals

We have developed a fully automatic measurement set-up, capable of measuring light yields arising from scintillating crystals in a linear range of about four orders of magnitude. The photodetector is a Hybrid Photomultiplier Tube especially developed to optimize linear range and photon detection. Crystal and photodetector are temperature controlled by a closed water circuit, as this is essential when measuring low light yield scintillating crystals with a marked temperature dependence of their light yield. Gamma sources can be placed either on top or on the side of the crystal. In this latter case, the source can be automatically moved by a computer-controlled step motor to provide a uniformity profile of the light yield along the crystal. Tagged and not-tagged operation modes are possible. The whole set-up is computer-controlled in an effort to provide fast and reliable measurements, to characterize many crystals per day. This is important for the quality control of the Lead Tungstate crystals that will be applied in the electromagnetic calorimeter of the CMS-detector at the LHC at CERN

Deregulation of the endogenous C/EBPβ LIP isoform predisposes to tumorigenesis

Two long and one truncated isoforms (termed LAP*, LAP, and LIP, respectively) of the transcription factor CCAAT enhancer binding protein beta (C/EBPbeta) are expressed from a single intronless Cebpb gene by alternative translation initiation. Isoform expression is sensitive to mammalian target of rapamycin (mTOR)-mediated activation of the translation initiation machinery and relayed through an upstream open reading frame (uORF) on the C/EBPbeta mRNA. The truncated C/EBPbeta LIP, initiated by high mTOR activity, has been implied in neoplasia, but it was never shown whether endogenous C/EBPbeta LIP may function as an oncogene. In this study, we examined spontaneous tumor formation in C/EBPbeta knockin mice that constitutively express only the C/EBPbeta LIP isoform from its own locus. Our data show that deregulated C/EBPbeta LIP predisposes to oncogenesis in many tissues. Gene expression profiling suggests that C/EBPbeta LIP supports a pro-tumorigenic microenvironment, resistance to apoptosis, and alteration of cytokine/chemokine expression. The results imply that enhanced translation reinitiation of C/EBPbeta LIP promotes tumorigenesis. Accordingly, pharmacological restriction of mTOR function might be a therapeutic option in tumorigenesis that involves enhanced expression of the truncated C/EBPbeta LIP isoform. KEY MESSAGE: Elevated C/EBPbeta LIP promotes cancer in mice. C/EBPbeta LIP is upregulated in B-NHL. Deregulated C/EBPbeta LIP alters apoptosis and cytokine/chemokine networks. Deregulated C/EBPbeta LIP may support a pro-tumorigenic microenvironment