Abstract
A new type of beam loss monitor has been developed based on
the detection of fast neutrons produced by beam losses in hadron
linear accelerators. This neutron sensitive Beam Loss Monitor ...(nBLM)
has been concieved to fulfil the requirements of the European
Spallation Source (ESS) and it will be part of the ESS neutron
sensitive BLM system (ESS-nBLM). It has been specifically designed
for the low energy part, where only neutrons and gammas produced by
the loss can exit the accelerator vessel. Here other types of BLM,
based on charged particle detection, suffer from the lack of signal
compared to the photon background induced by the radio-frequency
cavities. However, it can also be operated in regions of higher
energy. The detector is of the Micromegas type and have been
designed at IRFU to be able to detect fast neutrons while having a
small sensitivity to gammas and thermal neutrons. In this work we
focus on the proof of neutron-to-gamma rejection and the first
operation of the detector in real beam conditions during the
commissioning of LINAC4 (CERN). Controlled beam losses were provoked
and have been detected by the nBLM detector installed, demonstrating
also the discrimination of the neutron signal from RF x-ray
background.
The European Spallation Source (ESS), currently under construction in Lund, Sweden, will be a neutron source based on a partly superconducting linac. The ESS linac will be accelerating protons to 2 ...GeV with a peak current of 62.5 mA and ultimately delivering a 5 MW beam to a rotating tungsten target for neutron production. For a successful tuning and operation of a linac, a beam loss monitoring (BLM) system is required. BLM systems are designed to protect the machine from beam-induced damage and unnecessary activation of the components. This paper focuses on one of the BLM systems to be deployed at the ESS linac, namely the neutron sensitive BLM (nBLM). An overview of the ESS nBLM system design will be presented. In addition to this, results of the tests performed with the full nBLM data acquisition chain will be discussed. These tests represent the first evaluation of the system prototype in a realistic environment. They served as an input to initial study of the procedure for neutron detection algorithm configuration discussed in this contribution as well.
We report here that a number of commonly used small peptide caspase inhibitors consisting of a caspase recognition sequence linked to chloromethylketone, fluoromethylketone or aldehyde reactive group ...efficiently inhibit other cysteine proteases than caspases. The in vitro studies included cathepsins B, H, L, S, K, F, V, X and C, papain and legumain. Z-DEVD-cmk was shown to be the preferred irreversible inhibitor of most of the cathepsins in vitro, followed by Z-DEVD-fmk, Ac-YVAD-cmk, Z-YVAD-fmk and Z-VAD-fmk. Inactivation of legumain by all the inhibitors investigated was moderate, whereas cathepsins H and C were poorly inhibited or not inhibited at all. Inhibition by aldehydes was not very potent. All the three fluoromethylketones efficiently inhibited cathepsins in Jurkat and human embryonic kidney 293 cells at concentrations of 100 microM. Furthermore, they completely inhibited cathepsins B and X activity in tissue extracts at concentrations as low as 1 microM. These results suggest that data based on the use of these inhibitors should be taken with caution and that other proteases may be implicated in the processes previously ascribed solely to caspases.
Human dipeptidyl peptidase I was expressed in the insect cell/baculovirus system and purified in its active (rhDPPI) and precursor (pro-rhDPPI) forms. RhDPPI was very similar to the purified enzyme ...(hDPPI) with respect to glycosylation, enzymatic processing, oligomeric structure, CD spectra, and catalytic activity. The precursor, which was a dimer, could be activated ∼2000-fold with papain. Cathepsin L efficiently activated pro-rhDPPI in vitro at pH 4.5 (k app ∼ 2 × 103 min-1 M-1), and two cleavage pathways were characterized. The initial cleavage was within the pro region between the residual pro part and the activation peptide. Subsequently, the activation peptide was cleaved from the catalytic region, and the latter was cleaved into the heavy and light chains. Alternatively, the pro region was first separated from the catalytic region. Cathepsin S was a less efficient activating enzyme. Cathepsin B and rhDPPI did not activate pro-rhDPPI, and the proenzyme was incapable of autoactivation. Incubation of both pro-rhDPPI and rhDPPI with cathepsin D resulted in degradation. Cystatin C and stefins A and B inhibited rhDPPI with K i values in the nanomolar range (K i = 0.5−1.1 nM). The results suggest that cathepsin L could be an important activator of DPPI in vivo and that cathepsin D and possibly the cystatins may contribute to DPPI downregulation.
Diamond pixel modules Asner, D.; Barbero, M.; Bellini, V. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2011, Letnik:
636, Številka:
1
Journal Article
Recenzirano
With the commissioning of the LHC in 2010 and upgrades expected in 2015, ATLAS and CMS are planning to upgrade their innermost tracking layers with radiation hard technologies. Chemical Vapor ...Deposition diamond has been used extensively in beam conditions monitors as the innermost detectors in the highest radiation areas of BaBar, Belle, CDF and all LHC experiments. This material is now being considered as a sensor material for use very close to the interaction region where the most extreme radiation conditions exist. Recently the RD42 collaboration constructed, irradiated and tested polycrystalline and single-crystal chemical vapor deposition diamond sensors to the highest fluences expected at the super-LHC. We present beam test results of chemical vapor deposition diamond up to fluences of 1.8×10
16
protons/cm
2 illustrating that both polycrystalline and single-crystal chemical vapor deposition diamonds follow a single damage curve. We also present beam test results of irradiated complete diamond pixel modules.
Voltage measurement at a given forward current in dedicated dosimetric diodes is used to monitor displacement damage in silicon caused by energetic hadrons in the LHC experiments. The diodes operate ...in a strong magnetic field which influences their performance. In this work, measurements of the effect of the magnetic field on two types of devices: high sensitivity CMRP diodes and commercial BPW34F silicon p-i-n diodes are presented. Our results show that the magnetic field effects are manageable and will not significantly deteriorate the performance of the displacement damage measurements.
The invariant chain (Ii) is associated with major histocompatibility complex class II molecules during early stages of their intracellular transport. In an acidic endosomal/lysosomal compartment, it ...is proteolytically cleaved and removed from class II heterodimers. Participation of aspartic and cysteine proteases has been observed in in vitro degradation of Ii, but the specific enzymes responsible for its in vivo processing are as yet undefined. We have previously isolated a noncovalent complex of the lysosomal cysteine protease cathepsin L with a peptide fragment derived from the p41 form of Ii from human kidney. Here we show that this Ii fragment, which is identical to the alternatively spliced segment of p41, is a very potent competitive inhibitor of cathepsin L (equilibrium inhibition constant Ki = 1.7 X 10(-12) M). It inhibits two other cysteine proteases, cathepsin H and papain, but to much lesser extent. Cysteine proteases cathepsins B, C, and S, as well as representatives of serine, aspartic, and metalloproteases, are not inhibited at all. These findings suggest a novel role for p41 in the regulation of various proteolytic activities during antigen processing and presentation. The Ii inhibitory fragment shows no sequence homology with the known cysteine protease inhibitors, and may, therefore, represent a new class.
ATLAS diamond Beam Condition Monitor Gorišek, A.; Cindro, V.; Dolenc, I. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2007, Letnik:
572, Številka:
1
Journal Article
Recenzirano
The ATLAS experiment has chosen to use diamond for its Beam Condition Monitor (BCM) given its radiation hardness, low capacitance and short charge collection time. In addition, due to low leakage ...current diamonds do not require cooling. The ATLAS Beam Condition Monitoring system is based on single beam bunch crossing measurements rather than integrating the accumulated particle flux. Its fast electronics will allow separation of LHC collisions from background events such as beam gas interactions or beam accidents. There will be two stations placed symmetrically about the interaction point along the beam axis at
z
=
±
183.8
cm
. Timing of signals from the two stations will provide almost ideal separation of beam–beam interactions and background events. The ATLAS BCM module consists of diamond pad detectors of
1
cm
2
area and
500
μ
m
thickness coupled to a two-stage RF current amplifier. The production of the final detector modules is almost done. A
S
/
N
ratio of 10:1 has been achieved with minimum ionizing particles (MIPs) in the test beam setup at KEK. Results from the test beams and bench measurements are presented.
Beam conditions and the potential detector damage resulting from their anomalies have pushed the LHC experiments to plan their own monitoring devices in addition to those provided by the machine. ...ATLAS decided to build a telescope composed of two stations with four diamond pad detector modules each, placed symmetrically around the interaction point at
z
=
±
183.8
cm
and
r
∼
55
mm
(
η
∼
4.2
). Equipped with fast electronics it allows time-of-flight separation of events resulting from beam anomalies from normally occurring
p–
p interactions. In addition it will provide a coarse measurement of the LHC luminosity in ATLAS. Ten detector modules have been assembled and subjected to tests, from characterization of bare diamonds to source and beam tests. Preliminary results of beam test in the CERN PS indicate a signal-to-noise ratio of
14
±
2
.
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