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In search to identify extremely stable materials to perform the collimation function of the 7-TeV proton beam halo at the Large Hadron Collider (LHC), oxide dispersion strengthened (DS) copper alloys were explored. These internally oxidized copper alloys known as GlidCop are also leading candidates for high heat flux applications in fusion reactors and as divertor and first wall structure in ITER. These considerations have led to an extensive body of research on neutron-induced changes in the microstructure and physio-mechanical properties. This study focused primarily on the damage induced by 200 MeV protons on as wrought and cold-worked GlidCop Al15 DS copper ally selected as a candidate material of the LHC beam collimation structure to damage levels up to ∼10 displacements-per-atom (dpa) and irradiation temperatures up to ∼600 °C. For reference, low dose spallation neutron damage at sub-zero irradiation temperature was included in the study. Proton irradiation effects on dimensional stability, mechanical behavior, electrical resistivity and X-ray diffraction-based microstructural changes are presented in the paper. GlidCop Al15 exhibited excellent thermal stability and superior to pure Cu resistance to conductivity loss. Proton irradiation-induced hardening and embrittlement at distinct irradiation temperature regimes were shown to follow similar trends to what was reported under neutron exposure to even higher dpa damage. At T$_{\tt{irr}}$ ∼600 ± 20 °C the cold-worked DS copper alloy exhibited softening accompanied by elongation reduction while at T$_{\tt{irr}}$ ∼200 ± 10 °C the as-wrought experienced hardening with elongation increase. High resolution X-ray diffraction revealed that even low-dose neutron irradiation has a strong influence on the size and distribution of dispersed Al$_2$O$_3$ particles.

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 1020 p/cm2. We employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

Core SiO2 quartz fibers of the Large Hadron Collider (LHC) ATLAS Zero-degree Calorimeter (ZDC) are expected to experience integrated doses of a few giga-Rad (Grad) at their closest position to the LHC beam. An array of fibers was irradiated with 200 MeV protons and spallation-generated mixed spectra (primarily fast neutrons) at the Brookhaven National Laboratory (BNL) Linac. Specifically, 1 mm- and 2 mm-diameter quartz (GE 124) rods of 50 mm length were exposed to direct 200 MeV protons leading to peak integrated dose of ∼ 28 Grad ( ∼ 0.28 GGy). Exposure of 1 mm-diameter SiO2 fibers to a neutron flux was also achieved in the spallation field generated by 128 MeV protons. In the post-irradiation analysis, the quartz fiber transmittance was evaluated as a function of the absorbed dose. Significant degradation of the transmittance and increased radiation damage of the material were observed. Microscopic evaluation of the fibers revealed extensive micro-structural damage and irradiation-induced defects. The measurements revealed that a threshold fluence ( ∼ 2.6 1016 p/cm2) or dose of ∼ 10 Grad (0.1 GGy) appears to exist beyond which light transmittance drops below 10%. Also observed is that fiber transmittance loss increased drastically with SiO2 fiber diameter (1 mm vs. 2 mm diameter). This is attributed, in part, to the earlier lateral leakage from the 1 mm fiber of knock-on electrons and primary protons implying that more damage-inducing protons travel within the bulk of the 50 mm long 2-mm fibers. While Monte Carlo simulations performed tend to support such assumption, future experiments and sensitivity studies are envisioned to address the fiber diameter influence on degradation.

The accurate determination of the ambient dose equivalent in the mixed neutron-photon fields encountered around high-energy particle accelerators still represents a challenging task. The main complexity arises from the extreme variability of the neutron energy, which spans over ten orders of magnitude or more. Operational survey instruments, which response function attempts to mimic the fluence-to-ambient dose equivalent conversion coefficient up to GeV neutrons, are available on the market, but their response is not fully reliable over the entire energy range. Extended range rem counters (ERRC) do not require the exact knowledge of the energy distribution of the neutron field and the calibration can be done with a source spectrum. If the actual neutron field has an energy distribution different from the calibration spectrum, the measurement is affected by an added uncertainty related to the partial overlap of the fluence-to- ambient dose equivalent conversion curve and the response function. For this reason their operational use should always be preceded by an “in-field” calibration, i.e. a calibration made against a reference instrument exposed in the same field where the survey-meter will be employed. In practice the extended-range Bonner Sphere Spectrometer (ERBSS) is the only device which can serve as reference instrument in these fields, because of its wide energy range and the possibility to assess the neutron fluence and the ambient dose equivalent (H⁎(10)) values with the appropriate accuracy. Nevertheless, the experience gained by a number of experimental groups suggests that mandatory conditions for obtaining accurate results in workplaces are: (1) the use of a well-established response matrix, thus implying validation campaigns in reference monochromatic neutrons fields, (2) the expert and critical use of suitable unfolding codes, and (3) the performance test of the whole system (experimental set-up, elaboration and unfolding procedures) in a well controlled workplace field. The CERF (CERN-EU high-energy reference field) facility is a unique example of such a field, where a number of experimental campaigns and Monte Carlo simulations have been performed over the past years. With the aim of performing this kind of workplace performance test, four different ERBSS with different degrees of validation, operated by three groups (CERN, INFN-LNF and Politecnico of Milano), were exposed in two fixed positions at CERF. By using different unfolding codes (MAXED, GRAVEL, FRUIT and FRUIT SGM), the experimental data were analyzed to provide the neutron spectra and the related dosimetric quantities. The results allow assessing the overall performance of each ERBSS and of the unfolding codes, as well as comparing the performance of three ERRCs when used in a neutron field with energy distribution different from the calibration spectrum.

Detectors based on the micromegas principle have already been used in several atomic, nuclear and particle physics experiments. They have also been proposed as one of the options to upgrade the ATLAS muon spectrometer in the very forward/backward region. To meet this end, it is imperative to study their performance in a mixed (neutron and gamma) radiation field. The general-purpose Monte-Carlo code FLUKA has been employed in the present work in order to study the effect of 5.5 MeV neutrons impinging on a prototype micromegas detector developed for sLHC. The response of the detector to the photons originating from the inevitable neutron inelastic scattering on the surrounding materials of the experimental facility was also studied, through comparisons with experimental data. (C) 2012 Elsevier B.V. All rights reserved.