A novel technique for the rejection of gamma background from charged-particle spectra was demonstrated using a CVD diamond detector with a 6Li neutron converter installed at a thermal neutron ...beamline of the TRIGA research reactor at the Atominstitut (Vienna University of Technology). Spectra of the alpha particles and tritons of 6Li(n,T)4He thermal neutron capture reaction were separated from the gamma background by a new algorithm based on pulse-shape analysis. The thermal neutron capture in 6Li is already used for neutron flux monitoring, but the ability to remove gamma background allows using a CVD diamond detector for thermal neutron counting. The pulse-shape analysis can equally be applied to all cases where the charged products of an interaction are absorbed in the diamond and to other background particles that fully traverse the detector.
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In this paper we introduce a novel analysis technique for measurements with single-crystal chemical vapor deposition (sCVD) diamond detectors in fast-neutron fields. This method exploits the unique ...electronic property of sCVD diamond sensors that the signal shape of the detector current is directly proportional to the initial ionization profile. In fast-neutron fields the diamond sensor acts simultaneously as target and sensor. The interaction of neutrons with the stable isotopes
12
C and
13
C is of interest for fast-neutron diagnostics. The measured signal shapes of detector current pulses are used to identify individual types of interactions in the diamond with the goal to select neutron-induced reactions in the diamond and to suppress neutron-induced background reactions as well as
-background. The method is verified with experimental data from a measurement in a 14.3 MeV neutron beam at JRC-IRMM, Geel/Belgium, where the
13
C(n,
)
10
Be reaction was successfully extracted from the dominating background of recoil protons and
-rays and the energy resolution of the
12
C(n,
)
9
Be reaction was substantially improved. The presented analysis technique is especially relevant for diagnostics in harsh radiation environments, like fission and fusion reactors. It allows to extract the neutron spectrum from the background, and is particularly applicable to neutron flux monitoring and neutron spectroscopy.
Abstract
Fusion product diagnostics based on four commercially
available single-crystal chemical vapor deposition (s-CVD) diamond
detectors are installed in the Large Helical Device (LHD) in order
to ...understand energetic ion confinement. Characteristics of s-CVD
diamonds were surveyed using alpha and D-T neutron sources. It is
found that the energy resolutions of s-CVD diamonds for ∼ 5 MeV
alpha particles and 14 MeV neutrons are 1%–3% and ∼ 1.7%,
respectively. Moreover, the response of four s-CVD diamond detectors
to alpha particles and D-T neutrons is almost identical. The
installation positions of the diamond detectors in the vacuum vessel
are searched for, based on the loss points of charged fusion
products reckoned by Lorentz orbit calculations. Energy- and
time-resolved measurement of fusion product flux will progress in
further understanding of energetic ion confinement in LHD.
Abstract The average energy and multiplicity of prompt $$\gamma $$ γ -rays from slow neutron-induced fission of $$^{235}$$ 235 U have been measured using the STEFF spectrometer at the neutron ...time-of-flight facility n_TOF. The individual responses from 11 NaI scintillators were corrected for multiple $$\gamma $$ γ -ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission $$\gamma $$ γ -rays. The results give an average $$\gamma $$ γ -ray energy $${\bar{E}}_{\gamma }$$ E ¯ γ of 1.71(5) MeV and multiplicity $$\bar{\nu }_{\gamma }$$ ν ¯ γ of 2.66(18) considering $$\gamma $$ γ -rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger $${\bar{E}}_{\gamma }$$ E ¯ γ and smaller $$\bar{\nu }_{\gamma }$$ ν ¯ γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.
For the first time, a diamond sensor was operated for the characterisation of a high average-intensity gamma-ray beam. Data was collected for gamma beam energies between 2 and 7MeV, at the HIγS ...facility of TUNL. The nanosecond-fast resolution of diamond detectors is exploited to distinguish bunches of gamma rays 16.8ns apart. It allows a precise direct determination of the time-structure of the gamma beam. The strong potential of such a detector for precise absolute flux, position and polarisation measurements is exposed. It is thus shown that diamond detectors are a decisive and unique tool for the detailed characterisation of upcoming gamma sources, such as ELI-NP and HIγS-2.
•First operation of a diamond sensor for the characterisation of a beam of photons.•Clear distinction of photon bunches separated by 16.8ns.•Polarisation measurements possible through beam shape evaluation.•Essential diagnostic tool for ELI-NP machine.
As a result of the foreseen increase in the luminosity of the Large Hadron Collider, the discrimination between the collision products and possible magnet quench-provoking beam losses of the primary ...proton beams is becoming more critical for safe accelerator operation. We report the results of ongoing research efforts targeting the upgrading of the monitoring system by exploiting Beam Loss Monitor detectors based on semiconductors located as close as possible to the superconducting coils of the triplet magnets. In practice, this means that the detectors will have to be immersed in superfluid helium inside the cold mass and operate at 1.9K. Additionally, the monitoring system is expected to survive 20 years of LHC operation, resulting in an estimated radiation fluence of 1×1016 proton/cm2, which corresponds to a dose of about 2MGy. In this study, we monitored the signal degradation during the in situ irradiation when silicon and single-crystal diamond detectors were situated in the liquid/superfluid helium and the dependences of the collected charge on fluence and bias voltage were obtained. It is shown that diamond and silicon detectors can operate at 1.9K after 1×1016p/cm2 irradiation required for application as BLMs, while the rate of the signal degradation was larger in silicon detectors than in the diamond ones. For Si detectors this rate was controlled mainly by the operational mode, being larger at forward bias voltage.
•Silicon and diamond detectors are proposed for beam loss monitoring at LHC.•The first in situ radiation test of Si and diamond detectors at 1.9K is described.•Both diamond and silicon detectors survived after 1×1016p/cm2 irradiation at 1.9K.•The rate of Si detectors degradation depends on bias polarity and is larger at Vforw.•Sensitivity of Si detectors irradiated to 1×1016p/cm2 is independent on resistivity.
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The paper describes the testing of the NEUTON detection system into CROCUS, the zero-power reactor of the École Polytechnique Fédérale de Lausanne (EPFL). NEUTON is composed of a
4
mm
×
4
mm sCVD ...diamond detector with a
6
Li converter and the associated acquisition electronics. It is developed by CIVIDEC Instrumentation GmbH. The use of a diamond detector with converter in the mixed radiation field of a nuclear reactor is challenging because these detectors are sensitive to gamma-rays, fast neutrons and thermal neutrons through conversion in
6
Li . In NEUTON, the rejection of gamma-rays is achieved in real time, via the analysis of the signal pulse shape from the detector. To do so, a few signal characteristics (amplitude, area and FWHM) are recorded in the integrated Field Programmable Gate Arrays (FPGA) of the system. This treatment does not induce any dead time. Measurements in CROCUS demonstrated for the first time the capability of a system like NEUTON to detect and separate fast neutrons, thermal neutrons, and gamma-rays. The system response was shown to be linear with respect to the reactor power (up to 35W) and its thermal sensitivity was found to be
(
3
.
5
±
0
.
2
)
×
10
-
5
cps/nv.
The neutron flux of the n_TOF facility at CERN was measured, after installation of the new spallation target, with four different systems based on three neutron-converting reactions, which represent ...accepted cross sections standards in different energy regions. A careful comparison and combination of the different measurements allowed us to reach an unprecedented accuracy on the energy dependence of the neutron flux in the very wide range (thermal to 1 GeV) that characterizes the n_TOF neutron beam. This is a pre-requisite for the high accuracy of cross section measurements at n_TOF. An unexpected anomaly in the neutron-induced fission cross section of
235
U is observed in the energy region between 10 and 30keV, hinting at a possible overestimation of this important cross section, well above currently assigned uncertainties.
The time resolution of the detectors currently in use is limited by 50-70 ps due to the spontaneous processes involved in the development of the response signal, which forms after the relaxation of ...carriers generated during the interaction. In this study, we investigate the feasibility of exploiting sub-picosecond phenomena occurring after the interaction of scintillator material with ionizing radiation by probing the material with ultra-short laser pulses. One of the phenomena is the elastic polarization due to the local lattice distortion caused by the displacement of electrons and holes generated by ionization. The key feature of the elastic polarization is its short response time, which makes it prospective for using as an optically detectable time mark. The nonlinear optical absorption of femtosecond light pulses of appropriate wavelength is demonstrated to be a prospective tool to form the mark. This study was aimed at searching for inorganic crystalline media combining scintillation properties and non-linear absorption of ultra-short laser pulses. The nonlinear pump-and-probe optical absorption technique with 200 fs laser pulses was used to study the effects in lead tungstate, garnet-type, and diamond scintillator crystals.
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