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This presentation describes experimental measurements with thin scCVD diamond detectors and their DD and DT neutron sources. This presentation will be given at the NNSS Prompt Radiation Detection and Imaging Workshop April 25-28, 2022.
An avalanche effect yielding inherent gain can be exploited in thin, single-crystal chemical vapor deposition (scCVD) diamond. It occurs when a high enough bias is applied across the diamond thickness while avoiding breakdown. This charge multiplication effect was studied previously with alpha particles and heavy ions either by using the transient current technique or by measuring the energy spectrum. The measurements we obtained to evaluate the charge multiplication performance of a 10 μm thick scCVD diamond detector used a novel approach—we employed an electrometer to characterize the response of the detector by performing directly coupled current measurements (time-averaged charge, at 1 Hz sampling) when exposed to 14.1 MeV neutrons from deuterium-tritium fusion. We measured both the dark and irradiated currents from the detector over a range of applied displacement field values from 2 to 75 V/μm. A histogram method with central mean and standard deviation width was used to determine the current over each measurement duration typically from 100 to 300 seconds. The dark-subtracted irradiated current (i.e., contrast) was used to evaluate the gain of the detector at each applied displacement field. The contrast at an applied displacement field between 15 and 20 V/μm was higher than the expected linear increase in contrast proportional to the increased applied bias, indicating the possible presence of avalanche events in the diamond. The detector response also indicated possible polarization and charge depletion effects. These results provide an opportunity to further explore the use of thin scCVD diamond as a fast neutron current mode detector with inherent gain.
Here the performance characteristics of single-crystalline diamond detectors at varying rates of heavy-ions below 50 MeV/u have been investigated. When tested with a 228 Th source, the energy resolution of these detectors is better than 1.0% FWHM for 8.8 MeV α-particles. With a slight reduction in the energy resolution, simultaneous timing resolution of 314 ps has been achieved. Isotopic resolution has been achieved up to magnesium using a diamond telescope at low rates with a 20 MeV/u 20 Ne + 12 C reaction. At moderate rates of direct 7.5 MeV/u 78 Kr, polarization effects are observed, though this effect can be diminished by increasing the applied voltage on the detector up to a limit. After an accumulated dose of 6.9 × 10 8 direct 78 Kr particles transmitting through the detector, a degradation in the energy resolution of the 8.8 MeV peak from 1.6% to 5.3% is observed, indicating that permanent damage has been done to the detector.
The first prototype of a fast scanning diamond beam profile detector (DBPD) suitable for invasive high power CW electron beam core profile measurements in transmittance mode was developed. It consists of a multi-strip solid state diamond detector to scan with high speed (up to 1 m/s) and precision (about 5 μm) through the core of an electron beam. The diamond sensor was made from a thin polycrystalline diamond (PCD) plate with highly B-doped diamond conductive strips both grown by CVD. Transient currents from the multi-strip detector were measured with fast digitizing electrometers. Successful operation of the DBPD was demonstrated for pulsed (5 Hz) and CW (78 kHz) CeC beams, including the detector’s ability to withstand a 20 sec insertion into the CW CeC beam core. The X-Y beam spatial profile was measured in one scan. Thermal modelling demonstrated a manageable thermal impact even from a relatively long insertion of the diamond sensor into the CW CeC core and very short (0.2 s) insertion into the CW LEReC beam core. Electrical impedance modelling of the detector and vacuum chamber assembly demonstrated minimal impact on beam line impedance with diamond sensor insertion.
The inverse-kinematics p( 7 Li,n) 7 Be reaction produces forward-focused neutron emission, offering enhanced usable flux and reduced shielding requirements. Reliable simulation of such neutron fields is essential for the development of compact accelerator-based neutron sources. In this study, a PHITS-based simulation framework for the reaction was experimentally assessed using fast-neutron measurements. Forward-directed neutrons were measured with a diamond neutron detector and quantitatively compared with simulations with newly prepared IK-Frag cross-section file based on the proton-induced reaction data in ENDF/B-VIII.1, TENDL-2023, and JENDL-4.0/HE. Measurements and simulations were performed for incident 7 Li 3+ energies ranging from 15.0 to 25.0 MeV using a 50 μm-thick polypropylene target. For all conditions, the PHITS-based simulation framework reproduced the deposited energy spectra at the correct order of magnitude. The comparison of deposited energy spectra in the diamond detector showed high correlation coefficients across all investigated energies, indicating reasonable agreement in spectral shape between simulations and measurements. This work represents an initial step toward establishing a benchmark for PHITS simulations of the inverse kinematic reaction between an incident lithium-ion and a proton target.
This presentation will be presented at FY 2020 SDRD Annual (Webex) Meeting scheduled for September 23–24, 2020. Multi-layered Avalanche Diamond Detector for Fast Neutron Applications NLV-003-20, Year 1
A novel detector based on a polycrystalline diamond sensor is here employed in an advanced time-of-flight scheme for the characterization of energetic ions accelerated during laser-matter interactions. The optimization of the detector and of the advanced TOF methodology allow to obtain signals characterized by high signal-to-noise ratio and high dynamic range even in the most challenging experimental environments, where the interaction of high-intensity laser pulses with matter leads to effective ion acceleration, but also to the generation of strong Electromagnetic Pulses (EMPs) with intensities up to the MV/m order. These are known to be a serious threat for the fielded diagnostic systems. Here we report on the measurement performed with the PW-class laser system Vega 3 at CLPU (~30 J energy, ~10 21 W/cm 2 intensity, ~30 fs pulses) irradiating solid targets, where both tens of MeV ions and intense EMP fields were generated. The data were analyzed to retrieve a calibrated proton spectrum and in particular we focus on the analysis of the most energetic portion (E > 5.8 MeV) of the spectrum showing a procedure to deal with the intrinsic lower sensitivity of the detector in the mentioned spectral-range.
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Application for an R&D 100 award
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Presentation to be presented during the Site-Directed Research and Development (SDRD) Program FY 2021 Meeting (Webex), September 22–23, 2021.
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Element6 has come out of a two year production pause (pre-COVID) with material that lacks their previous QC – some is excellent, but screening is needed. Applied Diamond can now make usable polycrystalline material, for applications not requiring absolute flux calibration. A large area possible (1cm 2 ). Great Lakes Crystal Technology has made great progress in two years, but still needs development to become a trusted supplier of single crystal material. LANL staff (Dongsung Kim) has developed proficient lithography and bonding expertise at CINT to make devices from vendor supplied material. LANL staff has continued and expanded capabilities for device testing at NSLS-II.
A newsletter article to appear in the FY 2022 Q1 issue of the LDRD Quarterly Highlights, https://www.lanl.gov/projects/ldrd-tri-lab/quarterly-highlights.php.