NSUF 23-4683: Neutron Detection Via Defects Created in Hexagonal Boron Nitride
Very sensitive neutron detection is possible from the changes in the optical properties of boron-10 enriched hexagonal boron nitride (hBN) single crystals. The boron-10 isotope has one of the largest neutron capture cross-sections of any isotope of any element in the periodic table. Neutron irradiation transmutates boron-10 isotope into lithium and alpha particles, thereby leaving behind boron vacancies. The formation of these vacancies and the accumulation of lattice damage creates new peaks in its Raman spectra, new color centers, and new signatures in its electron resonance spectra. While unirradiated, pristine hBN has only two peaks at 1394.5 cm^-1 and ~53 cm^-1 for B-10 enriched hBN, neutron irradiation creates new Raman peaks, a broad peak at 450 cm^-1 (full width at half maximum of 250 cm^-1) and a narrow peak at 1295 cm^-1 (FWHM of 35 cm^-1). Because the Raman spectra of hBN is very simple, and background signal from single crystal material is very low, the signal to noise for these new peaks is high. Irradiation also produces color centers in hBN around 2 eV (620 nm, ie orange) that are also single photon emitters. These are bright and are stable at room temperature. Evidence for negatively charged boron vacancies also emerges from new peaks in the electron spin resonance spectra.
To develop quantitative models for this phenomena, hBN single crystals would be subjected to three different neutron doses. They will be exposed to 1, 10, and 60 hours at a thermal neutron flux of 4E12 neutrons·cm-2·s-1, to produce thermal fluences of 2.9E16 cm-2, 1.45E17 cm-2, and 8.6E17 cm-2. Subsequently, the Raman peak intensity ratios of the new peaks to the original intralayer vibrational mode (the E2g mode) will be measured. Shifts in the new peak positions and/or widths will also be measured and correlated with the neutron irradiation dose.
Furthermore, the optical/spin properties of the neutron irradiated hBN will be determined by electron spin resonance (EPR) and optically detected magnetic resonance (ODMR). The parameters to be measured include the optical and magnetic properties and quantum coherence time of the defects as functions of neutron dose and impurity concentration. This may provide an additional method of measuring the neutron fluence. Confocal imaging of the ODMR response will also provide spatial resolution of these properties, shedding light on the effects of local defects and microstructures on the spin properties of these materials.
The irradiation can be completed in two months or less. The ESR and ODMR measurements can each be completed in six weeks. These experiments will establish control and the properties of the VB- defect, and its suitability for neutron detection. As a bonus, the irradiated hBN samples are also of interest for their potential quantum information science applications. Both magnetic resonance techniques can also reveal and track other defects that may arise under the varying neutron fluence conditions. Such defects could potentially play important roles in the hBN sensing behavior. Furthermore, this project will provide material not just for the fundamental property measurements, but also for devices based on and incorporating these materials.
Additional Info
| Field | Value |
|---|---|
| Abstract | Very sensitive neutron detection is possible from the changes in the optical properties of boron-10 enriched hexagonal boron nitride (hBN) single crystals. The boron-10 isotope has one of the largest neutron capture cross-sections of any isotope of any element in the periodic table. Neutron irradiation transmutates boron-10 isotope into lithium and alpha particles, thereby leaving behind boron vacancies. The formation of these vacancies and the accumulation of lattice damage creates new peaks in its Raman spectra, new color centers, and new signatures in its electron resonance spectra. While unirradiated, pristine hBN has only two peaks at 1394.5 cm^-1 and ~53 cm^-1 for B-10 enriched hBN, neutron irradiation creates new Raman peaks, a broad peak at 450 cm^-1 (full width at half maximum of 250 cm^-1) and a narrow peak at 1295 cm^-1 (FWHM of 35 cm^-1). Because the Raman spectra of hBN is very simple, and background signal from single crystal material is very low, the signal to noise for these new peaks is high. Irradiation also produces color centers in hBN around 2 eV (620 nm, ie orange) that are also single photon emitters. These are bright and are stable at room temperature. Evidence for negatively charged boron vacancies also emerges from new peaks in the electron spin resonance spectra. To develop quantitative models for this phenomena, hBN single crystals would be subjected to three different neutron doses. They will be exposed to 1, 10, and 60 hours at a thermal neutron flux of 4E12 neutrons·cm-2·s-1, to produce thermal fluences of 2.9E16 cm-2, 1.45E17 cm-2, and 8.6E17 cm-2. Subsequently, the Raman peak intensity ratios of the new peaks to the original intralayer vibrational mode (the E2g mode) will be measured. Shifts in the new peak positions and/or widths will also be measured and correlated with the neutron irradiation dose. Furthermore, the optical/spin properties of the neutron irradiated hBN will be determined by electron spin resonance (EPR) and optically detected magnetic resonance (ODMR). The parameters to be measured include the optical and magnetic properties and quantum coherence time of the defects as functions of neutron dose and impurity concentration. This may provide an additional method of measuring the neutron fluence. Confocal imaging of the ODMR response will also provide spatial resolution of these properties, shedding light on the effects of local defects and microstructures on the spin properties of these materials. The irradiation can be completed in two months or less. The ESR and ODMR measurements can each be completed in six weeks. These experiments will establish control and the properties of the VB- defect, and its suitability for neutron detection. As a bonus, the irradiated hBN samples are also of interest for their potential quantum information science applications. Both magnetic resonance techniques can also reveal and track other defects that may arise under the varying neutron fluence conditions. Such defects could potentially play important roles in the hBN sensing behavior. Furthermore, this project will provide material not just for the fundamental property measurements, but also for devices based on and incorporating these materials. |
| Award Announced Date | 2023-06-01T08:59:02.667 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Raymond Cao |
| Irradiation Facility | Ohio State University Research Reactor |
| PI | James Edgar |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |