Abstract
This paper proposes a new graphene gamma- and beta-radiation sensor with a backend RF ring oscillator transducer employed to convert the change in the graphene resistivity due to ionizing irradiation into a frequency output. The sensor consists of a CVD monolayer of graphene grown on a copper substrate, with an RF ring oscillator readout circuit in which the percentage change in frequency is captured versus the change in radiation dose. The novel integration of the RF oscillator transducer with the graphene monolayer results in high average sensitivity to gamma irradiation up to 3.82 kΩ/kGy, which corresponds to a percentage change in frequency of 7.86% kGy−1 in response to cumulative gamma irradiation ranging from 0 to 1 kGy. The new approach helps to minimize background environmental effects (e.g., due to light and temperature), leading to an insignificant error in the output change in frequency of the order of 0.46% when operated in light versus dark conditions. The uncertainty in readings due to background light was analyzed, and the error in the resistance was found to be of the order of 1.34 Ω, which confirms the high stability and selectivity of the proposed sensor under different background effects. Furthermore, the evolution of the graphene’s lattice defect density due to radiation was observed using Raman spectroscopy and SEM, indicating a lattice defect density of up to 1.780 × 1011/cm2 at 1 kGy gamma radiation, confirming the increase in the graphene resistance and proving the graphene’s sensitivity. In contrast, the graphene’s defect density in response to beta radiation was 0.683 × 1011/cm2 at 3 kGy beta radiation, which is significantly lower than the gamma effects. This can be attributed to the lower p-doping effect caused by beta irradiation in ambient conditions, compared with that caused by gamma irradiation. Morphological analysis was used to verify the evolution of the microstructural defects caused by ionizing irradiation. The proposed sensor monitors the low-to-medium cumulative range of ionizing radiations ranging from 0 to 1 kGy for gamma radiation and 0 to 9 kGy for beta radiation, with high resolution and selectivity, filling the research gap in the study of graphene-based radiation sensors at low-to-medium ionizing radiation doses. This range is essential for the pharmaceutical and food industries, as it spans the minimum range for affecting human health, causing cancer and DNA damage.
Highlights
Licensee MDPI, Basel, Switzerland.Radiation sensors are widely used to monitor radioactive activities continuously in multiple applications such as biomedical diagnostics, pharmaceutical applications, border security, agriculture, environmental applications, astrophysics, and nuclear power plants [1,2]
In this paper, we introduce the criteria for transforming the change in graphene resistivity caused by cumulative ionizing radiation into a change in oscillating frequency detected via the oscillating frequency of a backend RF ring oscillator circuit, with no need to monitor gate voltages and drain currents
An experiment was conducted on our sensor assembly in order to determine the impact of light photons on the oscillating output frequency generated by the RF ring oscillator circuit under different light conditions, where cumulative gamma-radiation doses ranging from 0.8 kGy to 1 kGy were applied to the two graphene sensors and oscillating frequency readings were recorded from the oscilloscope under three different environmental conditions: (i) with the two graphene films subjected to light, (ii) with one graphene film subjected to light and the other kept in darkness, and (iii) with both graphene films kept in darkness
Summary
Licensee MDPI, Basel, Switzerland.Radiation sensors are widely used to monitor radioactive activities continuously in multiple applications such as biomedical diagnostics, pharmaceutical applications, border security, agriculture, environmental applications, astrophysics, and nuclear power plants [1,2]. Gamma radiation is electromagnetic radiation consisting of photons emitted by the relaxation of the daughter nucleus after radioactive decay of the unstable or parent nucleus [7]. Gamma radiation is very harmful because it is ionizing radiation, i.e., it causes the absorbing matter to emit electrons. It may interact with the nucleus of the matter, causing positron emission. This may damage DNA and cause different types of cancers in humans, including skin, bone, breast, and lung cancer and leukemia [8]
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