A Study of the Radiation Tolerance of CVD Diamond to 70 MeV Protons, Fast Neutrons and 200 MeV Pions

Abstract

We measured the radiation tolerance of commercially available diamonds grown by the Chemical Vapor Deposition process by measuring the charge created by a 120 GeV hadron beam in a 50 μm pitch strip detector fabricated on each diamond sample before and after irradiation. We irradiated one group of samples with 70 MeV protons, a second group of samples with fast reactor neutrons (defined as energy greater than 0.1 MeV), and a third group of samples with 200 MeV pions, in steps, to (8.8±0.9) × 10¹⁵ protons/cm², (1.43±0.14) × 10¹⁶ neutrons/cm², and (6.5±1.4) × 10¹⁴ pions/cm², respectively. By observing the charge induced due to the separation of electron-hole pairs created by the passage of the hadron beam through each sample, on an event-by-event basis, as a function of irradiation fluence, we conclude all datasets can be described by a first-order damage equation and independently calculate the damage constant for 70 MeV protons, fast reactor neutrons, and 200 MeV pions. We find the damage constant for diamond irradiated with 70 MeV protons to be 1.62±0.07(stat)±0.16(syst)× 10^-18 cm²/(p μm), the damage constant for diamond irradiated with fast reactor neutrons to be 2.65±0.13(stat)±0.18(syst)× 10^-18 cm²/(n μm), and the damage constant for diamond irradiated with 200 MeV pions to be 2.0±0.2(stat)±0.5(syst)× 10^-18 cm²/(π μm). The damage constants from this measurement were analyzed together with our previously published 24 GeV proton irradiation and 800 MeV proton irradiation damage constant data to derive the first comprehensive set of relative damage constants for Chemical Vapor Deposition diamond. We find 70 MeV protons are 2.60 ± 0.29 times more damaging than 24 GeV protons, fast reactor neutrons are 4.3 ± 0.4 times more damaging than 24 GeV protons, and 200 MeV pions are 3.2 ± 0.8 more damaging than 24 GeV protons. We also observe the measured data can be described by a universal damage curve for all proton, neutron, and pion irradiations we performed of Chemical Vapor Deposition diamond. Finally, we confirm the spatial uniformity of the collected charge increases with fluence for polycrystalline Chemical Vapor Deposition diamond, and this effect can also be described by a universal curve.

Keywords: Chemical Vapor Deposition; charge collection distance; mean drift path; polycrystalline diamond; radiation damage constant; radiation tolerance; schubweg; single-crystalline diamond.

Figure 1

Lethargy neutron spectrum of channel F19 in Core 189 of the JSI TRIGA reactor used for all our neutron irradiations, at full reactor power (250 kW) [12].

Figure 2

The signal charge spectrum evolution for samples irradiated with 70 MeV protons biased at $E = +2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The pulse height spectrum before irradiation was measured using a setup with a ⁹⁰Sr $\beta$-source and a single pad metallization on the diamond. The integral of each spectrum has been normalized to unity.

Figure 3

The signal charge spectrum evolution for samples irradiated with fast neutrons biased at $E = -2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The pulse height spectrum before irradiation was measured using a setup with a ⁹⁰Sr $\beta$-source and a single pad metallization on the diamond. The integral of each spectrum was normalized to unity.

Figure 4

The signal charge spectrum evolution for the scCVD diamond sample irradiated with 200 MeV pions biased at $E = +2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The pulse height spectrum before irradiation was measured using a setup with a ⁹⁰Sr $\beta$-source and a single pad metallization on the diamond, biased at 1 V/$\mathsf{\mu }\mathrm{m}$, since the detector collects all the charge at a bias voltage of 200 V. The integral of each spectrum was normalized to unity.

Figure 5

The $1/\lambda$ for pCVD diamond in the 70 MeV proton irradiation. The two values shown at each fluence are the values for positive (solid markers) and negative (open markers) bias at $E= \pm 2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The data were fit with a first-order damage curve independently for each sample.

Figure 6

The $1/\lambda$ for pCVD diamond in the fast neutron irradiation. The two values shown at each fluence are the values for positive (solid markers) and negative (open markers) bias at $E= \pm 2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The data were fit with a first-order damage curve independently for each sample.

Figure 7

The $1/\lambda$ for scCVD and pCVD diamond in the pion irradiation. The two values shown at each fluence are the values for positive (solid markers) and negative (open markers) bias at $E= \pm 2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The data were fit with a simple damage curve independently for each diamond type. The uncertainty for unirradiated scCVD diamond comes from not knowing the upper initial mean drift distance exactly.

Figure 8

The $1/\lambda$ for scCVD (solid markers) and pCVD (open markers) diamond. As reference, the 800 MeV proton and 24 GeV proton data from [4] are plotted. Each point is shifted by $1/{\lambda }_{0,j}$. The dotted box indicates the zoom area shown in Figure 9.

Figure 9

The $1/\lambda$ for scCVD (solid markers) and pCVD (open markers) diamond up to a fluence of 7 × 10¹⁵/cm² (zoom of dotted box in Figure 8). As reference, the 800 MeV proton and 24 GeV proton data from [4] are plotted. Each point is shifted by $1/{\lambda }_{0,j}$.

Figure 10

The $1/\lambda$ for scCVD (solid markers) and pCVD (open markers) diamond. Each point is shifted by $1/{\lambda }_{0,j}$. The fluence of each point was scaled by the relative damage constant, ${\kappa }_i$, to the 24 GeV proton equivalent fluence. The damage model (dashed line) is fitted to the data points.

Figure 11

The $\lambda$ for scCVD (solid markers) and pCVD (open markers) diamond. The fluence of each point was scaled by the relative damage constant to the 24 GeV proton equivalent fluence. Each point is shifted by ${\varphi }_{0,j}$ which represents the starting value of sample j in 24 GeV proton equivalent fluence space. The dashed line is the fit of the damage model in Equation (3) to the data points. The gray band indicates the variation of the fit parameters by one standard deviation.

Figure 12

The $\mathrm{FWHM}/\mathrm{MP}$ as a function of fluence in the 70 MeV proton irradiation measured in a $+120 \mathrm{GeV}/c$ hadron beam at CERN. The two values shown at each fluence are the values for positive (solid markers) and negative bias (open markers) at $E=2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$.

Figure 13

The $\mathrm{FWHM}/\mathrm{MP}$ as a function of fluence in the fast neutron irradiation measured in a $+120 \mathrm{GeV}/c$ hadron beam at CERN. The two values shown at each fluence are the values for positive (solid markers) and negative bias (open markers) at $E=2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$.

Figure 14

The $\mathrm{FWHM}/\mathrm{MP}$ as a function of fluence in the pion irradiation measured in a $+120 \mathrm{GeV}/c$ hadron beam at CERN. The two values shown at each fluence are the values for positive (solid markers) and negative bias (open markers) at $E=2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$.

Figure 15

The $\mathrm{FWHM}/\mathrm{MP}$ for scCVD (solid markers) and pCVD (open markers) diamond. The fluence of each point was scaled by the relative damage constant to the 24 GeV proton equivalent fluence.

Figure 16

The $\mathrm{FWHM}/\mathrm{MP}$ of scCVD and pCVD diamond samples irradiated with 24 GeV protons, 800 MeV protons, 70 MeV protons, fast reactor neutron, and 200 MeV pions for positive (solid markers) and negative bias (open markers) at $E=2 \mathrm{V}/\mathsf{\mu }\mathrm{m}$. The fluence of each point was scaled by the relative damage constant to the 24 GeV proton equivalent fluence. The dashed line represents a constant fit to the scCVD diamond data points (blue) extrapolated to 40 × 10¹⁵ p/cm² for illustrative purposes.

Figure 17

The $1/\lambda$ for CVD diamond and silicon for proton, neutron and pion irradiations at an electric field of 2 V/$\mathsf{\mu }\mathrm{m}$. The charge collection was measured at room temperature. The dashed lines are diamond results from this work and those in [4] for irradiations at 24 GeV protons (blue), 800 MeV protons (red), 70 MeV protons (green), fast neutrons (orange), and 200 MeV pions (purple), and the solid lines are the silicon damage data from RD50 [28] for proton (blue and red), neutron (orange), and pion (purple) irradiations. The curves for irradiations with 25 MeV protons were taken from [24].