# First evaluation of a heteroepitaxial diamond ionization chamber operating at low voltage for diagnostic X‐ray dosimetry

## TL;DR

This paper evaluates a new diamond-based ionization chamber for X-ray dosimetry, showing it can work efficiently at low voltages and small sizes.

## Contribution

First evaluation of a heteroepitaxial diamond ionization chamber for low-voltage diagnostic X-ray dosimetry.

## Key findings

- HED-IC showed excellent dose linearity (R² > 0.997) and weak energy dependence (<10%) under X-ray conditions.
- The detector's sensitive volume is 1/1250th of conventional air chambers, with volume-normalized sensitivity exceeding theoretical predictions.

## Abstract

Heteroepitaxial diamond has recently gained attention as a radiation detector material due to its wide bandgap, radiation hardness, and near‐tissue equivalence. Despite these advantages, its use as a solid‐state ionization chamber for diagnostic X‐ray dosimetry has not yet been established. Demonstrating stable, high‐efficiency operation at low voltage would enable compact dosimeters with a very small sensitive volume, which is difficult to achieve with conventional air ionization chambers.

To perform the first characterization of a heteroepitaxial diamond ionization chamber (HED‐IC) operated at low bias voltage under diagnostic X‐ray conditions and to evaluate its feasibility as a compact, high‐efficiency dosimeter.

A heteroepitaxial diamond detector (4 × 4 × 0.5 mm3) with Ti/Au electrodes was fabricated and evaluated using diagnostic X‐ray beams at tube voltages from 50 to 120 kV. Charge‐collection characteristics, dose linearity, energy dependence, and temporal response were assessed at negative bias voltages with magnitudes between −1 and −100 V. Monte Carlo simulations were performed using PHITS to compute the expected diamond‐to‐air sensitivity ratio under the same beam qualities for comparison with the experimental measurements.

The HED‐IC exhibited excellent dose linearity (R
2 > 0.997) and weak energy dependence (< 10%) across effective energies from 28.4 to 40.1 keV. The detector enables dose measurements within a very small sensitive volume, only 1/1250 of that of a typical air ionization chamber. The volume‐normalized sensitivity exceeded theoretical expectations, suggesting enhanced effective ionization efficiency. An increased response with higher bias voltage further indicated potential for high‐sensitivity operation.

The results demonstrate that the HED‐IC can operate as a low‐voltage, high‐efficiency solid‐state ionization chamber under diagnostic X‐ray conditions. Owing to the scalability of heteroepitaxial diamond growth, this detector concept provides a promising basis for compact, tissue‐equivalent dosimeters capable of real‐time dose monitoring across a wide range of radiological applications.