Physics of Inductive Detection

Direct-Conversion Inductive Radiation Detectors

The inductive conversion method is based on the detection of the inductive load on the coil by the charge carriers produced in the semiconductor by the high energy radiation (X-ray, Gamma-ray) rather than collection of these charges at the electrodes by applying electrical field. This load is associated with the energy losses due to absorption of RF radiation by the radiation produced charge carriers reducing quality factor (Q) of a coil-capacitance resonant circuit.

Absorption of the radiation by the free charge carriers relates to any electromagnetic radiation, the visible light, the infrared and longer wavelengths radiation such as RF. The longer the wavelength of the electromagnetic radiation the larger contribution of the free carriers to the absorption. This contribution is approximately proportional to the square of the radiation wavelength. Therefore, while measurable free carrier contribution to the absorption of the infrared radiation requires high density of carriers (high doping), free carrier absorption of the RF radiation allows to detect number of charge carriers equivalent to that produced by a single high-energy photon.

Unlike detectors based on the photoconductive principle, inductive radiation sensing technology detects radiation generated charge carriers at the location where they are created and does not require high carrier mobility, low defect density materials and does not require high voltage biasing. Performance of inductive detectors even improves with increasing density of the defects. Therefore the use of polycrystalline materials results in a substantial increase of the readout sensitivity and energy resolution as compared to detectors based on low defect density monocrystalline materials such as high resistivity CdZnTe (CZT)., Patents: US 10,018,738 B2, U.S. 10,338,237 B2.

Inductive Radiation Detector Technology
E. Kamieniecki, DOI: 10.13140/RG.2.2.11508.40322

Inductive radiation sensing technology (US 10,018,738 B2) based on a low-cost non-crystalline material offers a substantial increase of energy resolution and sensitivity as compared to conventional, photoconductive detectors based on the crystalline materials. A preliminary evaluation performed using a high defect density segment of a CZT wafer indicated that sensitivity of the inductive radiation sensors based on the non-crystalline materials will increase by at least one order of magnitude as compared to sensors based the crystalline materials. It is projected that additionally to higher energy resolution, higher sensitivity and decreased cost of imaging detectors, use of non-crystalline materials would also offer greater flexibility in the construction of x-ray and gamma-ray imaging detectors, an improvement of their spatial resolution and detector size.

Energy Resolution
In commonly used photoconductive radiation detectors (phRD) the radiation produced charge carriers are collected at the electrodes at preset time intervals. Therefore, delays in the charge collection time due to carrier mobility and charge trapping at crystal defects affect height of the peaks and reduce energy resolution of detectors. Unlike phRD detectors, detectors based on the inductive radiation (iRD) technology are sensing X-rays produced charges at the location where they are created in the sensor bulk with signal propagating at the speed of light and therefore not limited by the carrier mobility and charge trapping. The detection efficiency of iRD is only limited by the performance of the detection electronics. It should be noted that scintillation detectors while not limited by the charge collection time are lacking energy resolution offered by semiconductor detectors and therefore are not suitable for applications requiring high energy resolution. [1]

E. Kamieniecki, High-sensitivity photon-counting multi-energy inductive detector technology, Research Gate,

DOI: 10.13140/RG.2.2.17233.79202

In the case of the photoconductive radiation detectors, carrier scattering reduces carrier mobility resulting in a decrease of the sensitivity of detectors. On the other hand, inductive detection of radiation requires the presence of carrier scattering which is a necessary factor enabling absorption of the electromagnetic radiation (RF photons).* Therefore, materials with a low carrier mobility and hence high rate scattering will offer higher sensitivity than perfect crystalline material when using inductive radiation detection. It is well established that presence of the crystal defects reduces carrier mobility. Therefore, a high density of crystal defects, and ultimately replacement of the monocrystalline with micro- or poly-crystalline material, would increase free carrier absorption of the electromagnetic radiation and sensitivity of detectors.

*Comment: Change of the electron energy by absorption of the RF photon requires also change of the electron momentum. Since RF photon has no mass and no momentum such transition requires interaction with crystal atoms. This interaction would cause lattice vibrations (phonons) and/or with crystal defects. Therefore effectiveness of the inductive radiation sensing increases with increasing defect density or best with micro- or poly-crystalline materials.

  1. K.Kovler, S.Levinson, N.Lavi, U.Gherman, B.Dashevsky, H.Nassar, S.Antropov, Scintillation vs. Semiconductor Spectrometers for Determination of NORM in Building Materials, NORM & Environmental Radioctivity (Wednesday, February 12, 2014 16:30).