China
Africa
Explore chapters and articles related to this topic
Radiation Dosimetry
Published in Kwan Hoong Ng, Ngie Min Ung, Robin Hill, Problems and Solutions in Medical Physics, 2023
Kwan Hoong Ng, Ngie Min Ung, Robin Hill
An ionisation chamber operates based on the principle of measuring the number of ion pairs produced in a volume of air due to radiation. In the simplest arrangement, the ionisation chamber exists as two-electrode plates spaced apart in air. A large potential (100–400 V) is applied to the plates. Radiation dose is delivered by charged particles in excitation and ionisation events. Charged particles are either the radiation of interest themselves (e.g., electron and proton radiotherapy) or indirectly produced by non-charged radiation (e.g., photons and neutrons). When charged particles traverse between the plates, they ionise the air producing free negative electrons and positive ions. The positive- and negative-charged particles are then swept by the electric field between the plates towards the appropriate electrodes, producing a steady current flow in the external circuit, which can be measured by an electrometer. The important premise of an ionisation chamber is that each interaction of the charged particle produces exactly one ion pair and therefore allows for accurate quantification of dose.
Radiometry
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
The ions and electrons will be attracted by the electric field and migrate to the cathode and anode, respectively, if the electric field is sufficiently high. If the electric field strength is weak, < 100 V cm-1, the charges will not reach the electrodes before being absorbed in the gas (recombination). The charge collected at the electrodes can either be collected continuously as a current, or as a charge pulse during a specified time. The pulse can then be further analysed as a count rate or energy distribution of the radiation particles. However, the positive charge carriers (the ions) in gaseous detectors have low mobility, and it requires a comparably long time to collect those charges, which means that the time resolution is much poorer in most gaseous detectors than in semiconductor detectors. This can be mitigated by removing this slow component, thus shortening the rise time of the pulse, by using so-called gridded ionization chambers.
Introduction to Radiation and Its Detection
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
During his many experiments on X-rays, Röntgen had also observed that X-rays were able to discharge electrified bodies in air [22] and postulated that the effect was due to some change in the air which then acted on the electrified body. Thomson [23] showed that that air would conduct electricity when traversed by X-rays and Thomson and Rutherford [24] went on to demonstrate that this conduction was due to ionization (i.e., the stripping of electrons from air molecules by the radiation). By placing two conducting plates with opposite charges at opposite ends of an air filled chamber, they were able to quantify the intensity of X-rays by measuring current flowing through the chamber. This led the development of the ionization chamber (for a review, see Frame [25]). Conventionally, the term “ionization chamber” is used to describe detectors that collect charge created by direct ionization of a gas through the application of an electric field. Specifically, it uses only the charge created by interaction between the incident radiation and the gas and does not exploit gas multiplication mechanisms used in Geiger-Müller or proportional counters. As such, ionization chambers tend to be mostly used for radiation intensity monitoring.
Research on performance of ionization chamber used in medical laser proton accelerator based on Garfield++
Published in Radiation Effects and Defects in Solids, 2023
Xi-Cheng Xie, X.Q. Yan, K. Zhu, Hui-Lin Ge, Ke-Dong Wang
After we got the laser pulse proton beam, how to accurately measure the dose and position of it is the key to the whole beam diagnostic system (21). At present, the gas ionization chamber has the advantage of accurate and reliable measurement data and is widely used in the beam current monitoring of proton and heavy ion beam therapy systems. Most of the current design schemes of gas ionization chambers are based on slow extraction beams, which are mainly used to measure the long pulse low peak current generated by cyclotron and synchronization, and suitable for detection of the conventional proton accelerator beam which is a quasi-single energy beam with small energy dispersion ratio, close to Gaussian distribution and with high average current intensity. Compared with the traditional proton accelerator beam, the laser proton accelerator beam's energy range and dispersion are large. Although its average current intensity is low, the peak value of the transient current intensity is large and the repetition frequency is 1 Hz (22–25) (Figure 2).
The comparison of a thin-film ZnO nanodevice with silicon-based electronic devices for diagnostic X-ray beam detection
Published in Radiation Effects and Defects in Solids, 2022
Claudia P. V. Valença, Luiz C. Gonçalves Filho, Aline N. Alves, Marcelo A. Macedo, Divanizia N. Souza, Luiz A. P. Santos, Daniel A. A. Santos
It is well known that the PT has a strong signal, making the measurement process easier. From this point of view, the ionization chamber is more complicated to use because the current value produced is extremely low (with noisy signal). Typically, electronic systems for ultra-low current are more expensive, which is a disadvantage. Thus, the ZnO nanodevice is advantageous since it provides a signal three times stronger than the ion chamber, and it can be deposited on mechanical strength material, as stated above. Also noteworthy is that photodetectors generate more noise in light environments, supporting the premise that the ZnO semiconductor can also be advantageous if a daylight filter is used to coat the ZnO thin film. Although the transistors have high sensitivity (strong electrical signal), in general, they show variation of sensitivity to X-ray beams when they are under certain doses of radiation (5–11).
Recent progress in diamond radiation detectors
Published in Functional Diamond, 2022
In this section, we will introduce the characteristics of diamond radiation detectors and the parameters which determine their performance. Diamond radiation detectors have a structure consisting of high-purity diamond sandwiched between two electrodes. This structure is called MSM (Metal-Semiconductor-Metal) or MIM (Metal-Insulator-Metal) structure. In the field of radiation measurements, it is also called a solid-state ionization chamber because it operates on the same principle as gas ionization chambers. Figure 1 shows the schematic of the detector. When a charged particle is injected into the detector, it generates electron-hole pairs. The generated charge carriers move along the electric field. This movement of electrons/holes induces current following Shockley-Ramo theorem [15]. By detecting this induced current/charge, incidence of radiation can be obtained. The timing of the arrival of the radiation can be determined by the current pulse, and the energy of the radiation can be determined from the amount of charge. Since the amount of charge is linear to that of incident energy in the detector and energy spectrum is unique to nuclide, energy spectroscopy is a powerful tool to identify nuclide. The following is a list of performance specifications for diamond radiation detectors.