X Ray Detector | Definition | 2 Important Types

X Ray Detectors

Contents : X Ray Detectors

What is X Ray?

X Ray Definition

X-rays are electromagnetic radiations having frequencies ranges in-between 3×1019 and 3×1016 Hertz ( and wavelength range in- between 10-8 – 10-11 m). X-Rays can be used for several applications in medical, material inspections and industrial usage such as X-Ray machines, material analysis , food irradiations etc.

What are the different source of X Rays ?

  1. Natural X ray sources
  2. Artificial X-ray sources

Source of X Rays

As we discussed the X Ray sources can be both natural and artificial or manmade.

Natural X Ray Sources:

 Some natural sources of X-rays are astrophysical X-ray source that is observed during X-ray astronomy, X Ray background from galactic x-ray emissions, naturally occurring radio-nuclides.

Artificial X Ray Sources:

Some artificial x-ray sources are radiopharmaceuticals present in radiopharmacology (such as radioactive tracer), synchrotron radiation, X-ray tube, cyclotron radiation, a vacuum tube generating X-rays due to flow of current, X-ray laser, X-ray generator, several instruments that use X-ray tubes, lasers, or radioisotopes.

What are X Ray detectors? | What are imaging detectors ?

X Ray detectors are specially designed instruments that are used for measuring and analyzing the spatial distribution, flux, spectrum, and several properties of X-Ray. These X Ray detectors can be classified into two broad categories based on their functioning:

X Ray Image Detector

Example of imaging detectors are X-ray film (photographic film) and photographic plates.

X Ray detector for Measurement Device

Measurement devices (such as ionization chambers, dosimeters, and Geiger counters) use X ray detector for different direct and indirect measurement.

Use of X Ray Radiation Detector

X ray detectors are widely used for X-ray analysis, medical purposes, X-ray astronomical observation,  physics experiments, etc as they provide high energy resolution and very high detection efficiency.

(X-Ray machine with detectors) Image source: Blausen Medical Annotations by Mikael HäggströmProjectional radiography componentsCC BY-SA 4.0

What does an X Ray Detector do?

X Ray detector are capable to detect primary and secondary X ray radiation and can be further used for analyzing the spatial distribution, flux, spectrum, and several properties of X-Ray.

What is X Ray sensor ?

X Ray sensor is same as X ray detector.

What are the types of X Ray imaging detectors?

X Ray film | Photographic film:

X-Ray films are made up of silver halide (primarily silver bromide) crystal “grains”. The composition and size of the grain are varied to adjust the properties of the X-Ray film according to the user’s requirements. The halide gets ionized once the film is exposed to radiation. This traps the free electrons in the crystal defects forming a latent image and will attracts silver atoms which then creates a cluster of transparent silver-atom. These transparent atoms are then converted into opaque silver atoms which ultimately leads to the formation of an image. This image is dark at places where the detection rate is high.

X-Ray films rapidly replaced the glass plates that were previously used for medical and industrial purposes.

x-ray detector
A photographic film. (X-ray detector) Image source: Evan-AmosKodak-Max-400-35mm-Film, marked as public domain, more details on Wikimedia Commons

Photostimulable phosphors:

Photostimulable phosphor plate radiography is a technique used for measuring  X-rays with the help of photostimulated luminescence (PSL).  The excited electrons present in the phosphor material after being X-Rayed get trapped in the “color centers” of the crystal lattice. This is then stimulated by using a laser beam and passed over the surface of the plate. The photomultiplier tube collects the light given off during the laser simulation process. The signal produced is then converted into images via computer software.

Photostimulable phosphor plate (PSP) replaced the use of photographic plates. 

How do X Ray Detectors work ?

X Ray Detector Working principle

There are various X Ray detector and working principle is different as per their types but for most the energy of the incoming X ray (generated by X ray source or secondary X ray radiation ) are absorbed by the X ray detector material, exciting a molecule of the detector material. The specific material like Scintillators can be utilized to convert the X ray energy into visible light and photomultiplier tube is used to amplify the signal.

The phosphor plate radiography process. (X-Ray detectors)
Image source: BeevilComputed Radiography ProcessCC BY-SA 4.0

Image intensifiers:

In X Ray Detector, image intensifier is one of the important component. An image intensifier uses X ray for realtime procedure i.e., contrast studies by utilizing fluoroscopy or for angiography, image intensifier is a specific instrument as explained below.

Schematic of an X-ray image intensifier. (X-Ray detectors) Image source: KieranmaherXiiSchematic, marked as public domain, more details on Wikimedia Commons

Semiconductor X Ray Detectors:

Semiconductor detectors are solid-state detectors or sensors that use semiconductors for sensing X-rays. These devices can be direct digital detectors i.e. they directly transform x-ray photons into electrical charge that forms a digital image. In the case of indirect digital detectors, the x-ray photons are first converted into visible light and then into electrical signals. Both the direct and indirect digital detectors detect and convert the resultant electronic signal to a digital image with the help of thin-film transistors. Obtaining a digital image does not require any kind of manual scanning or development step, unlike the film or CR.

Direct x-ray imaging system (DXIS) – real time display. (X-Ray detectors) image source: Cata56RotatingPanCC BY-SA 4.0

What are the types of X-Ray measurement detectors?

Gaseous ionization detectors:

Gaseous ionization detectors are devices in which x-rays are used for ionizing gases to produce positive ions and free electrons. The number of ion pairs formed depends on the energy of the incident photon. In the presence of an electric field inside the gas chamber, the direction of movement of positive ions and electrons leads to current flow inside the chamber. This flow of charges is dependent on the voltage applied and the shape of the chamber. Based on this, gas detectors can be divided into different types such as Ionization chambers, Proportional counters, Geiger–Müller counters, etc. Gas detectors generally measure only the average rate of dose over the gas volume and are therefore known as single-pixel sensors.

Plot of ion current as function of applied voltage for a wire cylinder gaseous radiation detector. (X-Ray detectors) Image source: Doug SimDetector regionsCC BY-SA 3.0

Silicon PN Solar Cells | Silicon X ray Detector

Silicon PN solar cells are used for efficiently sensing all types of ionizing radiation such as extreme UV, soft X-rays, and hard X-rays. These types of instruments work on the principle of photoionization. Photoionization, as the name suggests is a process in which ionizing radiation incident on atom results in the atom releasing a free electron. These sensors are also known as broadband ionizing radiation sensor and they are set up by using solar cells, an ammeter, and a visible light filter that is placed on top of the solar cell for blocking the unwanted wavelengths while letting the ionizing radiation pass to hit the solar cells at the same time.

Radiochromic Film:

Radiochromic film is an instrument that is capable of providing very high-resolution measurements for profiling and dosimetry processes. These self-developing radiochromic films are widely used in radiotherapy physics for the characterization of radiographic instruments such as radiotherapy linacs and CT scanners.

X Ray Image Plate Detector | Image Plate X Ray Detector

Photostimulated luminescence or PSL refers to the process of releasing the energy accumulated within a phosphor. This energy release is achieved by using visible light to stimulate the phosphor for producing a luminescent signal. X-rays can also be used to induce such an energy accumulation. The photostimulable phosphor (PSP) plate or X-ray plate is based on this mechanism.

These plates are also used as an X-ray beam detector for projectional radiography. Image formation is achieved by illuminating the X-ray plate twice: first, the radiation of interest is exposed (this “writes” the image), and second, illumination (generally conducted by a laser with visible wavelength) which “reads” the image. The instrument used to read or retrieve images from such a plate is called a phosphorimager.

X-ray imaging. source: Hellerhoff – Own work
CC BY-SA 3.0 Wikipedia

X Ray Detector Sensitivity

X ray detectors are widely used for several applications such as medical instruments, safe industrial material test, nuclear plant operations, scientific inspection, etc. But x-rays from detectors indirectly bombard high radiation doses to the human body (through medical diagnostics and security inspections). For reducing this, high sensitivity X ray detectors are required.

Sensitive X ray detectors can be built from the solution-grown inorganic lead perovskite (CsPbBr3) single crystals and by synthesizing high-quality inorganic lead perovskite (CsPbBr3) single crystals with the help of a developed low-temperature solution technique.

The detector can be designed in an asymmetric electrode configuration in which ion migration is efficiently reduced under the influence of a high voltage along with a low dark current and a great photoresponse. These detectors demonstrated a very high sensitivity of about 1256 μC Gy−1 cm−2 for 80 kVp X ray detection under the influence of a low electric field of 20 V mm−1. Commercially, α-Se detectors are used that produce an electric field about 60 times higher than the one mentioned above. However, nowadays CsPbBr3 is considered for building commercial X ray detectors because of its facile synthesis, low cost, durability, and high detection sensitivity.

What nuclear detector is used to detect X rays ?

HPGe detectors.

Are X Ray sensors damaged by the X Rays they detect ?

Yes, Actually most of the X Ray sensors are damaged by the every x ray detection and longevity will decrease.

Types Of X Ray Detectors:

Soft X Ray Detectors

Soft X-ray detectors are those detectors that operate in the low-energy X-ray region ranging from a few hundred eV to around 20 keV. Some direct detectors like Silicon PIN photodiodes, Silicon APDs, and Charge-coupled devices or CCD area image sensors are used in soft X ray detectors. Soft X ray detectors are known for providing very effective detection efficiency and high energy resolution. These attributes make soft X ray detectors suitable for application in X-ray material inspection, X-ray astronomical observation, scientific research, etc.

Solid State X Ray Detector

Solid-state detectors are built by using semiconductors for detecting x-rays. These solid-state x-ray detectors may fall in the direct digital detectors category when they are capable of directly converting x-ray photons into electrical charges to form a digital image. At times, solid-state x-ray detectors are a part of indirect systems that work with intervening steps such as transforming x-ray photons to visible light first and then converting the visible light to an electronic signal. Both these arrangements generally work with thin-film transistors for reading out and converting the electronic signal into a digital image.

It can be noted that in these systems there is no requirement of manual scanning or development like film or CR for obtaining a digital image. Therefore, in a broader sense, both these arrangements can be termed as “direct” and serve a noticeably higher quantum proficiency than CR.

X Ray Output Detector

The X-ray Output Detector is devices that help to calibrate and troubleshoot the x-ray generators. The output detector is built in such a way that it can be directly linked with an oscilloscope. The waveform of the x-ray is examined for finding a range of abnormalities or issues innate in x-rays. The wavefronts of X-rays are then recorded with the help of a storage scope, a digital scope, or an oscilloscope camera.

The x-ray detector is then put in the path of the x-ray beam and then the detector is linked with the standard oscilloscope with the help of a cable. The resultant oscilloscope display shows the relation between the intensity and time of the x-ray.

CMOS Flat Panel X Ray Detectors | X Ray Flat Detectors

A flat-panel X-ray detector or sensor is a variant or type of digital solid-state x-ray radiography instrument. These detectors work on the same principle that is used by image sensors for digital photography and videography. These x-ray detectors are used for projectional radiography and as a replacement for x-ray image intensifiers for fluoroscopy. Flat-panel x-ray detectors are considered to be quicker and more sensitive compared to x-ray films.

The sensitivity of these detectors is capable of serving a lesser radiation dose for particular picture quality than x-ray films. They are widely used in fluoroscopy because they are lighter, more durable, compact, more accurate, provides a lower image distortion than image intensifiers, and can also be designed having greater areas. However, when compared to x-ray image intensifiers, these detectors can serve more defective image elements, cost more and provide lower spatial resolution.

X Ray Flat Panel Detector Picture

Image credit : “File:Flat panel detector.jpg” by Mcapdevila is licensed under CC BY-SA 3.0

CMOS X Ray Detectors

CMOS x-ray detector is a variant of x ray detectors that uses a CMOS sensor, taper fiber optic, and image intensifier screen. CMOS sensors are used for their small size, reduced power requirements, and cost-effectiveness.  For using the CMOS sensor in an x-ray detector first conversion from x ray to visible light is needed. This conversion from x-ray to visible rays is carried out with the help of an image intensifier screen that is fixed one end (wider) of taper fiber optic. The other end (narrower) of the taper fiber optic is tied on the 0.5in CMOS sensor. For obtaining a better image quality, a more flexible and adaptable system, we usually prefer a CMOS image-sensor controller.

Developing such complex systems is conceivable because of the formation of complete VHDL reconfigurations and programmable components (that are known as FPGA or Field Programmable Gate Array). The CMOS-based x-ray detectors are especially verified for capturing bony structures.

Portable X Ray Detector | Portable X Ray Flaw Detector

A portable X-ray detector unit as the name suggests is a mobile device that uses x-ray to form images. It is mainly used for navigating crowded ICUs, EDs, or a patient room easily. These detectors form fast, reliable, and high-quality images in a tightly packed set-up. Portable x ray detectors are easy to use and

Backscatter X Ray Detectors

Backscatter X ray detectors are a form of x ray sensing instrument that is based on a developed X-ray imaging technology. Earlier X-ray machines are capable of detecting hard and soft items. This is done by sensing the X-ray intensity variation that is transmitted through the selected material. Unlike this method, backscatter X-rays can sense the reflected radiation from the selected material.

It is mainly used for processes that require a less-destructive inspection and is capable of serving even when only one of the material’s sides is present for the inspection. This technique is one of the most widely used whole-body imaging techniques. It is used for performing full-body scans of passengers in airplanes in order to sense some kind of hidden items, metal items, tools, liquid items, narcotic substances, and other contraband.

Direct and Indirect X Ray Detectors

Direct Conversion X Ray Detector | Digital X Ray Detector

Direct conversion x ray detectors are sensing devices that are capable of directly converting x-ray photons into electrical charges to form a digital image. Certain direct conversion x-ray detectors work with intervening steps such as transforming x-ray photons to visible light first and then converting the visible light to an electronic signal. However, the steps involved are still less compared to indirect conversion x ray detectors. Solid-state and semiconductor (such as CdTe) x ray detectors are examples of direct conversion x-ray detectors.

Direct x-ray imaging system (DXIS) – real time display. (X-Ray detectors) image source: Cata56RotatingPanCC BY-SA 4.0

X Ray Detectors for Digital Radiography

Digital radiography or DR refers to the process of direct transformation of X-ray photons to a digital image with the help of a set of solid-state detectors like amorphous silicon or selenium by using computer processing techniques. The resultant image is then displayed. Digital X-ray detectors are rapidly replacing x-ray films and computed radiography (CR) plates. This technique involves a direct digital transmission of X-ray images into the picture archiving and communication system or PACS. Digital radiography X-ray detectors are available for both static base room installation systems and mobile digital radiography, or portable digital radiography systems that can be transported from one place to another to conduct imaging inspections.

Where is the image detector placed during an X Ray ?

It is placed between person to be x rayed and the image receptor platform or table.

Photon Counting X Ray Detector

Photon counting x ray detector is used for converting each and every sensed X ray photon in terms of energy unit i.e. kilo electron volt to a voltage pulse having the pulse amplitude unit in Millivolt. The variation between each pixel in the photon counting detector is characterized and compensated by calibrating the energy response between the energy of the photon and the height of the pulse.

Photon-counting x ray detector is considered to be an innovative technique for future computed tomography (CT) systems as it is capable of eliminating several restrictions of the traditional computed tomography detectors. Photon counting x ray detectors can deliver energy-resolved computed tomography information at extremely high spatial resolution minus any form of intervention caused by electronic noise.

X Ray Area Detector

X ray area detector is an instrument that is used for calculating the intensity, gain, linearity, noise, and dynamic range of a detected x ray flux with particular efficiency, in terms of functions of time, position, and energy. The factors of time that are measured are frame rate, decay time, and readout dead time. The factors of position that are measured are spatial distortions, modulation transfer function or MTF, and line spread function or LSF. The factors of energy that are measured are energy threshold and energy resolution.

X Ray Line Detector | X Ray Detector Array

X ray line detectors are used for developing or building end-to-end sensor subsystems for several X ray screening methods and structures. High-performance linear detector arrays or LDAs are built by applying dual-energy and single-energy systems within the conventional linear detector arrays. X ray line detectors are considered to be useful for several industrial instrument observation and material sorting applications. These detectors can serve as an alternative for modern digital radiography.  Additionally, these X-ray line detectors are capable of providing strong data transmission and fast harmonization between the digital systems and detector units by allowing high scanning speeds.

Energy Dispersive X Ray Detector

Energy-dispersive X ray spectroscopy or EDS detectors (also known as energy dispersive X ray analyzer EDXA or EDAX) is an instrument that conducts elemental analysis and chemical characterization of a given material. This device operates on the basis of interactions with certain X ray excitation sources and a given material. The instrument works on the fundamental principle that every element has its own unique atomic configuration that provides a rather unique array of maxima on its electromagnetic emission spectrum.

Flexible X Ray Detectors

Flexible X ray detectors are especially capable of forming images of 3D objects. These detectors comprise of a transparent sheet of polymer that is embedded with luminescent nanoparticles. Flexible x ray detectors are being developed for replacing the use of flat x ray detectors in several applications such as medical imaging. Organic manganese halide is the material that can be used for developing low-cost and flexible x ray detectors.

X Ray Leakage Detector system

In the X ray Leakage Detector system or XLS, the target X ray tube that has to be examined is placed on the center of a rotatable table in a semicircular arch. The table is then rotated constantly by 360° and simultaneously XLS observes and analyzes the dose rates from every sensor and documents the radiation intensities of the semicircular arch around the X ray tube.

X Ray Fluorescence | X Ray Fluorescence Detector

X ray Fluorescence or XRF refers to a type of indirect methodical technique that is used for determining the fundamental components of a given sample. XRF analyzers are capable of defining the chemical composition of a material by sensing and calculating the emission of fluorescent (or secondary) X rays from the given material after it is agitated by a primary X ray source. Every constituent element of the material is capable of producing its own unique set of characteristic fluorescent X rays (also termed as a fingerprint). This is why X ray Fluorescence spectroscopy is a brilliant method for qualitatively and quantitatively analyzing material composition.

Microcalorimeter X Ray Detector

Microcalorimeter x ray detectors are instruments that are capable of measuring the energy of a single x ray photon by using a transition-edge sensor. This type of x ray detector was developed by scientists at the NIST Boulder Laboratory. Microcalorimeter x ray detectors can serve incredible image resolution over a wider range of x ray frequencies. But these detectors demonstrate high stages of complexities that occur due to minimal area for detection, low operational temperatures, superconducting electronic systems, and complex data processing. For this reason, these detectors are not preferred commercially.

Ionization Chamber X Ray Detector

The ionization chamber refers to one of the simplest variants of gas-filled radiation sensors. These devices are extensively used for detecting and measuring various ionization radiations such as gamma rays, X rays, and beta particles. This chamber works on the phenomenon of the creation of discrete charges after the interactions of an incident electromagnetic radiation with gas. Unlike most radiation devices, the ionization chamber does not use the mechanism of gas multiplication.

X Ray Machines and Metal Detectors

Metal detectors are built of a stable, three-coil system that is used for detecting tiny non-ferrous and stainless steel particles. These coils are parallelly spiraled on a non-metallic structure and the center of the coil is linked with a radio transmitter having a very high frequency. The transmitter has two identical coils present on either side of it at equal distances serving as receivers. These coils accept the same signal and generate an equal output voltage. These coils are then connected in opposing positions such that their outputs get canceled giving a resultant value of zero.

Do Metal Detectors Use X Rays ?

When a metal object passes through these metal detector coils, it disturbs the high-frequency field influence in one of the coils and reduces its voltage by a few microvolts. As a result of this, the equilibrium established previously is lost and the resultant output from both the coils is no longer equal to zero. This is how a metal detector senses the presence of a metal object.

Difference between Metal Detector and X Ray Detectors

X ray detectors operate on the basis of the density of the material, its composition, and impurities. When an x ray beam infiltrates a material, it tends to give up a part of its energy. The presence of a dense impurity or contaminant can increase the amount of energy lost by the x ray. After passing through the sample material, the x-ray reaches a sensor. This sensor is used for converting the energy signal into a digital image of the inner configuration of the sample material.

The presence of any form of impurity, contaminant, or foreign substance is displayed as an image of the substance in a darker shade of grey. This helps in identifying a foreign or suspicious substance. Unlike metal detectors, x-ray detectors can sense any kind of substance, and are not limited to metals.

Metal Detector X Ray Machine | X Ray metal detector

This type of X ray machine is generally used for airport entrance, railway station and secured place for the security measures.

Image credit : “X-Ray Machines (02814594)” by IAEA Imagebank is licensed under CC BY 2.0

X Ray Camera

“X-ray Camera xr1” by uvw916a is licensed under CC BY 2.0

How can an object escape an X Ray Detection?

It is possible to hide an object from x ray detection. However, it depends on the type of object, the size of the object, and the specifications of the x ray detecting device. Hiding a smaller object is possible if it is presented in a way such that it is virtually undetectable.

Is Compton effect only valid for X Rays ?

No it is also valid for gamma ray for more click here.

To know more about IR sensors visit here

About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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