detectors Flashcards

Question

amorphous silicon

Answer 1

First, the scintillator converts X-ray energy into visible light photodiode: light is converted to electrical signals electric circuit image second way: x-ray is converted to electrical signals in sensor material electric circuit image

Answer 2

charge coupled devices crystalline silicon small requires optical coupling high quality, low noise

Answer 3

The CCD is divided up into a large number of light-sensitive small areas (known as pixels) which can be used to build up an image of the scene of interest. A photon of light which falls within the area defined by one of the pixels will be converted into one (or more) electrons and the number of electrons collected will be directly proportional to the intensity of the scene at each pixel. When the CCD is clocked out, the number of electrons in each pixel are measured and the scene can be reconstructed.

Answer 4

the pixels are defined by the position of electrodes above the CCD itself. If a positive voltage is applied to the electrode, then this positive potential will attract all of the negatively charged electrons close to the area under the electrode. In addition, any positively charged holes will be repulsed from the area around the electrode. Consequently a "potential well" will form in which all the electrons produced by incoming photons will be stored. prevent full well light must be prevented from falling onto the CCD for example, by using a shutter as in a camera. Thus, an image can be made of an object by opening the shutter, "integrating" for a length of time to fill up most of the electrons in the potential well, and then closing the shutter

Answer 5

Each pixel actually consists of three electrodes IØ1, IØ2, and IØ3. Only one of these electrodes is required to create the potential well, but other electrodes are required to transfer the charge out of the CCD. all 0V, now IØ2 has 10V charge being collected under one of the electrodes. To transfer the charge out of the CCD, a new potential well can be created by raising IØ3 voltage, the charge is now shared between IØ2 and IØ3 . If IØ2 is now 0V, the charge will be fully transferred under electrode IØ3

Answer 6

complementary metal oxide semiconductor less expensive lower power usage lower quality more noise

Answer 7

CMOS sensors convert photons into electrons to a voltage & after that into a digital value through an on-chip ADC array of photodiodes can add transistors: source follower transistor to amplify signal reset transistor to clear pixel of charge row select transistor to select row for readout passive and active designs

Answer 8

gas between electrodes photon ionises gas voltage causes charges to move charge collected at electrodes no, of ions collected vs voltage graph

Answer 9

used in CT operates in ionisation region Use of xenon gas ensures higher sensitivity and thinner design of the detector

Answer 10

multi wire proportional chamber a type of proportional counter that detects charged particles and photons and can give positional information on their trajectory, by tracking the trails of gaseous ionization. gives x and y coordinates uses an array of wires at high voltage (anode), which run through a chamber with conductive walls held at ground potential (cathode)

Answer 11

solid-state ionisation chambers Take a p-n-diode * Segment it * Apply a voltage * Wait for a MIP to deposit charge * Charges separate and drift in E-field * This gives a signal in the p-strips This detector will deliver 2D information – we need one more coordinate: