2.7 Classification of X-ray Detectors
71
order to keep the absorber cooling. When a calorimetric resistance of semiconductor
is approximate to superconductivity and its temperature rises, its resistance value will
quickly increase. Therefore, the energy of the incoming photons can be obtained by
measuring the resistance value.
The calorimeters can detect a single photon. Due to the required cryogenic cooling,
the detector power usage is high and must utilize a significant amount of supporting
electronics and hardware. The absorber is typically very small, with an order of 1
mm
3 , and thus the detection area is small. For these types of detectors, a multilayer nested optical system is usually required to increase the collection area. The
calorimeters have higher energy resolution, and their photon arrival-time accuracies
are usually better than nanosecond level.
2.7.2 Positioning and Imaging Technologies of X-rays
It is well known that the larger is the effective detection area of a detector, the more
the number of X-ray photons collected during a unit time and the higher its sensitivity
also. However, there is not the capability positioning and imaging the X-ray photons
for the detector’s major body. According to the different incident X-ray preprocessing
structures and imaging principles, the X-ray imaging detector systems can usually be
classified into two categories: one is collimated aperture imaging detector, applied to
soft X-ray imaging and another is modulated imaging detector, applied to hard X-ray
imaging. For the collimated aperture imaging detectors, the concept of aperture has
been extended. The aperture is a general term of devices, components or methods
which made the X-ray detectors to have positioning and imaging capability. The
collimators with a shape of grid or honeycomb, made by using a sheet of metal, are
usually installed on the front end of the incident surface of the detectors. And thus,
only X-rays within certain angle range in the collimators can enter into the detectors,
forming the collimator’s apertures, also called field-of-view angles. Furthermore,
according to different aperture design functions, the aperture imaging detectors are
subdivided into two basic types, collimated detector and focused detector. The former
has simple design and can effectively control incoming background photons outside
the aperture angle; the latter can not only control the incoming background photons,
but also focus on incoming effective X-ray photons to increase detecting area and
enhance the sensitivity and the space resolution.
The basic principle of the modulated imaging detectors is: the strength of X-ray
source within sky coverage is modulated by designing the corresponding collimators
and detectors while isotropic background counters within the field of view will not
be modulated and are regarded as white noise; the modulated X-ray images can be
got by the inversion calculation of the sky coverage. By using the modulated imaging
technologies, it is easy to get wider field of view, accurately locate X-ray sources
and simultaneously measure background and X-ray sources in the same direction.
Conventional optics-telescope designs require reflection or refraction in a manner
that does not work well for X-rays. Visible light optical systems use either lenses or
71
order to keep the absorber cooling. When a calorimetric resistance of semiconductor
is approximate to superconductivity and its temperature rises, its resistance value will
quickly increase. Therefore, the energy of the incoming photons can be obtained by
measuring the resistance value.
The calorimeters can detect a single photon. Due to the required cryogenic cooling,
the detector power usage is high and must utilize a significant amount of supporting
electronics and hardware. The absorber is typically very small, with an order of 1
mm
3 , and thus the detection area is small. For these types of detectors, a multilayer nested optical system is usually required to increase the collection area. The
calorimeters have higher energy resolution, and their photon arrival-time accuracies
are usually better than nanosecond level.
2.7.2 Positioning and Imaging Technologies of X-rays
It is well known that the larger is the effective detection area of a detector, the more
the number of X-ray photons collected during a unit time and the higher its sensitivity
also. However, there is not the capability positioning and imaging the X-ray photons
for the detector’s major body. According to the different incident X-ray preprocessing
structures and imaging principles, the X-ray imaging detector systems can usually be
classified into two categories: one is collimated aperture imaging detector, applied to
soft X-ray imaging and another is modulated imaging detector, applied to hard X-ray
imaging. For the collimated aperture imaging detectors, the concept of aperture has
been extended. The aperture is a general term of devices, components or methods
which made the X-ray detectors to have positioning and imaging capability. The
collimators with a shape of grid or honeycomb, made by using a sheet of metal, are
usually installed on the front end of the incident surface of the detectors. And thus,
only X-rays within certain angle range in the collimators can enter into the detectors,
forming the collimator’s apertures, also called field-of-view angles. Furthermore,
according to different aperture design functions, the aperture imaging detectors are
subdivided into two basic types, collimated detector and focused detector. The former
has simple design and can effectively control incoming background photons outside
the aperture angle; the latter can not only control the incoming background photons,
but also focus on incoming effective X-ray photons to increase detecting area and
enhance the sensitivity and the space resolution.
The basic principle of the modulated imaging detectors is: the strength of X-ray
source within sky coverage is modulated by designing the corresponding collimators
and detectors while isotropic background counters within the field of view will not
be modulated and are regarded as white noise; the modulated X-ray images can be
got by the inversion calculation of the sky coverage. By using the modulated imaging
technologies, it is easy to get wider field of view, accurately locate X-ray sources
and simultaneously measure background and X-ray sources in the same direction.
Conventional optics-telescope designs require reflection or refraction in a manner
that does not work well for X-rays. Visible light optical systems use either lenses or