70
2 Observations of Radio and X-ray Pulsars
income a scintillator, atoms inside it will be ionized and excited, and then visible
light (also called luminescence) is emitted during the atomic de-excitation. The
devices to detect X-ray photons or charged particles by collecting and measuring the
luminescence are called scintillation detectors. A typical scintillation detector is
composed of scintillator, photomultiplier tube and electronic readout circuit. Moreover, the scintillators can also be divided into three types: inorganic scintillators,
organic scintillators and gas scintillators. Most of the inorganic scintillators belong
to solid crystals, and have a lot of advantages, such as quick light, high light yield,
appropriate wavelength, high density and low cost. The photomultiplier tubes absorb
the light emitted by the scintillator and re-emit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those photoelectrons results in an
electrical pulse which can then be analyzed and yield meaningful information about
the particles or photons that originally strike the scintillator.
In 1903, a British chemist and physicist Sir William Crookes (1832–1919) first
built a scintillator in nuclear physics experiments. By a microscope in a darkened
room, the naked eyes could see the luminescence in which alpha particles struck a ZnS
screen. In 1944, when the photomultiplier tube to replace the naked eyes was used to
measure the luminescence, the scintillators gained additional attention and thus the
modern scintillation detector birthed. Currently, besides the photomultiplier tubes,
the scintillators can still be coupled to other electronic light sensors like photodiode
or silicon photomultiplier to build the scintillation detectors. Vacuum photodiodes
are similar but do not amplify the signal while silicon photodiodes detect incoming
photons by the excitation of charge carries directly in the silicon. Silicon photomultipliers consist of an array of photodiodes which are reverse biased with sufficient
voltage to operate in avalanche mode, enabling each pixel of the array to be sensitive to single photons. The scintillation detectors have many advantages, like quick
response time, flexible structure design, as well as high detection efficiency, sensitivity and energy resolution, but can only be used to detect the hard X-ray with the
energy range of 20–200 keV.
2.7.1.6 Calorimeters
The calorimeters are composed of super-cooled solid matter. As the incoming X-ray
photons enter into the absorbent solid material, the temperature pulse induced in the
material is measured. The material must be kept near 0 K. The amount of temperature
rise is proportional to the energy of the incoming photons, so the photons can be
detected by measuring the temperature pulse. The types of devices mainly utilize
the thermal effects of X-rays, in which most of the energy of the incoming X-ray
photons absorbed by the material is transformed into such thermal energy so that its
temperature increases. Typically, a calorimeter has three core components, namely,
absorber, calorimetric resistance and heat conductor. The absorber is used to absorb
the thermal energy resulting from the incoming X-ray photons; the calorimetric
resistance is used to measure rising temperature, which is dependent on the energy of
the incoming photons; the heat conductor is used to transfer out the amount of heat in
2 Observations of Radio and X-ray Pulsars
income a scintillator, atoms inside it will be ionized and excited, and then visible
light (also called luminescence) is emitted during the atomic de-excitation. The
devices to detect X-ray photons or charged particles by collecting and measuring the
luminescence are called scintillation detectors. A typical scintillation detector is
composed of scintillator, photomultiplier tube and electronic readout circuit. Moreover, the scintillators can also be divided into three types: inorganic scintillators,
organic scintillators and gas scintillators. Most of the inorganic scintillators belong
to solid crystals, and have a lot of advantages, such as quick light, high light yield,
appropriate wavelength, high density and low cost. The photomultiplier tubes absorb
the light emitted by the scintillator and re-emit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those photoelectrons results in an
electrical pulse which can then be analyzed and yield meaningful information about
the particles or photons that originally strike the scintillator.
In 1903, a British chemist and physicist Sir William Crookes (1832–1919) first
built a scintillator in nuclear physics experiments. By a microscope in a darkened
room, the naked eyes could see the luminescence in which alpha particles struck a ZnS
screen. In 1944, when the photomultiplier tube to replace the naked eyes was used to
measure the luminescence, the scintillators gained additional attention and thus the
modern scintillation detector birthed. Currently, besides the photomultiplier tubes,
the scintillators can still be coupled to other electronic light sensors like photodiode
or silicon photomultiplier to build the scintillation detectors. Vacuum photodiodes
are similar but do not amplify the signal while silicon photodiodes detect incoming
photons by the excitation of charge carries directly in the silicon. Silicon photomultipliers consist of an array of photodiodes which are reverse biased with sufficient
voltage to operate in avalanche mode, enabling each pixel of the array to be sensitive to single photons. The scintillation detectors have many advantages, like quick
response time, flexible structure design, as well as high detection efficiency, sensitivity and energy resolution, but can only be used to detect the hard X-ray with the
energy range of 20–200 keV.
2.7.1.6 Calorimeters
The calorimeters are composed of super-cooled solid matter. As the incoming X-ray
photons enter into the absorbent solid material, the temperature pulse induced in the
material is measured. The material must be kept near 0 K. The amount of temperature
rise is proportional to the energy of the incoming photons, so the photons can be
detected by measuring the temperature pulse. The types of devices mainly utilize
the thermal effects of X-rays, in which most of the energy of the incoming X-ray
photons absorbed by the material is transformed into such thermal energy so that its
temperature increases. Typically, a calorimeter has three core components, namely,
absorber, calorimetric resistance and heat conductor. The absorber is used to absorb
the thermal energy resulting from the incoming X-ray photons; the calorimetric
resistance is used to measure rising temperature, which is dependent on the energy of
the incoming photons; the heat conductor is used to transfer out the amount of heat in