58
2 Observations of Radio and X-ray Pulsars
Telescope, Nancy Radio Telescope and Effelsberg Telescope, as well as the Sardinia
Radio Telescope to be added upon completion; the third is the North American
Nanohertz Observatory for Gravitational Waves (NANOGrav), using data from the
Arecibo and Green Bank radio telescope. The three projects have begun collaborating
under the title of the International Pulsar Timing Array (IPTA) project. The goal of
the IPTA is to detect gravitational waves using an array of approximately 30 pulsars.
2.5 X-ray and Its Physical Characteristics
X-ray is a form of electromagnetic radiation, discovered by a German physicist,
Wilhelm Röntgen (1845–1923). On November 8, 1895, Röntgen was investigating
cathode rays from a Crookes tube, an early experimental electrical discharge tube
invented around 1875, using a fluorescent screen painted with barium platinocyanide.
The so-called cathode rays are the electron streams in which the electrons emitted
from the cathode of low-voltage gas discharge tube are accelerated to form under
the electronic fields. Although Röntgen convinced that the cathode rays would not
cross through the wall of the vacuum discharge tube, the tube was still wrapped in
black cardboard to avoid the interference of the visible light. After electrified, the
cathode rays were obscured, while a faint green glow from the screen about 1-m
away occurred. By repeating the experiments, Röntgen eventually concluded that it
was an unknown type of radiation, and thus he referred to the radiation as “X-ray”.
Moreover, Röntgen found that the X-rays could also pass through books and papers
on his desk, as well as penetrate the muscles to show the skeleton of the hand. He
made a picture of his wife’s hand on a photographic plate formed due to the X-rays.
The photograph of his wife’s hand is the first image of a human body part using the
X-rays.
In fact, Röntgen was not the first to have observed the effects, but he was the first
to systematically study them. He wrote an initial report “On a New Kind of Ray:
A Preliminary Communication” and submitted it to Würzburg’s Physical-Medical
Society journal on December 28, 1895. This was the first paper written on X-rays.
The discovery of X-rays not only has a significant impact on medical diagnosis, but
also leads to subsequent major scientific discoveries. It was just inspired by Röntgen’s
discovery of X-rays that a French physicist Antoine Henri Becquerel (1852–1908)
discovered the radioactivity of spontaneous materials in 1896. In 1901, Röntgen won
the first Nobel Prize in Physics for his discovery of X-rays. In order to commemorate
the great discovery of Röntgen, sometimes X-rays are also referred to as Röntgen
rays.
X-rays are a kind of high-energy photons, and have usually a wavelength range
from 0.01 to 10 nm, corresponding to frequencies in the range of 2.4 × 10
16 –3.0
× 10
19 Hz and energies in the range of 0.1–200 keV. Generally, the X-ray within
energy range of 0.1–20 keV is called soft X-ray, and that within energy range of
20–200 keV is called hard X-ray. The X-ray has physical properties as follows:
2 Observations of Radio and X-ray Pulsars
Telescope, Nancy Radio Telescope and Effelsberg Telescope, as well as the Sardinia
Radio Telescope to be added upon completion; the third is the North American
Nanohertz Observatory for Gravitational Waves (NANOGrav), using data from the
Arecibo and Green Bank radio telescope. The three projects have begun collaborating
under the title of the International Pulsar Timing Array (IPTA) project. The goal of
the IPTA is to detect gravitational waves using an array of approximately 30 pulsars.
2.5 X-ray and Its Physical Characteristics
X-ray is a form of electromagnetic radiation, discovered by a German physicist,
Wilhelm Röntgen (1845–1923). On November 8, 1895, Röntgen was investigating
cathode rays from a Crookes tube, an early experimental electrical discharge tube
invented around 1875, using a fluorescent screen painted with barium platinocyanide.
The so-called cathode rays are the electron streams in which the electrons emitted
from the cathode of low-voltage gas discharge tube are accelerated to form under
the electronic fields. Although Röntgen convinced that the cathode rays would not
cross through the wall of the vacuum discharge tube, the tube was still wrapped in
black cardboard to avoid the interference of the visible light. After electrified, the
cathode rays were obscured, while a faint green glow from the screen about 1-m
away occurred. By repeating the experiments, Röntgen eventually concluded that it
was an unknown type of radiation, and thus he referred to the radiation as “X-ray”.
Moreover, Röntgen found that the X-rays could also pass through books and papers
on his desk, as well as penetrate the muscles to show the skeleton of the hand. He
made a picture of his wife’s hand on a photographic plate formed due to the X-rays.
The photograph of his wife’s hand is the first image of a human body part using the
X-rays.
In fact, Röntgen was not the first to have observed the effects, but he was the first
to systematically study them. He wrote an initial report “On a New Kind of Ray:
A Preliminary Communication” and submitted it to Würzburg’s Physical-Medical
Society journal on December 28, 1895. This was the first paper written on X-rays.
The discovery of X-rays not only has a significant impact on medical diagnosis, but
also leads to subsequent major scientific discoveries. It was just inspired by Röntgen’s
discovery of X-rays that a French physicist Antoine Henri Becquerel (1852–1908)
discovered the radioactivity of spontaneous materials in 1896. In 1901, Röntgen won
the first Nobel Prize in Physics for his discovery of X-rays. In order to commemorate
the great discovery of Röntgen, sometimes X-rays are also referred to as Röntgen
rays.
X-rays are a kind of high-energy photons, and have usually a wavelength range
from 0.01 to 10 nm, corresponding to frequencies in the range of 2.4 × 10
16 –3.0
× 10
19 Hz and energies in the range of 0.1–200 keV. Generally, the X-ray within
energy range of 0.1–20 keV is called soft X-ray, and that within energy range of
20–200 keV is called hard X-ray. The X-ray has physical properties as follows: