الحلم الأزرق
09-29-2007, 04:09 PM
X-rays are a type of electromagnetic radiation with wavelengths of around 10-10 meters. When medical X-rays are being produced, a thin ****llic sheet is placed between the emitter and the target, effectively filtering out the lower energy (soft) X-rays. This is often placed close to the window of the X-ray tube. The resultant X-ray is said to be hard. Soft X-rays overlap the range of extreme ultraviolet. The frequency of hard X-rays is higher than that of soft X-rays, and the wavelength is shorter. Hard X-rays overlap the range of "long"-wavelength (lower energy) gamma rays, however the distinction between the two terms depends on the source of the radiation, not its wavelength; X-ray photons are generated by energetic electron processes, gamma rays by transitions within atomic nuclei.
X-ray K-series spectral line wavelengths (nm) for some common target materials.[5] Target Kβ₁ Kβ₂ Kα₁ Kα₂
Fe 0.17566 0.17442 0.193604 0.193998
Ni 0.15001 0.14886 0.165791 0.166175
Cu 0.139222 0.138109 0.154056 0.154439
Zr 0.070173 0.068993 0.078593 0.079015
Me 0.063229 0.062099 0.070930 0.071359
The basic production of X-rays is by accelerating electrons in order to collide with a ****l target. (In medical applications, this is usually tungsten or a more crack resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialised applications, such as when soft X-rays are needed as in mammography. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem). Here the electrons suddenly decelerate upon colliding with the ****l target and if enough energy is contained within the electron it is able to knock out an electron from the inner ****l of the ****l atom and as a result electrons from higher energy levels then fill up the vacancy and X-ray photons are emitted. This process is extremely inefficient (~0.1%) and thus to produce reasonable flux of X-rays plenty of energy has to be wasted into heat which has to be removed.
The spectral lines generated depends on the target (anode) element used and thus are called characteristic lines. Usually these are transitions from upper ****ls into K ****l (called K lines), into L ****l (called L lines) and so on. There is also a continuum Bremsstrahlung radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton number) nuclei.
X-rays can detect cancer, cysts, and tumors. Due to their short wavelength, in medical applications X-rays act more like a particle than a wave. This is in contrast to their application in crystallography, where their wave-like nature is most important.
Nowadays, for many (non-medical) applications, X-ray production is achieved by synchrotrons (see synchrotron light).
To create a blood or artery X-ray, also called digital angiography, iodine is injected into the veins and a digitized image is created. Then, a second image is established of only the parts of the X-rayed section without iodine. The first image is subtracted then a final image is produced containing both the first and second images together. Lastly, the results are printed. The doctor or surgeon then compares the results of the angiography to a perfect angiography structure to see if there are any malfunctions.
To take an X-ray of the bones, no iodization is required. Short X-ray pulses are shot through a body at first. Next, the bones absorb the most waves because they are more dense and contain Ca which absorbs stronger than C,O,N atoms of soft tissue (due to more electrons in Ca atom). The X-ray film see the bones through the X-ray.
X-ray K-series spectral line wavelengths (nm) for some common target materials.[5] Target Kβ₁ Kβ₂ Kα₁ Kα₂
Fe 0.17566 0.17442 0.193604 0.193998
Ni 0.15001 0.14886 0.165791 0.166175
Cu 0.139222 0.138109 0.154056 0.154439
Zr 0.070173 0.068993 0.078593 0.079015
Me 0.063229 0.062099 0.070930 0.071359
The basic production of X-rays is by accelerating electrons in order to collide with a ****l target. (In medical applications, this is usually tungsten or a more crack resistant alloy of rhenium (5%) and tungsten (95%), but sometimes molybdenum for more specialised applications, such as when soft X-rays are needed as in mammography. In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem). Here the electrons suddenly decelerate upon colliding with the ****l target and if enough energy is contained within the electron it is able to knock out an electron from the inner ****l of the ****l atom and as a result electrons from higher energy levels then fill up the vacancy and X-ray photons are emitted. This process is extremely inefficient (~0.1%) and thus to produce reasonable flux of X-rays plenty of energy has to be wasted into heat which has to be removed.
The spectral lines generated depends on the target (anode) element used and thus are called characteristic lines. Usually these are transitions from upper ****ls into K ****l (called K lines), into L ****l (called L lines) and so on. There is also a continuum Bremsstrahlung radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton number) nuclei.
X-rays can detect cancer, cysts, and tumors. Due to their short wavelength, in medical applications X-rays act more like a particle than a wave. This is in contrast to their application in crystallography, where their wave-like nature is most important.
Nowadays, for many (non-medical) applications, X-ray production is achieved by synchrotrons (see synchrotron light).
To create a blood or artery X-ray, also called digital angiography, iodine is injected into the veins and a digitized image is created. Then, a second image is established of only the parts of the X-rayed section without iodine. The first image is subtracted then a final image is produced containing both the first and second images together. Lastly, the results are printed. The doctor or surgeon then compares the results of the angiography to a perfect angiography structure to see if there are any malfunctions.
To take an X-ray of the bones, no iodization is required. Short X-ray pulses are shot through a body at first. Next, the bones absorb the most waves because they are more dense and contain Ca which absorbs stronger than C,O,N atoms of soft tissue (due to more electrons in Ca atom). The X-ray film see the bones through the X-ray.