Why do x-rays penetrate crystals and not reflect with longer wavelengths?

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In summary, in x-ray diffraction with crystals, scattering occurs when incident x-rays or photons interact with atoms in the crystal, and the peaks seen in diffraction data can be attributed to specific planes. The largest plane-spacing in a crystal is determined by the lattice parameter, and no wavelength greater than twice this parameter can produce a diffraction peak. X-rays can penetrate into the interior of the crystal, but only when multiple planes contribute to the reflection can sharp Bragg diffraction occur at certain angles. This phenomenon is described by the structure factor and is affected by parameters such as wavelength and the number of contributing planes.
  • #1
photon79
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In x-ray diffraction with crystals, what actually happens with the incident x-ray beem or photon? scattering occurs due to which atoms (plane) of the crystal?(can it penetrate into the interior of the crystal?) why doesn't the reflection occur with big wavelengths?
 
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  • #2
All the planes diffract the x-rays to some extent. The peaks you see in diffraction data can be index to specific planes, ie 100, 110, ...Keyword lookup: Structure factor. Of course you could use longer wavelengths but the spacing between the planes would have to be larger.
 
  • #3
The largest plane-spacing will be the largest lattice parameter. All other planes are closer together. So, [itex]d \leq a[/itex]. Also, [itex]sin \theta < 1 [/itex] and [itex]n \geq 1 [/itex] .

Hence, [tex] \lambda = \frac {2dsin \theta}{n} \leq 2a [/tex]

So, no wavelength greater than twice the largest lattice parameter can produce a diffraction peak.
 
  • #4
photon79 said:
can it penetrate into the interior of the crystal?
X-rays penetrate humans; they also penetrate crystals. A single plane of atoms absorbs very little. A single plane also reflects very little. Only when hundreds or thousands of planes contribute to the reflection, you can get sharp Bragg diffraction at certain angles (when phases add constructively).
 

1. What is an x-ray and how does it work?

An x-ray is a form of electromagnetic radiation that can pass through objects and create images of the internal structures. It works by using a machine to produce high-energy rays that pass through the body and are captured on a digital detector.

2. Are x-rays harmful?

Exposure to a small amount of x-rays is considered safe, but repeated or high levels of exposure can potentially cause harm. It is important for medical professionals to carefully control and limit the amount of exposure a patient receives during x-ray procedures.

3. How are x-rays used in medical diagnosis?

X-rays are commonly used in medical diagnosis to create images of bones and other dense structures inside the body. These images can help doctors identify fractures, tumors, and other abnormalities.

4. What precautions are taken during an x-ray procedure?

To minimize the risk of harm from x-ray exposure, patients are often asked to wear a lead apron and other protective gear. The x-ray machine is also carefully calibrated to deliver the minimum amount of radiation necessary to create an accurate image.

5. Can x-rays be used to diagnose all types of medical conditions?

No, x-rays are limited in their ability to diagnose certain medical conditions. They are most effective at creating images of bones and other dense structures, but are not as useful for soft tissues like muscles or organs. Other imaging techniques, such as MRI or ultrasound, may be used for these types of diagnoses.

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