# Understanding X-ray Emission: Unraveling the Confusion

• Pavoo
In summary, the conversation discusses the emission of characteristic X-rays and the process of bombarding a metal target with high speed electrons in an X-ray tube. The emitted X-rays have sharply defined frequencies associated with the difference between the atomic energy levels of the target atoms. The conversation also addresses the concept of binding energy and potential energy, correcting a mistake in the second text regarding the sign of the binding energy. Finally, the conversation concludes with a clarification on the confusion regarding the term "higher binding energy".
Pavoo

## Homework Statement

Although not a computational problem, I still have difficulties understanding emission of characteristic X-rays.

Can someone please clear up my confusions about the topic? Here's where I'm stuck, with two texts as an example:

X-ray production typically involves bombarding a metal target in an x-ray tube with high speed electrons which have been accelerated by tens to hundreds of kilovolts of potential. The bombarding electrons can eject electrons from the inner shells of the atoms of the metal target. Those vacancies will be quickly filled by electrons dropping down from higher levels, emitting x-rays with sharply defined frequencies associated with the difference between the atomic energy levels of the target atoms.

Source for the above: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/xrayc.html

Following this explanation, let's say we shoot out an electron from the K-shell, and an electron from the L-shell fills its place. The X-ray that will then be emitted will be of equivalent energy size as the difference between binding energies of the K-shell and L-shell of the atom.

However, look at the following text:

1. When electrons are knocked out of their orbit, they leave behind vacancies, making the atom unstable. The atom must immediately correct the instability by filling the vacancies that the displaced electrons left behind. Those vacancies can be filled from higher orbits that move down to a lower orbit where a vacancy exits. For example, if an electron is displaced from the innermost shell of the atom (the one closest to the nucleus), an electron from the next shell up can move down to fill the vacancy. This is fluorescence.
2. Electrons have higher binding energies the further they are from the nucleus of the atom. Therefore, an electron loses some energy when it drops from a higher electron shell to an electron shell closer to the nucleus. The amount of energy lost is equivalent to the difference in energy between the two electron shells, which is determined by the distance between them. The distance between the two orbital shells is unique to each element, as mentioned above.

Source: https://www.bruker.com/products/x-r...ntal-analysis/handheld-xrf/how-xrf-works.html

Here confusion begins. How can an electron have a higher binding energy if it is further away from the nucleus? Looking at this table, I can't understand how an electron further away from the nucleus can have higher binding energy: http://xdb.lbl.gov/Section1/Table_1-1a.htm

My question is this: what type of difference of energy is an x-ray made of? The difference between the shells or the difference in the energy state of an electron?

P.S. Not used the template for posting assignment, since this is not a computational problem.

The second text is in error: it should be higher potential energy, not binding energy.

M Quack and Pavoo
The amount of energy that has to be supplied to remove the electron is greater when it is closer to the nucleus, so the binding energy has the opposite sign to the potential energy of the electron. I think it should refer to higher potential energy, not binding energy.

Pavoo
There might be a confusion due to the SIGN.

A binding energy is often quoted with the knowledge that it is negative. For example, the ground state of H atom is Eb = -13.6 eV. While the magnitude of the binding energy is large, it is considered to be "lower" than, say, the vacuum level which, by definition, has 0 eV. So mathematically, the vacuum level has a "higher binding energy" than the ground state.

Zz.

M Quack
DrClaude and Jonathan Scott

That certainly clears up my confusion! Thanks for pointing that out!

## 1. What are X-rays and how do they work?

X-rays are a type of electromagnetic radiation with a very short wavelength, which allows them to penetrate through soft tissues in the body. They work by emitting high-energy photons that can pass through the body and create an image on a detector, such as photographic film or a digital sensor.

## 2. Why is it sometimes difficult to understand X-ray images?

X-ray images can be difficult to understand because they are two-dimensional representations of a three-dimensional object. This can make it challenging to accurately interpret the location and size of structures within the body. Additionally, X-ray images can be affected by factors such as patient movement, equipment malfunction, or incorrect positioning.

## 3. What are the risks associated with X-ray exposure?

X-rays are a form of ionizing radiation, which means they have enough energy to remove electrons from atoms. This can potentially damage cells and DNA, leading to an increased risk of cancer. However, the amount of radiation used in medical X-rays is very low and the benefits of diagnosis and treatment often outweigh the risks.

## 4. How do X-rays differ from other types of medical imaging?

X-rays differ from other types of medical imaging, such as MRI or ultrasound, in terms of the type of radiation used and the resulting image produced. X-rays use ionizing radiation, while MRI and ultrasound use non-ionizing radiation. Additionally, X-rays produce images that show the density of tissues, while MRI and ultrasound produce images that show the structure or movement of tissues.

## 5. Can anyone undergo an X-ray procedure?

In general, anyone can undergo an X-ray procedure as long as it is deemed necessary by a healthcare professional. However, certain individuals may be more sensitive to the effects of X-ray radiation, such as pregnant women and children. In these cases, the benefits and risks must be carefully considered before proceeding with the procedure.

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