What is the minimum voltage required to get characteristic spectrum

In summary, the conversation discusses the process of producing x-rays using a Coolidge tube and the two types of spectra involved: bremsstrahlung and characteristic. The question is raised about determining the minimum voltage needed for the characteristic spectrum to appear, and a solution is presented using the equation E=hc/λ. However, there is disagreement about the value used for the wavelength in the solution and its relevance to the characteristic spectrum. The conversation also addresses the concept of ionization energy and its role in determining the required voltage for the characteristic spectrum.
  • #1
Samar A
10
0
Hi,
The x-ray consists of the bremsstrahlung spectrum and the characteristic spectrum. We can get x-rays by using Coolidge tube where there are an applied voltage on the tube between the filament and the target. The bremsstrahlung is depeding on the PD between the filament and the target, but it is produced anyways. The characteristic spectrum requires a high PD to be produced.
I wonder how could we determine the less voltage is sufficient for the emergence of characteristic spectrum by using a diagram of the two spectra, like this:
KCyJ8.jpg

(Note: the information on the photo were not clear so I deleted them and wrote them again using my cellphone)
Anyways, in my textbook it tried to give the less voltage needed for the characteristic spectrum, and it did this:
E=hc/λ =(6.625*10^-34)*(3*10^8)/ (0.8*10^-10)
=2.48*10^-15 J
And then, because E=eV:
2.48*10^-15= (1.6*10^-19) *V
So, V= 1.55*10^4 Volts.

I am not convinced with the way it used and I don't know how to determine it myself, either.
Could someone explain me way it used the value (0.8*10^-10) in the first part of the solution, because I don't think it is the longest wavelenght the characteristic would appear.
 
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  • #2
Samar A said:
because I don't think it is the longest wavelenght the characteristic would appear.
Why not? Characteristic radiation occurs as soon as the total energy of the electrons hitting the cathode is sufficient to excite the atoms in it. You can determine this energy based on the wavelength the atoms emit.
 
  • #3
Isn't this "Elemtehan"? xD
I'm really happy to see another student in Egypt wants to study correctly
Ok... I know that it's an old topic and you no longer need it, but I think I can help. After googling it for a long time, I've found that you (and I) are right. It shouldn't be calculated this way. 0.08nm doesn't indicate anything to be used as characteristic spectrum wavelength. It's 0.06323nm and 0.07101nm. Also, even if it were the correct wavelength, the calculated energy would be the difference in energy between M and K and between L and K. The required voltage should be the ionization energy of K (as it is required to eject an existing electron and get another into its place to emit an X-ray photon)
I wish it helps.
 

1. What is the minimum voltage required to get characteristic spectrum?

The minimum voltage required to get characteristic spectrum varies depending on the elements present in the sample and the specific characteristics being observed. Generally, a minimum voltage of at least 10 kV is required for characteristic X-ray production.

2. Why is a minimum voltage required for characteristic spectrum?

A minimum voltage is required for characteristic spectrum because it is necessary to provide enough energy to the electrons in the sample to excite them and produce characteristic X-rays. Without a minimum voltage, the X-rays would not be produced and the spectrum would not be visible.

3. Is there a specific voltage needed for each element in the sample?

Yes, each element has a specific minimum voltage required for characteristic spectrum. This is because each element has a unique atomic structure and energy levels, which determine the amount of energy needed to excite electrons and produce characteristic X-rays.

4. Can the minimum voltage be adjusted for different types of characteristic spectrum?

Yes, the minimum voltage can be adjusted for different types of characteristic spectrum. This is because different types of characteristic spectrum, such as X-ray, ultraviolet, and infrared, require different levels of energy to be produced. Therefore, the minimum voltage can be adjusted to meet the specific requirements of each type of characteristic spectrum.

5. How does the voltage affect the intensity of the characteristic spectrum?

The voltage directly affects the intensity of the characteristic spectrum. As the voltage increases, so does the energy of the electrons, resulting in a higher intensity of characteristic X-rays. However, there is a limit to this relationship, as increasing the voltage beyond a certain point can lead to sample damage and decrease in intensity.

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