# Homework Help: Microscope Theory - Alternatives to the use of light?

1. Jun 13, 2009

### mohammed_a

Microscope Theory - Alternatives to the use of visible light?

Hey guys. I've been googling for ages but I've had no luck with this so I thought you guys could help me figure this out.

Why can't UV light or gamma rays be used to observe objects in microscopy?
I know the main idea behind the use of electron microscopes is that electrons can behave as waves with much smaller wavelengths than light can, thus allowing us to observe smaller objects. However, why can't UV light or Gamma Rays (X rays cannot be focused) be used instead of visible light or electrons to observe objects? They have a smaller wavelength than visible light and will therefore result in improved magnification.

2. Relevant equations
N/A

3. The attempt at a solution
I've checked my textbook but it fails to address gamma rays and UV light is only mentioned to be difficult to work with. Are gamma rays too hazardous to use? As for UV rays, I really have no idea why specifically they're difficult to use in this context.

Thanks for reading, and I hope what I'm asking is relatively clear.

Last edited: Jun 13, 2009
2. Jun 13, 2009

### Redbelly98

Staff Emeritus
Near UV is not a problem. But at wavelengths below around 250 nm, glass becomes opaque, so reflective optics (i.e. curved mirrors) must be used instead of lenses.

At even shorter wavelengths (x-rays, gamma rays), waves are not refracted strongly even though they can pass through objects, so there are no suitable lens materials at those wavelengths.

x-rays can be imaged using grazing-incidence mirrors, and in fact x-ray microsopes have been built:
http://en.wikipedia.org/wiki/X-ray_microscope

p.s. Welcome to Physics Forums.

3. Jun 13, 2009

### tiny-tim

Last edited by a moderator: Apr 24, 2017
4. Jun 13, 2009

### mohammed_a

Hey thanks for the speedy welcome.

I'm just a little confused about when you say glass becomes opaque... does that mean once photons have a wavelength of below around 250nm they do not penetrate glass? This is just for a high school project and I just need to give brief reasoning why electrons are chosen over UV light, X rays and Gamma rays.

So far I have:
Gamma rays: High energies can possibly alter and destroy the samples they are observing, cannot be focused.
UV light: Cannot penetrate glass (?), therefore curved mirrors must be used instead of lenses which is difficult to work with
X rays: Similar to UV light, cannot be focused very easily

It's not very detailed and I think I may need to go into a tad more detail. Thanks tiny-tim for the link to that thread, it covered gamma rays quite nicely.

Last edited: Jun 13, 2009
5. Jun 13, 2009

### Redbelly98

Staff Emeritus
Yes. Glass does not transmit electromagnetic waves below a certain wavelength. After googling, I've found it can be as low as 170-180 nm if the glass is made especially for uv transmission:

http://www.glassdynamicsllc.com/images/material-S1-UV-transmission.gif [Broken]
Transmission of uv grade fused silica glass
from http://www.glassdynamicsllc.com/SI-UV Material Data Sheet.htm

A less expense glass, such as "BK7 glass", does not transmit below 300 nm:
http://www.glassdynamicsllc.com/BK7%20Material%20Data%20Sheet_files/image002.jpg [Broken]
from http://www.glassdynamicsllc.com/BK7 Material Data Sheet.htm

Last edited by a moderator: May 4, 2017
6. Jun 13, 2009

### mohammed_a

Oh, ok that makes sense. That's a great pic, thanks for explaining it so well.

Last edited by a moderator: May 4, 2017