If you have no experience with setting up an x-ray generator you should probably find someone who does just for the safety issues.

i have experience with setting up an x ray generator but need collimating the x rays, avoiding bremsstrahlung radiation and distances between x ray tube and a detector. 

to get rid of bremsstrahlung you should use a monochromator. There are optics which will act as a collimator and a monochromator (for example Gobel mirrors). You could also use a filter to remove bremsstrahlung and beta radiation. If you have a Cu source then Ni is the filter you would use. Simple slits or Soler slits can also be used to help increase the collimation. It really depends on the resolution you want to achieve. Will it be in Bragg-Brentano geometry?

Here are some typical configurations.

http://www.labxa.de/images/braggbrentsystem.jpg

http://www.labxa.de/images/braggbrentsystem.jpg

I try to understand your problem. Do you want to diminuish bremsstralung at the detector. Then you should use special filtering with K-edges, a monochromator as Lawrence mentioned. It´s impossible to avoid the generation of BS, because this is the main interaction process of electrons with anode material. Please give some hints.

I have Ag and Au target which filters should I use?I want to reduce BS radiation.But set up with low energy X ray tube is more important reducing BS. Your answers are practical for me. thank you very much

Tell me your voltage and anode (target) material. We could try to find an answer. Very helpful is filtering with anode material because of existing K-edges. A prominent example is mammography radiation and filtering (Mo anode, Mo filtering creates nearly monoenergetic spectra).

I want to represent the problem briefly.I aim to excite K shells of 3d elements or L shells of higher atomic numbers elements from X ray tube with Ag K X-rays.But at the same time I want to reduce BS radiation so i want to study with monocenergetic X rays without using monochromator. How can I fix this problem while considering this situation.Basic properties of the system. X-Ray tube 50 kV / 80 µA power supply. Ag target, low power.

I repeat my proposal,

if you use AG target, take Ag as filter material too.

how about monochromator? Because i do not have.

I´ve no quantitative info about monochromators for your purpose. Of course it´s use is a matter of X.ray intensity.

It depends of how monochromatic you need your beam to be. What energy band width are you hoping for? If you are doing spectroscopy (I had assume you were setting it up for diffraction, which is much easier with a lab source. Fluorescent yield can be quite small, and with a lab source could be very difficult as you need to have a beam pipe which can be in vacuum or He since if you are looking at low energy K or L lines then the c-ray energies produced can be quite low and easily absorbed by Oxygen. Could you explain a bit more what kind of measurements you what to do?

I aim to excite K shells of 3d elements or L shells of higher atomic numbers elements from X ray tube with Ag K X-rays.But at the same time I want to reduce BS radiation so i want to study with monocenergetic X rays without using monochromator. How can I fix this problem while considering this situation.Basic properties of the system. X-Ray tube 50 kV / 80 µA power supply. Ag target, low power.

What kind do you do a measurement?

I attend a graph from one of my textbooks, which demonstrates the quasi monochromatiing effect of correct filtering. The example is for Mo anode and Mo filtering. You get nearly identical spectra for Ag anode and Ag filtering. 

do you want to say monochoromotor is not necessary for monochromoting..i can supply with using the same marerial as a target and filter?

No, it´s not totally monochromatic. But have a look at the spectra. May be, it´s enough monochromatic for your purpose and you don´t get problems with intensity.

When using a filter, you will want to use a material that is just below the anode material in Z. I don't think that a filter alone will be sufficient for your purposes. If you are doing spectroscopy measurements with an energy sensitive detector you will need a monochromator for quantitative measurements.

Mr. Margulies i understand what you say. But i do not have any monochromator...Is monochromotor is essential for monochromating the radiation.

If you want a monochromatic beam then I'm afraid you will need a monochromator. Have you measured the energy spectrum from your source? If the intensity is low enough (especially after filtering) in the energy range you are interested in, then you can probably get away without one, however it depends one exactly what you are trying to measure. I understand you want to excite K and L shells, but what do you want to measure? Do you want to measure the fluorescence signal and if so for what purpose? Elemental identification?

I want to study many things about XRF using X ray tube.But first of all i want to determine chemical composition.What should i do?