Bremsstrahlung is a German term that means "braking rays." It is an important phenomenon in the generation of X-rays. In the Bremsstrahlung process, a high speed electron travelling in a material is slowed or completely stopped by the forces of any atom it encounters. As a high speed electron approaches an atom, it will interact with the negative force from the electrons of the atom, and it may be slowed or completely stopped. If the electron is slowed down, it will exit the material with less energy. The law of conservation of energy tells us that this energy cannot be lost and must be absorbed by the atom or converted to another form of energy. The energy used to slow the electron is excessive to the atom and the energy will be radiated as x-radiation of equal energy.

My question is about the energy lost by the electron, once it's transmitted from the electron and before its absorbed or transformed, what is the initial form of it?? I think that it were kinetic energy transformed to a mechanical energy causing other electrons in the atom to change their state energy and by that a photon is emitted by stimulation and this photon is the xray, am I right??

The most common way to generate X-rays is using an X-ray tube. Within such a high vacuum tube (10^-9 bar) made of glass, high voltages are used to accelerate electrons from a hot cathode to an anode.

Now you have to consider two different processes of generating X-rays:

• Characteristic X-rays
• Bremsstrahlung

Characteristic X-ray emission occurs also by direct interaction of high energy electrons with atomic bound electrons. If electrons of high enough kinetic energy hit and remove the shell electrons of the target material a hole is created after ionization. Electrons from higher energy levels will transition to the risen vacancies and emit photons of element specific characteristic energy. The characteristic energy is equivalent to the energy difference of the involved shells of the atom.

The continuous X-ray spectrum, which is getting generated during the deceleration of electrons in the Coulomb field of the atomic nucleus, is called Bremsstrahlung. During this process kinetic energy of an electron is converted into electromagnetic radiation.

But only a small amount of energy used in an X-ray tube is converted into X-rays (typically around 0.1 - 1%). Most of the energy is transferred into heat and the amount of energy produced in an X-ray tube is limited by the exciting voltage.

The text excerpt is a little confusing. An electron passing through matter interacts with atomic (duh) electrons. The atoms along the path are ionized and the electron loses energy bit by bit. Generally this process is described by the Bethe-Bloch Equation. Materials with lots of electrons (per volume) have the best stopping power.

Bremsstrahlung radiation is different: the electron interacts with the very strong electric field near an atomic nucleus, losing energy and emitting a photon. The photon can have any energy from 0, to all of the electron's kinetic energy. The cross section is proportional to $Z^2$ (plus all kinds of corrections describe in the Bethe-Heitler formula), As large $Z$ nuclei have strong electric fields, these materials are used when Bremsstrahlung or the related processes of pair-production are desired. (So, lead for shielding, leaded-glass and liquid xenon for detection).

Regarding your question the energy after transmission and before it is absorbed/transformed: I think it's best to think about the initial and final states, of which we can speak with certainty. What happens in-between is, according to the Feynman path integral, "everything"--but the Bethe-Heitler formula provides an approximation to that.