Bremsstrahlung: Acceleration / Deceleration?

[Rennhack]

In the process known as Bremsstrahlung, some books say that the electron accelerates, others say it decelerates.  Here is a breakdown, which should enlighten us all.

Either way:

Argon National Lab-7291 Radiation Safety Technician Training Course, better known as “Moe study guide.” By H.J. Moe

When a charged particle is either accelerated or decelerated in an electronic field, electromagnetic radiation may be given off.  If an electron passes close to an atom while traversing a substance, the charge Z on the nucleus will exert a force on the electron.  This will cause its path to be bent.  During this acceleration the electron may radiate energy of any amount from zero up to its total kinetic energy.

Health Physics, Principals of Radiation Protection. D.J. REES, M.I.T. Press, p. 23, 1967. 

Continuous x-rays, a.k.a. Bremsstrahlung, is due to the acceleration of free electrons or charged particles.  Produced by x-ray machines or by stopping of B-rays in an absorber.

Health Physics, Principals of Radiation Protection. D.J. REES, M.I.T. Press, p. 48, 1967. 

... The continuous spectrium is due to the rapid slowing down of electrons in the target due to interaction the atomic electric field.  This radiation is known as 'Bremsstrahlung'.  ...

Accelerated:

Atoms, Radiation and Radiation Protection by James E. Turner

A beta particle, having little mass, can be accelerated strongly by the electromagnetic force within an atom and thereby emit radiation, called Bremsstrahlung.  Bremsstrahlung occurs when a beta particle is deflected in the electric field of a nucleus.

Introduction to Health Physics by Herman Cember

Bremsstrahlung consists of X-rays emitted when high-speed charged particles suffer rapid acceleration.  When a beta particle passes close to a nucleus, the strong attractive coulomb force causes the beta particle to deviate sharply from its original path.  The change in direction is due to radical acceleration, and the beta particle, in accordance with classic theory, loses energy by electromagnetic radiation at a rate proportional to the square of the acceleration.

Decelerated:

Radiation Protection in Medical Rediography. Ststkiewicz-Sherer, Mosby, p. 374, 1993. 

Ionozing electromagnetic radiation that is nonuniform in energy and wavelength and that is produced when a bombarding beam of electrons in an x-ray tube undergoes deceleration by interaction with the nuclei of the x-ray tube target atoms.

Bjorken, J. D. and Drell, S. D. "Bremsstrahlung." §7.6 in Relativistic Quantum Mechanics. New York: McGraw-Hill, pp. 120-127, 1964. 

Electromagnetic radiation that occurs when charged particles with energies large compared to their rest energies are decelerated over a very short distance. Since electrons are much lighter than protons, electron bremsstrahlung is the most common. In bremsstrahlung, a continuous spectrum with a characteristic profile and energy cutoff (i.e., wavelength minimum) is produced. In addition, lines can appear super imposed, corresponding to the ejection of K and L shell electrons knocked out of atoms in collisions with the high-energy electrons.

The Health Physics Fundamentals Study Guide from Combustion Engineering, better known as the “North East Utilities Study Guide”

When a high energy beta particle passes close to a heavy nucleus it is deflected sharply by the strong electric field.  When the beta particle is deflected (and thus slowed down) it emits electromagnetic energy in the form of X-rays.

Handbook of Health Physics and Radiological Health, better known as the Rad Health Handbook.

Bremsstrahlung – Secondary electromagnetic radiation (x-rays) produced by the deceleration of charged particles through matter.

Fundamentals of Radiation Protection by H.F. Henry

Higher energy electrons also lose energy by their deceleration in the electric field of an atom, with the emission of electromagnetic waves.  Such radiation is called Bremsstrahlung.

Too vague:

US Department of Energy Radiological Control Technician Phase I Core Academic Training Study Guide., better known as the DOE Core study guide

A high energy beta penetrates the electron cloud surrounding the nucleus of the atom, and experiences the strong electrostatic force of the positively charged nucleus.  This results in a change in velocity and the emission of a Bremsstrahlung X-ray.

Basic Nuclear Physics, Bureau of Naval Personnel, NAVPERS 10786, 1958 pp. 112-113

When a high-energy beta particle passes close to a heavy nucleus, it is deflected sharply by the strong electric field.  In being deflected, a beta particle is found to emit energy in the form of an X-ray.  Radiation produced in this way is called bremsstrahlung, which is a german word meaning "breafing radiation".  This term arises because a beta is continually slowed down by successive bremsstrahlung processes.

The Final Word:

Radiation Protection by Jacob Shapiro

Bremsstrahlung production by acceleration of bombarding electrons.  Electrons accelerated (shown here as a change of direction) near the highly charged nucleus of a heavy element may lose all or most of their energy through the emission of photons (called Bremsstrahlung, meaning “breaking radiation”)

The most important mechanism, from the point of view of the use of x-rays in radiography, is through a violent acceleration of the electron, resulting in the sharp deflection, as it interacts with the electrical field around the nucleus.  Such acceleration results in the emission of photons of x-radiations. The photons are generally referred to as Bremsstrahlung (breaking radiation), because the electrons lose energy and slow down in the process of emitting the radiation.

NRRPT Prep Course 1st Edition 1991 RI-Tech Inc.

Bremsstrahlung is an interaction that produces x rays from the kinetic energy of charged particles.  It is predominantly a beta particle interaction.  It occurs when a charged particle undergoes a rapid acceleration.  (Remember that acceleration is a vector quantity and that it can be either positive or negative in value.)  When a beta comes in close proximity to an atom, it will be deflected, which is a negative acceleration.  The energy of the photon given off is equal to the loss in kinetic energy of the beta.

Basic Radiation Protection Technology 4th Edition 2000 by Daniel Gollnick

Bremsstrahlung is a word of German extraction which translates literally as “breaking radiation”, that is, radiation generated when the charged particle puts on the breaks.  The causative agent is again the Coulomb force which produces a deflection in the path of the charged particle.  This change in direction is, in the physics sense, a negative acceleration (a de-celeration if you prefer) because the velocity vector changes with the directional change and the speed of the particle is reduced due to the energy loss.  The radiation emitted by the particle, the Bremsstrahlung, is electromagnetic in nature.  

[Rennhack]

Sounds to me like the Coulumbic force accelerates the electron, causing the energy to be emitted, which then leaves with less kinetic energy, decelerated.

I think some of those books should be a little more complete in their explanation.  I remember the last NEU test I took in 2000 had a question about this, and "accelerate" was the answer. However, the NEU study guide never mentions 'accelerate', but does mention 'decelerate'.

The Health Physics Fundamentals Study Guide from Combustion Engineering, better known as the “North East Utilities Study Guide”

When a high energy beta particle passes close to a heavy nucleus it is deflected sharply by the strong electric field.  When the beta particle is deflected (and thus slowed down) it emits electromagnetic energy in the form of X-rays.

[alphadude]

 Electromagnetic radiation that occurs when charged particles with energies large compared to their rest energies are decelerated over a very short distance. Since electrons are much lighter than protons, electron bremsstrahlung is the most common. In bremsstrahlung, a continuous spectrum with a characteristic profile and energy cutoff (i.e., wavelength minimum) is produced.

the increase in energy (acceleration) dont make sense when energy is lost at the same time? (photons being produced)

remember how an xray machine works- the electrons are accelerated to increase their effect when they slam (brakes) into the target to produce those wonderful xrays.  xrays dont happen when the electrons are in flight or being speeded up-  energy should be conserved

[SloGlo]

"Radiation Protection by Jacob Shapiro
Quote:
Bremsstrahlung production by acceleration of bombarding electrons.  Electrons accelerated (shown here as a change of direction) near the highly charged nucleus of a heavy element may lose all or most of their energy through the emission of photons (called Bremsstrahlung, meaning “breaking radiation”)

The most important mechanism, from the point of view of the use of x-rays in radiography, is through a violent acceleration of the electron, resulting in the sharp deflection, as it interacts with the electrical field around the nucleus.  Such acceleration results in the emission of photons of x-radiations. The photons are generally referred to as Bremsstrahlung (breaking radiation), because the electrons lose energy and slow down in the process of emitting the radiation."  

interesting choice of quote, mike.  i was always under the impression that bremsstrahlung was "braking" radiation.  however, the "breaking" radiation terminology mr. shapiro uses would work for both acceleration and deceleration.  look at it as radition that is breaking off from the electron as it undergoes velocity changes.  hmmm  :-?
cool thread, nowz eye gotz sumtin ta think bout twoday.

[metalman40]

Acceleration is the rate at which the velocity vector changes   Acceleration = change in velocity/time it can be either negative or positive. Decelleration is an undefined term in physics. When the beta interacts with the high Z electron cloud it is accelerated by a negative or positive value.

[Rain Man]

See attached link on the mathematics of "coherent bremsstrahlung":


http://zeus.phys.uconn.edu/halld/cobrems-7-97/

[St Raphael]

Rain Man - great site.  Here are a few more  


www.slac.stanford.edu/grp/rd/epac/Meeting/200011/bosted1.pdf

http://personal.tcu.edu/~quarles/bremspec.htm

http://scienceworld.wolfram.com/physics/Bremsstrahlung.html

[CheeseheadNuke]

Metalman is correct. An object traveling at some velocity in a given direction is defined as acceleration in classical physics. Even if the velocity decreases, the electron accelerates due to the directional change. Deceleration is not a classical physics term.

[Rennhack]

When the beta interacts with the high Z electron cloud

I hate to be picky, no one likes to be corrected, but I dojn't want the juniors to read that and take it as gospel... It isn't an interaction with the electron cloud, it is with the coulomb force from the protons. (At least most of the time.)

[alphadude]

perhaps we are discussing the limitations of english language-deceleration is a common term in our language and is readily moving into the classical sciences- (why say negative acceleration when one word says it all-) the definitions should express it classically as negative acceleration.. maybe thats why its bremsstrahlung in lieu of negative acceleration energy quantum....

[RAD-GHOST]

  Hey, it's all in the wording!  Is that braking, as in slow down, or brake left/right?  Once again my allergies have increased due to the amount of dust I have to wipe from these antiques.  My opinion, for what it is worth, is that the person who wrote that NU test question, with the answer as Accelerating, is WRONG!  I believe that person compiled a number of events, beyond the Bremsstrahlung theory, to justify an ambiguous answer.  I guess it's just the nuclear mantality!  Bremsstrahlung, in German, translates to," Braking Radiation".  Therefore someone has to make a stand and say it doesn't!  

  As I was taught, Brensstrahlung Radiation is emited when a high energy electron is deflected off of its mean free path, due to the influence of a high mass nuclide.  At the time of this event, the electron does in fact decrease in its energy state, or in layman terms," Brakes "!  This can be measured by comparing the resulting electron energy and the secondary photon produced.  The Bremsstrahlung photon is produced at the time of the vector change, not after the vector change.  Based on this immediate radical change in electron direction and the secondary photon produced, it all falls under the conservation of mass/energy.  Mass is energy and energy is mass, they convert directly to each other.  

  However the electrons energy is influenced, after the change in direction, due to the influencing nuclide, seems unrelated to the actual Bremsstrahlung event, even if it happens simultaniously.

  I guess you'd just have to say, " It's one of those physics things"!

[Rain Man]

Rad-Ghost.  That may be very true.  The term "bremsstrahlung" may be one of those words in a foreign language that defies easy translation in to english.

[St Raphael]

According to Merriam-Webster OnLine

Main Entry: brems·strah·lung
Pronunciation: 'brem(p)-"shträ-l&[ng]
Function: noun
Etymology: German, literally, decelerated radiation
Date: 1939
: the electromagnetic radiation produced by the sudden retardation of a charged particle in an intense electric field (as of an atomic nucleus); also : the process that produces such radiation

Also, IN/US Systems, Inc. states;
"Bremsstrahlung - When ß-particles interact with their surroundings to give up their energy, one of three processes occur:

Elastic collisions. Appreciable amounts of energy are transferred to whole atoms and then largely dissipated as heat.

Inelastic collisions. Energy is transferred to the electronic structure of the surrounding medium and subsequent energy loss proceeds via processes involving the activated surroundings. Incidentally this is the first step of the scintillation process.

Radiative loss (Bremsstrahlung). Deceleration of the charged particle in the coulomb field of a nucleus gives rise to the emission of electromagnetic radiation.
Bremsstrahlung, from the German for retarded radiation, is a continuous spectrum largely of soft X-rays but extending into the visible. The precise distribution of the energy is a function of both the energy of the charged particles and the atomic number Z of the target atom."

[actinium224]

Let's not limit Bremsstrahlung to electrons.  Any charged particle can undergo Bremsstrahlung, but the probability of an occurrence is inversely proportional to the square of the mass of the charged particle.  This means that although protons can undergo the interaction, it is ~3 million times less likely to occur than for electrons/positrons.  With Bremmstrahlung only accounting for 2-3% of all coulombic interactions, this would truly put it into the hair-splitting category.  
As an aside, actually seeing the results of Bremmstrahlung was interesting.  Especially since it was from strontium contaminated dog effluent in a metal drum.  

[Already Gone]

Well, technically Metalman is right.  I used to have a Physics instructor who would fly into a fit if someone used the word "deceleration".  Since acceleration is defined as the rate of change of velocity, and velocity is a vector quantity (speed is one variable and direction is the other) whenever the velocity changes, you have acceleration.  For example, a yo-yo being spun in a circle at constant speed is constantly accelerating, or stepping on the brakes in a northboud car causes acceleration in the southbound direction even though the car continues to move northward.
The same instructor was adamant that there was no such thing as centrifugal force.  Technically, he was correct there also, but the concept of centrifugal force is a convenient way to describe the combination of the forces that are acting on a body.
Likewise, deceleration is a commonly accepted term for negative acceleration.  I guess the correct answer to the question is "BOTH".

[RAD-GHOST]

Again, It's all in the wording!  Accelerate or Decelerate, who cares.  How about just describing the concept of what happens in it's simplest form.  There are a lot of high tech terms available in this industry, the use of which, will impress your friends and neighbors.  But, these recently posted question, seem like a great tool for others who may have never seen the topics, or understood the concepts. It is also very interesting to see the input from the members.  Although it may be hard to any two of us to agree 100% on a simple solution , it's great to see the Effort, Energy, Research and Opinions on these topics.

[Rain Man]

Again, It's all in the wording!  Accelerate or Decelerate, who cares.  How about just describing the concept of what happens in it's simplest form.

Amen Rad-Ghost.  We aren't counting schleptons at Fermi-Lab.  No reason to make things any more complicated.  Keep it simple, unless you are going for an MS or PhD.

[1010011010]

I'll join the "no such thing as deceleration" crowd.

I tend to think of Bremsstralung as a free state version of the photoelectric effect.

[alphadude]

hey we americans can change the language any way we wants too.. its good to be right....its our culture

Main Entry: de·cel·er·ate
Pronunciation: (")dE-'se-l&-"rAt
Function: verb
Inflected Form(s): -at·ed; -at·ing
Etymology: de- + accelerate
Date: 1899
transitive senses
1 : to reduce the speed of : slow down
2 : to decrease the rate of progress of
intransitive senses : to move at decreasing speed

bite my american ass

[RAD77DOG]

In the first quote on this subject from the "Moe Study Guide" by H.J. Moe; he appears to legitimize the term decelerate by using it in the text. Later he says "During this acceleration the electron may radiate energy of any amount from zero up to its total kinetic energy."  No matter if you call it deceleration or negative acceleration the electron will slow its velocity if it is giving up kenetic energy in the process of radiating energy, according to the law of conservation of energy. This means that while an electron may or may not accelerate when affected by the coulomb forces of a nucleus, it is only the loss of kinetic energy that produces the light.

[Rennhack]

No matter if you call it deceleration or negative acceleration

If they called it negative acceleration, we wouldn't be here talking about it.  They simply called it acceleration.

I just updated the original post with quotations from more texts.  (My HP library is ever growing).

[Fermi2]

Since it's defined in form of a physics term then any  change in the vector whether in direction of "speed" is acceleration. There is no such thing as decleration.

Mike

[Rennhack]

Since it's defined in form of a physics term then any  change in the vector whether in direction of "speed" is acceleration. There is no such thing as decleration.

Mike

If the majority of texts use the term decelerated, then it has to be a valid term to use in the description of this interation.

My bissue isn't with negative acceleration vs deceleration, I'm very clear, and fine with that.

My issue is with the NEU study guide NEVER using the word accelerated to describe the interaction.  Then the NEU test, which should be based on the study guide uses a description that is not in the study guide.  I think that is 'bunk'.

[hamsamich]

I think we are splitting hairs over terminology, but maybe for a dang good reason.  I know what the PHD will most likely be looking for: acceleration is positive or negative and is the only way to fly.  Maybe the problem is this: if you say you are decelerating at minus 32 ft/sec2, than what does this mean?  Does it mean - (-32), which is a +32, or does it mean (-32)?  And then, what does that mean if a body is exerting a force on another body and the vector is constantly changing; for instance:  a body was traveling at 6 ft/sec Southbound, and a force caused it to now be heading 6 ft/sec Northbound; when was it decelerating and when wasn't it?, since it is traveling in a whole different direction now.  When it was going precisely 0 ft/sec and some Northbound vector, do we all of a sudden say the force is aceleration now?  This seems redundant and problematic terminology.  If you use one term, this may eliminate the error likely situation.  Just a thought.  I do think it is confusing and unfair on tests to use one and then the other, so the test needs to reflect the MOST (not always black and white) correct version and the study material needs to teach the same terminology as the test.

[Fermi2]

Texts can be incorrect. ASk a physicist they'll tell you there's no such thing. Anytime you are changing a component on the vector you are changing the vector itself. There's no such thing as deceleration.

Mike