Ionizing Radiation Energy Coupling

[FrankM]

I can find topics that state that ionizing radiation is harmful to biological material, but I can not find any description of how the energy of ionizing radiation is coupled to biological material. The last topic on radioactive material,How Harmful Is Nuclear Radiation?, mentioned absorption and dosage, but never see a discussion of the absorption mechanism.

 

Specifically, I am interesting in how electromagnetic forms of ionizing radiation, x-rays and gamma-rays, transfer their energy to biological material.

[Turtle]

I can find topics that state that ionizing radiation is harmful to biological material, but I can not find any description of how the energy of ionizing radiation is coupled to biological material. The last topic on radioactive material,How Harmful Is Nuclear Radiation?, mentioned absorption and dosage, but never see a discussion of the absorption mechanism.

 

Specifically, I am interesting in how electromagnetic forms of ionizing radiation, x-rays and gamma-rays, transfer their energy to biological material.

 

try this Frank.

 

the full report with specifics: How Does Radiation Affect Humans @ DOE

 

intoductory quote:

Radiation may come from either an external source, such as an x-ray machine, or an internal source, such as an injected radioisotope. The impact of radiation on living tissue is complicated by the type of radiation and the variety of tissues. In addition, the effects of radiation are not always easy to separate from other factors, making it a challenge at times for scientists to isolate them. An overview may help explain not only the effects of radiation but also the motivation for studying them, which led to much of the research examined by the Advisory Committee.

...

[CraigD]

Specifically, I am interesting in how electromagnetic forms of ionizing radiation, x-rays and gamma-rays, transfer their energy to biological material.

My quick internet search doesn’t find a clear, step-by-step answer to your question, Frank. Given this paucity, perhaps you’ll find my made-up-on-the-spot ionizing radiation injury scenario helpful:

• Photons of sufficiently high energy are absorbed by electrons in atoms in protein molecules the DNA in an animal’s cells;
  
• Due to their now greater energy, the bond between the electrons and their atoms’ nuclei are broken; The atoms now have fewer electrons than protons – that is, they have been ionized;
  
• These ions no longer form the same chemical bonds with their neighbors in their proteins – that is the proteins are broken;
  
• The structure of the proteins change, causing their bonds with neighboring proteins to change – that is, the DNA, and the genes it encodes are broken;
  
• The usual cellular mechanisms (transcription factors, etc.) transcribe these broken genes into abnormal proteins;
  
• The abnormal proteins result in the cells’ failure - that is, the cells are broken;
  
• The cells’ and the animal’s immune system’s failure-detecting mechanisms detect the failing cell, causing it to be killed and removed from the organism by lymphocyte cells.
  

This scenario, one of many, occurs frequently (the ordinary environment has many small sources of ionizing radation – that is, photons of sufficient energy to produce the above scenario), and results in no disease, as the animal’s disease-prevention mechanisms are successful - that is, the animal isn't broken. Sometimes, however, these mechanisms fail, and the abnormal cell is not killed, leading to diseases such as cancer.

 

If an animal is exposed for long enough to an intense source of ionizing radiation (examples: direct radiation and radiation from fallout from an atomic bomb; an unusually intense solar or cosmic radiation burst striking the occupants of a spacecraft), even though abnormal cells don’t immediately proliferate in its body causing disease, so many cells are destroyed that its various body systems cease to function properly, and it sickens and/or dies quickly of acute radiation poisoning.

[FrankM]

Craig, the first item in your suggestion set essentially repeats what I have read in all the various govt and academia reports.

 

"Photons of sufficiently high energy are absorbed by electrons in atoms in protein molecules the DNA in an animal’s cells;"

 

The term "absorbed" does not describe the mechanism of how electromagnetic (EM) energy, composed of two field vectors, magnetic and electric, are transferred to a biological structure. Basically, once transferred, the current created by the transfer electrocutes that portion of the cellular structure affected by displacing electrons from their molecular bonds.

 

How is the energy in the form of EM fields transferred to biological structures?

[CraigD]

"Photons of sufficiently high energy are absorbed by electrons in atoms in protein molecules the DNA in an animal’s cells;"

By “absorb”, in this statement, I don’t mean a vague biological process, but a specific quantum mechanical one as detailed in the Standard Model, expressed in pseudoclassical terms (that is, considering quantum mechanical events to be certain, not probabilities). The photon, a real boson interacts with the electron, a fermion. In so doing, the momentum of the electron is changed, and the photon ceases to exist. We call this interaction "the electron absorbing the photon". The electron's new momentum results in it no longer being able to remain in its atomic shell. If the photon’s energy is sufficiently low, the electron will transition to an "excited" shell, then back to its original emitting a photon of the same of energy. This is how materials reflect EM radiation. If it is higher, the electron can occupy no shell in the atom, and becomes “free”, while its former atom becomes ionized.

 

Basically, once transferred, the current created by the transfer electrocutes that portion of the cellular structure affected by displacing electrons from their molecular bonds.

Compared to the large number of electrons moving among cells in an animal, the actual increase in current from the much smaller number of electrons being freed from their atoms by ionizing radiation is insignificant. The animal’s cells are not damaged by electrocution, but by changes to the structure of their proteins, especially in DNA.

 

The net energy of the ionizing radiaton photons is much smaller than that of the animal’s interactions internal and external mechanical interactions, the lower energy photons it absorbs, such as light and heat, and conductive heat. It is not the amount of energy involved in ionizing radiation that makes it potentially damaging, but its ability to critically change individual atoms and molecules. A rough analogy is of an American footballer being tacked, vs being stabbed in the aorta with an thin ice pick. The tackle transfers much more energy – a large force (1000+ N) over a long distance (1+ m), but is usually harmless. The ice pick transfers very little energy – less than 10 N over a perhaps 0.1 m, roughly 1/1000th that of the tackle – but, because it critically injures an vital organ, is likely fatal. To apply this analogy to the effect of ionizing radiation on animals, replace the tackle with the warmth and bustle of the external world, the ice pick with a single high energy photon, and the aorta with a single critical gene in the DNA.

 

The question

How is the energy in the form of EM fields transferred to biological structures?

is, I think, best put in the right context by first asking “how much energy in the form of ionizing EM radiation is transferred to biological structures”, and noting that the amount is miniscule compared to the amount transferred by non-ionizing EM radiation and mechanical and thermal effects. An ionizing radiation photon (such as a gamma ray) has an energy of about 10^-18 J. A collision with a fruit fly carries about 10^-6 J, roughly a trillion times that of a gamma ray. The fly, however, doesn’t hit you in a single atom of your DNA, so is harmless, while the ionizing radiation may not be.

[FrankM]

I have difficulty envisioning the one-way mechanical force of an ice pick or gnat to describe the plus and minus energy fields of an EM pulse.

 

The question in my last post is relevant, "How is the energy in the form of EM fields transferred to biological structures?" Within biological material, if the electron is the only part of an atom that is effected by an EM pulse, how much energy is transferred from an EM pulse is conditioned on how the "structure" of an electron "captures" and "converts" the energy to a form usable by its processes. An EM pulse has an alternating field, one-half cycle positive and the other half cycle negative, which makes the pulse, a photon, electrically neutral. If the electron captures all the energy without some type of conversion structure, the net energy capture is zero.

 

I find it a little difficult to believe that the conducting structures within biological material are not in someway being directly influenced by the very short wavelengths attributed to ionizing EM radiation. The EM energy does not have to be at what is termed "ionizing frequencies" to effectively neutralize some of the activities of biological material.

 

http://www.molecularstation.com/research/radio-frequency-electromagnetic-fields-mild-hyperthermia-and-safety-standards-17645917.html

 

If someone has access to the full paper, I would like to know which four frequencies that were used. There is a conditional statement in the summary, "presumably by thermal mechanisms", which suggests they are not exactly sure if the "neutralization" is a thermal process.

[sanctus]

FrankM, I see it this way the photon might be (and is) electrally neutral as you say, but it still has energy. The electron of an atom in some biological tissue absorbs the photon (and hence its energy) and then has too much energy to stay where it was and hence breaks free (in case the photon energy is high enough).

 

A even more simplified way to see it: the electron aborbs the energy from the photon and transforms it to kinetic energy...

[FrankM]

Sanctus, I have a problem with the term absorb. Absorb is a generic term for a type of action, not a description of the mechanism that produces the action. An EM wave itself is an energy transfer mechanism, but the term EM wave does not describe its mechanism. An EM wave does not come into existence until some type of mechanism converts another form of energy into an EM wave. The EM wave will propagate until another type of suitable mechanism intercepts it and converts it into a different energy form.

 

The human body intercepts EM waves. There are multiple mechanisms in the body that can intercept EM waves. Depending upon frequency and intensity, the mechanisms can dissipate (convert) the energy beneficially or can be damaged by the converted energy such that the mechanism(s) that converted the energy no longer support their intended biological purpose.

 

Put the terms "electromagnetic biology" into your favorite search engine. There are a number of organizations that are examining the reaction of biological material to EM waves.

[CraigD]

Sanctus, I have a problem with the term absorb. Absorb is a generic term for a type of action, not a description of the mechanism that produces the action.

I find that a lot of the difficulty with intuitively understanding quantum mechanical terms and description comes from conflating them with everyday, visible-to-the-naked eye terms and concepts.

 

“Absorb” is a term often subject to such conflation. In everyday experience, “absorption” usually describes a complicated sequence of phenomena, such as, in the example “my skin absorbs the lotion”, pores of a membrane – my skin admitting a liquid – the lotion. In quantum mechanics, “absorption”, or more descriptively spontaneous absorption, it the reverse of spontaneous emission. In the example of a photon being absorbed by an electron, a measurement detects the electron with a velocity of 0 in a volume known to be shared with a photon of frequency x, then a later measurement detects the electron to have velocity of magnitude approximately [imath]\sqrt{2 h m_e x}[/imath].

 

In our everyday experience, objects are made up of many smaller parts (even though we usually can’t see many or any the smaller parts), so interactions with them are complicated, and require lengthy explanations. Photons and electrons are elementary (also called fundamental) particles not made up of smaller parts. Their interactions are likewise elementary, and cannot be broken down into lengthy explanations involving smaller parts. There is no “mechanism that produces the action” of this interaction. The interaction is the smallest theoretically describable component of any describable mechanical process.

 

I have difficulty envisioning the one-way mechanical force of an ice pick or gnat to describe the plus and minus energy fields of an EM pulse.

Finding apt metaphors for formal concepts is at best a hit-or-miss endeavor, but the alternative – every participant in a thread learning the formalism of the subject beforehand – isn’t a practical option. Very bright folk take years learning physics and biology formalism.

 

I’ll try another metaphor.

 

Consider an automobile operated by a driver. The driver does a series of small works – stepping inside, sitting and shifting around on the seat, turning the ignition switch, moving the transmission selector, pressing the accelerator pedal, etc. – most of which – the getting in and shifting around – have negligible effect – the car rocks and squeaks a bit. Some, however – moving the various controls – cause dramatically larger work – the car forcing its way at high speed and drag down the road. The potential to do this additional work (energy) comes from the car’s fuel, via its engine and other mechanical systems.

 

Though the car would not have sped down the road without it, the energy from the driver, though “transferred to the car”, is much less than the energy from the car’s fuel, and negligible in describing the work done by the car.

 

Now consider an animal irradiated with ionizing radiation. The high-energy photons exert very small works on the electrons of the atoms in the animal’s cells, most have negligible effect – a few molecules change bonds, among the much larger than do due to normal biochemical processes, causing no ill or good effect. Some, however, “flip switches” analogous to the controls of a car, causing dramatically larger work – cells expressing large numbers of abnormal proteins, the immune system detecting and causing other cells to interacting with the radiation-damaged cells, the body either recovering from or succumbing to disease. The energy for these disease processes comes from the animal’s “fuel” – primarily glycogen in the liver an muscles, replenished by glucose digested from food – via its various complicated metabolic systems.

 

Though the body would not have experienced disease without it, the energy from the ionizing radiation, though “transferred to biological materials”, is much less than the energy from the animal’s “fuel”, and negligible in describing the metabolic work done in the course of the disease.

 

A physics terms and concepts correction, and a suggestion:

The electromagnetic fields associated with electromagnetic radiation aren’t “plus and minus energy fields” They are alternating fields of vectors describing the force that would be exerted on stationary (in the case of their electric component) or moving (in the case of their magnetic component) electrically charged particle for a given point.

 

It can be confusing to conflate quantum mechanical ideas with classical ones. EMR is carried by a particle, the photon. Classical EM radiation is emitted and absorbed by moving charged particles. The photon is NOT, however, a moving charged particle that generates EM radiation. It IS, the radiation.

 

To avoid this confusion, I recommend consciously ignoring the classical description of EMR as a self-propagating transverse oscillating wave of electric and magnetic fields, and concentrating exclusively on the QM description of it as one or many photons traveling (as they always do) at the speed of light. Rather than attempting to visualize the photon in the full formalism of QM, as a field corresponding to the probability of a measurement detecting the particle at a particular place and time, I recommend using, for the sake of gaining intuitive comprehension, a “pseudoclassical” view, where you imagine the particle to have a definite position and velocity. It doesn’t, really, but our brains are adapted – “wired” if you will – to comprehend large bodies that practically do – rocks etc – so it’s wise, I think, to try “meeting our brains halfway” when seeking an intuitive grasp of physics.

[FrankM]

In my initial post I stated: (I have added bold to the text to highlight a specific term)

Specifically, I am interesting in how electromagnetic forms of ionizing radiation, x-rays and gamma-rays, transfer their energy to biological material.

CraigD, In your newest metaphor you are using the term that I prefer, transfer.

Though the car would not have sped down the road without it, the energy from the driver, though transferred to the car, is much less than the energy from the car’s fuel, and negligible in describing the work done by the car. ...

You then used the term transfer in the context I am seeking an answer.

Though the body would not have experienced disease without it, the energy from the ionizing radiation, though “transferred to biological materials”, is much less than the energy from the animal’s “fuel”, and negligible in describing the metabolic work done in the course of the disease.

 

To avoid this confusion, I recommend consciously ignoring the classical description of EMR as a self-propagating transverse oscillating wave of electric and magnetic fields, and concentrating exclusively on the QM description of it as one or many photons traveling (as they always do) at the speed of light.

EMR is not self-propagating, it requires some type of energy transfer mechanism to create the energy form that possess alternating EM fields that we describe as propagating. Alternating EM fields by definition are those that possess plus and minus electric and magnetic fields, which can be described as vectors with magnitude and direction. I describe the magnetic fields as plus and minus to avoid the terrestrial term for a specific physical earth direction.

 

In quantum mechanics, “absorption”, or more descriptively spontaneous absorption, it the reverse of spontaneous emission.

There is nothing spontaneous, there is a reason, and associated process, for every action and reaction. I view the QEM terms spontaneous absorption and spontaneous emission as a cop out to avoid stating we do not understand the details of the process

 

I am not willing to state I know everything there is to know about any specific subject, because I have seen many changes of position over the years. I realize we are in a constant learning process. I had considered using the following Schechtman quote in my FQXi essay,

 

"The main lesson that I have learned over time is that a good scientist is a humble and listening scientist and not one that is sure 100 percent in what he read in the textbooks," ...

 

http://www.foxnews.com/scitech/2011/10/05/daniel-shechtman-wins-nobel-chemistry-prize/

 

There are multiple publications that used the quote.