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How do electrons destroy DNA bonds in radiation?

How do electrons destroy DNA bonds in radiation?


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Malignant tumors can be treated by radiation therapy. Most commonly it's radiotherapy with photons, or protons and so on. The common denominator for both types is that the radiation creates electrons inside the body via different effects.

What I haven't quite understood is how these electrons destroy the DNA bonds in the tumor and how this aids in killing off the cancer cells? Is it due to the generation of heat, or otherwise?


I think you have a fundamental misunderstanding of the chemical reactions involved in radiation therapy. Neither photon based or proton based therapies "create electrons", but they do cause ionization by adding enough energy to existing electrons around atoms so that the electron is ejected from the atom, creating an ion or free radical, which can then undergo chemical reaction.

Photons, typically gamma rays, X-rays, and high energy UV, typically interact with water molecules and produce free radicals, including the dangerous hydroxyl radical. The hydroxyl radical can interact with proteins and DNA and damage those molecules, but has a very short half-life. Molecular oxygen can help increase the damage by reacting with the hydroxyl radical to produce Reactive Oxygen Species, ROS, which can also damage DNA or protein. However, many tumors have low oxygen concentration that reduces the effectiveness of photon based radiation therapy.

To overcome this, many patients receive proton based radiation therapy. Protons are much heavier than photons (I guess infinitely heavier than a photon, since photons have no mass) and therefore scatter to a much smaller extent. They just sort of plow through tissue and knock electrons out of orbitals as they collide with molecules such as DNA or protein. They don't rely so much on free radical generation or ROS, so low oxygen levels don't reduce their effectiveness.

The goal is damage the DNA to induce double strand breaks which are hard to repair in fast growing cancer cells. Because they grow so quickly, they are already stressed and their DNA repair machinery is less effective than in healthy cells. If their DNA can be sufficiently damaged, the cell will die.

For more information about these processes, please see these wikipedia articles on Radiation Therapy, Radiolysis, Linear Energy Transfer, and Free Radical Damage to DNA.


DNA And The Microwave Effect

Can microwaves disrupt the covalent bonds of DNA? The fundamentals of thermodynamics and physics indicate this is impossible. Numerous studies have concluded that there is no evidence to support the existence of the ‘Microwave Effect’, and yet, some recent studies have demonstrated that microwaves are capable of breaking the covalent bonds of DNA. The exact nature of this phenomenon is not well understood, and no theory currently exists to explain it. This report summarizes the history of the controversy surrounding the microwave effect, and the latest research results.

The effectiveness of microwaves for sterilization has been well established by numerous studies over the previous decades (Latimer 1977, Sanborn 1982, Brown 1978, Goldblith 1967). The exact nature of the sterilization effect and whether it is due solely to thermal effects or to the ‘microwave effect’ has been a matter of controversy for decades.

The dielectric effect on polar molecules has been known since 1912 (DeBye 1929). Polar molecules are those which possess an uneven charge distribution and respond to an electromagnetic field by rotating. The angular momentum developed by these molecules results in friction with neighboring molecules and converts thereby to linear momentum, the definition of heat in liquids and gases. Because the molecules are forced to rotate first, there is a slight delay between the absorption of microwave energy and the development of linear momentum, or heat. There are some minor secondary effects of microwaves, including ionic conduction, which are negligible in external heating. Microwave heating is, therefore, not identical to external heating, at least at the molecular level, and the existence of a microwave effect is not precluded simply because the macroscopic heating effects of microwaves are indistinguishable from those of external heating.

During the 1930s the effects of low frequency electromagnetic waves on biological materials were studied in depth by physicists, engineers and biologists. Studies of the effects of microwaves on bacteria, viruses and DNA were performed in the 1960s and included research on heating, biocidal effects, dielectric dispersion, mutagenic effects and induced sonic resonance. Some of the early biophysicists investigating microwave absorption claimed evidence of a ‘microwave effect’ which was distinct in its biocidal effects from the effects of external heating (Barnes 1977, Cope 1976, Furia 1986). Most biologists in turn claimed there was no evidence of a microwave effect and that the biocidal effects of microwaves were either due entirely to heating or were indistinguishable from external heating (Goldblith 1967, Lechowich 1969, Vela 1978, Jeng 1987, Fujikawa 1991, Welt 1994). These experiments were repeated with increased sophistication right up to the present with the majority consensus being that the microwave effect did not exist.

These experiments typically fell into two categories, ‘controlled temperature’ experiments and ‘dry’ experiments. In the controlled temperature experiments the researchers controlled the temperature of the irradiated specimen through various timing, pulsing or cooling techniques (Welt 1994, Lechowich 1968).

For example, Welt (1994) investigated the effects of microwave irradiation on Clostridium spores and found no additional lethality caused by microwaves that could not be accounted for by conventional heating. However, spores may not be representative of microwave irradiation effects on active growing bacterial cells. The results of this and other experiments showed that controlling the temperature prevented biocidal effects, and this was taken as conclusive evidence that the microwave effect did not exist. However, the assumption that the microwave effect is independent of, and separable from, temperature was always implicit in these studies, but was never acknowledged.

The second type of experiment, the dry experiment, also contains unacknowledged assumptions. Studies have shown that in the absence of water or moisture, biocidal effects of microwaves are severely diminished, or require considerably longer exposures (Jeng 1987, Vela 1979). This was typically taken as evidence that nonthermal microwave effects did not exist, however, since water is the primary medium by which microwaves are converted to heat, the absence of biocidal effects in the absence of water would only indicate that water is necessary for sterilization whether or not heating is the cause. Furthermore, the possibility that the specific frequency used, 2450 MHz, only affects water and not bacteria or spores was overlooked. DNA has a dielectric dispersion, where microwaves are readily absorbed, at much lower frequencies than water (Takashima 1984). The experiments may simply be indicating that the wrong frequency is being used for targeting ‘dry’ bacteria and spores.

Most of the studies mentioned above concluded that the microwave effect, if it existed, was indistinguishable from the effects of external heating. However, it was recently demonstrated (Kakita 1995) that the microwave effect is distinguishable from external heating by the fact that it is capable of extensively fragmenting viral DNA, something that heating to the same temperature did not accomplish. This experiment consisted of irradiating a bacteriophage PL-1 culture at 2450 MHz and comparing this with a separate culture heated to the same temperature. The DNA was mostly destroyed, a result that does not occur from heating alone. These photos are borrowed from Kakita et al (1995), permission pending.

In the Kakita experiment the survival percentage was approximately the same whether the samples were heated or irradiated with microwaves, but evaluation by electrophoresis and electron microscopy showed that the DNA of the microwaved samples had mostly disappeared. In spite of the evolving complexity of all the previous experiments, electrophoresis had not been used to compare irradiated and externally heated samples prior to this. Electron microscopy had been used to study the bacteriocidal effects of microwaves (Rosaspina 1993, 1994) and these results also showed that microwaves had effects that were distinguishable from those of external heating.

The energy level of a microwave photon is only 10-5 eV, whereas the energy required to break a covalent bond is 10 eV, or a million times greater. Based on this fact, it has been stated in the literature that “microwaves are incapable of breaking the covalent bonds of DNA” (Fujikawa 1992, Jeng 1987), but this has apparently occurred in the Kakita experiment, even though this may be only an indirect effect of the microwaves.

There is, in fact, plenty of evidence to indicate that there are alternate mechanisms for causing DNA covalent bond breakage without invoking the energy levels of ionizing radiation (Watanabe 1985, 1989, Ishibashi 1982, Kakita 1995, Kashige 1995, Kashige 1990, 1994). Still, no theory currently exists to explain the phenomenon of DNA fragmentation by microwaves although research is ongoing which may elucidate the mechanism (Watanabe 1996).

The results of microwave irradiation affected two bacteria, S. aureus and E. coli. The death curves exhibited classic exponential decay with ab appararent shoulder, as well as a possible second stage. These curves are based on data from Kakita etal (1999).

The microwave frequency used in the Kakita study was the standard 2450 MHz used in conventional microwave ovens. This is the same frequency that was used in essentially all prior studies, except for the earliest studies (which looked at lower frequencies), and sonic resonant studies, which looked at much higher frequencies. The early studies showed that DNA tended to absorb microwave radiation “in the kilocycle range” (Takashima 1963, 1966, Grant 1978, Grandolfo 1983), but no biocidal effects in the range of 1 MHz to 60 MHz were observed.

One notable exception, however, was an early experiment which found that frequencies between 11 and 350 MHz had lethal effects on bacteria, with a peak at 60 MHz (Fleming 1944). As far as could be determined, the contradiction between the results of Fleming and those of Takashima has never been resolved or re-addressed. In any event, there is no evidence in these studies to indicate any undue attention was paid to control the actual absorbed dose or the precise geometry of the irradiation cell, and therefore the differences in the results of these investigators may reflect differences in their cell geometries, among other things.

In summary, it would seem there is reason to believe that the microwave effect does indeed exist, even if it cannot yet be adequately explained. What we know at present is somewhat limited, but there may be enough information already available to form a viable hypothesis. The possibility that electromagnetic radiation in the non-ionizing frequency range can cause genetic damage may have profound implications on the current controversy involving EM antennae, power lines, and cell phones.

A Theory of Microwave Induced DNA Covalent Bond Breakage A review of the data from the various referenced experiments shows a common pattern — for the first few minutes of irradiation there is no pronounced effect, and then a cascade of microbial destruction occurs. The data pattern greatly resembles the dynamics of a capacitor first there is an accumulation of energy, and then a catastrophic release. It may simply indicate a threshhold temperature has been reached, or it may indicate a two-stage process is at work.

The second stage of this process may very well be the accumulation of oxygen radicals, which would certainly seem to be primary suspects as they have a considerable propensity for dissociating the covalent bonds of DNA. Oxygen radicals can be generated by the disruption of a hydrogen bond on a water molecule. Water molecules exist alongside DNA molecules as “bound” water, two or three layers thick. These water molecules share a hydrogen bond with component atoms of the DNA backbone, including carbon, nitrogen and other oxygen atoms. At any given point in time one of the hydrogen atoms may be primarilly bonded to either an oxygen atom on the water molecule, or to an oxygen (or other) atom on the DNA backbone.

The fluctuating character of these shared and exchanged bonds is enhanced by temperature and by the dynamics induced by microwaves. Although the amount of oxygen radicals which may be produced by this process cannot presently be determined, the production of some number of oxygen radicals is inevitable in these circumstances. It must be noted here though, that most of the oxygen radicals produced in this manner would exist only briefly, as they would almost immediately bond to the nearest available site. If this site is an oxygen atom on the DNA backbone, we get a covalent bond break, albeit probably only a brief one. Although DNA tends to repair itself naturally, the simultaneous breakage of a sufficient number of covalent bonds would lead to a catastrophic failure of the entire DNA molecule.

Due to the exceedingly large number of bonds involved, the matter boils down to a reproducible function of pure probabilities. In other words, after a set and reproducible amount of time determined by probability functions, you would expect to see DNA disintegration. And so, what we have is a two-stage process of DNA covalent bond breakage resulting from oxygen radicals generated by microwave irradiation. This is one theory, and it awaits experimental verification.

An alternate theory comes from investigators at Fukuoka University in Japan. In a series of studies not specifically involving microwaves, these investigators established that certain ions can stimulate DNA breakage and OH radical production (Kashige eta al 1990, Kashige et al 1994). They also determined that amino sugars and derivatives could induce DNA strand breakage (Kashige et al 1991). It is possible that microwaves may be causing generation of cupric ions and hydroxyl radicals, and that auto-oxidation of aminosugars in solution are involved in DNA strand breakage (Watanabe et al 1990, Watanabe et al 1986). The link between microwaves and these secondary products remains to be established.


How does radiation add up in our bodies?

I have read that radiation exposure is cumulative. But I don’t understand how it could build up inside of you. And then, how does this “build up” result in a greater risk of negative health effects? Why does this risk not go down with time? Also if you want to be extra awesome I have been curious if any company is working on developing something to aid the human body is being resistant to radiation. I feel like that would be a cool endeavor, but I don’t even know if it is possible since I know so little about radiation.

Not going in too much detail here and cutting some corners, but this is the main concept: Radiation damages our DNA. Damaged DNA gets repaired, but sometimes this repair fails. The more damage, the higher the risk that a dangerous error in your DNA sequence eventually happens. One of the most classic errors is a deactivation of this repair/error feedback mechanism. No error repair leads to many errors in DNA transscription, leading to mutations, leading to tumors.

Thanks for the reply. So not all damage is dangerous? It’s just that the more exposure you have, the more likely it is that a dangerous mutation will occur?

It's not so much that the radiation itself builds up in the body, it's that the damage caused by radiation is often irreparable, so the damaging effects slowly build up over time.

As far as radiation resistance, it's difficult to study and develop that, since it would be unethical to intentionally expose people to radiation for clinical trials. Most everything we do know about how radiation effects the body is by studying the victims of radiation disasters and nuclear bombings.

You’ve got some good answers here already, I will just add something to cover a bit more of the molecular mechanisms: radiation is essentially just bursts or waves of high energy. These packets of energy, when in contact with certain molecules (namely nucleotides of the DNA), break bonds and can cause molecular rearrangement to change the identity of some DNA bases (which results in mutations).

The more radiation you come into contact with, the greater the number of mutations it will generate. If/when one of these mutations compromise the repair machinery in your cell, the integrity of your DNA will deteriorate quickly as mutations accumulate. When one of these mutations inevitably damages cell checkpoint machinery, cancer will follow.

Excuse my dumbness but this is what I understand so far: Radiation leads to damage (mutations). Your body repairs this damage most of the time. Sometimes it misses some. Eventually, one of these mutations could turn into cancer. And the more mutations you have, the more likely cancer is to occur. So technically you could have a ton of radiation exposure and not get cancer if you are very lucky. . Please correct me

There are two models: deterministic effects and stochastic effects.

Deterministic effects have a threshold dose under which no damage will occur and these occur as tissue damage (think sunburn). Tissue damage increases proportionally with dose.

Stochastic effects, as other replies detail, are random effects that typically describe induction of cancer and occur as a result of cumulative, irreparable DNA damage. The accepted thinking is that these effects also increase proportionally with dose in a linear fashion, however there is no threshold.

Not a ton of radiation exposure at once, that would kill you from creating too much damage to your cells (DNA and other structures) all at once, your body wouldn’t be able to keep up.

Over time, like I think you are thinking, yes, we can be exposed to a significant amount of radiation without that exposure to radiation increasing our risk of death due to cancer. Not just if you are lucky, though, that actually appears to be the case for everyone based on radiobiology research. Even though most people understand the overall risk as being linear and cumulative, that is not accurate. Those who work on underlying radiobiology favor the “radiation hormesis hypothesis”. Basically, below a certain threshold, radiation does not actually harm you, and can actually be beneficial. Above that threshold is when things become linear and cumulative. I am told this theory of radiation having benefits inspired the Hulk, Spider-Man, and Godzilla (theory has been around for a while but no longer gets much press). Not sure if that part is true, but the theory/hypothesis has been around for a long time and has decent evidence it’s true. Idea of why it doesn’t harm you and may help you is that we have a LOT of filler DNA, and odds are that a little damage here or there won’t affect an area that is important, and that gives your body time to find the error and fix it if necessary. At the same time, if it does hit somewhere important, your cell’s DNA replication cycles aren’t always 100% perfect, so a little nick might help you by making your DNA double check a coded area for errors it may have made on its own.

Yes, I read about radiation hormesis when i was still a radiographer student. The hypothesis, as you said have been around for quiet a long time.

I remembered there should be a few animal studies which supported this theroy, it said something like, the radiation will trigger the immune system and beneficial to human body. But I think this is a relatively minority theory.

The majority of the scholar/lecturer in my university still think that radiation should be harmful to human being and supported the linear no thershold model.

But afterall I think we cannot be absoultely sure what will happen in low dose range (diagnostic range), I dont think we will ever be sure due to the ethical problem of obtainting significant sample size for research

Wow that is very interesting. Thank you! I think I understand now :)

55 y/o nuclear med tech. Having cataract surgery in a week.

this is the most important takeaway IMO.

always keep in mind that the biology of radiatiation damage in the human body, especially long term effects, is incompletely understood at best. the radiation hormesis theory is interesting, but unlike skeletal muscle, bones, and other tissue types that we know respond to damage with hypertrophy, there is no "stronger" DNA. DNA damage is either repaired or it isn't, and if it isn't we rely on programmed cell death to eliminate the error. if that fails, cancer and bad things appear.

the types of adaptations that let tardigraves endure cosmic radiation might slowly evolve at the species level, but are not available to individual humans. research into the biology of aging (see David Sinclair) suggests the DNA repair capacity of all living cells is finite and limited. to oversimplify, if your repair mechanisms are always busy repairing radiation damage, mutations are more likely to slip through uncorrected. even if they are all silent mutations and don't cause serious badness, the additional time spent repairing that damage takes away from regular age-related damage repair - in other words, you age more rapidly.

published "safe" threshold exposure levels vary according to a number of factors, including tissue type - the eye being one of the most sensitive, along with regions of rapidly dividing cells (hair, gonads). these are at best approximations (safe-ish levels, we think), and certainly not based on human subjects research.

dose-related cancer risk is an even looser approximation, derived from outcomes of human tragedies like hiroshima/nagasaki. how many survivors got which cancers, at what rate, is a straightforward counting exercise, however estimating how much exposure to what type of radiation each individual received ventures pretty deep into the realm of conjecture.

extrapolating outcomes following those massive doses onto clinically relevant exposure doses is essentially how we arrive at risk estimates that are quoted to patients/HCW. although this is probably the best we can do without violating ethical codes, it is a mistake to consider this knowledge rather than theory.

this comment about cataracts highlights one of the more visible/traceable gaps in our thinking about radiation safety. there is a body of literature on early cataracts among interventionalists that OP might find interesting and instructive, particularly the efforts to lower the safetyy threshold for "safe" exposure levels for eyes. anecdotally, the rates of hair loss among HCW within fluoro-heavy clinical settings is probably much higher than analogous non-ionizing settings.

NMN/NAD+ seem to be necessary ingredients for DNA repair to even occur, and many people (including a good number of aging researchers) take these as supplements. i'm not aware of any therapeutics that increase the human body's resistence to radiation damage in the first place - if it exists or is being developed, it's probably for human space travel.

TLDR: minimizing exposure and protecting yourself is the most effective strategy in the hospital, so lead up always. if your employer/program doesn't provide you with lead glasses, get a pair of your own and raise a stink that they aren't provided, and quote the early cataracts literature. if you have macho colleagues that give you a hard time about being cautious, rest assured that is beyond silly.

ALARA (as low as reasonably achievable) applies across the board to anyone exposed to radiation in a clinical setting not just patients.

I think this is a problem of probability.

to my knowledge, I think everytime the ionizing radiation strike your body, they can damage your genetic material through ionization. Or, indirectly, through the production of reactive oxygen species.

This kind of damage can be repaired by the body itself, actually, our body are doing it everyday even "in theory" in the absent of radiation. mistakes are made and be corrected every moment.

However, this is not a 100% efficient mechanism, if the correction mechanism failed, and plus other factors, then, cancer may develop (multiple step carcinogensis).

Now, it is just, in theory, more radiation that you exposed to, there are more chance that your genetic material be damaged, and hence, more occasions that your repair mechanism failed. So called "build up".

So. will the damage "actually build up"? to be honest, i am not sure. But I think "in theory", it can be. There are multiple genes in your genome that can contribute to carcinogensis, those are the oncogenes and tumor supression gene, so. for a cell to mutate to cancer, you might need multiple hit on multiple numbers of such gene, so. before the cell death, will those damages accumulate? why not? I think it is possible.

Radiobiology is very complicated, the area that you irradiated can also affect other areas of cells by chemical signaling or other mechanisms, which is known as the bystander effect. Such an effect may also be accumulated (possibly).

For radiation resistance, I dont know whether there are such thing exist. However, there are similar things for radiation protection. Like in nuclear medicine scan, if we are using radioactive iodine (I131), we might ask the patient to drink some non-radioactive KI3 solution to protect their thyroid.

In contrast, the reverse exists which by my understanding was applied in Radiation thearpy (I am not a RT radiographer, i might be wrong), they will use some drugs or method to increase the oxygen supply to the tissue and increase their radiosensitivity to radiation.

You're right, there are radio-sensitisers that are mostly in development. They are injected into tumours and can create oxygen free radicals when exposed to radiation to damage local tissues (the tumour). Many conventional chemotherapies also work to sensitise tissues, by impairing DNA repair mechanisms. Certainly a cool place to be.

I pre apologize for a long answer, but I am going to try for a simple explanation in lay terms.

First we need to understand that by potentially harmful radiation, we are referring to radiation that has enough energy to cause chemical reactions through ionization. The physics is more complex, but basically the radiation can "knock off" electrons turning stable molecules (like water) into unstable ones (like a hydroxyl radical). These chemical reactions caused by ionizing radiation can damage the molecules that make up our cells, the most important of which is DNA. Damage can kill cells both directly and indirectly and with enough ionizing radiation there is going to be tissue damage. Although our bodies have natural mechanisms for repairing DNA, these are not perfect and mutations (changes in the DNA sequence) can develop in affected cells. DNA controls cell division which controls tissue growth, and so these mutations can set cells on a pathway towards uncontrolled cell division which means cancer. Additionally, mutations in cells of a developing embryo can cause developmental problems like birth defects and mutations in sperm or eggs cells can be passed on to offspring.

How does this affect the human body and its organs? Direct tissue damage caused by radiation is predictable once a certain dose is reached and known as "deterministic effects". Examples of such effects are skin burns, eye cataracts, bone damage or acute radiation poisoning from nuclear accidents (or nuclear bomb attacks). It is possible to accurately predict who will get these effects based on a measurement known as absorbed dose (measured in Gray or rads). You need a lot of radiation to cause this kind of damage, and for a member of the general public they only time they are likely to experience this is if they receive radiation therapy for cancer. Modern radiation therapy is carefully planned such that the risks to tissue damage are outweighed by the benefits of cancer treatment.

Remember those special situations I talked about with embryos, sperm, and egg cells? Pregnancy and radiation is a complex area we will simply say that exposing an embryo to extra radiation is only done when there is a clear benefit, like diagnosing a immediately life-threatening disease. Fortunately, the whole sperm-and-egg issue is proven to be theoretical. Epidemiologic studies of people with large radiation exposures like atomic bomb survivors do not suggest their children are at increased risk of birth defects or cancer.

What about the cancer risk? Unlike tissue damage, the cancer risk caused by radiation occurs randomly and is known as "stochastic effects". Unlike tissue damage, cancer risk may occur with small amounts of radiation as well. For most people, their main source of exposure is commonly performed medical imaging tests and procedures. Based on our knowledge of radiation biology and studies of people exposed to large amount of radiation, we can estimate cancer risks and fortunately they are small. This is the thinking behind the commonly accepted concept of cancer risk, known as a "linear no-threshold model". It is alsoimportant to remember we are always being exposed to some ionizing radiation, which is known as background exposure.

I like to think of radiation cancer risk as a lottery, except instead of winning a million dollars you develop cancer. This is good analogy because the chance of winning the lottery or getting cancer is low, and both occur by random chance. What's the chance, though? Unfortunately the absorbed dose measurement is not a good enough predictor, and you need to take into account the kind of radiation, the parts of the body exposed, and individual factors pertaining to a person's body size and age. Even then medical physics models disagree significantly on the precise odds or cancer, and making an individual estimate of risk based on your life is fraught with difficulty. Unlike the lottery, it is impossible to provide an accurate individualized assessment of risk, other than to conclude the risk for common exposures is very small.

We can try to compare the risks of different exposures to create a common currency. This is a complex calculation that is based on population data, and provides an estimate of risk in order to protect the general public. Accounting for the different types of radiation leads to a measurement known as equivalent dose and accounting for the kind of tissue exposed leads to a measurement known as effective dose. Both are measured in units of Sieverts or rems. I like to think of effective dose dose as money, or how many dollars of lottery tickets you get. Each year you might get $30 of lottery tickets at baseline and with every CT scan you get an extra $20-50 of lottery tickets. The more tickets you buy the higher the chance of getting a losing cancer ticket, but that chance is still very low. It doesn't build up inside of you although the cumulative risk does. Like lottery tickets, the "value" of an individual ticket winning or losing is not affected by how many other tickets you own, so you should make decisions based on the risks and benefits of that individual test or procedure and not your personal history or radiation exposure. This is a big misconception and even many doctors say things like "well you already had a CT scan maybe you shouldn't get that stress test this year". It does not work that way. You should undergo the test as long and the risk of dying from undiagnosed disease is greater than the radiation risk of the test.

One big problem is that we as humans have a naturally high risk of cancer as we age and there are lots of risk factors from cancer. In fact, everyone on average has about a one in three chance of developing cancer. As a result, it is very difficult to tease apart the small radiation risk from medical imaging from background risk. There also exist minority opinions that cancer risk does have a threshold or possibly even a benefit from a small dose compared to no dose (radiation hormesis). All are in agreement that medical care as commonly performed is unlikely to meaningfully change your personal risk of cancer.


Ionising Radiation and Its Effects on DNA | Genetics

In this article we will discuss about: 1. Introduction to Ionising Radiation 2. Measuring Ionising Radiation 3. Effects.

Introduction to Ionising Radiation:

Due to their shorter wavelength, X-rays and gamma rays penetrate tissues deeper than visible and UV light. They can impart enough localised energy to absorbing tissue to ionize atoms and molecules. When a highly energetic wave moving at high speed is stopped, it releases energy. This energy makes an atom lose an electron and become a charged particle or ion. The process is called ionisation.

The free moving electron causes other atoms to lose electrons and become positively charged ions. The two processes generate pairs of positively and negatively charged ions. A number of ions may be clustered together to form an ion track.

Ions undergo chemical reactions to neutralize their charge to reach a more stable configuration. While doing so they (ions) produce breaks in chromosomes (DNA) thereby inducing mutations. The free ions moreover, may combine with oxygen and produce highly reactive chemicals which may also react with DNA and cause mutagenesis.

Some ionising radiation is electromagnetic such as X-rays and gamma rays and some consists of subatomic particles such as electrons, protons, neutrons and alpha particles. X-rays and gamma rays have a low rate of linear energy transfer as they produce ions sparsely along the ion track and penetrate deeply into the tissue. Charged particles have a higher linear energy transfer, they do not penetrate deeply and produce more damage than X-rays and gamma rays.

Measuring Ionising Radiation:

Radiation is measured in terms of an ionisation unit called roentgen or r unit, one r being equal to 1.8 x 10 9 ion pairs per cubic cm of air. In tissue which is ten times as dense as air, a high energy radiation produces about 1000 times the number of ion pairs per cubic cm as it does in air.

Another unit called rad measures the total amount of radiant energy absorbed by the medium. One rad equals 100 ergs per gram of tissue. Another unit called gray is equivalent to 100 rads.

In the case of X-rays about 90 % of the energy left in the tissue is used to produce ions, the rest produces heat and excitation. Ultraviolet (UV) is a non-ionising type of radiation and is measured in rads instead of r units. When ionisation is caused by subatomic particles, the doses are measured in different units called rem and sievert.

One rem is defined as the amount of any radiation that produces a biological effect equivalent to that resulting from one rad of gamma rays. A sievert is equal to 100 rems. For detecting radiation the Geiger-Muller tube is used. The tube contains a gas which is ionised by radiation. The amount of radiation is gauged from suitable amplifiers and counters.

Effects of Ionising Radiation on DNA:

Zirkle in 1930 showed that in plants the nucleus is more sensitive to ionising radiation than the cytoplasm. It is now known with certainty that many molecules including DNA are affected by ionising radiation. The purines are less sensitive to radiation than pyrimidines.

Out of the pyrimidines, thymine is most sensitive. Large doses of ionising radiation destroy thymine, uracil and cytosine in aqueous solutions. By depolymerizing DNA, ionising radiations prevent DNA replication and stop cell division.

Several mechanisms have been proposed to explain the effects of X-rays and gamma rays. They can break different kinds of chemical linkages and damage genetic material in a variety of ways. Figure 20.2 shows that the effect may be direct or indirect. When a hydrogen atom consisting of one proton and one electron is ionised, the free electron may directly interact with DNA.

Or the electron may interact with a molecule of water to produce OH, a free radical which can cause damage to DNA in the same way as the free electron. The following types of destruction of DNA are possible hydrogen bonds may break between chains a base may be changed or deleted a single or double chain fracture may occur cross linking might take place within the double helix a deoxyribose may become oxidised.

If a cell is irradiated in the S phase, DNA replication is inhibited resulting in failure of cell division and cell death. But if the cell is irradiated during mitosis or in G1, in that case DNA replicates normally but mitosis is delayed.

Ionising radiation causes breakage and rearrangements in chromosomes which may interfere with normal segregation of chromosomes during cell division. When breaks in two different chromosomes in a cell occur close together in time and space they can join to produce chromosomal aberrations such as inversions, translocations and deletions.

Micro-organisms are more resistant to ionising radiation than higher organisms. It is found that D37 dose, that is the radiation dose to a cell population with 37% survival is about 2000 to 30000 rads in bacteria. In human cells D37 is about 120 rads.

Some chemicals have a protective effect on the cell in reducing the effect of a radiation dose. Aminothiols which have an – SH and – NH2 group separated by two carbon atoms are most powerful in reducing the effect. The protective effect is expressed as dose reduction factor (DRF).

DRF is the ratio of LD50(30) for protected animals to LD50(30) for unprotected animals. LD is the lethal dose or the amount of radiation that kills all individuals in a large group of organisms. LD50(30) is the dose which kills 50 % of organisms within 30 days of exposure. LD50 for dog is estimated to be 350 rads, for mouse 550, goldfish 2300.

Whether the natural background radiation, though small in amount is dangerous for human beings or not has been questioned. The background radiation consists mainly of cosmic rays, emissions from radioactive elements in the earth such as uranium, radium and thorium, as well as emissions from radioactive isotopes (carbon 14, potassium 40) occurring naturally in the body.

People living at sea level receive an average dose of about 0.8 millisievert of radiation per year. A study of the coastal area of Kerala in South India, a region having high background radiation, has revealed a high incidence of Down’s syndrome in the population. Radiation-induced genetic and chromosomal anomalies were also observed.


Ultraviolet Radiation

Ultraviolet radiation with a wavelength of 260 nm will form pyrimidine dimers between adjacent pyrimidines in the DNA. The dimers can be one of two types (Figure 7.11). The major product is a cytobutane-containing thymine dimer (between C5 and C6 of adjacent T's). The other product has a covalent bond between position 6 on one pyrimidine and position 4 on the adjacent pyrimidine, hence it is called the "6-4" photoproduct.

Figure (PageIndex<2>): Pyrimidine dimers formed by UV radiation, illustrated for adjacent thymidylates on one strand of the DNA. (A) Formation of a covalent bond between the C atoms at position 5 of each pyrimidine and between the C atoms at position 6 of each pyrimidine makes a cyclobutane ring connecting the two pyrimidines. The bases are stacked over each other, held in place by the cyclobutane ring. The C-C bonds between the pyrimidines are exaggerated in this drawing so that the pyrimidine ring is visible. (B) Another photoproduct is made by forming a bond between the C atom at position 6 of one pyrimidine and position 4 of the adjacent pyrimidine, with loss of the O previously attached at position 4. (Public Domain Master Uegly).

The pyrimidine dimers cause a distortion in the DNA double helix. This distortion blocks replication and transcription.


Understanding DNA damage: Modeling how low energy electrons damage DNA may improve radiation therapy

Photograph of the device used for Electron Stimulated Desorption. Credit: M.FROMM/Université de Franche-Comté

Every day, all day, our DNA gets beaten up by chemicals and radiation—but remarkably, most of us stay healthy. Now, an investigation by a team of French and Canadian researchers has produced insights into a little-studied but common radiation threat to DNA: low-energy electrons (LEEs), with energies of 0-15 electron volts.

The team has devised the first rough model of a close DNA cellular environment under threat from LEEs, revealing for the first time their effects on DNA in natural, biological conditions. Their work appears in The Journal of Chemical Physics.

The team's work is an important step forward in understanding how LEEs injure DNA because it provides a realistic experimental platform for analysis of results. The goal is to use this knowledge to improve current uses of radiation, such as in cancer treatments.

"The way by which these electrons can damage DNA, and how much damage they inflict, quantitatively, is of major importance not only for general radiation protection purposes, but also for improving the efficiency and safety of therapeutic and diagnostic radiation therapy," said Michel Fromm, the lead researcher from Université de Franche-Comté in Besançon, France, whose expertise is in creating nanometer-scaled DNA layers. His co-author on the paper is Leon Sanche, of Sherbrooke University Québec, Canada, who is one of the world's leading authorities on LEE research.

This is a schematic of the deposition method used to produce nanometer-scaled DNA layers. Credit: M.FROMM/Université de Franche-Comté

The team explored specific features of a small DNA molecule called a plasmid on a specialized thin film they created, which was irradiated by an electron gun. The impact produced transient particles called anions, which dissociate into "pieces" of DNA. When analyzed, these molecular fragments provide insight into the mechanisms of DNA strand breaks and other DNA injuries that health researchers seek to understand, repair and prevent.

"The fascinating point is that each time the close environment of DNA changes, new mechanisms of interaction of LEEs appear," Fromm said.


ELI5: How does radiation exposure alter DNA in such a way that the mutations can be inherited by the person's offspring?

Ionizing radiation has enough energy to completely knock electrons out of the atoms in the materials is strikes. This creates ions--atoms that have either a positive or negative charge. A good example of this is when radioactive decay produces an alpha particle. This is essentially a helium nucleus with two protons and two neutrons, with a +2 charge. An alpha particle will do almost anything to get two electrons and become ordinary helium and it will steal electrons from any nearby atoms. Thus, the atoms it stole the electrons from become ionized and they re-bond somehow, thus altering the atomic structure. If it's your DNA being atomically altered, that will create tons of problems as your DNA becomes "corrupted" and copies itself. The result of this is cancer and mutated offspring.

If the mutation occurs in the germ cells (those cells in the testes that produce sperm in males, or in the eggs of females), then the mutation can be passed to the offspring. This why when you get x-rays, they will cover your crotch with a lead apron to limit exposure of your germ cells.

Health Physicist here Heritable effects of radiation damage are actually quite rare. The key mechanism of cell damage from radiation is the splitting of DNA. Many things can happen at this point:

One or both strands of of the DNA can split. Sometimes they reattach normally.

Strands don't reattach properly or in a timely manner and the cell dies during normal division (Apoptosis, aka programmed cell death).

DNA can reattach incorrectly leading to improper gene action. If this happens with genes regulating cell growth and/or genes for tumor suppression, cancers become possible.

Both strands break from more than one DNA chain and they reattach to the wrong place! Leading to weird things after cell division like [rings and dicentric chromosomes] (http://www.usuhs.edu/afrri/outreach/images/figure9.jpg).

The take away here is that the vast majority of these effects will cause the cell to die, undergo apoptosis, or go dormant because it won't work (senescence). The damage has to be just right to be able to cause a heritable effect. This wouldn't look like someone having extra arms or strange sci-fi stuff, but rather a non-viable fetus or some type of retardation similar to other chromosomal disorders (ex. Down Syndrome).

I believe the radiation damages and mutates the gametes (sex cells) which makes the genes able to be transmitted to the offspring.

imagine you have a bunch of blocks chained together, each of those blocks is connected to another block which is itself part of a chain they fit together like a peg and a hole. you have 4 basic shapes for these: square, triangle, hexagon, and circle. and around you are a bunch of pegs and a bunch of similarly shaped holes.

you want to make a copy so you pull the pegs out of the holes and for each peg you grab a similarly shaped hole and for each hole a similarly shaped peg, you hook them together and you now have 2 chains where you once only had one. now imagine you couldn't look at the pegs and holes and just had to randomly grab at pegs and holes until you got one that fit. under normal circumstances it wouldn't be possible to get a hexagon into a circle peg for instance, but if you put some force into it, well they go together. this is what radiation does, when your DNA is copying it matches A to T and G to C, but radiation can get in there and give some energy, and when energy is added A can bind to C or G. for that particular cell this could mean death, but often it means nothing really. what happens next is when the cell divides.

remember before we had A to T so when the dna split the side that had T would get an A attached to it and the side with T would get an A and the two would be identical. but now the A is bonded to something else, let's say C. so the dna gets split apart and A gets a T and c gets a G. now these it a totally different protein being made at that spot. one cell continues being like it was (A to T) but one now has a GC pair.

how how does this get inherited, simple: if it happens in the testes or ovaries any mutations in those cells will be inherited, or i should say have a chance to be inherited.

so let's recap. for a mutation to be inherited it must first: be in such a way it doesn't kill the cell, be in such a way the body's natural defenses don't kill the cell, be in the testes or ovaries, be in a cell that makes the sperm or ova, and be one of the sections of dna randomly selected for gene shuffling.

with all these things needed to converge you would think mutations from radiation never happen, but they do, they just happen so much and amongst so many cells eventually these probabilities converge.


I don't understand "Nuclear Radiation". How does it work and what separates it from other forms of matter/elements in our world that seem to make it so much more dangerous?

I understand that it's 𧮭', is most closely related nuclear power plant meltdowns and atomic bombs. But I don't understand HOW it works. Are there different types of radiation? Is the radiation our phones give off the same exact thing, except at a much lower level?

What is happening to our body when radiation gives us cancer? Why do we use radiation therapy to cure cancer when it also gives us cancer.

It also seems a property of it is that you can't really stop it - it seems like putting up walls or barriers is not effective unless they are ridiculously thick, and even then it seems like we just do that because we don't really know what else to do and it's better than nothing

Basically just looking for Nuclear Radiation 101 explanation.

Regular matter is made of atoms. And every atom has a nucleus, made of protons and neutrons. Some nuclei are unstable, meaning that they decay. When a nucleus decays, it emits radiation.

There are different kinds of nuclear radiation. Some examples are alpha particles, beta particles, gamma rays, protons, neutrons, conversion electrons, fission fragments, clusters, and more. These are generally ionizing radiation, which means that the particles have enough energy to break chemical bonds or knock electrons out of atoms. This is the kind of radiation that can cause cancer. The radiation emitted by a phone or a WiFi router is not ionizing.

What is happening to our body when radiation gives us cancer?

On a very basic level, ionizing radiation damages your DNA. This causes mutations which can lead to cancer.

Why do we use radiation therapy to cure cancer when it also gives us cancer.

Ionizing radiation can be used to kill cells. If you point your beam of radiation at cancerous cell, it will kill them. We have sophisticated techniques to specifically target the cancerous tissue with beams of radiation. The treatment kills cancerous tissue while delivering a much smaller dose to the surrounding healthy tissue.

It also seems a property of it is that you can't really stop it - it seems like putting up walls or barriers is not effective unless they are ridiculously thick, and even then it seems like we just do that because we don't really know what else to do and it's better than nothing

You can't stop radioactive nuclei from decaying, but you can certainly shield against radiation. Different types of radiation are easier to stop than others. For example, alpha particles are very easy to stop with a piece of paper, or even just a few inches of air. On the other hand, fast neutrons are much harder to stop.

On a very basic level, ionizing radiation damages your DNA. This causes mutations which can lead to cancer.

What about a very strong dose of radiation which would kill you within hours or minutes? That can't be because of DNA damage.

Where does the decayed stuff go? Does it just cease to exist?

I was of the impression that energy is never lost, but only changes form. Is that wrong?

Thank you for your answers And also to everyone else :)

But I got a bit more curious:

What are the factors that decide if an atom is/becomes 'stable' or 'unstable'?

Does that question even make sense or am I far off?

So if I had one Cesium atom, it would decay and that would be it correct? It would be very dangerous until I had a lot of them right?

Follow up: Are there any truths to the claims that prolonged exposure to radiation emitted by phones, wi-fi devices etc can be harmful?

To add a bit to /u/RobusEtCeleritas's nice coverage:

The reason some types of radiation are so penetrating is that those types have no electric charge, so they don't interact very often with matter. This includes x-rays and gamma rays, which are just high-energy forms of light, and neutrons, which are one of the particles that make the nuclei of atoms.

To focus on the x-rays and gamma rays, while they don't interact very often with matter, when they do interact they tend to dump most of their energy into it at once. So we just need to make the shielding thick enough so that most of the radiation will hit something.

As an example: for the high-energy x-rays used in radiation therapy, about 40 cm of concrete will stop 90% of x-rays. Another 40 cm will beef that up to 99%, another 40 cm 99.9%, and so on. Usually in radiation therapy vaults, the main shielding is concrete about 200 cm (6 feet) thick, which will stop 99.999% of the radiation, which is enough to make working outside the vaults quite safe.

This is all a very well-understood science, and experts such as Health Physicists and Medical Physicists exist to make sure radiation can be used safely.

Let's start with nuclear radiation is neither bad nor good it simply is.

Radiation is a natural phenomenon that happens in the universe it powers the stars, and thus the plants and and all life on earth.

Radiation can come from many sources through natural decay, everything decays you me, the air, that rock over there everything. What that means is that some parts of the core of an atom called the nucleus breaks apart from the atom and escapes. This for most element doesn't happen very often, we however know that half of will decay in the same amount of time as the rest of it.

We consider something radioactive when it decays at a rate which is high.

What radiation is, is complicated. But as you assumed there are different types of radiation out there.

Let talk about the major different kinds of radiation.

Alpha radiation means a helium core (consisting of two protons and two neutrons) escapes a larger atom. Notice how I say the core because alpha particles have no electrons, and thus have a charge.

Beta radiation is a type of decay inside the protons or neutrons that release a electron (or a positron) and neutrino (elementary particle) in essence it what's happens when a neutron and proton change into one another they release a beta wave.

A Gamma ray is electromagnetic discharge from excited atoms coming back to normal States, they have very high energy. Gamma rays also tend to penetrate most objects they are the rays that the large walls are really protecting you from as almost anything can block an alpha ray and it takes very little to block a beta rays.

Now what does all this mean? It means that radiation comes from processes that are changing the core and thus element of an atom. When atoms changes into one another, they use fusion (two small make one big) or they fission (one big makes two small). It also means that these radiations at certain levels are capable of marking other atoms decay.

Now when we are talking about nuclear energy we are talking about controlling this decay. Because these things have a weird property, when you add all the mass from before the decay and then add up all the mass after they don't equal each other, some of the mass was turned into energy this energy is carried by the alpha, beta or gamma ray (and many times all three). We can use this energy to turns a magnet which creates electricity in a turbine. Basically we take elements that are already have a high rate of decay and then we send in some focused rays to cause them to start decaying enough that it creates a chain reaction of atoms splitting and there splitting parts being used to make more of the split and so on.

When we are talking about bombs we means we cause a lot of decay to happen as close to instantaneously as we can and thus making the release of energy high and explosive. We basically crush the particles so that they end up so compact they have no other choice but to run into each other, which causes the chain reaction in much more spectacular and less controlled form.

Radiation is dangerous because they can change the structures of other atoms, through enough radiation at a nuclear cell and some of the cells will start to have serious problem because the atoms and molecules will have changed structure, which means they won't act the way the cell wants them to anymore, they will decay.

One should mention nothing is going to make you or anything else more radioactive. You won't become suddenly start b OMG radioactive more because you experience radiation (the radiation may affect you in a certain way but not in that way), you are already giving off radiation just at a rate so small it doesn't matter. You however can become contaminated, meaning cover in a radioactive material (usually meaning in a fine dust or somehow soaked in it) you are not radioactive you are contaminated with radioactive elements. So no you won't start flowing and nor will anything else.

Now certain types of tissue for various reason are more affected than others and some are most affected by certain types of radiation rather than others.

This is much more complicated than this and is meant to be an introduction there are whole courses on the affects, causes and sources of just alpha radiation. And so a reddit post isn't exactly going to explain everything or truly explain it accurately.


Polymer Reactions

2.9.1 Ionizing Radiation

Interactions of ionizing radiation with cellulose to form macrocellulosic radicals may be divided into those in which the energy is initially selectively absorbed by specific groups on the molecule, mainly UV, and those in which energy is randomly absorbed by the molecule, mainly high-energy radiation, including gamma, X-ray and electron radiation . The gamma radiation may emanate from X-ray or nuclear sources, usually 60 Co. Electron radiation from machine sources is also used. In each case, after absorption of the radiant energy, oxidative depolymerization of cellulose is initiated and macrocellulosic radicals are formed. 51 Thermal radiation of cellulose also initiates oxidative depolymerization and the formation of high concentrations of radicals. However, most of these carbon-type radicals are resonance-stabilized and do not initiate grafting reactions. 55

UV radiation is weakly absorbed by dried purified cellulose to generate a radical which has a single-line ESR spectrum. 56 In the presence of monomer, a characteristic ESR spectrum for the propagating radical of the grafting polymer, e.g. poly(methacrylic acid), is obtained. In a typical grafting reaction (equation 27 ), a five-line spectrum for the propagating grafting polymer is generated at 298 K.

The freely rotating α-1 methyl group and one of the methylene hydrogens on the β-carbon bond interact with the radical to generate the ESR spectrum. The structure and rotation about the C(α)C(β) bond of the grafting copolymer are evidently restricted. 57, 58 Comparisons with the ESR spectra of monomer in methanol, photosensitized with FeCl3, confirm the restricted rotation in the propagating grafting polymer radical. 59, 60 Photosensitizers used with cellulose and UV radiation increase the number of radicals, including macrocellulosic radicals. Many of these radicals may initiate homopolymerization rather than grafting reactions. Photosensitization is used to yield cellulosic products with polymeric coatings. 51, 57


The Interaction of Ionizing Radiation with Biologic Materials

As mentioned in the introductory section of this chapter, ionizing radiation deposits energy as it traverses the absorbing medium through which it passes. The most important feature of the interaction of ionizing radiation with biologic materials is the random and discrete nature of the energy deposition. Energy is deposited in increasingly energetic packets referred to as “spurs” (100 eV or less deposited), “blobs” (100 to 500 eV), or “short tracks” (500 to 5000 eV), each of which can leave from approximately three to several dozen ionized atoms in its wake. This is illustrated in Figure 1-4, along with a segment of (interphase) chromatin shown to scale. The frequency distribution and density of the different types of energy deposition events along the track of the incident photon or particle are measures of the radiation’s linear energy transfer or LET (see also the “Relative Biologic Effectiveness” section, later). Because these energy deposition events are discrete, it follows that although the average amount of energy deposited in a macroscopic volume of biologic material may be rather modest, the distribution of this energy on a microscopic scale may be quite large. This explains why ionizing radiation is so efficient at producing biologic damage the total amount of energy deposited in a 70-kg human that will result in a 50% probability of death is only about 70 calories, about as much energy as is absorbed by drinking one sip of hot coffee. 27 The key difference is that the energy contained in the sip of coffee is uniformly distributed, not random and discrete.

Adapted from Goodhead D: Physics of radiation action: microscopic features that determine biological consequences. In Hagen U, Harder D, Jung H, et al, editors: Radiation research 1895-1995, proceedings of the 10th international congress of radiation research, vol. 2. congress lectures, Wurzburg, 1995, Universitatsdruckerei H Sturtz, p 43.

The most highly reactive and damaging species produced by the radiolysis of water is the hydroxyl radical ( • OH), although other free radical species are also produced in varying yields. 29, 30 Ultimately, it has been determined that cell killing by indirect action constitutes some 70% of the total damage produced in DNA for low LET radiation.