There is no radiation sickness at 100 mrem (1 mSv) acute dose.

One Gy (100 rad) in air would result in about 0.2 Gy (20 rad) skin energy deposited for 10 KeV mono-energetic photons. The threshold for skin erythema is 0.5 Gy (50 rad).

For dose level around 100mRem (m for milli) acute exposure, there will not be any detectable effect on the skin (as suggested by Prof. Joseph L Alvarez). Please note that the yearly (skin) dose limit by ICRP is 500mSv i.e. 500m*100Rem=50000mRem. The dose received from low energy x-rays is similar to what Sr/Y-90 beta source would deposit at skin. Please note that photons below 15 keV energy are considered as weakly penetrating radiations like beta particles.

For 100 mrem (in modern units 1 mSv) single short time exposition you will not expect any deterministic effect to the skin. Erythema threshold dose is as Joseph L Alvarez already stated at least 0,5 Gy, the normal value depending on the type and pigmentation of the exposed skin is higher (2-6 Gy). Deterministic effects to the skin are erythema and early aging, for high doses even nekrosis. All these effects are out of the dose region you have proposed.

Of course you have to take into account the stochastic effects to the skin like the different skin cancers (Basaliom, Spinaliom or maligne melanom = black skin cancer). They are supposed to have no dose threshold, that means they start with very small doses even below 1 mSv. The low energy photons (10 keV) show a similar exposition depth like very soft betas and this is therefore restricted to the surface of the skin (0,1 -2mm range).

Biological Effects of Ionizing Radiation

We hear many seemingly contradictory things about the biological effects of ionizing radiation. It can cause cancer, burns, and hair loss, yet it is used to treat and even cure cancer. How do we understand these effects? Once again, there is an underlying simplicity in nature, even in complicated biological organisms. All the effects of ionizing radiation on biological tissue can be understood by knowing that ionizing radiation affects molecules within cells, particularly DNA molecules.

Let us take a brief look at molecules within cells and how cells operate. Cells have long, double-helical DNA molecules containing chemical codes called genetic codes that govern the function and processes undertaken by the cell.

According to Opexstar College, it is for unraveling the double-helical structure of DNA that James Watson, Francis Crick, and Maurice Wilkins received the Nobel Prize. Damage to DNA consists of breaks in chemical bonds or other changes in the structural features of the DNA chain, leading to changes in the genetic code. In human cells, we can have as many as a million individual instances of damage to DNA per cell per day. It is remarkable that DNA contains codes that check whether the DNA is damaged or can repair itself. It is like an auto check and repair mechanism. This repair ability of DNA is vital for maintaining the integrity of the genetic code and for the normal functioning of the entire organism. It should be constantly active and needs to respond rapidly. The rate of DNA repair depends on various factors such as the cell type and age of the cell. A cell with a damaged ability to repair DNA, which could have been induced by ionizing radiation, can do one of the following:

• The cell can go into an irreversible state of dormancy, known as senescence.

• The cell can commit suicide, known as programmed cell death.

• The cell can go into unregulated cell division leading to tumors and cancers.

Since ionizing radiation damages the DNA, which is critical in cell reproduction, it has its greatest effect on cells that rapidly reproduce, including most types of cancer. Thus, cancer cells are more sensitive to radiation than normal cells and can be killed by it easily. Cancer is characterized by a malfunction of cell reproduction, and can also be caused by ionizing radiation. Without contradiction, ionizing radiation can be both a cure and a cause.

To discuss quantitatively the biological effects of ionizing radiation, we need a radiation dose unit that is directly related to those effects. All effects of radiation are assumed to be directly proportional to the amount of ionization produced in the biological organism. The amount of ionization is in turn proportional to the amount of deposited energy. Therefore, we define a radiation dose unit called the rad, as 1/100 of a joule of ionizing energy deposited per kilogram of tissue, which is 1 rad=0.01 J/kg.(1)

For example, if a 50.0-kg person is exposed to ionizing radiation over her entire body and she absorbs 1.00 J, then her whole-body radiation dose is (1.00 J)/(50.0 kg)=0.0200 J/kg=2.00 rad .(2)

If the same 1.00 J of ionizing energy were absorbed in her 2.00-kg forearm alone, then the dose to the forearm would be (1.00 J)/(2.00 kg)=0.500 J/kg=50.0 rad(3), and the unaffected tissue would have a zero rad dose. While calculating radiation doses, you divide the energy absorbed by the mass of affected tissue. You must specify the affected region, such as the whole body or forearm in addition to giving the numerical dose in rads. The SI unit for radiation dose is the gray (Gy), which is defined to be 1 Gy=1 J/kg=100 rad.(4)

However, the rad is still commonly used. Although the energy per kilogram in 1 rad is small, it has significant effects since the energy causes ionization. The energy needed for a single ionization is a few eV, or less than 10−18J. Thus, 0.01 J of ionizing energy can create a huge number of ion pairs and have an effect at the cellular level.

The effects of ionizing radiation may be directly proportional to the dose in rads, but they also depend on the type of radiation and the type of tissue. That is, for a given dose in rads, the effects depend on whether the radiation is α,β,γ, X-ray, or some other type of ionizing radiation. In the earlier discussion of the range of ionizing radiation, it was noted that energy is deposited in a series of ionizations and not in a single interaction. Each ion pair or ionization requires a certain amount of energy, so that the number of ion pairs is directly proportional to the amount of the deposited ionizing energy. But, if the range of the radiation is small, as it is for α s, then the ionization and the damage created is more concentrated and harder for the organism to repair. Concentrated damage is more difficult for biological organisms to repair than damage that is spread out, so short-range particles have greater biological effects. The relative biological effectiveness (RBE) or quality factor (QF) is given in Table 1 for several types of ionizing radiation—the effect of the radiation is directly proportional to the RBE. A dose unit more closely related to effects in biological tissue is called the roentgen equivalent man or rem and is defined to be the dose in rads multiplied by the relative biological effectiveness. rem=rad×RBE (5)

So, if a person had a whole-body dose of 2.00 rad of γ radiation, the dose in rem would be (2.00 rad)(1) = 2.00 rem whole body. If the person had a whole-body dose of 2.00 rad of α radiation, then the dose in rem would be (2.00 rad)(20) = 40.0 rem whole body. The α s would have 20 times the effect on the person than the γ s for the same deposited energy. The SI equivalent of the rem is the sievert (Sv), defined to be Sv=Gy×RBE, so that 1 Sv=1 Gy×RBE=100 rem.(6)

The RBEs given in Table 1 are approximate, but they yield certain insights. For example, the eyes are more sensitive to radiation, because the cells of the lens do not repair themselves. Neutrons cause more damage than γ rays, although both are neutral and have large ranges, because neutrons often cause secondary radiation when they are captured. Note that the RBEs are 1 for higher-energy β s, γ s, and X-rays, three of the most common types of radiation. For those types of radiation, the numerical values of the dose in rem and rad are identical. For example, 1 rad of γ radiation is also 1 rem. For that reason, rads are still widely quoted rather than rem. Table 2 summarizes the units that are used for radiation.

A high level of activity doesn’t mean much if a person is far away from the source. The activity R of a source depends upon the quantity of material (kg) as well as the half-life. A short half-life will produce many more disintegrations per second. Recall that R=0.693Nt1/2. Also, the activity decreases exponentially, which is seen in the equation R=R0e−λt.

Table 1: Relative Biological Effectiveness

Type and energy of radiation RBE1

X-rays 1

γ rays 1

β rays greater than 32 keV 1

βrays less than 32 keV 1.7

Neutrons, thermal to slow (20 Fatal within hours due to collapse of central nervous system.

Immediate effects are explained by the effects of radiation on cells and the sensitivity of rapidly reproducing cells to radiation. The first clue that a person has been exposed to radiation is a change in blood count, which is not surprising since blood cells are the most rapidly reproducing cells in the body. At higher doses, nausea and hair loss are observed, which may be due to interference with cell reproduction. Cells in the lining of the digestive system also rapidly reproduce, and their destruction causes nausea. When the growth of hair cells slows, the hair follicles become thin and break off. High doses cause significant cell death in all systems, but the lowest doses that cause fatalities do so by weakening the immune system through the loss of white blood cells.

The two known long-term effects of radiation are cancer and genetic defects. Both are directly attributable to the interference of radiation with cell reproduction. For high doses of radiation, the risk of cancer is reasonably well known from studies of exposed groups. Hiroshima and Nagasaki survivors and a smaller number of people exposed by their occupation, such as radium dial painters, have been fully documented. Chernobyl victims will be studied for many decades, with some data already available. For example, a significant increase in childhood thyroid cancer has been observed. The risk of a radiation-induced cancer for low and moderate doses is generally assumed to be proportional to the risk known for high doses. Under this assumption, any dose of radiation, no matter how small, involves a risk to human health. This is called the linear hypothesis and it may be prudent, but it is controversial. There is some evidence that, unlike the immediate effects of radiation, the long-term effects are cumulative and there is little self-repair. This is analogous to the risk of skin cancer from UV exposure, which is known to be cumulative.

There is a latency period for the onset of radiation-induced cancer of about 2 years for leukemia and 15 years for most other forms. The person is at risk for at least 30 years after the latency period. Omitting many details, the overall risk of a radiation-induced cancer death per year per rem of exposure is about 10 in a million, which can be written as 10/106rem⋅y.

If a person receives a dose of 1 rem, his risk each year of dying from radiation-induced cancer is 10 in a million and that risk continues for about 30 years. The lifetime risk is thus 300 in a million, or 0.03 percent. Since about 20 percent of all worldwide deaths are from cancer, the increase due to a 1 rem exposure is impossible to detect demographically. But 100 rem (1 Sv), which was the dose received by the average Hiroshima and Nagasaki survivor, causes a 3 percent risk, which can be observed in the presence of a 20 percent normal or natural incidence rate.

The incidence of genetic defects induced by radiation is about one-third that of cancer deaths, but is much more poorly known. The lifetime risk of a genetic defect due to a 1 rem exposure is about 100 in a million or 3.3/106 rem⋅y, but the normal incidence is 60,000 in a million. Evidence of such a small increase, tragic as it is, is nearly impossible to obtain. For example, there is no evidence of increased genetic defects among the offspring of Hiroshima and Nagasaki survivors. Animal studies do not seem to correlate well with effects on humans and are not very helpful. For both cancer and genetic defects, the approach to safety has been to use the linear hypothesis, which is likely to be an overestimate of the risks of low doses. Certain researchers even claim that low doses are beneficial. Hormesis is a term used to describe generally favorable biological responses to low exposures of toxins or radiation. Such low levels may help certain repair mechanisms to develop or enable cells to adapt to the effects of the low exposures. Positive effects may occur at low doses that could be a problem at high doses.

Even the linear hypothesis estimates of the risks are relatively small, and the average person is not exposed to large amounts of radiation. Cosmic rays are partially shielded by the atmosphere, and the dose depends upon altitude and latitude, but the average is about 0.40 mSv/y. A good example of the variation of cosmic radiation dose with altitude comes from the airline industry. Monitored personnel show an average of 2 mSv/y. A 12-hour flight might give you an exposure of 0.02 to 0.03 mSv.

Doses from the Earth itself are mainly due to the isotopes of uranium, thorium, and potassium, and vary greatly by location. Some places have great natural concentrations of uranium and thorium, yielding doses ten times as high as the average value. Internal doses come from foods and liquids that we ingest. Fertilizers containing phosphates have potassium and uranium. So we are all a little radioactive. Carbon-14 has about 66 Bq/kg radioactivity whereas fertilizers may have more than 3000 Bq/kg radioactivity. Medical and dental diagnostic exposures are mostly from X-rays. It should be noted that X-ray doses tend to be localized and are becoming much smaller with improved techniques. Table 5 shows typical doses received during various diagnostic x-ray examinations. Note the large dose from a CT scan. While CT scans only account for less than 20 percent of the X-ray procedures done today, they account for about 50 percent of the annual dose received.

Laws regulate radiation doses to which people can be exposed. The greatest occupational whole-body dose that is allowed depends upon the country and is about 20 to 50 mSv/y and is rarely reached by medical and nuclear power workers. Higher doses are allowed for the hands. Much lower doses are permitted for the reproductive organs and the fetuses of pregnant women. Inadvertent doses to the public are limited to 1/10 of occupational doses, except for those caused by nuclear power, which cannot legally expose the public to more than 1/1000 of the occupational limit or 0.05 mSv/y (5 mrem/y). This has been exceeded in the United States only at the time of the Three Mile Island (TMI) accident in 1979. Chernobyl is another story. Extensive monitoring with a variety of radiation detectors is performed to assure radiation safety. Increased ventilation in uranium mines has lowered the dose there to about 1 mSv/y.

To physically limit radiation doses, we use shielding, increase the distance from a source, and limit the time of exposure.

Table 5: Typical Doses Received During Diagnostic X-ray Exams

Procedure Effective dose (mSv)

Chest 0.02

Dental 0.01

Skull 0.07

Leg 0.02

Mammogram 0.40

Barium enema 7.0

Upper GI 3.0

CT head 2.0

CT abdomen 10.0

Thanking you all for your valuable suggestions. Special thanks to Dr.Jorge Morales Pedraza for his elaborative explanations...

Dear Prasanta Kumar Sahani,

Low energy X-ray is often referred to as "soft x-ray," but that is a potentially misleading designation that tends to diminish the potentially dangerous biological effects of low energy x-ray.

"Hard" ultraviolet radiation is taken to be non-ionizing radiation and x-ray radiation is by definition ionizing radiation. However, there is no clear cut boundary between "hard ultraviolet" radiation and "soft x-ray" radiation. The definition of "ionizing" and "non-ionizing" depends largely upon the medium a given energy of electromagnetic energy is propagating in, for example, whether propagating through air or water.

I do not have much time this evening to expound, but "soft x-ray" can be extremely dangerous to the the live skin and eyes. Medical and dental x-ray machines in the U.S. are required by the FDA to have aluminum filters built in to them to largely eliminate the lower energy x-rays that tend to damage skin and eyes in patients subjected to x-ray for this very reason.

In prior postings in this thread, some of the contributors mentioned that for x-ray photons at 10 keV maximum energy, the predominant mode of ionization is by the Photoelectric Effect where the incoming x-ray transfers all of its kinetic energy into orbital electrons of the medium in which the x-ray is interacting, thus producing photoelectrons of about the same kinetic energy as the incoming x-ray photons. Keeping in mind that a sufficient intensity and quantity of hard  U.V. radiation can produce severe skin and eye burns if it is intense enough, one would expect that "soft" x-ray at even higher energy than the hard U.V. would be at least as penetrating and biologically damaging as "hard" U.V. photon for photon.  The primary mode of biological damage in both cases is similar, biological damage results primarily from "indirect" ionization products (reactive free radicals produced in water) in both cases. Peroxyl moieties and peroxides chemically react with and damage cellular components which can result in deterministic tissue injury at sufficient exposure intensities of soft x-ray.  Probabilistic injury (DNA damage) occurs at both low and high doses of x-ray radiation to biological tissues.

10 keV x-ray photons are essentially at the same energy as those generated by the cathode ray tubes (CRT) in old style TVs and computer monitors. Prolonged unprotected exposure of the eyes and skin to CRT generated x-rays can cause severe burns and damage to these organs, including cataracts (but cataracts show up later).

I will be glad to add more information about biological effects of low energy x-rays later if you wish.

Regards,

Daniel Van Gent

The equivalent dose limit for the skin, hands and feet of 500 mSv/year recommended by the International Commission on Radiological Protection (ICRP) is based on the threshold of 20 Gy for cosmetically unacceptable skin changes (i.e., 20 Gy is the dose causing cosmetically unacceptable skin changes in 1% of exposed individuals), although historically, the tolerance dose recommended in 1934–1950 by IXRPC (predecessor of ICRP) and the maximum permissible dose recommended by ICRP in 1950s and 1960s were both basically predicated on skin erythema dose. For more details, please see the following paper.

https://www.researchgate.net/publication/262054513_Classification_of_radiation_effects_for_dose_limitation_purposes_History_current_situation_and_future_prospects

Article Classification of radiation effects for dose limitation purp...

The International Commission on Radiological Protection (ICRP) judges that acute doses up to approximately 0.1 Gy produce no functional impairment of tissues is maintained, so that the stochastic risks (cancer and hereditary effects) continue to be the principal risks to consider for most applications of ICRP recommendations in occupational or public situations. However, However, after acute, protracted or fractionated doses of >0.5 Gy, the risk of tissue reactions becomes increasingly important, particularly for the lens of the eye and the circulatory system, at very long times after radiation exposure (>20 years for vision impairing cataracts and >10 years for circulatory disease).

On one hand, a series of the in vitro radiation biology studies have shown that the low energy photons are about three times more effective at inducing DNA double strand breaks and chromosome aberrations, compared with high energy photons. An example is the following paper.

https://www.researchgate.net/publication/6975400_Histone_H2AX_Phosphorylation_in_Normal_Human_Cells_Irradiated_with_Focused_Ultrasoft_X_Rays_Evidence_for_Chromatin_Movement_during_Repair

On the other hand, for radiation protection purposes, radiation weighting factor (wR) defined by the International Commission on Radiological Protection (ICRP) is 1 for all types of photons independent of its energy.

Article Histone H2AX Phosphorylation in Normal Human Cells Irradiate...

The US National Council on Radiation Protection and Measurements (NCRP) has just published Report No. 181 “Evaluation of the Relative Effectiveness of Low-Energy Photons and Electrons in Inducing Cancer in Humans”, which will be interesting to all those who asked and read this question.

https://www.ncrppublications.org/Reports/181

PLoS One. 2018; 13(1): e0190330.Published online 2018 Jan 4. doi: 10.1371/journal.pone.0190330PMCID: PMC5754078PMID: 29300773

The effect of well-characterized, very low-dose x-ray radiation on fibroblasts

Article The effect of well-characterized, very low-dose x-ray radiat...