Biological effects of radiation

Radiation may damage DNA in several ways. It may cause breaks in the sugar-phosphate backbone and the base crosslinks. It may also result in incorrect repair. (Rae Dejur) 

It is important to consider the type of radiation with respect to whether a radiation source is external or internal to the body. External alpha, and to some extent beta radiation, are not as hazardous as external gamma radiation. Clothing or the outer layer of the skin will stop alpha radiation. Beta 

As long as radiation dose equivalent exposures are low, radiation damage is non-detectable. General effects of short-term radiation exposure are summarized in Table 17.5. The dose equivalents in Table 17.5 are listed in rems. These values are several orders of magnitude greater than what humans received in a year. Annual human exposure 

Biological Effects of Short-Term, Whole Body Radiation Exposure 

101-200 Permanent decrease in some white-blood cell, nausea vomiting, lethargy 

Under normal circumstances, no radiation worker or patient undergoing diagnostic investigation by radiopharmaceutical or radiographic procedures should ever suffer from any acute or long-term injury. Typical radiation doses to patients from radiopharmaceuticals arc similar to. or less than, those from radiographic procedures. 

The first artificial radionuclide (phosphorus-30) was pnv duced by the French radiochemists Frederic Joliet and Irene Curie. Nuclear medicine became a specialty in 1946 when radionuclides became available from cyclotrons and nuclear reactors. In many medical centers, nuclear medicine is con- 

Imagine viewing a living process as it is occurring. This was the dream of many scientists in the past as they tried to extract this knowledge from dead tissue. Today, because of innovations in nuclear chemistry, this dream is a common, everyday occurrence. 

In an early use of the tracer technique, the pathway by which CO2 becomes fixed into carbohydrate (C6H12O6) during photosynthesis was determined. The net equation for photosynthesis is 

Radioactive C02 was injected into a colony of green algae, and the algae were then placed in the dark and killed at selected time intervals. When the radioactive compounds were separated by paper chromatography and analyzed, the results elucidated a series of light-in-dependent photosynthetic reactions. 

Biological research using tracer techniques have determined 

the rate of phosphate uptake by plants, using radiophosphorus 

The study of the biological effects of radiation is a very complex and difficult task for two main reasons. 

The human body is a very complicated entity with many organs of different sizes, functions, and sensitivities. 

Pertinent experiments are practically impossible with humans. The existing human data on the biological effects of radiation come from accidents, through extrapolation from animal studies, and from experiments in vitro. 

How and why does radiation produce damage to biological material To answer the question, one should consider the constituents and the metabolism 

This is only one example of the many reactions which occur with water and other molecules when they are subjected to radiation, the end effect being the formation of ions, atoms, and free radicals. 

We have seen that the fundamental unit for the amount of a radioactive isotope is the becquerel or the curie, which are measures of the number of disintegrations per second. For the assessment of the biological effects of high-energy radiation, such as that emitted by radioactive substances, we obviously need another kind of unit. There are several in common use. 

It is found empirically that it requires 5.2 x 10 J to create an ion pair in air at S.T.P., from which it follows that 

Another commonly employed unit is the rep, which stands for roentgen equivalent, physical. This measures the energy absorbed by water or soft tissue. On the average, 1 rep is approximately 9.3 x 10 J per g of tissue, which is somewhat more than one roentgen. There is considerable variation of absorption in soft tissue, from 6 to 10 X 10 J per g, and bone absorbs about 100 x 10 J per g. Therefore, the rep is fairly satisfactory for soft tissue, but not for the whole body. 

To circumvent this difficulty of the energy dependence on the medium, the unit rad was introduced. Rad stands for radiation absorbed dose, and is defined as 10 J kg It relates to the absorption of any kind of energy in any medium. In 1975 the rad was replaced by the gray (Gy), defined as I J kg 1 rad = 10 Gy. 

In this section we will examine briefly the effects of radiation on biological systems. But first we must define the quantitative measures of radiatioa The fundamental unit of radioactivity is the curie (Ci) 1 Ci corresponds to exactly 3.70 X lO nuclear disintegrations per second. This decay rate is eqnivalent to that of 1 g of radium. A millicurie (mCi) is one-thousandth of a curie. Thus, 10 mCi of a caibon-14 sample is the quantity that undergoes (10 X 10 (3.70 X 10 °) = 3.70 X 10 disintegrations per second. 

The intensity of radiation depends on the number of disintegrations as well as on the energy and type of radiation emitted. One common unit for the absorbed dose of radiation is the rad (radiation absorbed dose), which is the amorrrrt of radiation that resirlts in the absorption of 1 X 10 J per gram of irradiated rrraterial. The biological effect of radiation depends on the part of the bod  

Of the three types of nuclear radiation, a particles usually have the least-penetrating power. Beta particles are more penetrating than a particles, but less so than y rays. 

The chemical basis of radiation damage is that of ionizing radiation. Radiation (of either particles or y rays) can remove electrons from atoms and molecules in its path, leading to the formation of ions and radicals. Radicals (also called free radicals) are molecular fragments having one or more impaired electrons they are usually short lived and highly reactive. When water is irradiated with y rays, for example, the following reactions take place  

The electron (in the hydrated form) can subsequently react with water or with a lydrogen ion to form atomic hydrogen, and with oxygen to produce the superoxide ion (O2 ) (a radical)  

Nuclear Chemistry—alpha, beta, and gamma emission (Interactive). 

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Health Effects Of Exposure to Row Revels oflonifing Radiation, Report of Committee on the Biological Effects of Radiation (BEIR Report V), National... 

Radiation Dosimetry. Radioactive materials cause damage to tissue by the deposition of energy via their radioactive emissions. Thus, when they are internally deposited, all emissions are important. When external, only those emissions that are capable of penetrating the outer layer of skin pose an exposure threat. The biological effects of radiation exposure and dose are generally credited to the formation of free radicals in tissue as a result of the ionization produced (17). 

The biological effect of radiation is expressed in rems (radiation equivalent for man). The number of rems is found by multiplying the number of rads by a "damage" factor, n ... 

Why we need to eat d-metals, p. 670 Nuclear medicine, p. 708 Biological effects of radiation, p. 709... 

Biologic Effectiveness of Radiation—See Relative Biological Effectiveness. 

Duggar, Biological Effects of Radiation, McGraw-Hill Book Co., New York (1936). Chapters XXXV11I-LII. 

Abstract Radiation induced DNA damage is die most significant biological effect of radiation. 

Sievert (Sv) It is a more modem unit that substitutes the rem, as it reflects the biological effect of radiation. It is defined as the absorbed dose in Gy multiplied by a somewhat complicated factor that takes into account for example the quality factor defined above, the part of the body irradiated and the time and volume of exposure. 1 Sv = 100 rems. 

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