Internal radiation sources

The ion dose rate transmitted by a point-like fS emitter can be calculated by an equation similar to eq. (22.7), 

In contrast to ky, however, kp r) depends strongly on the distance, because of the much stronger absorption of j3 particles in air. kp r) is higher than ky by about two orders of magnitude. Below r k 0.3 i niax (7 max = maximum range), a rough estimate is 1 R m h GBq  

The influence of the distance r indicates the importance of remote handling of higher activities. 

Internal radiation sources are always more dangerous than external ones, because shielding is impossible, and incorporated radionuclides may be enriched in certain organs or parts of the body and affect them over long periods of time. 

With respect to radiotoxicity, possible storage in the body and half-lives of radionuclides are therefore most important. Removal from the body is characterized by the biological half-life, and the effective half-life ri/2(eff) is given by the relation (section 21.5)  

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In a method using a radioisotope, e.g., as an internal radiation source, the difference in a fluorescence intensity with and without a d.c. electric field is assumed to be due to electron-ion recombination, and the kr value is determined by the time-resolved measurement of the fluorescence with the known number density of ionization, which is separately determined. 

It is an attractive object of research to synthesize labelled compounds that are taking part in specific biochemical processes or able to pass specific barriers in the body, with the aim of detecting malfunctions and of localizing the origin of diseases. Complexes of short-lived no-carrier-added radionuclides and high yields of the syntheses are of special interest. In the case of short-lived radionuclides, such as fC, the synthesis must be fast and as far as possible automated. Labelled organic molecules can also be used to transport radionuclides to special places in the body for therapeutical application, i.e. as specific internal radiation sources. 

For therapeutical purposes, natural radionuclides, mainly Ra and Rn, were the first to be applied as external and internal radiation sources. For example, encapsulated samples of Ra have been attached to the skin or introduced into the body, and Rn has been recommended for the treatment of the respiratory tract by inhalation in radon galleries or it has been encapsulated in small thin-walled gold tubes and introduced into the body for treatment of cancer. 

Internal radiation sources (medical application of radionuclides such as " Tc) Diagnosis 1-1000 mSv O.l-lOmSv a 0.02mSv/y... 

Recognize that radiation can be hazardous (and that it is different from chemical hazards) and recognize the potential for exposures to external and internal radiation sources. 

For whole body radiation the most critical organs and tissues are the lens of the eye, the blood-forming organs (red bone marrow), and the gonads. Internal radiation sources may affect several vital organs. 

Radiation from internal heat sources is not directly considered in thermal comfort calculations. 

For a person at a certain location in a room, direct radiation from internal heat sources may significantly affect the thermal comfort level. However, in the codes, room (or operative) temperatures are calculated on the basis of the room air and the wall surface temperatures only (both calculated considering the internal heat source, however). 

Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode...

Radiation, Internal—Radiation from a source within the body (as a result of deposition of radionuclides in body tissues). 

D.3.1.2 Absorbed Dose and Absorbed Dose Rate. The absorbed dose is defined as the energy imparted by the incident radiation to a unit mass of the tissue or organ. The unit of absorbed dose is the rad 1 rad = 100 erg/gram = 0.01 J/kg in any medium. An exposure of 1 R results in a dose to soft tissue of approximately 0.01 J/kg. The SI unit is the gray which is equivalent to 100 rad or 1 J/kg. Internal and external exposures from radiation sources are not usually instantaneous but are distributed over extended periods of time. The resulting rate of change of the absorbed dose to a small volume of mass is referred to as the absorbed dose rate in units of rad/unit time. 

Chemat and his coworkers [92] have proposed an innovative MW-UV combined reactor (Fig. 14.7) based on the construction of a commercially available MW reactor, the Synthewave 402 (Prolabo) [9[. It is a monomode microwave oven cavity operating at 2.45 GHz designed for both solvent and dry media reactions. A sample in the quartz reaction vessel could be magnetically stirred and its temperature was monitored by means of an IR pyrometer. The reaction systems were irradiated from an external source of UV radiation (a 240-W medium-pressure mercury lamp). Similar photochemical applications in a Synthewave reactor using either an external or internal UV source have been reported by Louerat and Loupy [93],... 

IAEA, International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series 115, International Atomic Energy Agency, Vienna, 1996. 

Radiation therapy The use of high-energy radiation from x-rays, gamma rays, neutrons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body in the area near cancer cells (internal radiation therapy, implant radiation, or brachytherapy). Systemic radiation therapy uses a radioactive substance, such as a radiolabeled monodonal antibody, that circulates throughout the body. Also called radiotherapy, [nih]... 

Definition of the role of forest gifts as a source of internal radiation exposure of the local population in Ukrainian Polissya... 

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... 

ICRU (1988). International Commission on Radiation Units and Measurements. Determination of Dose Equivalents from External Radiation Sources Part2, ICRU Report 43 (International Commission on Radiation Units and Measurements, Bethesda, Maryland). 

Okamura, S., International Conference on Application of Large Radiation Sources in Industry, Warsaw, Poland, Sept. 8 to 12, 1959. 

The internal standard ratio method for quench correction is tedious and time-consuming and it destroys the sample, so it is not an ideal method. Scintillation counters are equipped with a standard radiation source inside the instrument but outside the scintillation solution. The radiation source, usually a gamma emitter, is mechanically moved into a position next to the vial containing the sample, and the combined system of standard and sample is counted. Gamma rays from the standard excite solvent molecules in the sample, and the scintillation process occurs as previously described. However, the instrument is adjusted to register only scintillations due to y particle collisions with solvent molecules. This method for quench correction, called the external standard method, is fast and precise. 

International Atomic Energy Agency,1 Industrial Uses of Large Radiation Sources/ National Agency for International Publications, New York, 1963. 

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