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It is important in most radiation experiments to have both a quantitative measure of the amount of radiation involved, and a qualitative description of the radiation which uniquely defines its significant properties. The required quantitative measure is the absorbed dose, which is the amount of energy absorbed per unit mass of the irradiated material. This can be expressed in rads (1 rad = 100 ergs/gm.). The most pertinent qualitative description is that of the spatial distribution of the collisions by which the electrons (or other ionizing and exciting particles) which are responsible for the actual energy dissipation lose their energy. This concept has been termed “linear energy transfer” (LET) and is defined in terms of the energy lost per unit path length by the particle (1, p. 6). The LET is usually written as a function, L(T), of the kinetic energy, T, of the particle and is conveniently expressed in units of kev/µ where µ is 1 micron of path length. The significant information concerning the distri...

The LET-energy dissipation spectrum and mean LET of a 14 MeV monoenergetic electron beam has been calculated using a method proposed by Burch, and the importance of δ-electrons in such calculations is discussed. The mean LET of the beam is equal to the instantaneous LET of a 15 KeV electron; its variation with depth in a water phantom is negligible over the first few centimetres. The biological effectiveness of such electrons should not differ significantly from that of 60Co γ-rays. A short discussion of some calculations for high energy ion beams is also given.

The energy absorbed by a material traversed by any ionizing radiation may be investigated at three levels of complexity: 1. The dissipation of energy may be considered as continuous in space, the only relevant quantity being then the dose in ergs per gram. 2. The dissipation of energy may be considered as continuous along the tracks of the ionizing particles, varying with their charge and velocity. The relevant quantities are then the ergs per gram, as before, and the ergs per centimeter of track, or the distribution of this quantity when it is not constant for all tracks. 3. The dissipation of energy may be considered as a series of discrete eventsionizations and excitations-occurring in the vicinity of the tracks of the ionizing particles. A complete description of the situation at this level would require a knowledge of the nature and spatial distribution of the separate events. Experimental measurements of dose by ionization chamber or thermal dosimeters will indicate only the dose in ergs per gram. The individual particle energies in an irradiated medium may be determined, within certain limits, by means of scintillation counters, but the determination of the structure of the tracks is not at present accessible to experimental techniques except in the case of gaseous media, where cloud chamber photographs give an indication of the longitudinal spacing of the ions (1-3) and measurements on the saturation curve for a-particle ionization give a rather indirect clue to the effective diameter of the tracks (4, 5). It has usually been assumed (6, 7), for want of exact knowledge, that the structure of the tracks in liquid media would resemble the structure deduced for gases, reduced in proportion to the relative densities of gas and liquid; and the rate of energy loss along the tracks has, therefore, usually been quoted in terms of ion pairs per micron, or some such unit. There are, however, serious theoretical objections (8, 9) to the view that the track structure is similar in liquids and gases, but no satisfactory theoretical picture of the structure of the tracks in liquids has yet been given. At the present time it is, therefore, less speculative to focus attention on the rate of energy loss of the particles, for which a satisfactory theory and accurate experimental observations exist, i.e., to concentrate on the second level of complexity. Zirkle (10) has proposed the term "linear energy transfer" (LET) for the rate of energy loss of the particle, which is, of course, the same thing as "stopping power" but with the

Abstract The radiobiological influence of linear energy transfer (energy transferred per unit length of the track of an ionizing particle) was investigated with respect to inhibition of cell division in three microorganisms: a diploid strain of the yeast Saccharomyces cerevisiae; a haploid yeast derived form the diploid; and the unicellular green alga Stichococcus. Complete survival curves were obtained for each organism at each of nine different values of linear energy transfer (LET), ranging from 0.73 to 190 k.e.v. per micron of path in tissue. Most of these values of LET were obtained by using different portions of the paths of very speedy deuterons, accelerated helium nuclei, and natural α-particles in such fashion that, in any given exposure, the value of LET was essentially the same for all particles that traversed the cell sample. At all values of LET, the survival curves of the haploid yeast were exponential, while those of the diploid were strongly sigmoid and of a shape essentially independent of LET. The relative biological effectiveness (RBE) (a quantity inversely proportional to the 50 % survival dose) of the nine radiations for both yeasts was practically constant for LET values from 0.73 to 27 k.e.v./μ but increased by about a factor of four or five between 27 and 190 k.e.v./μ. The yeast survival curves are consistent with a theory that, in the haploid, cell division can be inhibited by inactivating any one of some tens of chromosomal sites by means of a single ionizing particle, whereas in the diploid it is necessary to inactivate both members of any one allelic pair of corresponding sites. The variation of RBE with LET is not consistent with simple target theory but is readily explained in terms of chemical intermediates which can diffuse from their places of origin in the ionization tracks to the chromosomal sites. The survival curve of Stichococcus was sigmoid, and the RBE increased by a factor of twelve as LET varied from 1.5 to 190 k.e.v./μ.

In this paper we report radical and molecular yields for the range of LET 0.2 to 0.4 ev/A, obtained by using protons of xvarious energies in the range 11 to 23 Mev. Initial yields were measured for oxidation of ferrous sulfate and for reduction of ceric sulfate both with and without thallous ion present. These solutes quantitatively scavenge the intermediates produced by decomposition of the water and,

In order to investigate the effect of the changing linear energy transfer along an alpha particle track in the radiolysis of water, aqueous solutions of 0.1N H/sub 2/SO/sub 4/ containing either ferrous, ceric, or ceric and thallous ions were irradiated by a flat external alpha source. G(Fe/sup +3/) and G(Ce/sup +3/) were plotted against the length of an alpha track in the solution. For comparison, the linear energy transfer was also plotted for various distances from the end of the track. Beta irradiation of the solutions was also studied. When D/sub 2/O was used an isotopic effect was observed which first increased with increasing mean linear energy transfer, then passed through a maximum, and decreased in the region of mean linear energy transfer corresponding to low energy alpha particles. (M.C.G.)

Recent developments in radiobiology have created a need for a more detailed description of physical exposure conditions. In particular, the relative biological effectiveness (RBE) is believed to be related to the linear energy transfer (LET) (1) of the charged particles traversing irradiated tissues. In fact, permissible exposure to ionizing radiations has been based on both absorbed dose and ion density or LET (2). In the case of uncharged primary radiations there is in general a complex relation between the externally incident radiation field and the LET distribution of the dose imparted by internally produced ionizing secondaries. However, Boag (3) has computed the LET distribution of protons liberated in water by neutrons. This work is of considerable intrinsic interest, since it discloses characteristic LET distributions which should be considered in the planning of radio-biological experiments. In addition, the data provided may be applied directly in practical cases whenever known neutron spectra are employed. On the other hand, direct measurement of LET distributions substantially obviates the need for any knowledge of the characteristics of the primary radiation.

The linear energy transfer (LET) distribution and the number and energy average LET of electrons set in motion by primary and water-scatiered beams of radiation with primary half value layer from 1.25 mm Cu to 11 mm Pb are presented. The effect of energy degradation due to scatter in H₂O is very small. Few biological systems are likely to be sensitive enough to changes in LET to make the effect of energy degradation in an absorber biologically significant. (auth)

The use of microelectronic products in outer space is possible if protection is provided against special external influencing factors, including radiation effect. For digital integrated circuits manufactured using submicron CMOS processes, the greatest influence is exerted by radiation effects caused by exposure to a heavy charged particle. The use of special design tools in the development of dual-purpose microcircuits, with increased resistance to the impact of heavy charged particles, prevents single events from occurring. Thus, the use of modern software products for device and technological modeling in microelectronics when developing the element base of radiation-resistant microcircuits for space purposes will cut the time to develop new products and make it possible to modernize (improve performance) already existing device and circuitry solutions. The paper delivers the results of modeling the impacts of heavy charged particles with a magnitude of linear energy transfer equal to 1.81, 10.1, 18.8, 55.0 MeV·cm2/mg, corresponding to nitrogen ions 15N+4 with an energy E = 1,87 MeV; argon 40Ar+12 with an energy E = 372 MeV; ferrum 56Fe+15 with an energy E = 523 MeV; xenon 131Xe+35 with an energy E = 1217 MeV, on electrical characteristics of n-MOSFET device structure. The dependences of the maximum drain current IС on the motion trajectory of a heavy charged particle and the ambient temperature are shown.

To study the response characteristics of LiF detectors to proton fluence rate and energy, and to observe the thickness effect of the detector.Protons were generated by an accelerator. Proton energy was changed in two ways, i.e. changing the accelerator energy directly, or using detector stacks to absorb the proton energy. The incident proton energy on each chip of detector stacks was calculated according to proton range in LiF.The response of the detector to proton fluence rate was almost constant; when proton energy was above 9 MeV, the response of the detector to proton energy was constant (less than 10% errors). When proton energy was below 9 MeV, the response reduced gradually with the decrease of proton energy. Thickness effect for LiF thicknesses of 0.4mm and 0.8mm was not obvious.The homemade LiF detector is suitable for measurement of space radiation dose. When proton component (below 9 MeV) was abundant in radiation field, the decrease of the relative thermoluminescence efficiency should be taken into consideration.