[en] Experimental data on the dose-response for the induction of mutation to 8-azaguanine resistance are presented for asynchronous Chinese hamster cells exposed to gamma rays and several fast neutron spectra. The LET distributions of the neutron spectra are calculated, and the biological data are interpreted in terms of the 'dual action' formulae of Neary and of Keller and Rossi. The two formulae are nearly the same, and give a site diameter of approximately 0.7μm. The observed linear component of the gamma response is larger than would be expected, and this is attributed to a single-target component of response. A similar analysis is made of published data on mutation in Tradescantia occidentalis; the site diameter in this organism is 1.6μm and there is no evidence of a single target component of response. The ratio of cell killing to mutation is much higher in the Chinese hamster cells than in Tradescantia

[en] A new experimental approach to the determination of track structure properties of ions which allows information to be obtained also on statistical fluctuations is described. A specially constructed proportional counter was traversed by a collimated beam of monoenergetic protons or deuterons in the energy range of 0.7 to 2.0MeV and the spectra of delta-rays escaping a cylinder round the ion path were measured. The radius of the cylinder could be varied from 100A to 1500A of unit density tissue. The obtained distributions were analyzed in terms of their moments. Dose profiles and distance-restricted LET were calculated for comparison with published data and general agreement was found. Determination of the variance of the measured spectra showed that the relative importance of statistical fluctuations increases with radial distance and decreasing ion energy

[en] Heavy ion tracks in Ilford K-2 emulsion are simulated with a computer program which makes use of the delta-ray theory of track structure, and the special assumption that the response of this emulsion to gamma-rays is 8-or-more hit. The simulations demonstrate that the emulsions K.5 through K.0 to K-1 are 1-or-more hit detectors, while K-2 is an 8-or-more hit detector. It would appear that emulsions of intermediate hittedness might be produced by an intermediate desensitization, to mimic or match the RBE-LET variations of biological cells, perhaps to produce a ''rem-dosimeter''. In the K-2 emulsion no developable grains are produced by stopping H, He and Li ions. The emulsion has ''threshol-like'' properties, resembling etchable track detectors. It should prove useful in the measurement of high LET dose in a strong low LET background, as for pions or neutrons. Since it can be expected to accumulate and repair ''sub-lethal damage'', to display the ion-kill and gamma-kill inactivation modes, the grain-count and track width regimes, it may serve to model biological effects

[en] A unique mesh wall ionization chamber (approximating a wall-less ionization chamber) was used to measure dose as a function of radial distance from a 930MeV ⁴He ion beam in air. Measurements were made at distances from about 10 to 40cm from the ion path. This represents simulated distances of approximately 102 to 404μm in tissue having a density of 1g/cm³. Experimental values are compared with theoretical calculations, and probable causes of differences found are discussed

[en] The RBE for fast neutrons (16MeV deuterons on beryllium) relative to 250kVp X-rays for a number of tissues differs by a fraction of 2 at most at any one dose/fraction. These differences can be explained by different relative changes in D₀ and D(Q) for the cell survival curves of the limiting cells. For all tissues at low doses/fraction of neutrons it seems probable that there will be no sparing of damage. The dose/fraction where this will be apparent will depend on the D₀ for the neutron cell survival curve. In those tissues which accumulate and repair sublethal damage with neutron irradiation the damage at low doses will be predominantly due to the α and heavy recoil component of dose in the neutron beam

No abstract available

[en] The relationships between physical and genetic units are examined. Genetic mapping involves the detection of linkage of genes and the measurement of recombination frequencies. The genetic distance is measured in map units and is proportional to the recombination frequencies between linked markers. Physical mapping of genophores, particularly the simple genomes of bacteriophages and bacterial plasmids can be achieved through heteroduplex analysis. Genetic distances are dependent on recombination frequencies and, therefore, can only be correlated accurately with physical unit lengths if the recombination frequency is constant throughout the entire genome. Methods are available to calculate the equivalent length of DNA per average map unit in different organisms. Such estimates indicate significant differences from one organism to another. Gene lengths can also be calculated from the number of amino acids in a specified polypeptide and relating this to the number of nucleotides required to code for such a polypeptide. Many attempts have been made to relate microdosimetric measurements to radiobiological data. For irradiation effects involving deletion of genetic material such a detailed correlation may be possible in systems where heteroduplex analysis or amino acid sequencing can be performed. The problems of DNA packaging and other functional associations within the cell in interpreting data is discussed

[en] In order to investigate the joining process a plant, Haplopappus Gracilis, which has only four chromosomes in the diploid form, was cultured and root tip cells were collected and staining techniques were developed. Two staining techniques, Giemsa and Feulgen, both give clearly stained chromosomes showing characteristic banding such that each chromosome can be identified individually. The banding is especially convenient for the identification of the telomeres of the different chromosomes. Root tip cells were exposed to X radiation and then collected at the following metaphase using a colchicine treatment, the cell were stained and the preparation were examined for chromosome aberrations which showed joining such as dicentrics or translocations. When such a type of aberration was found, the banding pattern was used to identify the chromosomes involved and the position of joining. Results of this investigation will be presented which show that in this plant cell the joining of a broken end to a normal telomere is occurring, in accordance with the prediction of the molecular theory

[en] Definitions and relationships of microdosimetric spectra and parameters for fast neutrons are discussed in the continuous slowing-down approximation (c.s.d.a.). Regions of validity of various calculational methods, including Monte-Carlo and c.s.d.a. are considered. Calculations and measurements of energy deposition spectra are compared. Calculations of microdosimetric parameters (from the energy deposition spectra) are compared with determinations of parameters from experimental spectra. Future needs for experimental energy deposition measurements, nuclear data, and charged particle stopping-power data are considered

[en] Measurements of the energy deposition frequency distributions for intermediate energy protons were made in microscopic tissue sites by simulation with a tissue equivalent gas filled proportional counter constructed for use with heavy charged particle beams. Site sizes of 1.07μm and .535μm were simulated. The initial proton energy was 48MeV but various thicknesses of water were used to reduce the average energy of the beam. Proton energy spectra and energy deposition distributions for average proton energies in the range of 17.2MeV to 5.12MeV were measured. Radiobiology experiments were conducted in which chlorella cells were irradiated with the energy degraded 48MeV proton beam. The chlorella clonal survival data were analyzed and interpreted in terms of the measured microdosimetric parameters