[en] Variance-covariance measurements of dose mean lineal energy were made for 10-MeV x-rays and 9 and 18-MeV electrons from a pulsed linear accelerator at Rhode Island Hospital. Two independent analog-to-digital converters were used to obtain data from two spherical proportional counters in synchrony with the beam pulses. Measurements were made for 1/2, 1, and 2 micrometer simulated sizes. Comparison with previous work by the same authors using conventional techniques for the same machine yielded good agreement

[en] A major effort was made during the past year to do precision microdosimetry of neutrons at the RARAF facility. By precision microdosimetry the authors mean a special effort to understand, better than previously, some of the factors which go into the limitation of the accuracy and precision of microdosimetric measurements of neutrons. That such factors are still not clearly understood, or at least accounted for, is immediately evident upon examination of published microdosimetric measurements. What becomes immediately apparent upon examination of, say, the dose mean lineal energies reported, is that the spread of reported values for exceeds the reported experimental uncertainty, commonly taken as about 5%. Differences of 50% are not uncommon. It is easy to make the mistake that since classical microdosimetry uses a well-established experimental tool, the proportional counter, that sources of error should also be well understood. However, microdosimetry makes use of the proportional counter in a way which is quite different from its origins as a low-energy photon spectroscopy device. Microdosimetric spectra, particularly of neutrons, span 5 to 6 decades of event sizes. It is by no means certain that proportionality extends over such a range, and in fact it has been pointed out that it probably does not. Data analysis techniques vary from one experimenter to another, and can substantially affect mean values as well as spectral shape. The authors are examining these parameters, as well as others, such as calibration errors, but they are especially concentrating on the effect of counter design and performance on the resultant spectra which the counter measures

[en] A recent communication by Thacker et al. reported yields of chromosomal exchange aberrations in V79 hamster cells after irradiation by either 250-kVp x rays or carbon characteristic K x rays of energy 270 eV. These latter produce photoelectrons with ranges of less than 10 nm. Such a distance makes it prima facie unlikely that two chromosomes could be damaged by a single track with a significant frequency. Thacker et al., however, discuss the observed effective linear component of induction of chromosome exchanges by ultrasoft carbon x-rays, and are thus led to consider the possibility that only one chromosome needs to be damaged by radiation to lead to an exchange event. In this paper, the authors analyze the data of Thacker et al. using a simple model. For carbon x rays they take advantage of the fact that the cell nuclei are not subject to a distribution of specific energies, but will each undergo essentially the same number of photon absorption events (each consisting of an energy deposition of 270 eV) for a given dose. They define the probability that a given chromosome will be broken as a result of an energy deposition event. They further define the probability that two chromosomes will be broken as a result of a single energy deposition event

[en] In the 1984 Annual Report, the authors reported on theoretical particle production cross sections by neutrons incident on carbon in the energy range of interest for modern neutron radiotherapy machines (≤ 65 MeV). These were compared with experimental double-differential particle production cross sections. At high energies, (≥ 20 MeV), kerma factors for carbon and oxygen need to be known with roughly equal accuracy in terms of their contribution to the total dose. Therefore they report here on corresponding comparisons using oxygen as the target. The theoretical model basically is a time-dependent, intra-nuclear cascade model, incorporating clustering, the compound excited states decaying by a Fermi-breakup mechanism, incorporating intermediate particle-unstable states

[en] Rodent cells have become the mainstay of in vitro transformation assays with the mouse embryo derived cells lines designated C3H/10T-1/2 or Balb-c/3T3 being relatively stable in culture and possessing highly density-inhibited, non-transformed phenotypes. A number of cellular variants have been isolated from a Balb-c/3T3-A31 clone and show a range of susceptibilities to the induction of transformation by ultra-violet light without any changes for cytotoxic effects. One derived cell line designated Balb-C/3T3 cl. A31-1-13 was described as being highly susceptible to UV-induced transformation. In this study the authors use this highly susceptible cell line to examine the transformation potential of single and split doses of ¹³⁷Cs gamma rays and ²⁴¹Am alpha particles. The biological effectiveness of high LET alpha particles is imperfectly understood relative to low LET radiations, yet such radiations have considerable potential for contributing to ill effects (principally cancers) in humans

[en] By its nature the cloning technique that has been used for the past three decades to generate survival curves requires the use of controls that receive no radiation. In this way a plating efficiency (PE) is estimated from the controls and thus an estimate of survival can be made based on this and the results of the irradiated population. In a long series of experiments it is not always possible to obtain a set of survival curves within a day's experimentation. Thus it is normal to remeasure frequently the PE so that this random variable may be controlled as much as possible. Inherent in so doing is the idea that although the PE of the cells may vary from day to day, and thus should be constantly monitored, their radiation sensitivity is not systematically affected by these variations. It is the purpose of this note to investigate the hypothesis that the radiation sensitivity is independent of the PE. Such an investigation is of particular importance for cell lines such as human diploid fibroblasts which have low, and frequently highly variable, PE's. This analysis is carried out both through a specifically designed experiment - with normal human fibroblasts - and through retrospective analysis of some large-scale experiments

[en] The variance-covariance technique provides a way to measure mean microdosimetric quantities such as anti y/sub D/ for accelerator-produced radiation in simulated volumes with a wide range of sizes, including sizes an order of magnitude smaller than is possible with conventional methods of microdosimetry. The first experimental realization of the variance-covariance method was accomplished in 1984 by Lennart Lindborg of the Swedish National Institute of Radiation Protection in collaboration with members of this Laboratory. The measurements were of anti y/sub D/ for monoenergetic 6-MeV neutrons produced at the Radiological Research Accelerator Facility (RARAF). The recent measurements go beyond the earlier ones in a number of ways. It is important that the new detectors are spherical because for spherical sites there is an expression relating values of y/sub D/ in a range of site sizes to the energy transfer proximity function. In addition, good measurements with the new detectors have already been made in sites with mean chord lengths as small as 20 nm, compared with a useful minimum of 50 nm in the first experiments

[en] This annual report describes progress made on 14 individual research projects. These projects fall naturally into theoretical biophysics, experimental microdosimetry and radiation biology. Each project has been separately abstracted for the Energy Data Base

[en] The initial modest efforts of members of the Radiation Research Laboratory to perform microdosimetric measurements on heavy ions at Berkeley grew over the years into a substantial collaborative effort involving a considerable number of people. When the first measurements, done with different size wall-less counters showed that the large extension of delta rays and fragmentation products made a broad beam technique impractical, a large tank was constructed in order to do measurements in an impact parameter mode, taking spectra as a function of distance of a tightly focused beam from the detector. Improvements were made in this technique over a period of several years, since one of the major problems in the Bevalac experiment has always been the necessarily sporadic nature of the effort, due primarily to lack of substantial beam time. The latest evolution of this method utilized a position-sensitive solid state detector mounted behind the proportional counter, allowing acquisition of data over a range of impact parameters simultaneously. Measurements performed on iron ions of 600 MeV/ amu are reported

[en] Two kinds of measurements have been made in this experiment: one, the conventional split dose measurements for 50 kV x rays and 50 keV/m deuterons, and two, the sequential combination of the two radiations. The use of Chinese hamster V79 cells, synchronized in late S phase by hydroxyurea treatment of exponentially growing cultures makes this an extension of a previously published study in which it was shown that sequential irradiations of high LET charged particles and of low LET radiation, separated by only a few minutes, produced an enhanced cell killing beyond that predicted for independent agents. Separating the two irradiations by periods substantially longer than a few minutes allows repair of sublethal damage. Comparison with the single source (conventional) split dose measurements of sublethal damage repair can be made