Joseph Rotblat

I. The Age Factor in Radiation Sensitivity in Mice

The effect of age on the sensitivity of man to ionizing radiations has for many years been recognised by radiotherapists who, on a somewhat empirical basis, have planned their treatment to take this factor into account. In animal work the importance of age as a factor influencing radiation sensitivity had virtually been neglected until a few years ago. One still finds papers describing work with animals, in which the age changes are relevant to the radiation effect studied, and yet the age of the animal is not even mentioned. Such neglect can lead to misleading interpretations, particularly when the effect studied is not large. There are two difficulties in attempting to take the age factor into account in the experimental design: (a) our knowledge of the normal variation with age of form, function and composition is inadequate; (b) the obtaining of large numbers of animals of a specified age is costly and time consuming. However, in proportion to the cost of most biological experiments, this additional b...

The response of C3H mammary tumours to Irradiation in single and fractionated doses

Abstract Both spontaneous and first generation isotransplanted mammary tumours in C3H mice have been irradiated with 14 MeV electrons. Irradiation has been in one or two equal fractions, split by 24 hours, with the mice breathing either oxygen or nitrogen at atmospheric pressure during irradiation. The response of the tumours has been assessed in terms of the number of volume doublings required for the irradiated tumour to regrow to its size at time of irradiation. Using spontaneous tumours, with irradiation while the mice were breathing oxygen, it was found that a dose in two equal fractions was more effective at total doses above 3,000 rads than a single dose. Below this dose no difference in response was detected. For transplanted tumours in these conditions a small amount of recovery was observed at low doses but above 2,500 rads it was again found that two fractions were more effective. Irradiations while the mice were breathing nitrogen (i.e. severely hypoxic) were performed with spontaneous tumours...

The elastic scattering of 3He particles of energy 24–29 MeV by C, N, A and I

Abstract The elastic angular distributions of 3 He particles scattered from carbon at 26.8 MeV, 25.3 MeV and 24.5 MeV, nitrogen at 25.7 MeV, argon at 26.4 MeV and iodine at 29.1 MeV, 28.2 MeV, 26.6 MeV, 24.6 MeV and 24.1 MeV have been measured using a nuclear plate camera. Results show a pronounced diffraction oscillation in light nuclei, becoming progressively weaker in argon, leaving an approximately exponential fall-off in cross-section in iodine. In iodine a ‘rise’ in cross-section above the Rutherford value immediately before fall-off has been observed. An optical model with a diffuse surface was used to analyse these data and the best fit parameters obtained.

The Effects of High Dose Rates of Ionizing Radiations on Solutions of Iron and Cerium Salts

The electron beam generated by a 15 MeV linear accelerator has been employed to induce reactions in aerated aqueous solutions of 1 to 25 mM ferrous sulphate, and of 0⋅1 to 1 mM ceric sulphate. The radiation was delivered in pulses of 1⋅3μs duration and over a range of dose rates from 0⋅5 to 20000 rads/pulse. Radiation yields at constant dose rate were compared with the aid of a chemical dose monitor. A system of two thin, widely spaced, irradiation vessels was employed to determine the variation of yield of any one system over successive known ranges of dose rate. The yield of ferric sulphate in the iron system was found to decrease with increasing dose rate in the range 0⋅01 to 10 krads/pulse by an overall factor of 0⋅85, and was appreciably dependent on the initial concentrations of dissolved oxygen and of ferrous sulphate at high dose rates. Yields of hydrogen and of hydrogen peroxide were practically independent of dose rate. The observations have been interpreted on the basis of inter-radical reactions which occur when the reaction zones of neighbouring clusters overlap. The following reactions can account for all the data: OH + Fe2+ → Fe3+ + OH¯, (1) H + O2 → HO2, (2) H + OH → H2O. (7) The values k1/k7 = 0⋅0062, and k2/k7 = 0⋅22 are reasonably consistent with the observations. In the ceric sulphate system the yield of cerous sulphate increases progressively over the range 0⋅01 to 10 krads/pulse by an overall factor of 1⋅4. The data accord with the view that at high dose rates OH radicals react with them selves ultimately to form hydrogen peroxide, in competition with their normal reaction with cerous sulphate.

The Inactivation of Formula-Chymotrypsin by Ionizing Radiations

The inactivation of α-chymotrypsin by low-voltage X-rays and by 15 meV electrons has been studied over a range of concentrations extending from the solid enzyme to dilute solutions and the sensitivity D37/c, where D37 is the dose required to cause in activation to 37 % of the original at concentration c, determined under varied circumstances. The sensitivity is constant in air over a wide range of concentrations, but in the solid state is greater by a factor of about 7. That the enhanced sensitivity in the solid state is connected with disorganization of the secondary structure is shown by the fact that after partial inactivation by irradiation the enzyme is more sensitive to in activation by heating. This view is also supported by the finding that oxygen has no significant effect on the irradiation (with 15 meV electrons) in the solid state, since there is no reason to expect that oxygen will influence the breakage of hydrogen bonds within the molecule. The sensitivities of the protease and esterase activities of the enzyme are the same, showing that only one kind of active centre is involved. The sensitivity also decreases at low concentrations of the enzyme. That this is not due to recombination of the radicals is shown by the finding that the effect is uninfluenced by varying the dose rate of the electron beam over a very wide range. An enhanced sensitivity is, however, observed in solutions from which the oxygen has been removed. It follows that secondary radicals, principally O2H , formed in the presence of oxygen are less effective than the primary radicals. Kinetic equations are deduced which represent the main features of this behaviour. A possible reason for the greater effectiveness of H than O2H is the ability of the former to penetrate into the protein molecule. It was also found that in dilute solutions containing oxygen the electron beam is more effective than the X-rays. This could be accounted for if equilibrium between the primary radicals and oxygen is not reached at the very high dose rates at which the electron pulses are delivered. In vacuo no differences in sensitiveness to the X-rays and the electrons were observed.

Leaving the bomb project

Working on the Manhattan Project at Los Alamos was a traumatic experience. It is not often given to one to participate in the birth of a new era. For some the effect has endured throughout their lives; I am one of those.

The scattering of 29 MeV 3He-particles by 14N and 16O nuclei

The nuclear emulsion technique was employed to study the scattering of 29-Mev He/sup 3/ particles by N/sup 14/ and O/sup 16/ nuclei. Elastic angular distributions were analyzed in terms of a diffuse surface optical model; good agreement was found up to 50 deg (cms). The inelastic processes were compared with the predictions of the direct interaction mechanism. (auth)

The relative effects of direct and indirect actions of ionizing radiations on deoxyribonucleic acid

The effectiveness of ionizing radiations in damaging the DNA particle, as determined by the number of primary ionizations in the volume occupied by each particle, which is required to reduce the intrinsic viscosity to half its original value has been determined over a range of concentrations from 0⋅01 to 100%. The different specimens of DNA employed differ considerably in sensitivity, but with each specimen the number of ionizations required is approximately constant from 1 to 100%. This means that over this range of concentration an ionization occurring in the water has the same effect as one within the DNA particle. The differences of sensitivity of the different samples are probably due to traces of protein contamination and disappear at the greater dilutions. The effects were independent of the dose rate and of the hardness of the radiations within the ranges used and identical effects were obtained with electrons and X-rays.

Effects of ionising radiation on the testis of the rat with some observations on its normal morphology

The following is a brief account of an investigation into the effects of high coses of 15 MeV electrons on the testes of the rat. The right testes only of 20 rats were irradiated, the dose being 10,000 r. The rest of the body was screened and received only about 30 r. The animals were killed at intervals after irradiation (3 days to 3 weeks).

Alpha-alpha scattering at 38.5 MeV

Abstract A measurement of the angular distribution of the scattering of alpha-particles by helium at 38.5 MeV is described. The c.m.s. cross-section is 110 mb/steradian at 90°, falling to a very sharp minimum of about 0.5 mb/steradian at 64°. Approximate calculations of the phase shifts show that °0 and °2 are large and δ4 small: these results are in agreement with other evidence for levels of spin 4 at about 11 MeV and of spin 0 and 2 near to 19 MeV.