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Chronic pain following partial nerve injury that is associated with objective signs of conduction loss presents few diagnostic difficulties. However, diagnosis of patients who present with diffuse symptoms in their limbs of unknown etiology is often a problem. Recent animal and human experiments suggest that diffuse painful symptoms may be a consequence of relatively minor nerve injuries in which signs of changed nerve function are not initially apparent. This paper reviews the experimental evidence that describes the rather surprising morphological and physiological consequences of such injuries and relates them to human studies on neuropathic pain. These studies demonstrate that pain and changed somatosensory thresholds may occur following relatively minor axonal damage and even nerve sheath inflammation when no axonal damage is present. It is proposed that in many patients with diffuse limb pain there may be a contribution from nerve injury, i.e. a neuropathic component. This has implications for treatment of these conditions. Manual techniques and exercises to relieve compressive effects and restore normal neural dynamics should be effective in the management of these conditions.

Measurements have been made of the relative ionization in small air-filled condenser chambers of graphite, copper, tin, tantalum and lead, exposed to 60Co, 137Cs and 198Auradiations. The variation of ionization with pressure between about 5 and 76 cm of Hg for these chambers and radiation sources was also investigated.In general the results agree well with the Spencer-Attix theory of cavity ionization, but there remain some small differences which are attributed chiefly to the cavity distorting the electron spectrum crossing it.

The ionization chamber measurements of other workers at low pressures have indicated (i) that the measured current is in excess of that to be expected on the Bragg-Gray theory; (ii) that there is a residual current even at sensibly zero pressure; (iii) that the gradient of the ionization-pressure curve at low pressures is less than that at atmospheric pressure, and (iv) that the saturation curves of chambers at low pressures are often grossly asymmetrical. Effects (i) and (ii) are attributed to the deflection by the chamber voltage of slow electrons emitted from the chamber walls. Expressions are derived for te number of electrons deflected between plane, spherical and cylindrical electrodes. The numbers of electrons emitted/cm2/r deduced from ionization chamber measurements are found to agree, within a factor of 2, with the corresponding numbers derived indirectly from other data, and are approximately 5 × 105/cm2/r and 1 × 106/cm2/r for graphite and elektron metal respectively irradiated by radium ? rays. The approximate energy distribution of these slow electrons is indicated. Effect (iii) is attrributed to the difficulty of achieving saturation without producing ionization by collision. At low chamber volts some ions have sufficient energy to reach the electrode of the same polarity. Effect (iv) is attributed to differences in electrode areas and the asymmetry of the electric field between te electrodes. An example of a calculated saturation curve is given for spherical electrodes. Finally it is suggested that similar effects would occur at atmospheric pressure in chambers having extremely small electrode separations.

A description is given of some measurements of the effective wavelength of the total and primary radiation reaching depths down to 15 cm. in a water phantom irradiated by beams of X rays. The effective wavelengths are determined by measuring the ratio of the ionizations in an “air-equivalent” and an aluminium lined chamber using a modified Kemp comparator, for which a new method of calibration is described. These measurements have been made for four primary radiations of H.V.L.s ranging from 0·49 to 2·4 mm. Cu, and for field areas up to 580 sq. cm. at 50 cm. F.S.D. From these measurements the wavelength of the scattered radiation is deduced and qualitative explanations of the phenomena observed are offered. The significance of the results for the conversion of doses measured in r to doses measured in ergs/gm. are pointed out and some applications to the case of bone are given.

Recent developments in radiological physics are briefly reviewed and an attempt is made to extrapolate these forward in time. The author expects to see (1) the establishment of a much more satisfactory data base in radiological physics; (2) a clarification of concepts in radiation protection; (3) the demise of the present special radiological units and their replacement by SI units; (4) the establishment of calorimetric standards of absorbed dose; (5) a decrease in the use of the quantity exposure; (6) further development of condensed state dosimetry in general and solid state dosimetry in particular; (7) neutron dosimetry more closely approaching the accuracy of photon dosimetry; (8) more use of computers and radiations other than photons in radiotherapy; (9) the growth of quantitative measurement in radiological diagnosis; and (10) greater use of radiological physics in the determination of body composition.

A parallel-plate vacuum chamber is described and the theory of its use as an electron energy spectrometer is given. The spectra of low-energy (up to about 10 eV) electrons both liberated within and emitted from sheets of copper, aluminium and graphite irradiated by 250 kV X rays, are derived under various assumptions of angular distribution. The total emission of low-energy electrons is found to be 1·63, 1·74 and 1·28 coulombs per rad cm2for copper, aluminium and graphite respectively, when irradiated by X rays having energies, based on HVTs in copper, ranging from 60 to 156 keV. Comparison is made with values of energy dissipation density derived from secondary electronemission studies. An explanation is advanced to account for the negative slope of the current-voltage characteristic of the spectrometer and similar devices at high bias voltages.

Part I considers methods of deriving and specifying approximate X-ray spectral distributions if either the time or facilities are not available for obtaining complete spectra. Tables are provided which simplify the representation of an X-ray beam by three monoenergetic components when the transmission curve of the radiation in a suitable absorber is known. In another approach three components are fitted graphically to the attenuation data. The various methods are compared.Part II considers the amount of information regarding an X-ray spectrum which can be derived from the various forms in which radiation quality may be expressed. The specifications examined are: (i) HVT only, (ii) HVT and kilovoltage, (iii) first and second HVT, (iv) first and second HVT and kilovoltage, and (v) full attenuation curve and kilovoltage. From these are derived representations by means of one, two or three monoenergetic components, and by approximate or accurate spectral distributions. The various methods are compared with each other and with those of Part I.

A free-air chamber is described which embodies a new field-guarding method, due to Kemp, not previously applied to practical free-air chambers. A compact design is achieved which facilitates the use of the chamber for the direct measurement of “in-air” outputs of X-ray units operated under clinical conditions. The design factors of the instrument and its performance are discussed.

Five thimble ionization chambers were compared with a free-air chamber using X rays produced at 20 to 55 kV with half-value layers between 0·05 and 0·20 mm Al. One chamber showed a difference of nearly 4 per cent in its correction factor for beams of the same H.V.L. produced at 20 and 55 kV. With this single exception H.V.L. appeared to be an adequate criterion of X-ray quality for the calibration of ionization chambers.

Consideration is given to the choice of the formula which best describes recombination between parallel plates. This formula is modified so that it may be applied to free-air ionization chambers. The modifications entail determining (i) the effective width of a circular cross-section X-ray beam, (ii) the effect of space charge and (iii) the effect of ion spread and distribution. The modified formula is checked experimentally with a small free-air chamber by varying field strength, dose-rate, beam quality and size and shape of the X-ray beam. Good confirmation is obtained.