Table of contents

Users of nuclear and atomic data for biomedical purposes often have difficulty in identifying the most up-to-date and appropriate sources of such data. The Biomedical Subcommittee of the UK Nuclear Data Committee have prepared a list of recommended data sources available at the beginning of 1978 on radioactive decay schemes; neutron cross-sections and data for neutron activation analysis; excitation functions for the production of radionuclides by charged particles; W-values for neutron and electron dosimetry; X- and gamma-ray cross-sections; stopping powers and ranges for charged particles; and dose deposition by electrons and beta particles.

A rapid system has been developed for computing charged-particle distributions generated in tissue by any neutron spectra less than 4 MeV. Oxygen and carbon recoils are derived from R-matrix theory, and hydrogen recoils are obtained from cross-section evaluation. Application to two quite different fission-neutron spectra demonstrates the flexibility of this method for providing spectral details of the different type of charged-particle recoils. Comparisons are made between calculations and measurements of event-size distributions for a sphere of tissue 1 mu m in diameter irradiated by these two neutron spectra. LET distributions have been calculated from computed charged-particle recoils and also derived from measurements using the conventional approximation that all charged particles traverse the chamber. The limitations of the approximation for these neutron spectra are discussed.

An expression relating the constant A to the characteristics of an ionisation chamber is developed. This constant, used to obtain the mass ionisation from the instrument reading, appears in expressions for C_E and C_lambda , and is a function of the chamber wall material. Measurements with a Baldwin-Farmer chamber are described, and indicate that the effective wall material is more nearly equivalent to Lucite than to air in ⁶⁰Co gamma radiation. The resulting value of A is nearly 1.5% lower than the figure commonly used.

The maximum permissible fluence is proposed as a practical concept in radiological monitoring of photon fields. It is virtually this concept that is used for monitoring neutron fields. The practicability of designing instruments with a required response function over a large energy range is examined. Cavity ionisation theory is employed to examine the effect of gas filling, wall material, chamber size and wall thickness on response function and the optimum parameters for the design of an ionisation chamber are thus identified. An experimental chamber of parameters close to the optimum has been constructed and its response compared with the response calculated from cavity ionisation theory. It is concluded that it is possible to design an instrument, the energy response of which follows the maximum permissible fluence. The approach and data given will facilitate any necessary design changes which would arise in the event of national regulations being modified.

In an earlier publication (Green, Major (1974)), an expression was derived for the sensitivity of a carbon-walled, carbon dioxide-filled ionisation chamber, for low-energy neutrons. This expression has been extended to allow its use for high-energy neutrons, and has been used to make detailed calculations for a particular ionisation chamber irradiated with either 15 MeV or 5.5 MeV neutrons. The results of these calculations are compared with experimental values and, within the stated limits, reasonable agreement is obtained.

The effect of storage on the lyoluminescence response of mannose was investigated and the dependence of the change in response on absorbed dose determined. It was found that for doses greater than the saturation value, there was an enhancement of response on storage. The hypothesis that the local concentration of oxygen near the free radical sites in the irradiated mannose is a determining factor in lyoluminescence response is postulated and discussed.

The energy response of lithium fluoride (LiF) thermoluminescent dosemeters has been determined at two temperatures. Glow peaks 3, 4, and 5 are measured at 240 degrees C and peaks 6 and 7 at 300 degrees C. In studying the response to X-radiation it was observed that the response of LiF chips to photons below 150 keV is greater, relative to cobalt-60, than that expected from the energy absorbed in the material. There is an enhancement of 10% at 240 degrees C and of about 100% at 300 degrees C for the same energy absorption. This effect is particularly important where precise measurement of X-ray dose is required and corrections of from 10 to 15% above the correction from rads in LiF to rads in water will be necessary depending upon the maximum read-out temperature. Qualitatively the enhancement may be explained in terms of the higher mean rate of linear energy transfer at low photon energies relative to cobalt-60 gamma rays.

The author investigates how one can estimate the total attenuation, p, of a polyenergetic X-ray beam what the total attenuation, m, of a monoenergetic beam would have been along the same ray. He finds that for beams with typical diagnostic X-ray spectra passing through the human body one can find a simple function f such that f(p) is a sufficiently close estimate of m to allow good reconstructions. He also finds that m cannot be accurately estimated from p based on the assumption that the human body consists of water alone. The author's results are demonstrated by reconstructions of a mathematical model of a cross-section of the human thorax. The article is self-contained and includes in its Appendices a detailed discussion of the mathematical nature of the problem of beam hardening in computed tomography.

A simple mathematical model has been developed which is able to fit the impedance waveform produced by normal and abnormal subjects throughout the cardiac cycle with reasonable precision. Contributions from both the aorta and vena cava are significant. Fitted values of model parameters offer potentially useful clinical information. Estimates of the stroke volume obtained from the model correlate well with values derived from the maximum rate of change of the thoracic impedance during systole but are in poorer agreement with values obtained using tracer dilution techniques.

A technique to measure total body calcium using the ⁴⁰Ca(n, alpha )³⁷Ar reaction has been developed. The technique is based on collecting ³⁷Ar exhaled in the breath following a 10 mrad uniform total body irradiation by 14 MeV neutrons. The ³⁷Ar in the exhaled breath is extracted by selective absorption and its radioactivity is measured inside a low-background proportional detector. The facilities developed include an activation facility providing a +or-2.7% activation uniformity, a closed circuit rebreathing and gas collection system, and a gas purification and counting system. The technique provides a precision of +or-2.4% as determined by repetitive measurements of human volunteers and has an accuracy of determination of total body calcium in grams of +or-5%.

A two-component cylindrical finger phantom was constructed from silica paraffin wax and animal bone ash. The diameter of the finger bone was estimated from X-ray examinations in two orthogonal projections. The bone mineral concentration was then estimated from the quotient of the number of coherent and Compton scattered primary photons. The lead concentration in the finger bones was then derived from a measurement on a finger phantom made of silica paraffin wax and bone ash with the same size and bone mineral concentration as the real bone. The minimum detectable lead concentration in a finger bone was 14 mu g g^-1 for 15 min measuring time. The lead concentration measured in workers from a metal industry was found to be in the range of 40-100 mu g g^-1.

A practical method of assessing ultrasonic A-scan pulse-echo scanner performance is described, which relies upon the identification and quantitation of an overall system transfer function. The mapping of reflecting elements into an image is then described by this transfer function, and indices of system performance, and particularly resolution and range accuracy, are developed in terms of the shape of the transfer function. Some advantages of this method compared to more conventional methods of assessing scanner performance are discussed.

Presents simple expressions for the correction functions for convolutional techniques in three dimensional image reconstruction. The intrinsic property involved in these techniques is clarified. It is shown that the introduction of the concept of the distribution is useful to derive the ideal or practical correction functions used in convolution methods. The ideal correction functions obtained are summarised. The concept of correction function defined as the distribution may be a starting point for deriving more advanced reconstruction schemes.

A number of inadequacies in the theoretical derivation of Almond and McCray's expression for the cavity correction factor f for electron beam dosimetry (see ibid., vol.15 p.335, 746 (1970)) are pointed out. The experimental results of Paliwal and Almond (see ibid., vol.20, p.547 (1975)), which at first seemed to verify Almond and McCray's theory, are in disagreement with the present author's calculations. Almond and McCray's attempt to explain the energy response of LiF dosimeters to high energy electrons is therefore inconclusive.

Considers the recoil protons and alpha particles from (n, alpha ) events in tissue and bone, assuming no single functional form for the range energy relationship and taking into account not only the variation of stopping powers of the protons and alphas along their tracks but also their variation from one medium to another. The heavy recoil contribution is included to obtain the total dose distribution. In addition, an estimate is made of the ratio of survival probabilities of a colony of cells in the region just under the bone and in the equilibrium region. The results are presented for a 14 MeV neutron beam.

The ⁴²K technique has been used to calibrate two dissimilar whole-body counters (liquid scintillator and NaI) for total body content of potassium (TBK) measurements over a wide range of body weight (50.6-119.1 Kg). The standard error of an estimate of a TBK of 140 g is in the range of 3.0 to 3.4% for both counters and is similar to values reported for other counters (Burkinshaw (1967), Body et al. (1971), Hawkins et al. (1976)).

Describes a general method for the measurement of radioactivity in an organ using anterior, posterior and lateral views. Its application to liver colloid imaging is described as the liver/spleen ratio is widely used as an indication of cirrhosis.

Describes the authors facility which was designed and built to measure regional changes in skeletal calcium of human subjects or animals, and to measure whole body calcium in small animals. This facility employs a collimated beam of neutrons obtained from a 3 mg²⁵²Cf source. The neutrons have a fission spectrum of mean energy 2.3 MeV.

The phantom described is designed to test the performance of a scintillation camera or scanner, including the display system, investigating the resolution over a wide range of contrast levels. It has been constructed as a cold spot phantom, since in clinical practice cold lesions are usually more difficult to detect than hot ones. The phantom consists of sets of square perspex blocks of different sizes, each set of a given size having a range of heights. The whole array is enclosed in a perspex box, the depth of which is equal to the maximum height of the blocks, so that when the box is filled with a radioactive solution a range of contrast levels is available for each size.

The Farmer dosemeter is extensively used in the measurement of beams of ionising radiation generated by a wide range of radiotherapy units. To measure the dose rate under steady state conditions an electronic timer has been developed. The components are easily available and assembled at a total cost of less than Pounds 38. The timer consists of a single large-scale integrated circuit fabricated by the CMOS process. This device (Intersil ICM 7250) is dedicated to stopwatch applications and incorporates oscillator circuitry, dividers, seven segment decoders and multiplexed output via 'on chip' digit drivers. The completed instrument provides a six digit 7.6 mm high LED display.