fee Cl cb iota bab i ods whaee de dhahad s elieehsLeaiaae 76 b Power function slope (due to diminution }. r Rate constant of final exponential (turnover rate of cortical bone), Excretory plasma clearance in gca/day (liters/ daytimesgo,/liter). nh lie k o ti, T 8. Manson, J. 2). and Waters, N. E. Assessment Osteon Maturation Rate in the Dog. Arch. Ora: 1577-1591 (1967). 9. Lee, W. R. Appositional Bone Formation in Cai A Quantitative Microscopic Study Using Tet Markers, J. Anaf. (London) 98, G65 (1964). Crossover time (the time at which bodyspecific 10. Marshall, J. W., Rowland, R. E., and Jowsey, J. Mi Endogenous excretion rate (ge,/day). 197-270 (1959). li. Rowland, R, E, Exchangeable Bone Calcium. activity B equals plasma specific uctivity 3S). Ratio of the turnover rates of trabecular to cortical bone (by apposition-resorption). Time at which falling Vz = B (crossover of trabecular and bodyspeeific aetivity). Fraction of skeleton that is trabecular bone (by calcium content). REFERENCES 1. Lloyd, E., Rowland, R. E., Hodges, D., and Marshall, J. H. Surface-to-Volume Ratios of Bone Determined by Computer Analysis of Microradiographs. Na/ure 218, 365 (1968). 2. Marshall, J. H. Measurements and Models of Skeletal Metabolism. Mineral Metabolism, Ed. C. Comar and F. Bronner. Academic Press, New York, 1969, Vol. JIT, pp. 1-122. 3. Marshall, J. H. The Retention of Radionuclides in Bone. Delayed Effects of Bone-Seeking Radionuclides, Ed. C. W. Mays, W.58.8. Jee, R. D. Lloyd, B. J. Stover, J. H. Dougherty, and G. N. Taylor. University of Utah Press, Salt Lake City, 1969, pp. 7-26. 4+. Marshall, J. H. Mieroscopie Metabolism of Calcium in Bone. Bone as a Tissue, Ed. K, Rodahl, J. T. Nicholson, and I. M. Brown, Jr. MeGraw-Hill, New York, 1960, pp. 144-155. 5. Marshall, J. H. Theory of Alkaline Earth Metabolism. The Power Function Makes Possible a Simple but Comprehensive Model of Skeletal Svstems. /. Theoret. Biel. 6, 386 (196-4). 6. Marshall, J. H. and Onkelinx, C. Radial Diffusion and Power Funetion Retention of Alkaline Earth Radigiso“I topes in Adult Bone. Vature 217, 742 (1968). . Manson, J. D. and Waters, N. E. Maturation Rate of the Osteon of the Cat. Naéure 200, 489 (1963). Metabolism of Calcium in Bone, I.-V. Radziai. thoped, 49, 233 (1966). 12. Heaney, R. P. Evaluation and Interpretationof Kinetic Data in Man. Clin. Orthoped. 31, 153 (1 13. Ellsasser, J. C., Farnham, J. E., and Marshall, J. parative Kinetics and Autoradiography of Ba™ in Ten-Year-Old Beagle Dogs. Argonne Laboratory Radiological Physies Division An port, July 1967 through June 1968. ANL-7489. p 14. Rowland, R, E. and Leuer, C. J. An Evaluation ¢. complete Gamma Function Over a Range of Bic Significant Values. Argonne National Laborator. logical Physics Division Semiannual Report, J June 1961. ANL-6398, pp. 24-35. 15. Rowland, R. E., Marshall, J. H., and Jowsey, J. in Human Bone: The Microradiographie App Radiat. Res, 10, 323 (1959). 16. Rowland, R. E. and Marshall, J. H. Radiumin Bone; The Dose in Microscopie Volumes of Bone Res. 11, 299 (1959). 17. Evans, R. D. The Atomic Nucleus, MeGraw-tli York, 1955, p. 479. 18. Jowsev, J., Kelly, P. J., Riggs, B. L., Bianco, A. J. D. A., and Gershon-Cohen, J. Quantitative radiographic Studies of Normal and Osteoporot J. Bone Joint Surg. 47-A, 785 (1965). 19, Villanueva, A. R., Ramser, J. R., Frost, H. M., A A. Tt., Frame, B., and Smith, R. W. TetracyclinQuantitative Measurements of the Tissue a Dynamics in 10 Cases of Osteoporosis. Clin. Ortho 203 (1966). 20. Lloyd, E. Non-Uniformityin the Retention of the .* Earths in Animals and Man. This report. 21. Keane, A. and Evans, R. D. Massachusetts Insti Technology Report 952-5, Part II (1968), p. S10. IMPROVED CONSTRUCTION OF RADIOACTIVE PHANTOMS WITH ARBITRARY SOURCE DISTRIBUTION* Harold May, L. D. Marinelli, and Paul Hess venient. whereas the use of loaded lattices offers simplification and use of a “library” of simulated and economical “organs.” * Presented orally at the 14th Annual Meeting of the Health Physics Society, June 8-12, 1969, Pittsburgh. A wide variety of devices has been used to sin the humanbodyandits internal organs for the pi of calibrating the response of radiation detection « ment. This variety is primarily the result of v: requirements upon the accuracy with whichthe pk: dimensions and atomic properties of the body ; wh active and inactive beads are perhaps most immediately con- INTRODUCTION tn ke The substitution of beads or pellets instead of liquids is proposed for the convenient loading of radioactive phantoms. An analysis of the general problem suggests that mixtures of