The activity of radon daughters in high-rise buildings.
Abstract Forty measurements are reported in similar rooms in two high-rise buildings. The geometrical means for the concentration of radon daughters including and excluding the basement results, respectively, were 0.90 and 1.00 mWL, which is less than the quoted mean 2.0 mWL for 65 measurements in typical houses in the same city. The frequency distribution of these measurements shows a log-normal distribution. The concentrations did not depend on the distance from ground level but may depend on the ventilation rate of the room examined. The correlation between the concentration of radon daughters in WL in rooms above the first floor in the two high-rise buildings with the inverse of their ventilation rate were 0.73 and 0.67, respectively.
NATURAL RADIATION IN THE URBAN ENVIRONMENT.
Natural radiation is the largest source of population dose and is important as a base line with which'radiation· protection standards may be compared. III this article preJ!i~us work on natural background radiation levels is summarized, and some new data from Boston, Mass., are reported. Gamma dose rates, corrected for cosmic radiation, were measured with large ionization chambers: dose rates inside wooden single· family dwellfngs were 25 to 50% lower than tJlOse outside; in masonry l11ulti,'Jle-family dwellings, they 'were about 10% lower. Concentrations of radon, daughters in the air were *Donovan B. ,Yeates is presently studying for his doctorate at the University of Toronto in the Department of Medical Biophysics. After receiving ail undergraduate degree from Perth Technical College, Perth, Western" Australia, he read for a Master of Science degree in radiation p,l'Otection' at the University of Surrey, England. Following graduation with distinction, he won a Rotary A ward for Technical Training that supported a year of stwdy as, a Research Fellow at the Harvard School of PUblic' lIealtll, during which time he collaborated on the preparation of this paper. tDr. Abrahani S. Golclin has been an Associate Professor of Radiochemistry '.at the H(!IVard Scho,ol of Public Health since 1968. Before that he was ,with the U. S. Public Health Service from 1951, with major responsibilities in the development of analytical methodology for environmental radionuc1ides. For much of this time, he was responsible for validation of analyticalresuIts in Public Health Service environmental surveillance programs: :j:Dade W. Moeller is Associate Director of the Kresge Center for Environmental Health, Harvard School of Public Health. Prior to taking this ,position, he was a commissioned officcr in the U. S. Public Health Service and served as Officer in Charge of the Northeastern Radiological Hcalth Laboratory (1961-1966) and as Chief, Radiolog!cal Health Training Activities, Robert A. Taft Sanitary Engineering Centcr (1957-1961). He currently serves as a lllt'mber of the NaHanal Council on Radiation Protection and Measurclllcnts and is the most recent Past President of the mitional Health Physics Society. He received his Ph. D. degree in nuclear engineering from North Carolina State University. measured by predecay and postdecay alpha spectrometry: concentrations in dwellings were compar.able with outdoor concentrations, but concentrations in basements were higher by a factor of about 5. Concentrations in office buildings were quite low, the radorz daughters being" removed by tlie venti/a· 'tion system. Effects of building type, construction materials, and ventilation on human dose are discussed, as are possible ways of reducing population dose. Radiation of natural origin is widely recogniz~d as the largest source of human exposure to ionizing radiation. Natural. radiation is generally considered to contrib,ute a dose equivalent of 80 to 200 mrems/year to peo+1.le in the United States.! This may be cO!]Jpared with the genetically significant dose·equivalent average of 55 mrems/year2 from medical radiation !lind of less than 5 mrems/year from all other man-made radiation sources. 1 Note Addrrd in Proof' A genetically Significant dose from medical radiation of 36 mre~s/year waS reported .from a 1970 survey at the 49th annual meeting of the American Congress of Radiology, Miami Beach, Fla., Apr. 6, 1972, by R. Brown, R. R. Fuchsberg, and J. N. Gitlin in "Preliminary Dose Estimates from the U. S. Public Health Service 1970 X-Ray Exposure Study:"] The natural radiation to which man is exposed in the United States has not yet been delineated in detail; how~ver, it seems that such a description is ne,cessary as a basis for the evaluation of the significance of man-made increments to radiation exposure. Presented in this article is a preliminalY report of a study to determine the feasibilify of establishing the dose of natural origin and ~f c~ploring possible:rnethods for its reduction. Sources of natural oJigin include cosmic C radiation, radiation from naturally o,c,curring radionuclides in the earth or in materials in man's immediate NUCLEAR SAFETY, Vol. 13, No.4, July-August 1972 , 276 GENERAL SAFETY CONSIDERATIONS environment, and radiation from radionuclides within the body: However, for purposes of this study, naturally occurring sources were considered only if they had not been intentionally concentrated. Thus masonry materials were included, whereas such sources as uranium mill tailings, radium dials, and medical radium sources 'were omitted. Also included is a review of previous measurements of natural-radiation doses supplemented by measurements of cosmic-radiation doses, terrestrial gamma doses inside and outside various buildings, and concentrations of radon,daughter products in the air.
Compressive and flexural properties of hemp fiber reinforced concrete
The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.