Merril Eisenbud

Alpha radioactivity in cigarette smoke

The ..cap alpha.. activity of cigarette smoke tar deposited onto membrane filters was found to be associated with the relatively insoluble fraction. Perfusion of the tar with physiological saline resulted in no change in the mean measured activity, but there was more variability in the measured values for the perfused tar than for the initial tar samples. Analysis of cigarette smoke condensate shows that radium and thorium are present, but over 99% of the ..cap alpha.. activity results from /sup 210/Po. Repeat measurements after a time lapse of 2 1/2 years indicate that the initial /sup 210/Pb content of the tar is roughly 30 to 40% of the original /sup 210/Po content for both unprocessed and perfused samples. An increase in the ..cap alpha.. activity concentration of smoke deposited in lung tissue may result from the lack of solubility of the radioactive material compared with other smoke constituents.

Distribution of polonium-210 in the human lung.

Polonium-210 has been measured in the tracheobronchial tree and parenchyma of cigarette smokers and nonsmokers in order to determine whether this ..cap alpha.. emitter is retained in smokers. The ratio of /sup 210/Po concentration in the tracheobronchial tree (T) to that in the lung parenchyma (P) in nonsmokers is T/P = 2.7 +- 0.5. The ratio in smokers is T/P = 1.1 +- 0.2. The difference in these ratios can be related to retention of /sup 210/Po, or its /sup 210/Pb precursor in the parenchymal tissue. About 5 pCi deposited and retained on alveolar surfaces and an average excess of 0.3 pCi /sup 210/Po retained on the tracheobronchial tree is estimated for smokers. Measurements in exsmokers result in a ratio (T/P) = 0.8 +- 0.4 and is possibly related to long-term retention of deposited /sup 210/Pb in alveolar tissue.

Measurement of the Alpha-radioactivity on the Mucosal Surface of the Human Bronchial Tree

A new technique has been developed to measure ultra low a-activity on the bronchial mucosa of human lung specimens using cellulose nitrate track etch film as the detector. The lower limit of detection of this system for a single film is 0.30 fCi/cm2 when the detector is exposed to about 1 cm2 of bronchial surface for 100 days and an average efficiency factor is used. Measurements to determine the a-activity along the bronchial mucosa were made in seven individuals. A few areas of slightly elevated activity were measured in each of the lungs examined except for that of a young smoker. One area of markedly elevated activity (180 fCi/cm2) was measured in the lung of an older smoker. The mean mucosal surface activity for an individual is determined from a large number of airway samples. The means ranged from 0.01 ?0.06fCi/cm2 for a young smoker to 0.26 i 0.04 fCi/cm2 for an older smoker. The mean value for a nonsmoker was 0.02 2 0.06 fCi/cm*. The average dose rates to the basal cells of the bronchial epithelium from the a-activity estimated for each of these seven individuals range from 0.1 to 2.0 mrad/yr. The small area of elevated activity (180 fCi/cm2) could deliver an annual dose of approx. 1 rad. However, total dose cannot be calculated since the residence time of any of these areas on the bronchial tree is unknown. The risk from these dose rates is evaluated in terms of the lung cancer experience of underground miners.

In vivo measurement of lead-210 as an indicator of cumulative radon daughter exposure in uranium miners.

The accumulation of lead-2 10 in the human skeleton can be measured in uranium miners by in vivo techniques at body burdens greater than about 4 nCi using transportable equipment designed to detect the 47 keV gamma-ray from this nuclide. A burden of two nanocuries is shown to be equivalent to a calculated cumulative exposure of about 800 workinglevel months. The instrumentation utilizes the Laurer system of twin crystal gamma spectroscopy in which an 8 in. x 1 mm cesium iodide crystal is optically coupled to an 8 in. x 2 in. sodium iodide crystal and is operated in anti-coincidence on a single photomultiplier tube utilizing the principle of rise-time discrimination. The method of measuring aloPb used and the equations used to estimate the cumulative exposure in working-level months are presented, with an evaluation of the uncertainties and the extent to which the estimates can be improved by additional experimental data. The results of field measurements undertaken on the Colorado Plateau showed that, among 37 control subjects with no history of employment in mines, only one individual had counts in excess of two sigma above the mean in the 47 keV region. In contrast, 26 out of 54 mean with uranium mining histories showed counts greater than two sigma above the mean.

THE NATURAL RADIATION DOSE TO INDIGENOUS RODENTS ON THE MORRO DO FERRO, BRAZIL

The feasibility of studying the dose from natural radioactivity received by indigenous rodents in remote areas has been demonstrated on the Morro do Ferro, a large hill in Minas Gerais, Brazil. The abnormally high ambient gamma radiation, 1 m above the ground, ranges from 0.05 to 3.2 mR/hr, and is due to the presence of thorium in the soils and rocks. Estimates were made of the dose from external gamma radiation, internally deposited 22aRa and 228Ra, and inhalation of z20Rn, 22zRn and their daughter products. The techniques used to obtain these data in the field and laboratory are described. External gamma exposure was measured by releasing trapped rodents into which fluoroglass rod dosimeters had been implanted subcutaneously. The dosimeters were remtoved after retrapping about 5 weeks later and indicated that the average dose over a several week period ranged from 0.15 to 0.76 mrad/hr, equivalent to 1.3-6.7 rad/yr. The bone dose from zzsRa has been estimated by radiochemical analysis, the preliminary results of which indicate concentrations of 0.7 to 2.8 pc/g bone ash leading to a dose in the order of 3 remlyr. Estimates of the dose from inhalation of the radioactive noble gases were made using field measurements of the z2zRn and z20Rn content of air aspirated from rodent burrows. I t was found that the 220Rn concentrations vary from near normal levels to 10“‘ ,uc/ml. The problems involved in calculating the dose to the lung and other organs from 2zoRn and Zz2Rn inhalation are discussed and preliminary data are given. Using alternative methods of calculation, the dose to the lung tissues is estimated to be in the range of 3 x lo3 to 3 x lo4 remlyr.

Monitoring distant fallout : The role of the Atomic Energy Commission Health and Safety Laboratory during the pacific tests, with special attention to the events following BRAVO

The fallout from test BRAVO in March 1954 has had scientific, political, and social implications that have continued for more than 40 years. The test resulted in serious injury to the people of the Marshall Islands and 23 men on a nearby Japanese fishing boat. Prior to BRAVO there was insufficient appreciation of the dangers of fallout to people living downwind from surface or near-surface explosions of megaton weapons. In the absence of sufficient preplanning for fallout monitoring beyond the test-sites of earlier smaller yield tests, and as a result of the concern of the photographic film manufacturers, the Atomic Energy Commission Health and Safety Laboratory, now the Department of Energy Environmental Measurements Laboratory, was requested to develop a program of fallout surveillance. Beginning with Operation IVY in 1952, these surveys included aerial monitoring of the islands of the mid and western Pacific, as well as establishment of fallout monitoring stations in the United States and abroad. The first evidence of the post-BRAVO fallout was detected by a Atomic Energy Commission Health and Safety Laboratory instrument installed on the atoll of Rongerik, where 28 military personnel were stationed. The results of radiation surveys conducted immediately after BRAVO, as well as the reports of medical investigations, radioecological studies, and dose reconstruction that have been conducted by many laboratories over the years have been available from the beginning in unclassified form. However, from the time of the fallout, and continuing to the present, there have been many unanswered questions about what happened during the hours immediately after the fallout was reported. No formal investigation of the circumstances of the fallout was ever conducted, and there were serious misrepresentations of the facts in the official statements made at the time.

REDUCTION OF RADON DAUGHTER CONCENTRATIONS IN MINES BY RAPID MIXING WITHOUT MAKEUP AIR.

Measurements of radon daughter concentrations and their relative states of equilibrium were made in closed sections of two uranium mines to investigate the removal of radon daughters from the atmosphere by rapid mixing. Recirculation of the air within the enclosed space once per minute reduced the working level by a factor of 20. This reduction was associated with extreme disequilibrium among the radon daughters. The lowest ratio observed between Ra-A and Ra-B was 0.06. In this sample Ra-C was not measurable. The mechanism involved may be convective or turbulent diffusion to the walls of the mine. Because the atmosphere sampled became extremely clean ( < 200 particles/cc measured with a condensation nuclei counter) the diffusion constant was probably that associated with free atoms. The state of equilibria measured indicates that removal of Ra-B and Ra-C was more efficient than that of Ra-A, probably because the Ra-B and Ra-C have longer mean lives. I t appears that with adequate stirring it may be possible to remove radon daughters from mine atmospheres without the introduction of burdensomely large amounts of fresh air. These results may not be applicable to atmospheres with higher particle concentrations. These results strongly suggest that further research should go into methods of ventilation in which large amounts of makeup air are not required.

PULMONARY DOSE FROM

The Morro do Ferro, a hill in the State of Minas Gerais, Brazil, is characterized by natural levels of ionizing radiation that are the highest reported of any natural habitats. The external radiation levels range from 0.1 to 3.2 mR/hour. The average concentrations of220 Rn and

sup 220

{}^{212}{\rm Pb}

Rn RECEIVED BY INDIGENOUS RODENTS OF THE MORRO DO FERRO, BRAZIL.

in rodent burrows are 27 nCi/liter and 23 pCi/liter. Because the dose to pulmonary tissue is highly dependent upon the metabolic fate of inhaled