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Biomedical subjects

R L Fleischer

Publications and source records attributed to R L Fleischer.

At least 19 recordsLinked to original sources
PubMed2001

Personal radon dosimetry from eyeglass lenses.

Eyeglass lenses are commonly composed of allyl-diglycol carbonate (CR-39), an alpha-particle detecting plastic, thus making such lenses personal radon dosemeters. Samples of such lenses have been obtained, etched to reveal that radon and radon progeny alpha tracks can be seen in abundance, and sensitivities have been calibrated in radon chambers as a primary calibration, and with a uranium-based source of alpha particles as a convenient secondary standard. With one exception natural, environmental (fossil) track densities ranged from less than 3,000 to nearly 70,000 per cm2 for eyeglasses that had been worn for various times from one to nearly five years. Average radon concentrations to which those wearers were exposed are inferred to be in the range 14 to 130 Bq x m(-3) (0.4 to 3.5 pCi x l(-1)). A protocol for consistent, meaningful readout is derived and used. In the exceptional case the fossil track density was 1,780,000 cm(-2) and the inferred (24 h) average radon concentration was 6500 Bq x m(-3) (175 pCi x l(-1)) for a worker at an inactive uranium mine that is used for therapy.

Eyeglasses↗
PubMed2001

Uncertainties in retrospective radon exposure of glass: possible effects of hydration and of leaching.

Embedded 210Pb in glass results from exposure to 222Rn and its prompt decay products and is used to estimate integrated, retrospective radon exposures for times up to the 32-y mean life of 210Pb. Certain established uncontrollable factors lead to rather large scatter in the results. We review briefly the known sources that contribute to this scatter and then point out that effects of water and, in particular, hydration layers on glass are probably further sources of error, possibly of major importance, but subject to straightforward checking to reject glass compositions that are unreliable.

Diffusion↗
PubMed2001

Hiroshima neutron fluence on a glass button from near ground zero.

A decorative glass button that was uncovered at a location that is 190 +/- 15 m from directly beneath the atomic explosion at Hiroshima on 6 August 1945 has been scanned for induced fission tracks produced mostly by the thermal neutrons from the bomb due to interactions with the trace uranium that is normally present in silicate glasses. In surveying 4.14 cm2 at 500x magnification, 28 tracks were seen. From a calibration irradiation in a nuclear reactor we infer that the neutron fluence in 1945 was 5.7(+/-1.1) x 10(11) cm(-2); and, allowing for shielding by the structure in which the button was probably located, the free-air (i.e., outside) value is estimated as 1.5(+/-0.5) x 10(12) cm(-2). A limit has been placed on possible fading of the radiation-damage tracks that could increase the fluence by at most a factor of 1.27. The values bracket the calculated value of 9 x 10(11) given in DS86 but are higher than the 3.6 x 10(11) inferred from induced radionuclides for the distance given. The difference is, however, within the observed variability of the two types of results.

Glass↗
PubMed2000

Eyeglass lenses for personal radon dosimetry.

Eyeglass lenses are commonly composed of allyl-diglycol carbonate (CR-39), an alpha-particle detecting plastic, thus making such lenses personal radon dosimeters. Samples of such lenses have been etched to reveal that radon and radon progeny alpha tracks can be seen in abundance, and sensitivities have been calibrated in radon chambers as a primary calibration and with a uranium-based source of alpha particles as a convenient secondary standard. Natural, environmental (fossil) track densities ranged from 3,000 to 25,000 cm(-2) for eyeglasses that had been worn for various times from 1 to nearly 5 y. Average radon concentrations to which the wearers were exposed are inferred to be in the range 20 to 130 Bq m(-3) (0.5 to 3.5 pCi L(-1)). Procedures for consistent, meaningful readout are described.

Air Pollutants, Radioactive↗
PubMed1992

Permeability of caulking compounds to 222Rn.

Caulking compounds have been tested as 222Rn barriers. Of these, the most effective is GE acrylic Latex Silicone Caulk, 0.2 cm of which attenuates 222Rn by 98% to 99.9%. The same thickness of two commercial 222Rn barriers attenuates radon by 75% to 90%. Permeabilities range from 0.3 to 140 x 10(-8) cm2 s-1.

Air Pollution, Indoor↗
PubMed1985

Field and laboratory tests of etched track detectors for 222Rn: summer-vs-winter variations and tightness effects in Maine houses.

Effects of tightness of homes and of bedrock character on indoor 222Rn concentrations were sought in 70 homes in the state of Maine by means of four 6- to 8-month-long surveys over a 1.5-yr period. Laboratory experiments were also performed that document the reliability of the track etching system used for the measurements. In this survey the Rn in tight homes was on the average 3.5 times that in drafty ones, and areas with granitic bedrock led to homes having 2.3 times the Rn as for homes on chlorite-biotite-rich bedrock. Winter-to-summer ratios ranged from 0.5-7, and averaged 1.5, implying that surveys of individual homes require a full year of monitoring.

Air Pollutants↗
PubMed1984

Indoor radon measurements in the New York Capital District.

Radon-222 concentrations have been measured in 21 "energy-efficient" homes and 14 conventional homes in the New York Capital District. Usual concentrations are averaged over six-month or 12-month periods using solid-state track detectors. Full-year averages are available for 23 of the homes, and the winter-to-summer variations have been observed. In a number of cases, 222Rn emanations from various construction materials and soil samples have been measured and correlations sought with indoor 222Rn. Two major patterns emerge. The living areas of the energy-efficient homes without heat-storage masses have median radon concentrations that are 1.6 times those for conventional homes, and the energy-efficient homes with heat-storage masses have four to five times the 222Rn of conventional homes.

Air Pollutants↗
PubMed1984

Passive measurement of working levels and effective diffusion constants of radon daughters by the nuclear track technique.

Measurements were made of working level ratios and the effective diffusion constants of radon daughters using a special housing designed to provide a uniform diffusional environment at the passive detectors. For 2 of 7 exposures, the measured scale of the diffusion was too large to satisfy the uniformity requirement. For the other 5, it was satisfied and reasonable working level ratios (WLR) were obtained. Such a housing could be used for extended area working level measurements but is too bulky to be suitable for personnel dosimetry. Personnel dosimetry could be done in mines using a passive area measurement of WLR combined with individual passive 222Rn measurements.

Bismuth↗
PubMed1984

Theory of passive measurement of radon daughters and working levels by the nuclear track technique.

A theoretical basis is described for long-term measurement of the activities of the alpha emitters in air by the track-etching technique. Inference of the other activities allows working levels to be derived. A set of absorber foils allows the differing response to alpha particles of different energies to be used to identify the relative abundance of the alpha emitters and the importance of diffusion to surfaces. The method is appropriate to measuring long-term exposures to radon atmospheres in homes or mines.

Air Pollutants↗
PubMed1984

Personnel neutron dosimetry using particle tracks in solids: a comparison.

Comparison of two nuclear track methods of dosimetry for fast neutrons shows similar uncertainties for manual counting of etched tracks as for electrochemical read-out by a commercial service. The standard deviation is approximately 30% under rigorous specification of conditions, i.e. monoenergetic neutrons and minimum neutron scattering. Because this or greater uncertainty is common to most methods, such doses should not be quoted to higher precision.

Fast Neutrons↗
PubMed1983

Indoor radon levels in the northeastern U.S.: effects of energy-efficiency in homes.

The expectation of elevated 222Rn levels in modern homes that have low air interchange rates with the out-of-doors caused us to survey both solar and conventional homes in northeastern New York State. The solar homes as a group have three times the 222Rn levels of the conventional homes, and specific problems exist that are introduced or exaggerated by modern construction. For example the highest two levels of radon in the solar homes give radiation doses over 30 yr that are known to produce lung cancer in 1% of uranium miners. Summer readings in more than half of the cases are different from winter ones by a factor of two or more, so that year-round measurements are necessary for precise dosimetry. The track etching technique is ideally suited for such measurements.

Climate↗