Reevaluation of the committed dose equivalent from 232Th and its radioactive progeny.

Multicompartmental models were used in ICRP Publication 30 to describe the metabolism of radioactive elements and their retention in specific organs and tissues. Despite their use of more complicated and sophisticated metabolic models than those used in its earlier ICRP Publication 2 in 1959, the ICRP assumed that the radioactive progeny of 232Th that are produced in the body metabolize like their parents in its Publication 30. This assumption was made for mathematical simplicity and out of necessity when organs and tissues named for the parent are not included in the model of the progeny. This simplifying assumption can lead to overestimates of doses to tissues, especially the critical cells on bone surfaces. More realistic metabolic models and parameter values for 232Th and its radioactive progeny have been developed to estimate the total committed dose equivalent from 232Th and all of its radioactive progeny per unit intake of 232Th only. It is believed that this research has led to (1) more realistic estimates of doses from 232Th and its radioactive progeny over any applicable period of time after an intake, (2) more appropriate derived limits, and (3) metabolic models that can be used in the design of bioassay programs.

Intake retention functions and their applications to bioassay and the estimation of internal radiation doses.

This paper describes a way of obtaining and gives applications of intake retention functions. These functions give the fraction of an intake of radioactive material expected to be present in a specified bioassay compartment at any time after a single acute exposure or after onset of a continuous exposure. The intake retention functions are derived from a multicompartmental model and a recursive catenary kinetics equation that completely describe the metabolism of radioelements from intake to excretion, accounting for the delay in uptake from compartments in the respiratory and gastrointestinal tracts and the recycling of radioelements between systemic compartments. This approach, which treats excretion as the 'last' compartment of all catenary metabolic pathways, avoids the use of convolution integrals and provides algebraic solutions that can be programmed on hand held calculators or personal computers. The estimation of intakes and internal radiation doses and the use of intake retention functions in the design of bioassay programs are discussed along with several examples.

A simple method for assessing exposure to internal emitters.

One of the most challenging aspects of regulatory compliance can be demonstrating compliance with internal dosimetry requirements. For long-lived alpha-emitting radionuclides in particular, the sensitivity and accuracy of bioassay analysis and whole body counting may not allow for adequate assessment of intakes. Simple and effective measures can be used to control the workplace for the internal hazards associated with long-lived radioactive material using methods that measure directly the air to which workers are exposed. This paper provides an easy assessment tool that uses direct measurement of the specific activity of dusts in breathing zone air to evaluate internal exposures. Using this method, sensitive assessments can be made to determine if intakes are likely to have occurred and, if so, at what magnitude. It is not a substitute for confirmatory bioassay or whole body counting but a simple method to evaluate expectations for internal exposures.

Basic applications of the chi-square statistic using counting data.

The chi-square statistic has many scientific applications, including the evaluation of variance in counting data and the proper functioning of a radiation counting system. This paper provides a discussion of the fundamental aspects of the chi-square test using counting data. Practical applications of the chi-square statistic are discussed, including the estimation of extra-Poisson variance and dead time for a counting system. The consequences of passing or failing the chi-square test are discussed regarding the proper estimator for the population variance of the counting data. Example scenarios are used to provide insight into the applications of the chi-square statistic and the interpretation of values obtained in hypothesis testing.

Theoretical response of a ZnS(Ag) scintillation detector to alpha-emitting sources and suggested applications.

The classic problem of alpha absorption is discussed in terms of the quantitative determination of the activity of "weightless" alpha sources and the specific alpha activity of extended sources accounting for absorption in the source medium and the window of a large area ZnS(Ag) scintillation detector. The relationship for the expected counting rate gamma of a monoenergetic source of active area A, specific alpha activity C, and thickness H that exceeds the effective mass density range Rs of the alpha particle in the source medium can be expressed by a quadratic equation in the window thickness x when this source is placed in direct contact with the window of the ZnS(Ag) detector. This expression also gives the expected counting rate of a finite detector of sensitive area A exposed to an infinite homogeneous source medium. Counting rates y obtained for a source separated from a ZnS(Ag) detector by different thicknesses x of window material can be used to estimate parameter values in the quadratic equation, y = a + bx + cx2. The experimental value determined for the coefficient b provides a direct estimation of the specific activity C. This coefficient, which depends on the ratio of the ranges in the source medium and detector window and not the ranges themselves, is essentially independent of the energy of the alpha particle. Although certain experimental precautions must be taken, this method for estimating the specific activity C is essentially an absolute method that does not require the use of standards, special calibrations, or complicated radiochemical procedures. Applications include the quantitative determination of Rn and progeny in air, water, and charcoal, and the measurement of the alpha activity in soil and on air filter samples.

Determining the specific alpha activity of thick sources using a large-area zinc sulfide detector.

A simple method using a large-area zinc sulfide detector to determine the total specific alpha activity of thick sources is presented. A previous paper shows how the linear absorption properties of weightless alpha sources can be applied to thick sources placed in direct contact with a varying thickness of window material. A quadratic relationship between the detector response and absorber thickness was derived for sources whose thickness exceeds the range of the alpha particle. The coefficient of the linear term in the quadratic expression is used to calculate the total specific alpha activity of a source in contact with the window of the detector. This relationship is tested by obtaining alpha absorption data from solid sources of known specific alpha activity, fitting the data to the theoretical relationship and comparing the results to the known activities.

Effects of oxygen on the electron transport chain of photosynthesis.

Oxygen was taken up by both intact and broken chloroplasts when catalase was posioned. In confirmation of other work we found that oxygen enters the electron transport chain of isolated chloroplasts by oxidizing the primary photoreductant of system I. In isolated intact chloroplasts this reaction proceeds in addition to oxygen evolution by PGA reduction. The reductant produced by photosystem II does not react with oxygen at a significant rate.In normal leaves oxygen depresses chlorophyll fluorescence. However, this depression does not take place in DCMU poisoned leaves or in a mutant having a nonfunctional photosystem II; furthermore, another mutant with a weakly functioning photosystem I gave only a very small fluorescence depression with oxygen. This shows that the site of interaction of oxygen is at the reducing end of the electron transport chain. This view is supported by the extent of the fluorescence depression in leaves as a function of oxygen concentration which is very similar to the oxygen dependence of oxygen uptake by isolated chloroplasts.An oxygen requirement of isolated intact chloroplasts reducing PGA and nitrate was indicated by lower reaction rates and faster decay of activity under nitrogen than under air.

Chlorophyll composition and photochemical activity of photosystems detached from chloroplast grana and stroma lamellae.

A stroma fraction that has photosystem 1 activity and grana lamellae fractions that have activities for both photosystems were isolated by differential centrifugation of a needle valve homogenate. Subsequent fractions, corresponding to photosystems 1 (F-1D) and 2 (F-2D) were isolated by digitonin treatment of the grana lamellae (P-10K) and compared with respect to their chlorophyll composition and electron transport activities.Fraction F-2D from grana lamellae having photosystem 2 activity is primarily active in photosystem 2 and contains only the four major forms of chlorophyll a with a predominance of chlorophyll a 677 nm. This fraction differs from the original grana membranes in the absence of the longwavelength form of chlorophyll a and in the widening of the absorption band of chlorophyll a 682 nm from 10.9 to 15.6 nm.Photosystem 1 particles from grana and stroma both have high photosystem 1 activity but differ from each other in the proportions of the four major forms of chlorophyll a. The short-wavelength forms of chlorophyll a and also chlorophyll b 650 nm in particles from grana lamellae comprise relatively more total area than these same forms in the particles from stroma. In addition, the fraction corresponding to photosystem 1 from grana lamellae is not shifted to the long-wavelength side of the main absorption maximum, as compared to the photosystem 2 particles from grana and the original grana membrane fraction; this is usually observed in fractions that have photosystem 1 activity. Furthermore, the longest wavelength form of chlorophyll a in the photosystem 1 particles from grana is at 700 nm, while in the same fraction from stroma, it is at 706 nm.The half-width of the four main forms of chlorophyll a and both forms of chlorophyll b in the photosystem 1 fraction from grana is narrower than that of the corresponding forms in the same fraction from stroma. This may indicate a different packing of pigment molecules that are aggregated on the surface of membranes of these two fractions.

The forms of native chlorophyll in Chlamydobotrys stellata and their changes during adaptation from photo-heterotrophic to autotrophic growth.

Absorption and fluorescence spectra were measured for Chlamydobotrys stellata cultured either photo-heterotrophically on acetate or autotrophically on CO2 as well as during adaptation from hetero- to autotrophic conditions. Curve analyses of the absorption spectra at liquid nitrogen temperature suggest the presence of chlorophyll-a forms with their main absorption peaks at 663, 670, 678, 685, 693 and 707 nm. The proportion of the longer wavelength forms, 685, 693 and 707 nm, decreases during adaptation to autotrophic growth. The chlorophyll-b content of the photo-heterotrophic culture was very low.

Four universal forms of chlorophyll a.

We have matched the red absorption band measured at -196 C in a variety of chloroplast preparations with four major component curves representing forms of chlorophyll a having peaks at 661.6, 669.6, 677.1, and 683.7 nanometers. Chloroplast fractions enriched in one or the other of the two photochemical systems both contain these four major components, but system 1 preparations contain relatively more chlorophyll a 684. Chlorophyll a 677 and chlorophyll a 684 have greater bandwidths in system 1. Bands at longer wavelengths near 693 and 704 nanometers also often occur, but with far smaller heights than the above major bands. The longer wavelength bands are more common in system 1 than in system 2. In system 1 the half-widths of the four major bands in typical spectra average 11.3, 10.0, 10.3, and 10.8 nanometers while in system 2 they are 11.6, 9.8, 9.4, and 9.6 nanometers. Some spectra with sharper and some with wider bands were found, but the wavelengths were identical.