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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 232 Th 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 232 Th and its radioactive progeny have been developed to estimate the total committed dose equivalent from 232 Th and all of its radioactive progeny per unit intake of 232 Th only. It is believed that this research has led to (1) more realistic estimates of doses from 232 Th 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.

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.

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 inmore » 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.« less

P was diffused into p-type Si wafers containing B at 1100/spl deg/C for six different times using a solid state source and a standard pre-deposition process. Secondary ion mass spectrometry (SIMS) provided profiles of dopant concentration versus wafer depth from which both the surface concentration and the junction depths for the six wafers were determined. These profiles were fitted acceptably well by the constant supply model of diffusion in the dilute "tail region" identified by Fair, although indications of concentration-dependent diffusion were observed. Two independent determinations of the sheet resistivity of each sample were made. The results confirmed the correct operation of our custom-built sheet resistivity system. The resulting data allow us to predict the junction depth within 0.2 /spl mu/m over a range from 1.0 to 2.0 /spl mu/m. A plot of the dopant surface concentration, N/sub 0/, versus the product of the sheet resistivity and the junction depth, R/sub s/x/sub j/, agrees well with data from the Irvin plot.

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. Health Phys.

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.

Jack C. Greene was born on June 3rd, 1921 in Roundup, Montana and died on September 4, 2001 in his home in Oxnard, California. He was a charter member and Fellow of the Health Physics Society and spent his career in civil defense and radiological preparedness. He served as an advisor to the National Council on Radiation Protection and Measurements (NCRP).

Purpose: Proper evaluation of a stereotactic radiosurgery(SRS) plan is challenging due to lack of a comprehensive evaluation index and variation of dose prescription. In this study, a new treatment plan index is proposed to evaluate the quality of an SRS treatment plan by incorporating planning parameters that describe tumor coverage, dose to surrounding normal tissues, and tumor dose uniformity. Method and Materials: The proposed index contains four factors. The first factor is MDPD (ratio of the maximum dose to the prescription dose), which specifies the tumor uniformity. The second factor is V100, percent tumor volume covered by 100% prescription dose. The third factor is characteristic of dose spillage to normal tissue. The fourth factor is a piecewise function used to differentiate the deviation of the treatment plans from the requirement of RTOG protocol. Thirty‐four SRS cases fulfilling the requirement of RTOG protocol were analyzed by our proposed index and Paddick's index. Two dose prescription approaches were considered for this comparison: one is to maximize the tumor coverage and maintain plan uniformity; the other is to maximize the tumor coverage and spare the surrounding normal tissue. Results: Our result indicates that the proposed index becomes negative value when the tumor coverage or PITV significantly deviates from RTOG protocol. The treatment plan index for different lesion size, irregularity and location of critical structure relative to tumor target were calculated with various techniques at two different dose prescription approaches. Conclusion: Comparison of the plan index recommended by Paddick and that proposed in this study for clinical 34 SRS cases in Baystate Medical Center indicates that our plan index is reliable and sensitive to the lesion size, irregularity, and location of critical structures and is easier for the selection of the treatment techniques and dose prescription during the process of SRS.

This article is a follow-up of a previous article, "The Issues Concerning the Use of an Annual as Opposed to a Committed Dose Limit for Internal Radiation Protection".

The scientific, technical, practical, and ethical considerations that relate to the use of an annual as opposed to a committed dose limitation system for internal radiation protection are evaluated and presented. The concerns about problems associated with the more recent ICRP committed dose recommendations that have been expressed by persons who are currently operating under an annual dose limitation system are reviewed and discussed in terms of the radiation protection programme elements that are required for an effective ALARA programme. The authors include in this and a follow-up article a comparison of how these alternative dose limitation systems affect the economic and professional livelihood of radiation workers and the requirements that they impose upon employers. Finally, they recommend the use of an ICRP based committed dose limitation system that provides protection of workers over an entire occupational lifetime without undue impact on their livelihood and without undue requirements for employers.

Exact and approximate kinetics equations relating to the transfer and elimination of radionuclides from the blood and various organs in the body are presented. Although they are limited to simple first order kinetics, instantaneous uniform mixing in the blood and all organ pools, and the behavior of a single metabolic species, they are not limited by the number of transfer organs. In addition, the approach used here may he extended to other less limiting cases (e.g. various metabolites or daughters, slug flow, etc.). These expressions may be used to estimate the instantaneous activity or the total number of disintegrations of a radionuclide in the blood or various organs of reference in the body, hence, also the respective dose rates and doses. The exact kinetics equations may be used to relate measurements of radionuclides in excreta to burdens in the body. The approximate expressions greatly simplify the mathematics and yet provide sufficiently accurate results with a maximum deviation of about 23% from exact mathematical expressions over most time intervals of interest. They do give better results for exposure intervals long compared to the effective mean lives of the radionuclide in the various organs of reference, and they yield the exact steady state expressions. Fortunately, this condition is often satisfied for the relatively long standard exposure interval of 50 years that is applied to occupational exposure. In addition, the steady state expressions may be used along with metabolic data of the distribution of elements in the body, diet and excreta to estimate values of the rate constants used in both the exact and approximate expressions. A comparison of the exact and approximate expressions is given for the uranium metabolic model of Wrenn et al. (Wr78), and a comparison is made with current ICRP models (ICRP68a).

International audience; Nicotine stimulates dopamine (DA) neurons of the ventral tegmental area (VTA) to establish and maintain reinforcement. Nicotine also induces anxiety through an as yet unknown circuitry. We found that nicotine injection drives opposite functional responses of two distinct populations of VTA DA neurons with anatomically segregated projections: it activates neurons that project to the nucleus accumbens (NAc), whereas it inhibits neurons that project to the amygdala nuclei (Amg). We further show that nicotine mediates anxiety-like behavior by acting on β2-subunit-containing nicotinic acetylcholine receptors of the VTA. Finally, using optogenetics, we bidirectionally manipulate the VTA-NAc and VTA-Amg pathways to dissociate their contributions to anxiety-like behavior. We show that inhibition of VTA-Amg DA neurons mediates anxiety-like behavior, while their activation prevents the anxiogenic effects of nicotine. These distinct subpopulations of VTA DA neurons with opposite responses to nicotine may differentially drive the anxiogenic and the reinforcing effects of nicotine.