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A thorough study and error analysis was made of the Van den Akker or "auxiliary sphere" method of determining a scale of directional-hemispherical reflectance factor. The effects of a non-Lambertian distribution of the reflected radiation, including retroreflection, were included in this study. Three working standards were measured to an uncertainty in reflectance of less than ±0.0015 and these will be used as a basis for a new, more accurate NBS scale of 6°-hemispherical reflectance factor. The new scale and the NBS scale established in 1965 are in agreement to within the uncertainty of ±0.005 assigned to the 1965 scale.

A geometric system for universal use in specifying and measuring retroreflectance is described. This system has been developed by the Subcommittee on Retroreflectance of CIE Committee 2.3 on Properties of Materials and is to be considered for adoption as part of a recommended practice.

A long-range retroreflectance instrument has been built in the photometric range of the Radiometric Physics Division of the NBS. It is designed to measure photometric properties of retroreflectors for different geometries. It satisfies many needs of the measurement community, and it is planned to use this instrument as the basis for a Measurement Assurance Program (MAP) and for Standard Reference Materials (SRM). This paper describes the design and testing of the instrument. Some estimated uncertainties for typical samples are given.

The authors examined the mortality experience of employees whose work assignments involved development or production of styrene-based products. To investigate potential relationships between mortality and work exposure in the diverse chemical operations under study, a multiple agent approach to exposure categorization was adopted. Mortality was less than that of the corresponding U.S. white male population and was consistent with that of an industrial comparison group. Although deaths due to malignant neoplasms were fewer than expected for the total cohort, an increase in lymphatic leukemia was observed among a subgroup of employees who had exposure to polymer extrusion fumes, solvents, and colorants. However, no relationship was found with duration or intensity of exposures experiences by these employees, and the etiology of the lymphatic leukemias was not established. The approach used to characterize exposure in this study may have application in other epidemiologic investigations involving complex work environments.

Through the use of an efficient design and a newly available sphere coating material, a simple, passive, sturdy averaging sphere was made that operates effectively over the wavelength range from 200 nm to 2000 nm. Data are reported for a sphere of this type in which the sphere transmittance is 0.32 at 200 nm and rises rapidly to near the maximum theoretical value of 0.56 over the remainder of the wavelength range. The several orders of magnitude reduction in error due to beam displacement more than compensate the slight reduction in signal for many spectrophotometric and radiometric applications.

The fertility status of male employees engaged in the production of chlorinated three-carbon compounds at Dow Chemical Company's Texas Division was investigated. Males who had not worked in the production of industrial chemicals for at least five years prior to the study period served as controls. Data were obtained from a reproductive medical history, from hormone determinations, from a physician's examination, and from a semen analysis. Sperm counts and percent normal sperm forms were major study variables. Comparisons were made between the control and the study groups and within the study group only for duration of exposure, strength of exposure and a combination of the two. Specific chemical exposure subgroups within the study group were also compared. Although the participation rate for the exposed group was relatively low (64%), results indicated no detrimental effect on fertility from exposure to chlorinated three-carbon compounds at levels occurring in the specified work environment.

Potential sources of errors in measuring the luminous reflectance and chromaticity of retroreflecting devices are reviewed. Examples are given from data for representative retroreflectors of different types.

Measurements to determine the radiance of one portion of a nonuniform source can be strongly influenced by radiation from other portions of the source scattered by the optical system used to transmit the radiation to the detector. Conditions under which such scattering is important and procedures to correct for it are discussed. An illustration is provided from measurements made on a nitrogen arc source.

To be useful, spectrophotometric measurements must be believable and practical. The basic standard tor any believable spectrophotometric measurements is the ability to accurately compare fluxes of radiation within the framework of a well-defined geometry. The emphasis in the program proposed for the Institute for Basic Standards is to develop such ability over the broadest range of spectrophotometric measurements. Establishing such a basis will enable the National Bureau of Standards to render real assistance to those who deal with the problem of making practical measurements.