Program, as Progra-m A 2, Pronlern 7.j -U C ill. Descrin-tion of Work( Durine! FY 1.159 :c-,uipmecnr was desi ;ncd, fab-ricated, and uised a determinle the raLm ation atenua~irse propertie s of clear atrro~hcres at cisc Nevada Tes-t Site. In BY 100C the -qui-mient was modified aad measuremc.,tz ode in atusospiirrs with overcast cl'oud conditions at the same :.oeatioi. In IY 961 aire-furtheir equipment nmodificction .rr~easnrrl:"teSr 'were zaeill the Sullmer atm.osnhercit of Lo Anacles ,0 Jaiornia. The measurements wzere made at wavelengths .. 40,, 0.5a, -0.77 and 0.88p (microns) with receiver fields of view up to 64"degrees half-angle. From these data attenuation coefficients were calculated for collimated transmission and aureoled transmission (km source and flat receiver facing the source).-Also calculated for aureoled transmission were values of R, the ratio of "scatteredin" radiation to direct radiation received -y the f lat rcie at various distances from the source. Angular scattering diagrams and attenuation coefficients for scattering were measured for radiation of wavelengths 0.40, 0.451 0.50 and 0.55%1. Relations between these optical characteristics of the atmosphere and meteoro'logical.characteristics such as visibility, relative humidity,, and contaminant contents were examined. Investigations of transmission variabilitywith respect to both time end space were made. Curves wer6 prepared from these and other experimental, data showing transmittances 'of four typical atmospheres as a function of range for the case of flat receivers and radiation from a 4n black body source at 6000 degrees K. 0The Problem:The amount of thermal tadiation delivered to a g ven receiverfrom the fireball of a nuclear explosion depends on the transmittance of the atmosphere as a function of wavelength, the spectral 4istri-.. * butio4 of the radiation, thq receiver field of view, the range, the albedo of the terrain, and the amount and height above the ground of clouds piesentMTh6 purpose of thit experiment was to'determine the. range of transmittance values of the Los Angles nighttime atmoshiI ie during the:months of Aughst and September 1960.-The Findings: 0 A Xenon flaslilamp 4r source and mobile photomultiplier receivers * w th adjustable fields of view and filters are used to determine atteuation coefficients for colllmaed transmisaion and aureoled A * transmission (4U-source and flat receiver and for calculating P,, the ratio of "scaPttered-in" to direct irradlance, at source-r ceiver dis-00 o .tanees ranging from 0.90 to 6 -,77 statute miles.

A prototype of a compact, portable microcalorimeter has been built which measures ionizing radiation dose rates as low as 3 rads/min measured in aluminum. The absorber and temperature sensing system are conventional but the temperature-controlled bath which usually surrounds a vacuum chamber in such microcalorimeters has been replaced by an aluminum isothermal shield bolted to the bottom surface of a copper reservoir containing liquid nitrogen. Both the shield and the reservoir are contained in a vacuum chamber. Calibration of the absorber is accomplished by observing the response of an imbedded thermistor when the calorimeter is placed in a gamma-ray field of known exposure level provided by a 200-Ci 60Co source.

Measurements of total hemispherical emittance of selected Irtran filters are reported for the temperature range 45 degrees K to 312 degrees K. Values obtained for 1-mm thick specimens are 0.38, 0.23, and 0.15 for Irtran 2, 4, and 6, respectively, at 312 degrees K; 0.49 for Irtran 2 at 75 degrees K and 0.35 and 0.43 for Irtran 4 and 6 at 45 degrees K. All three specimens have emittance maxima of approximately 0.5 at intermediate temperatures. Thicker specimens have somewhat greater values. Total normal emissivity calculated from spectral normal emissivity data for Irtran 2 and 4 agree well with the experimental results. Specific heat measurements of the Irtran specimens for the same temperature range are also reported.

The energy absorbed by aluminum, carbon, or tissue-equivalent (TE) material when exposed to gamma rays, fast neutrons, or 900-Mev alpha particles was measured with a microcalorimeter.The instrument was patterned after the one described by Reid and Johns, Rad. Res. 14, 1 (1961), but has an ethylene glycol bath instead of water. Spaced mylar sheets about 6-1/2 in. in diameter were mounted on one side of the absorber inside the evacuated cylindrical chamber in order that the detector could be thermally insulated in the direction of the beam without the presence of bath solution.Gamma-ray absorbed dose rates as low as 2 rads/min were measured with the instrument. The dose rates obtained from the exposures to Co 6 0 and Cs 1 37 sources at this Laboratory (NRDL) agreed with the output of the sources as measured with a National Bureau of Standards secondary standard cavity ionization chamber. Thirteen 10-mmn exposures of the TE absorber in the microcalorimeter to fast neutrons from the University of California 6 0-in. cyclotron at Crocker Laboratory resulted in absorbed dose measurements varying from 24 to 40 rads. The average absorbed dose value was 5 percent higher than the NRDL determination based on flux and spectrum measurements. Microcalorimeter exposures to the 900-Mev alpha particle beam from the University of California 18 4 -in. synchro-cyclotron at Lawrence Radiation Laboratory gave absorbed doses that agreed reasonably well with ionization chamber determinations. \i SU)LVARY The ProblemThe purpose of this experiment was to build and test a calorimeter capable of detecting temperature changes corresponding to absorbed energy rates of 2 rads/min in aluminum, carbon, and tissue-simulating absorbers when exposed to gamma rays, fast neutrons, or charged particles. The FindingsThe calorimeter was constructed and its use as a laboratory standard was demonstrated. Cs 1 37 gamma-ray absorbed dose rates of 2 rads/min were measured by the instrument. Co 6 0 and Cs137 gaa-raq dose rates agreed with ionization chamber measurements.Fast neutron absorbed dose rates with the tissue-simulating absorber vere slightly higher than the dose rate based on spectrum and flux measurements. Calorimeter and ionization chamber measurements of 900-Mw alrha particle absorbed doses were comparable for dose rates varying from 75 to 4000 rads/mIn.