Gamma densitometry for the measurement of skeletal density

A method is described for the measurement of the density of calcium carbonate materials from the attenuation of a narrow, collimated beam of gamma photons. For the measurement of density for slices, approximately 0.5 to 1.0 cm thick, from the skeletons of reef building corals, the optimum beam energy is 30–34 keV; and measurement is practical from approximately 22 to 100 keV. The potential utilities of five commercially available isotopic sources (¹⁰⁹Cd,¹²⁵I,²⁵³Gd,²¹⁰Pb and²⁴¹Am) are evaluated. Methods and results are presented for gamma densitometry using²¹⁰Pb and²⁴¹Am. The²¹⁰Pb point source had its principal gamma emission at 46.5 keV. Bremsstrahlung and high energy (800 keV) gamma emissions associated with the²¹⁰Pb decay grand-daughter were detected, and procedures were developed to accommodate the contribution of these emissions to the overall count rate. The attenuation of count rate by aluminium and aragonite absorbers closely followed simple theoretical considerations provided that narrow energy window settings were used at the radiation monitor. These theoretical considerations take account of the density of the material absorbing the radiation, and hence the density could be determined from the attenuation of the gamma beam. Increased accuracy was achieved by the use of²⁴¹Am and high speed counting equipment.²⁴¹Am has its principal gamma emission at 59.6 keV. The attenuation of this gamma beam follows simple theoretical considerations for targets with mass thicknesses from 0 to 6 g cm^-2. Aragonite from the shell of a giant clam was found to have slightly different properties in the absorption of gamma photons to aragonite from a coral skeleton. The differences were small but statistically significant.     

Prefrontal deep projection neurons enable cognitive flexibility via persistent feedback monitoring

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B cell genomics behind cross-neutralization of SARS-CoV-2 variants and SARS-CoV

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The influence of parity and maternal preimmunization on fetal survival in mice

It is known that as parity increases, cell-mediated immunity to paternal antigens increases in mice. The article reports an experiment designed to compare the results of normal parity with artificial immunization simulating maternal sensitization to paternal antigens in mice. Virgin females were immunized at weekly intervals by intraperitoneal injections of 50 mcl of heparinized blood from males with whom they would eventually be mated. The immunized virgins and multiparous females were mated for 4 to 6 weeks after their last injection or litter. The total and live litter size increased with immunization; the total size with natural parity also increased though the live litter size slightly decreased with parity. The mean fetal death rate was relatively the same for both groups. Fetal weight increased with parity but not change was observed in placental weight. Both fetal and placental weight did not change with immunization. There was no increase in the expected number of male fetuses. The increased litter size in the immunized group may be due to increased ovulation rates.