The photon total cross section on protons has been measured with high precision in the Fermilab tagged-photon beam for photon energies from 18 to 185 GeV. The cross section decreases to a broad minimum near 40 GeV, and then rises by about 4 fib over the remainder of the range 0 A p + u> +

Loss of fluids and samples during retrieval of cores of saturated, noncohesive sediments results in incorrect measures of fluid distributions and an inaccurate measure of the stratigraphic position of the sample. To reduce these errors, we developed a hollow drive shoe that freezes in place the lowest 3 inches (75 mm) of a 1.88‐inch‐diameter (48 mm), 5‐foot‐long (1.5 m) sediment sample taken using a commercial wire line piston core smapler. The end of the core is frozen by piping liquid carbon dioxide at ambient temperature through a steel tube from a bottle at the land surface to the drive shoe where it evaporates and expands, cooling the interior surface of the shoe to about ‐ 109°F (‐ 78°C). Freezing a core end takes about 10 minutes. The device was used to collect samples for a study of oil‐water‐air distributions, and for studies of water chemistry and microbial activity in unconsolidated sediments at the site of an oil spill near Bemidji, Minnesota. Before freezing was employed, samples of sandy sediments from near the water table sometimes flowed out of the core barrel as the sampler was withdrawn. Freezing the bottom of the core allowed for the retention of all material that entered the core barrel and lessened the redistribution of fluids within the core. The device is useful in the unsaturated and shallow saturated zones, but does not freeze cores well at depths greater than about 20 feet (6 m) below water, possibly because the feed tube plugs with dry ice with increased exhaust back‐pressure, or because sediment enters the annulus between the core barrel and the core barrel liner and blocks the exhaust.

Photoproduction cross sections for neutral n, 7, p, and 4 mesons have been measured a t the Stanford Linear Accelerator Center for photon energies between 5 and 17.8 GeV, and t (four-momentum transfer squared) between -0.12 and -1.4 (GeV/c)2, using a missing-mass technique. The pion production a t lower energies is characterized by a fast falloff with increasing It] a t small t 1 values, with a dip a t t= -0.5 (GeV/c)$ follo~ired by a secondary maximum around t = -0.9 (GeV/c)2 and a smooth falloff at larger I tl values. As the incident photon energy increases, the dip becomes less pronounced, in contradiction to the expectations of simple Regge theories based only on the exchange of the w and B trajectories. 7 photoproduction was measured around 6 GeV and a t 9 GeV. The cross section decreases smoothly with t and sho~irs no dip a t t= -0.5 (GeV/c)2, in disagreement with predictions based on Reggeized p exchange. p production rates agree well with predictions assuming diffraction production. The differential cross section varies approximately as e*."". The total cross section decreases from 16.0 pb a t 5.5 GeV to 12.3 pb a t 17.8 GeV incident photon energy. A quark-model relation between T-p elastic scattering and p photoproduction gives a good representation of the data. 4 production also appears consistent with the predictions of the diffraction-dissociation model. LVe also searched for evidence of photoproduction of other particles with mass up to 2 GeV. Production of one particle of mass 12401t20 MeV and width around 100 MeV was observed. T o particles with mass betxveen 1300 and 2000 MeV mere found. Any particle with cross section larger than 4y4 of the p cross section mould have been visible.

Final total cross sections a r e given for a counter experiment a t SLAC on hadronic photon absorption in hydrogen, deuterium, carbon, copper, and lead at incident energies from 3.7 to 18.3 GeV. Some of the nucleon cross sections have been revised and the C, Cu, and Pb data from 3.7 to 7.4 GeV have not been reported previously. The cross sections for complex nuclei vary approximately a s A Oe9 in our energy range, indicating that the photon interacts, at least partially, as a strongly interacting particle. The energy dependences of the proton and neutron cross sections a r e also similar to those of hadron-nucleon cross sections and hence may be fitted by a typical Regge parametrization, yielding a,(@) = (98.71. 3.6) +(65.0+ 10.1)v-"2 bb and o T ( y n ) = (103.41. 6.7) + (33.11. 19.4)v-"' j~b , where v i s the photon energy in GeV. These extrapolate to the same value a t infinite energy, consistent with Pomeranchukon exchange, and the energy-dependent part yields an isovector-to-isoscalar-exchange ratio of 0.18-t 0.06. While these observations a r e qualitatively consistent with vector meson dominance, quantitatively vector dominance fails in relating our results to p photoproduction on hydrogen or to experiments determining the p-nucleon cross section. Vector dominance cannot be rescued by assuming that the p-photon coupling constant depends on the photon mass. Instead, an additional short-range interaction i s apparently required, possibly due to a heavy (2 2 G~v/c') vector meson or to a bare-photon interaction. The additional interaction accounts for approximately 20% of the total photoabsorption cross section.

We have measured total hadronic photoproduction cross sections on carbon, copper, and lead. Tagged-photon energies ranged from 20 to 185 GeV for copper and from 45 to 82 GeV for carbon and lead. The energy and A dependence of shadowing were computed by comparing these results to the hydrogen cross section as measured nearly simultaneously with the same apparatus. We observed somewhat more shadowing than did most experiments at lower photon energies.The photoproduction cross section from complex nuclei should be less than the sum of individual nucleon cross sections because (naively) some nucleons "shadow" others by absorbing out the hadronic part of the photon beam. This effect has been observed in photoproduction by real photons of up to 18 GeV. 1 " 6 Although the results of Ref. 1 disagreed with the vector-meson-dominance (VMD) model used in that paper, it is possible to find models 7 that do give reasonable agreement with the shadowing observed in photoproduction. VMD models do, however, have difficulty accounting for the rapid decrease of shadowing when the photons become slightly spacelike. 8 More data will be useful for suggesting the direction in which models must be elaborated.We have measured the dependence of the total photoproduction cross section on A, the atomic weight of the target nucleus. One reason for doing so was to get a more accurate measurement of shadowing than has been hitherto possible. The cross section is easier to measure at high energies and our apparatus was designed to achieve the very high precision needed for detecting the small energy dependence of the hydrogen cross section. 9 Another reason for doing this measurement was to extend the energy range of shadowing data. Such an extension could, for example, show effects of higher-mass states. The higher the mass of a vector state, the higher the photon energy must be in order that the state contribute to shadowing. In fact, neutron and K L cross sections on nuclei do show an increase in the amount of shadowing with increasing energy,, 10 " 12 This increase can be interpreted as an effect of "inelastic screening" 13 of the forward scattering amplitude, in which an incident hadron diffractively dissociates (into a possibly higher-mass state) at one point within the nucleus and recombines at another. In VMD calculations of shadowing, this would correspond to including off-diagonal terms.The measurement was performed in the Fermilab tagged-photon beam. Tagged photons were produced from copper radiators of 6 and 15 mils (0.0107 and 0.0267 radiation lengths). The beam, detection apparatus, and trigger were the same as used in a measurement of the total photoproduction cross section on hydrogen. 9 However, the hydrogen target was replaced by carbon, copper, and lead targets-each a rectangle larger than the beam and each of approximately 0.1 radiation length in thickness. These targets were mounted in a vacuum box so that each could be rotated into the beam. An empty target slot permitted measurement and subtraction of the rate of hadronic...