A study of the nuclear and physical properties of the concrete shield of the ORNL Graphite Reactor was performed both to determine the radiation attenuation characteristics of the shield and to discover any effects of a long-term (12-year) irradiation, experiment neutron and gamma radiation measurements were made in a 4-5/8-in.-dia hole in the shield as the hole was drilled in increments of 1 or 1/2 ft. to simulate a homogeneous shield. gamma rays in the barytes-haydite concrete, of which most of the shield is made was found to be approximately 13.6 cm, increasing gradually from 13.0 cm at a shield thickness of 2 ft to 14.6 cm at a shield thickness of 5 ft. The fast-neutron relaxation length in the barytes-haydite concrete varied from 10.0 cm to 10.6 cm, the average being approximately 10.2 cm. were also made. to determine the chemical composition, water content, density, compressive strength, and radioactivity of the shield at the various depths. temperature gradient through the shield was also measured. This investigation showed that the chemical properties and density of the shield have not changed appreciably since a similar investigation in 1948, but its compressive strength is lower (40% near the reflector-shield interface). In the Concrete plugs were always placed behind the detectors The average relaxation length for Measurements of the streaming of radiation through the hole The concrete dust collected frcm the driilings was used The iii TABLE OF C O " T S
The energy deposited by neutrons, gamma rays, high-energy protons, and the nuclear secondaries resulting from the interaction of high-energy protons with several targets has been measured a t various points within a 42-cm-diameter spherical water-filled Lucite phantom. The proton source was the Harvard University Synchrocyclotron, producing protons of nominally 160-MeV energy. Targets were water, aluminum, carbon, copper and bismuth. For neutrons the H3(d, n)He4 reaction, giving -14.9-MeV neutrons, and a Po-Be source (& = 4.3 MeV) were used. The gamma-ray source was Co60. The detectors were small Lucite-walled ionization chambers filled with either ethylene or 97% Ar-3% CO, gas.Data were taken at the cyclotron both with the phantom on the beam axis and with the phantom offset -55" from the beam axis. The proton beam energy determined from a part of these results, -160 MeV, is in good agreement with published values. The energy deposited by secondary particles was found to increase with target-atomic number, as expected. The depth-dose curves have a steeply negative slope over the region near the surface of the phantom and a more gentle slope at greater depths. The magnitude of the dose in the region of the initial slope decreases with increasing target thickness, while the magnitude of the dose at greater depths increases with increasing target thickness. The dose in the region of initial slope is presumably due to secondary protons, while at greater depths the dose is principally controlled by secondary-neutron interactions.With an aluminum target thicker than the incident proton range, the absorbed dose a t -55" from the beam axis was only about 20 per cent of that at 0". Comparison of the slopes of the depth dose due to the secondaries (assumed to be largely neutrons) from this target with the slopes obtained with the neutron sources suggests that the effective energy of the secondaries is greater than 15 MeV.These experimental data were obtained to permit detailed comparisons with calculations of the physical dose due to secondaries from high-energy protons. The results of such calculations are not yet available. nuclear secondaries (neutrons, protons and gamma rays) resulting from the interaction of phantom by protons, second-of interest. Such data are needed to assess the aries from the interaction of these protons with validity of the Monte Carlo transport calcugamma rays has been physical dose due to the interaction of solar protons with spacecraft shields. Since calcuinferred from ionization measurements made as
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