Lead bricks

Lead bricks are generahy used as temporary shields for radiation sources at nuclear power stations, research institutes, hospitals, and fuel reprocessing plants. Plat, rectangular bricks requite a double layer with staggered seams whereas the interlocking bricks requite only one course. Lead shot can be poured into inaccessible areas like a Hquid. 

After a demonstration at the Hanford Site C Reactor in 1998, the DOE estimated that it would cost approximately 50,000 to remediate the 1956 contaminated lead bricks on site. Costs would range from 0.96 per pound if the bricks were presurveyed for contamination levels to 0.99 per pound if the bricks were not presurveyed. The presurveying option is less expensive because not all of the bricks would require decontamination. These estimates do not include money earned from the salvage value of the bricks (D198327, pp.l6, 17). The DOE notes that TechXtract was not cost effective at Hanford due to the cheap costs of landfill disposal at the facility (D222719, p. 6). 

Example Problem Estimate the fraction of 1.0 MeV photons that will be transmitted through a lead absorber that is 5 cm thick (the thickness of lead bricks commonly used in radiation shields). 

A 45-millicurie 60Co source, stainless steel encapsulated, is bolted onto an adjustable plastic jig (not shown) for. insertion into the source hole in the lead block. This allows the source to be precisely positioned in the slit for max radiation transmission. With the source in position an additional shield consisting of a combination of lead bricks and concrete blocks is placed around and under the assembly on the table to maintain a permissible level of radiation for the operator... 

The production of a radiopharmaceutical will normally take place within a contained box unit, consisting of either plastic walls or a combination of plastic and stainless steel. The latter is more optimal for clean-room work. The box units may be shielded by lead, either as large lead panels or as lead brick walls (see Figure 1). Depending on the kind of radionuclides used and the amount of radioactivity handled in the box, the walls are typically 5-15 cm in thickness. Shielded production units like these are often called hotcells. ... 

FIGURE 1 Shielding of box units (hot cells) with lead bricks. (Photo courtesy of Institute for Energy Technology.)... 

When using lead bricks to construct the wall of the production unit, they should have a special design. When they are stacked on top of each other, they should interlock (see Figure 3). This is important to avoid cracks in the wall through which radiation can escape. 

When lead bricks or concrete blocks are used as shielding materials, shielding must be done as near radiation sources as possible and the shielding effect must be confirmed with a survey meter. Care must be taken in regard to leaking and scattering rays through clearances between piled bricks and blocks. A lead container is usually used to carry radioactive materials. 

Lead sheets and lead bricks are used to shield workers and sensitive objects from X rays. 

Filled polymers play a role in primary and secondary protection against y-radiation. The photons interact with matter by photoelectric absorption and Rayleigh scattering. For primary partitions which separate an unshielded source from its surroundings, lead bricks or concrete blocks are used. For the secondary partitions which protect personnel from radiation, a protective shield or vest can be made by incorporating metal particles or lead oxide in rubber or plastic. Such shields are used by physicians and dentists or their patients to limit exposure to x-rays. The radiation... 

If 15% of the 511-keV photons of 18F are transmitted after passing through a lead brick of 7 cm thickness, calculate the HVL of the 511-keV photon in lead. 

Na Direct (radioactivity) Strong v radiation source centimeter-thick lead brick needed as shield. Epstein and Packer 1978 Rosenberg et al. 1984 ... 

K+ Direct (radioactivity) Strong y and p radiation source half-life 19 d centimeter-thick lead bricks needed as shield. Amer and Stallcup 1981 ... 

The finite size of the source (3-mm diameter) produces a larger focal spot than would be expected for a point source (2.0-cm diameter instead of 1.7 cm for an ideal point source). For several of the experiments performed, we required a focal spot size smaller than the pixel surface, so a collimator consisting of a lead brick (10 cm thick) with a cylindrical hole (8-mm diameter) was used. 

By afternoon a holiday spirit prevailed in our group. After several hours exposure to air the precipitated [plutonium] had taken on a pinkish hue. Someone photographed Cunningham and Werner at their crowded bench in the narrow, tile-walled room—trim, strong-jawed young men looking weary. The crew upstairs that muscled carboys and lead bricks shuffled in like clumsy shepherds to peer through the microscope at the miracle of the tiny pinkish speck. 

The warehouse section is a two-floor area. The lower floor is designed for storage of heavy materials such as lead bricks or steel shielding plates. The space in general, is to store items needed for exclusion area work. Some office space is also available on this floor. The upper floor is designed for lighter storage and/or offices. 

Hoods used for work with radioactive sources or materials should be designed so that they can be decontaminated completely on a regular basis. A usual feature is a one-piece, stainless steel, welded hner with smooth, curved comers, which can be cleaned easily and completely. The superstructure of radioisotope hoods is usually made stronger than that of a conventional hood in order to support lead bricks and other shielding that may be required in the hood. Special treatment of the exhaust from radioisotope hoods may be required by government agencies to prevent the release of radioactive mataial into the environment. This usually involves the use of high-efficiency particulate air (HEPA) filters (see section 8.C.8.4). 

Lead bricks used for shielding experiments were fabricated from lead wool used by the U.S. Navy during World War II. The radioactive impurities of lead wool were prechecked before fabrication with Ge(Li) gamma detector to assure their low level. The laboratory is housed in a single story, concrete-block building in Arvada, near Denver, at an elevation of approximately 5,000 feet above sea level. 

Item 1 plus 6 lead bricks arranged in 4" thickness covering a space 12 X 8 inches square, directly above the vial ... 

These experiments were made to determine the contribution of cosmic-ray components to the background. Because of the large size of the NCMS and the limited number of lead bricks (approximately 200 pieces), no further shielding experiments were conducted. 

The procedure for neutron measurements involved placing the detector near a neutron source storage drum. Measurements were made with a 3 Ci AmBe neutron source and a 3 mCi Cf spontaneous fission neutron source housed in 55-gallon drums. The drum contained a thick neutron moderator/absorber shield, and, thus, it was assumed that thermal neutrons predominated in the energy distribution outside the drum. The detector and PMT were shielded from fission gamma radiation by 5-cm thick lead bricks, and an additional 3-cm thick, high-density polyethylene moderator was interposed between the bricks and the source drum. Pulse-height spectra were accumulated over 1.5 x 10 s for each sample. 

Kitahara (1987) studied the self-irradiation of a commercial CaS04 Tm (UD-200S) TLD. This is a high-sensitivity TLD. Ten samples, one of each of 10 hatches, were used for the measurements. The samples were kept in a lead brick enclosure located underground for 20 days. The average self-irradiation obtained was 2.6 0.36pRadh. This radiation was found to be due to the cap of the holder which served as a Sn-Pb alloy for energy compensation. Tokuyama et al. (1990) studied the self-dose and the cosmic ray dose of a UD-200 S TLD. The self-dose was measured in a tunnel where the cosmic rays are attenuated. A self-dose of 0.26 nC kg h was measured with and without the Sn-Pb filter of the TLD. The dose of the cosmic rays at sea level was 0.74 nC kg h . ... 

It is important not to freeze the solution of radioiodine, as this leads to instability and volatilization. Radioiodine is routinely stored within a lead container and, when in use, is kept behind lead bricks in a fume hood vented to the outside. 

Lead in its pure state is very soft and has low mechanical strength. In this form it is used widely in the chemical industry, due to its high corrosion-resistance. Because of its low mechanical strength it is applied in the form of a lining to other, stronger materials. It is also used for radiation shielding. When alloyed with antimony, the strength and hardness is increased and it is used for the production of lead bricks for nuclear... 

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