Lead shielding

The isotope molybdenum-99 is produced in large quantity as the precursor to technetium-99y, a radionucleide used in numerous medical imaging procedures such as those of bone and the heart (see Medical imaging technology). The molybdenum-99 is either recovered from the fission of uranium or made from lighter Mo isotopes by neutron capture. Typically, a Mo-99 cow consists of MoO adsorbed on a lead-shielded alumina column. The TcO formed upon the decay of Mo-99 by P-decay, = 66 h, has less affinity for the column and is eluted or milked and either used directly or appropriately chemically derivatized for the particular diagnostic test (100). 

In NAA the sample is made radioactive by subjecting it to a high dose (days) of thermal neutrons in a reactor. The process is effective for about two-thirds of the elements in the periodic table. The sample is then removed in a lead-shielded container. The radioisotopes formed decay by B emission, y-ray emission, or X-ray emission. The y-ray or X-ray energies are measured by EDS (see Chapter 3) in spe-... 

Radiation exposure can be reduced by placing the radiation source or the potential target behind a shield that captures the radiation. During exposure to X rays for dental imaging, the patient wears a lead-lined pad, because X rays are absorbed more effectively by lead than by any other material. A lead shield a few millimeters thick is sufficient to stop X rays. 

Deviating from the setup discussed earlier, the y-ray beam can also be consistently collimated by structures other than the absorber holder. If this is the entrance window of the detector, the counter should have a lead shield, and the absorber must be sufficiently large to prevent radiation from passing by. For Mossbauer scattering experiments, the same arguments have to be considered. 

The laboratory notes of Marie and Pierre Curie detailing their discovery of radium still emit such strong radiation that they have to be stored behind lead shields. 

Figure 9.3 The whole-body counter of University Medical Centre, Utrecht, The Netherlands. The counter has a mobile shadow shield with two Nal(Tl) scintillation detectors (4x6 in) placed at opposite sites of the subject. The lead shielding is 100 cm long with a diameter of 90 cm. The scanner moves on rails over a distance of 240 cm with an adjustable speed. Extreme variations in geometry yield practically the same value for 59Fe activity. The equipment can be used for measurements in man and small animals.

Rn-222 is produced from a dry Ra-226 source with an activity of about 2 mCi housed in a lead shield. Radon is carried from the source by means of compressed air with a regulated flow rate of 200 cnr/min. The test chamber is operated with a 75 1/min air pump located downstream (Figure 1XDroullard, et al., 1984) that exhausts to the outside of the building. The flow rate of this air pump is monitored by a mass flow transducer whose signals are converted to volumetric flow rates. 

In the present state of art, the CUORE cryostat will consist of a room temperature enclosure, radiation shields at 45 K and at 4K, both cooled by pulse tubes. The Still radiation shield at about 700 mK (including lead shielding), 50 mK and a mixing chamber shield will be cooled by the different stages of a DR. All shields and the crystal + lead will be suspended from the top flange (see Fig. 16.7). 

The refrigerator itself is shielded with a 20 cm thick low activity lead and a 10 cm thick borated PET. Nitrogen is fluxed between the external lead shield and the cryostat to avoid any Rn contribution to the detector background. Measurements of residual radioactivity have been carried out on several Pb samples [103], For the roman lead, a contamination lower than 4 mBq/Kg (in 210Pb) is to be compared with 250 mBq/Kg of a modem lead (Johnson Mattey). 

Special precautions Store this radioisotope behind 3 mm thick lead shielding. The effective biological half-life in humans is around 140 days. The thyroid gland is the critical organ in terms of dose, and one would be well... 

Special precautions Store behind lead shielding. Follow institutional regulations regarding type and location of dosimeter. Avoid working immediately above open containers. Because no organ selectively concentrates sodium metabohtes, the entire body is considered to be... 

Figure 3. Alumina column in primary lead shielding in position for loading with Sr-82.

The distributions of americium on the fissure surfaces were then quantitatively determined by scanning the face of each fissure with a Nal scintillation crystal through a 0.3 cm slit in lead shielding. The 59 keV gamma ray emitted by Am was monitored. Histograms of the americium distributions on the fissure surfaces were produced and are presented in Figures 5, 7, and 9. 

The concentrations of tracers in solutions were determined periodically. The polyethylene containers were constructed in such a way that, when inverted, 50 ml of solution passed from the wafer compartment into a second compartment. The second compartment of the container was inserted through a hole in a lead shield which housed a... 

The outer container for the plastic phosphor and the Nal(Tl) is stainless steel. Aluminum sheet, 0.25 mm. thick, is used on the conjoining surfaces of the two annuli and on the inside walls. Shielding from external radiation is provided by a lead shield 10 cm. thick. 

Figure 2. y Background for an 8-inch X 8-inch Nal(Tl) well crystal with 4-inch lead shielding... 

Figure 25. Background for two opposed 2-inch diameter X 1.32-inch Nal(Tl) crystals with 2-inch thick lead shielding...

The tracer-injection equipment consists of four pans a /J-in.-lD steel transfer tube fitted at one end with hardened-steel teeth a 3-in.-diameter lead shield set at the other end of the tube a piston assembly complete with a latching device and a hand-operated hydraulic pump used to drive the piston into the chamber. 

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