Shield detector

Adjustable Workbench (PAW) instrument assembly. The SH shown in Figs. 3.15 and 3.16 contains the electromechanical transducer (mounted in the center), the main and reference Co/Rh sources, multilayered radiation shields, detectors and their preamplifiers and main (linear) amplifiers, and a contact plate and sensor. The contact plate and contact sensor are used in conjunction with the IDD to apply a small preload when it places the SH holding it firmly against the target. The electronics board contains power supplies/conditioners, the dedicated CPU, different kinds of memory, firmware, and associated circuitry for instrument control and data processing. The SH of the miniaturized Mossbauer spectrometer MIMOS II has the dimensions (5 x 5.5 x 9.5) cm and weighs only ca. 400 g. Both 14.4 keV y-rays and 6.4 keV Fe X-rays are detected simultaneously by four Si-PIN diodes. The mass of the electronics board is about 90 g [36],... 

Since the signal separation from the prime and rear detector primarily depends on the pulse shape discrimination and the expected event rate in the shield detector is much larger both due to large area and the higher detection efficiency, an ultra-fast RTD system is essential for a very low dead-time. We have developed... 

The EXGM is a watertight detector assembly including a lead shielded detector and two... 

Mechanical engineers are necessary for the design of filters, collimators, the sample position and the shielded detector assembly. 

The most prominent background peaks seen in a shielded detector are in bold type. 

When equation 12 is vaUd, the detector is said to be a background-limited infrared photodetector (BLIP). When this is the case, attempts often are made to improve D by cold shielding which reduces ( ). The ideal D is shown in Figure 3 as a function of wavelength with background photon flux as a parameter. The line of termination in the lower left corner represents TN values for a 180° (27T) detector field of view, 300 K ambient background... 

A number of devices suggest the possibiUty of improvement in the basic limitations of resolution and sensitivity for single-photon instmmentation. One device (24) employs an array of pinholes in a hemispherical shield that Hes inside a hemispherical soHd-state detector array. Simulations and initial experience using early models have suggested that the device could achieve a resolution in the brain of less than 3 or 4 mm and possibly as low as 1 mm. 

Radiation-Density Gauges Gamma radiation may be used to measure the density of material inside a pipe or process vessel. The equipment is basically the same as for level measurement, except that here the pipe or vessel must be filled over the effective, irradiated sample volume. The source is mounted on one side of the pipe or vessel and the detector on the other side with appropriate safety radiation shielding surrounding the installation. Cesium 137 is used as the radi-... 

Fig. 4.6. Cross section of the front end of an SSD (solid-state detector), here Gold contact with a grooved Si(Li) crystal. Crystal and preamplifier are connected with a cooled copper rod and shielded by a case with an end cap and Be window [4.21, 4.29].

A radioactive source was transferred from one container to another by remote operation in a shielded cell. A radiation detector, interlocked with the cell door, prevented anyone from opening the cell door when radiation could be detected inside it. To make sure the interlock was working, an operator tried to open the cell door, by remote control, during a transfer. He found he could open it. He then found that the closing mechanism would not work. Fortunately he had not opened the door very far. 

Another application of the Seebeck effect is to be found ill detectors of small quantities of heat radiation. These sensitive detectors comprise a thermopile, a pile of thermocoup)les (small pieces of two different metals connected in V form and put into series). Half of the junctions of the thermopile are shielded within the detector, whereas the other half are exposed to... 

The energy of the detected neutrons has an epithermal component because a high percentage of the incoming thermal neutron flux is absorbed as it passes through a 1 in. of drill collar steel. Furthermore, a wrap of cadmium under the detector banks shields them from the thermal neutron arriving from the inner mud channel. This mainly epithermal detection practically eliminates adverse effects caused by thermal neutron absorbers in the borehole or in the formation, such as boron. 

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

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 effective shielding of the detector system from direct and cascade radiation from the Co/Rh source is also very important. A graded shield consisting of concentric tubes of brass, tantalum, and lead was selected. The thickness and the shape of different parts of the shielding were optimized so that nearly zero direct 122 and 136 keV radiation (emitted by the Co source) was in a direct line with the detectors (see Fig. 3.16). 

The detector itself may be shielded from background y-rays by means of an annular shield of W or Pb, and absorbers in the form of appropriate metal foils are placed between the detector and the specimen. These reduce the intensity of the continuum of Bremsstrahlung radiation and also prevent back-scattered protons from entering the detector which would degrade the observed spectrum. 

Figure 2. Schematic of apparatus for ZEKE-PFI spectroscopy, including magnetically shielded electron flight path and microchannel plate detector. Not to scale flight path is 50 cm long interaction zone is 1 cm long.

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.

---