Detector endcap

To measure the reduction of side-incident gamma rays using collimators, the source was positioned at 40 cm from the front of the collimator center point (about 41 cm from the detector endcap). The source ( Ba or Co) was positioned at 10° intervals around the center point. Spectra were collected for 1200 seconds in each point for the uncollimated, steel, and tungsten collimators. The peak areas for 81 (a doublet), 356, and 1332 keV were measured for each condition. 

The CSCs are trapezoidal shaped multiwire proportional chambers which consist of 6 anode wire planes crossed with 7 copper strips cathode panels in a gas volume. They provide a two-dimensional position measurement, where the r and (p coordinates are determined by the copper strips and the anode wires, respectively. The muon detector endcaps consist of 4 CSC stations on each side and identify muons in the pseudorapidity range of 0.9 < V < 2.4. 

Figure 8.1 Efficiency curves on top of and at 115 mm from the detector endcap using Eu...

In Chapter 2, Section 2.5.2, I discussed backscatter, which can cause unwanted features in the spectrum. This win be minimized by having a larger shielded enclosure. If possible, have the lead-to-detector endcap distance greater than 100 mm. 

There is a specification by the lEC (see Further Reading) which describes two standard sizes. The dimensions are given in Table 13.4. Each has an annular layer of about 15 mm of material around the sides of the detector endcap, and calculation gives much the same thickness on top of the detector for each size h = A and 17.5mm when filled with 450 and 1000ml, respectively). If the contours of Figure 13.11 are typical, then this equal top-layer thickness may shghtly underexploit the efficiency potential of these standard Marinelli beakers. 

A significant practical difficnlty is that these dimensions do not necessarily accord with the actnal dimensions of detector endcaps. As larger detectors have become available, the diameter of the endcap has had to be increased. Standard endcap sizes are listed in Table 13.5. From that, it is evident that detector sizes of more than 40% cannot accommodate the smaller, 450 ml, lEC... 

Table 13.5 Germanium detector endcap diameters (inmm) ...

Binders (TbC) 671 Bipolar pulse conductivity detector (LC) 588 Bonded phases (GC) 125 crosslinked 126 estersils 125 nonextractable 126 siloxane 125 Bonded phases (LC) 324 carbon loading 335 cleavage of ligands 336 eluotropic strength (LSC) 382 endcapping 326 hydrophobicity 364 metal impurities 369 models for surface 337 physical characteristics 333, 366... 

Imazalil, OPP, and TBZ residues were determined using an HPLC system, consisting of a ternary HPLC pump attached to 250 X 4.6-mm-ID Hichrom RPB 5-/tm column with a 10 X 3.2-mm-ID guard cartridge column. The packing material of both columns was base-deactivated silica, fully endcapped with a bonded phase of Cg/C]8. The mobile phase was methanol/water at a flow rate of 1 ml/min at ambient temperature. Imazalil in the eluate was detected with UV detector at 204 nm a fluorescence detector was used to monitor OPP (excitation 285 nm, emission 350 nm) and TBZ (excitation 296 nm, emission 350 nm) (47). 

So far, capillary electrochromatography has found only a few applications to pesticides. Separation of cinosulfiiron and its by-products can serve as a good example. The separation was done with a C-8 non-endcapped 3 pm packing in a capillary whose dimensions were 33.5 cm (25.0 cm to the detector) x 100 pm internal diameter. A typical separation is presented in Fig. 10.27 [128],... 

It is a coaxial detector with a relative efficiency of 105% and was produced by CANBERRA Semiconductor n.v. in 2000. It is a so called extended range detector with a p-type crystal and a submicron deadlayer (0.5 Lim). It has also a high purity aluminium endcap. The entrance window thickness is 1.5 mm. The active volume of the crystal is 400 cm and the crystal diameter is 80 mm. The detector was first installed with a copper endcap with a carbon epoxy window glued to it. This paper describes the background reduction that was achieved by changing the endcap. 

Figure 2 Background spectra of the underground HPGe-detector before and after the change to an aluminium endcap.

Table 1 List of background y-ray peaks for the underground HPGe-detector before (2003) and after (2005) the installation of the new endcap as well as with mercury shield (2006-...

The system is shown in Fig. 1. The detector can be tilted at any angle for the best geometry for data collection, such as for walls or floors. It is not necessary to use low-background detectors because the natural activity in the field of view (FOV) is higher than the activity in the endcap material. 

The collimator impact for 81 keV is shown in Fig. 11. The counts are normalized to the counts at 90°. The 81 keV lines are almost completely absorbed by either the steel or tungsten. The upturn in the uncollimated curve at 0° and 180° is due to the difference in absorption by the endcap, cup and germanium dead layer for the 0° angle of incidence and the 10° angle of incidence. The combined circular (front face) and cylindrical surface area of the detector perpendicular to the gamma ray flux has a maximum at about 45°, but this is reduced by the change in... 

Fig. 4 Schematic of an ion trap MS instrument. This device consists of two endcap electrodes (entrance and exit) and a ring electrode. An ion trap MS separates ions based on mass-to-charge ratio (m/z). Once ions are introduced into the ion trap MS, the radiofrequency (rf) amplitude is increased so that ions are sequentially ejected (by increasing mass) and detected. This type of MS provides a routine (i.e., benchtop) and sensitive detector using either GC and LC interfaces. Furthermore, this instrument provides a unique format for multiple stages of MS analysis (MS ). (Courtesy of ThermoFinnigan, San Jose, CA.)...

The sample inlet is constituted of a heated fused silica capillary, which is maintained at approximately 200 "C and is encased in a flexible tube. The ion source, in the case of electronic ionization, is composed of electrically heated metallic filaments. Mass analyzers, separating the analytes, include time-of-flight (TOF), linear quadmpole (Q), linear quadrupole ion trap (LIT), quadmpole ion trap (QIT), Fourier transform ion cyclotron resonance (FT-ICR), etc. These detectors differ in their capacity to treat ion beams in a continuous or pulsed (TOF). Quadmpole mass analyzers stabilize and destabilize the ion paths with an oscillating electrical field. A triple quad is more recent technology and consists of three quadmpole stages. Quadmpole ion traps will sequentially eject ions that have been trapped in a ring electrode between two endcap electrodes. 

Fig. 7.1 Left Illustration of the mechtinical design of the three barrel layers and the four endcap disks of the CMS pixel detector. Right raditil cut through the mechanical frame of the first barrel layer...

The ECAL barrel has a volume of 8.14 m and its front face is at a radial distance of 1.29 m from the interaction point. It has a 360-fold azimuthal segmentation and two times 85-fold segmentation in pseudorapidity. The endcap has a coverage of 1.479 < 7l < 3 and is situated at a longitudinal distance of 3.15 m from the interaction point. A preshower detector with a thickness of 3 Xq is placed in front of the endcaps (1.653 < rj < 2.6) to guarantee a reliable discrimination of single photons and photons produced in pairs in neutral pion decays. 

If there is a risk that a detector will become contaminated, and in particular if the detector is liable to be used to measure radioactive solutions, consider covering the endcap with thin plastic film, such as Cling-film . Renew this regularly. 

Place this at precisely 250 mm from the centre of the top of the endcap on the detector axis. 

Figure 13.11 Response contours around a germanium p-type detector. Contours are for the 1332.5 keV full-energy peak from a point Co source, relative to the centre of the endcap all distances are in cm (adapted from drawing by R. Mercer)...

Counting efficiency is greater if the sample is placed on top of the detector, rather than at the side. This is because the detector is mounted close to the face of the encapsulation and there is likely to be a greater distance between the side of the germanium and the sidewall of the endcap. In addition, the detector crystal is mounted within an aluminium cup. That will absorb a proportion of the gamma-rays before they reach the detector itself. 

There is a rapid fall-off in efficiency with distance from the endcap. Moving the detector 1 cm away from this particular detector would reduce efficiency by 40 %. 

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