Background Compton suppression

Measurements were taken on 158Er at a total of 14 target-stopper distances. A portion of the total-projected spectra taken at four of the target-stopper separations is shown in Fig. 1. These spectra are of excellent statistical quality and reveal a favorable peak-to-background ratio in the 0° detector as a result of using the Compton suppression shield. 

The room-background data discussed here are based on a week-long measurement performed using the Compton-suppressed HPGe detector in Budapest (Belgya et al. 2003 Belgya et al. 1997 Revay et al. 2004). The majority of the peaks originate from the natural radioactive decay chains, i.e., the Th, Np series, and K. These nuclides are in... 

The detection limits can be further improved by lowering the background activity using a Compton suppression spectrometer (CSS). A fairly simple CSS would consist of a high resolution Ge detector surrounded by a Na guard detector and an array of electronic modules. The peak-to-Compton ratio can be improved to 550 to 650. The cost of a CSS can vary between US 75 000-100 000. 

A guided beam of cold neutrons will provide the highest intensity neutron beam with the lowest background at the sample position. Therefore, the use of a neutron guide is desirable. In addition, a pair spectrometer or a Compton suppression system is a desirable option, although this need is decreasing due to better detectors, MCAs and analysis software. 

Active background reduction is a means of reducing that continuum. I will discuss two aspects of this reduction in the Compton continuum within the spectrum and reduction of the cosmic ray continuum discussed above. Both involve additional detectors to detect gamma-rays that are either leaving the detector, in the case of Compton suppression, or might be about to enter the detector, in the case of background suppression. 

Currie et al. have described a 30 cm Ge(Li) anti-coincidence spectrometer shielded by a split annular NaI(Tl) detector. This design of shield also allows pair-escape peak suppression, but has a lower background and Compton suppression efficiency than the plastic scintillator systems because of the lower solid angle around the detector for which shielding is provided. 

Placement of the monochromator in the diffracted beam has the advantage of suppressing background radiation originating in the specimen, such as fluorescent radiation and incoherent (Compton modified) scattered radiation. For example, if a steel specimen or any iron-rich material is examined with copper radiation in an ordinary diffractometer, the background due to fluorescent Fe K radiation will be unacceptably high. But if a monochromator is added and oriented to reflect only Cu Aa, the background is reduced practically to zero, because the fluoresced Fe Kol and Fe K(i do not enter the counter. A monochromator may therefore... 

In the anticoincidence mode, the pulse applied to the MCA linear pulse input will only be processed if there is NO signal on the gate input at the time the linear gate is about to be opened. This is the more common use. It might be used by the pile-up rejector to prevent piled-up pulses being processed or by a Compton or background suppression system to indicate that the pulse is, in some way, invalid. 

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