Detector solid angle

Microbeam scanning of the sample cross-section was performed with an external microbeam (in air), using a focused 4 MeV proton beam and a 50 pm thick Kapton foil at the vacuum-air interface, with a 5 mm diameter beam exit hole. The 2 mm thick slice of gel polymer sample was placed less than 100 pm from the exit foil, with the cross-section facing the Kapton foil. A HPGe y-ray detector was placed just behind the sample in order to achieve as large as possible detector solid angle. The ion current was kept below 100 pA in order to minimize damage to the sample. 

Detector solid angle 3 to 5 msr, surface barrier detector area 25 to 300 mm2... 

We have carried out the first measurement of the 2S /2 — 2P3/2 interval in 7V6+. Our result is in good agreement with the theory, but the precision of 0.07 cm-1, or. 17% of the Lamb Shift interval, is not sufficient to provide a useful test. However the count rates and signal-to-background ratio achieved, 100 kHz/particle-nA and 25 respectively, are consistent with obtaining a statistical precision of 0.001 cm-1. The beam current and detector solid angle can be increased in future experiments if necessary. 

The detector solid angles depend on the index of refraction of the fluid in the cell because of refraction at the fluid-window interface. The solid angles are proportional to 1/n for both detectors. However, the... 

Detection limit based on 0.1 counts per second, 0.1% detector solid angle, and a neutron intensity of 6 x 10° s ... 

Intensities of the characteristic X-ray hnes can be converted into concentration data. X-ray yield depends on the number of atoms in the sample, the ionisation cross-section, the detector solid angle, intensity of the ion beam etc. and so the determination of an absolute concentration of an element in an unknown matrix represents a complicated problem. In practice, the evaluation of the sample composition involves the comparison of X-ray yields from the unknown sample with that from known standards. 

The chance that one particle from the beam ejects a recoil of element Z2, M2) in such a way that it starts moving in the direction of the detector is proportional to the areal density (atom cm ) of this element and the detector solid angle of the detector. Treating the interaction as purely Rutherford scattering (since the energy available in the center of mass is at least five times below the Coulomb barrier) the elastic scattering cross-section is given by Rutherford differential cross-section for ERD i.e.,... 

The yield of the detected recoils Y x) in a detector solid angle df (originating from depth x) during an irradiation of a sample of thickness Ax by N incident ions, is given by... 

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