Intermediate-Image Pair Spectrometer

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Abstract
An iron‐free intermediate‐image beta‐ray spectrometer has been constructed having a momentum spread (full width at half‐maximum) for a point source of conversion electrons continuously variable between limits of 0.5% and 4% with corresponding transmissions of 1% and 8% of 4π, respectively. The line half‐width contribution due to source size is 0.3% per mm of diameter. At a power dissipation of 100 kw the spectrometer focuses electrons of 9‐Mev energy allowing positron‐electron pair lines corresponding to transitions of up to 19 Mev to be measured using a double‐crystal statistical‐separation detector together with a fast coincidence circuit. In tests with the 6‐Mev nuclear transition in O16 using a Van de Graaff beam spot 1 mm in diameter the momentum half‐width of the pair line can be varied from 0.56% to 2.5% with corresponding absolute transmissions of 0.07 to 6.3 pair counts per 105 source transitions, respectively. The energy of this transition has been determined as 6.065±0.009 Mev. Electron‐gamma and electron‐electron coincidence measurements on radioactive sources may be made with the spectrometer in conjunction with crystal detectors placed near the source.

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