In-beam spectroscopy of low energy conversion electrons with a recoil shadow method ? A new possibility for subnanosecond lifetime measurements

Abstract

An electron spectrometer consisting of an electron transport system with normal conducting solenoidal coils and a Si(Li)-detector as the energy dispersive element is described. It can be used for in beam spectroscopy of electrons in three different modes. The first one is the usual broad range mode with a low energy cut offofthe transmission performed by a tantalum disk between target and detector. The second one is the lens spectrometer mode. An envelope baffle system permits electron detection in a momentum band A pip = 0.12. To cover a large energy range the magnet current is sweeped. In the third mode-the recoil shadow method -a longitudinal semicylindrical baffle between target and Si(Li)-detector allows spectroscopy of delayed electrons emitted from recoil nuclei in flight. Special features of this method are high transmission, and strong suppression of the prompt 3-electron background. Lifetime measurements based on the detection of conversion electrons are possible by variation of the target position. This was tested with the 152Sm(160, x n) 168 -xyb compound nuclear reaction at a recoil velocity vr = 0.01 c, where half lives between 0.1 ns and 1 ns were determined.

6 Modern Electron and Positron Spectrometers – Selected Aspects of a Broad Field

“…Here we like to present a pioneering experiment [35] which demonstrated the power of in-beam Si(Li) spectroscopy of conversion electrons with a long solenoid in light-ion collisions, where Doppler shifts are still small and not yet destructive for a reasonable energy resolution. The field is typically of the order B z = 0.6 Τ and is produced by an adapted solenoid coil ( Fig.…”

Isomeric transitions in203Bi and205Bi

“…The field at the detectors was chosen to be about four times lower than that at the target in order to reduce the maximum angle of incidence at the detectors to 30 ~ for an emission angle of 90 ~ with respect to the axis of the solenoid at the target [9]. This reduces the maximum fraction of backscattered electrons from f(90~ to f(30~ [9,10]. The radii of the electron orbits at the detectors are about twice as large as those at the target, but these are still much smaller than the dianaeter of the detectors (~ 2 cm).…”

Level schemes of163, 165Yb and backbending behaviour of neutron deficient Yb-isotopes

“…In order to separate conversion electrons from the large amount of low energy b-rays the recoil shadow method is applied. In this method described extensively in [8] a longitudinal baffle system shaped like an one ended semicylindrical tube is inserted into the solenoid between target and detector. The target is moved behind this diaphragm, so that no prompt electrons reach the detector and only delayed conversion electrons from the decay of the recoils leaving the target are detected with a peak efficiency of up to ~8~o.…”