The electron-neutrino angular-correlation coefficient was determined by measuring the shape o f the proton recoil spectrum from free-neutron decay. The protons leaving a highly evacuated tangential reactor beam tube were analyzed by a spherical condenser spectrometer and counted in an ion-electron converter detector. The design of the apparatus, the possible disturbing influences, and the measures to reduce their effects are discussed. The remaining corrections were either calculated or determined by auxiliary measurements and applied to the spectral shape. The sources of systematic errors are considered and included in the final results. We obtained a = -0.1017 +0.0051 giving /g,/g,l = 1.259 + 0.017.-
Measurements of the electron-neutrino angular correlation coefficient u in the freeneutron decay are reported. The method is based on the measurement of the energy spectrum of recoil protons obtained from neutrons inside a highly evacuated tangential reactor beam tube. Spectroscopy was done outside the reactor shielding by means of an electrostatic condenser and an ion-electron converter detector of the coincidence type. The result, based on 30 measured proton-energy spectra, is a =-0.099*0.011, giving jGA/GVI=1.250* 0.036. Thus a considerable improvement in accuracy concerning the measurement of a of the free unpolarized neutron has been achieved. The result is in good agreement with the data obtained from polarized neutron decay.The precise determination of weak-interaction p a r a m e t e r s (especially of the ratio of the coupling constants G,/G,) without a possible interference f r o m nuclear effects requires the study of the decay of f r e e neutrons with an accuracy better than previously reported. The most accurate value of GA/G, presently available f r o m a single experiment i s based on a measurement by Christensen et a1.l of the electron-asymmetry coefficient A in the decay of polarized neutrons, giving / G,/G, I = 1.26 k0.02. Measurements of the electron-neutrino angular correlation coefficient a of comparable accuracy have not been performed so f a r . The best experimental value of a is that of Grigor'ev et a1.' They measured coincidences between the electrons and the recoil protons from an unpolarized neutron beam and reported a = -0.091 i 0.039 and G~/ G , = -1.22 k0.08.The determination of a reported h e r e was done by a high-precision measurement of the energy spectrum of the recoil protons in free-neutron decay314 in an evacuated tangential through-tube near the c o r e of the ASTRA reactor. The theoretical shape of this spectrum had been computed by Riehs5 and by ~a c h t m a n n~ for various values of a. The shape to be expected in this experiment due to the finite source volume and to the neutron motion had been calculated by Nachtmann and P a~l .~ The spectrometer used (Fig. 1) i s an electrostatic spherical condenser8 with an ion-electron converter detector of the coincidence type.''1° Between c o r e and spectrometer a number of collimators and baffles w e r e used t o reduce the direct reactor radiation. The source aperture which restricted the effective source volume near the core of the reactor had a diameter of 4.0 c m and w a s situated 297.5 c m f r o m the spectrometer entrance aperture (3.8-cm diameter).After energy selection by the spherical condenser (90" deflection angle, 30.0-cm radius, 6.0-cm electrode distance) the protons were accelerated towards a self-supporting aluminum foil of 10-mm diameter (usable range of acceleration voltage -20 to -35 kV, foil thickness approximately 30 pg/cm2). The secondary electrons ejected f r o m both sides of the foil w e r e accelerated to ground potential (by the electron lenses shown) and were measured by means of scintillation detecto...
In the last years a series of measurements o~1 weak-interaction in neutron decay has been performed usiag the coincidence detector developed by O. BENKA. A_ short description of this detector will be presented with spccial emphasis on the problem of counting low-energy protons. Special care was taken in order to ensure the detection efficieacy being independent of partiele energy. l. IntroductionIn the last years a series of measurements on weak-interaction in neutron decay has been performed. The essential work was the precise measurement of the energy spectrum of the recoil protons from free-neutron decay [1,2]. For this purpose, the detecting device (developed by O. BENXA [3]) should have a very high counting efficiency for the low-energy protons (Tma x : 751,4 eV) under consideration. Special care had to be taken in order to ensure the detection efficiency being independent of the particle energy at the detector entrance [3,4]. Requirements and layoutAccording to the neutron decay measurement, the detecting device has to fulfil the following requirements (see also [2,4]): 1) to focus protons onto a converter foil (at U B ~ 25kV) independent of their primary energies T at the detector entrance (50 eV < T < 750 eV);2) to ensure a counting probability independent of the primary energy T of the protons;3) to discriminate against counting of heavy ions (from residual gas, etc.); 4) to keep the background low (for a typical radiation-background of lmr/h) and independent of energy setting.On this basis, O. BEr~xA has developed a coincidence type ion-electron converter detector consisting of four distinguishable units [3]:
Measurements of the radiation enhanced diffusion and permeation of hydrogen in stainless steel type 4301 (s. s. 304) in the temperature range of 350 to 600 ~ are reported. As radiation source an edge position of the ASTRAreactor core was used (dose rate 0.1 to 0.5 W/g). The permeation as well as the diffusion coefficient were found to be considerably larger during irradiation than the thermal effects at the same temperatures (measured by ohmic heating with the reactor shut down). A detailed description of the apparatus is given together with a discussion of the resuhs hitherto achieved.* This research was supported in part by the "Fonds zur F6rderung der wissenschaftlichen Forschung in Osterreich", Vienna (Proj. Nr. 3423).
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