The station for solid-state VUV spectroscopy on the dedicated SR source Siberia-1 of the Kurchatov Institute, USSR, is described. The station consists of a beam line, a Seya-Namioka monochromator with toroidal focusing mirrors, a high-vacuum sample chamber and a computer control system. Characteristics of the optical scheme are discussed.

The luminescence excitation spectra of anthracene, adenine and thymine have been measured within an excitation energy range from 4 to 30 eV. Anticorrelation between the excitation and absorption bands has been explained in terms of surface losses. Energy transformation of primary electron excitations and the dynamics of low-energy excitations and their effect on the luminescence excitation spectra are discussed.

The report deals with the results of developing the 450-MeV electron storage ring SIBERIA-1, i.e. the first phase of the specialized synchrotron radiation source of the I.V. Kurchatov Institute of Atomic Energy. The storage ring was designed, manufactured and put into operation by the staff of the Institute of Nuclear Physics of the Siberian Department of the USSR Academy of Sciences in 1983. In 1984 a superconducting “snake” with a 4.3 T field was mounted in the storage ring.

A multi-channel time-of-flight fast-neutron spectrometer is described which uses the natural modulation of a cyclotron beam. The time analyser operates on the ‘nonius’ principle, and has a channel width of 1 mμsec. There are 256 recording channels, each capable of accepting 2 16 pulses.

By means of the time of flight method the neutron spectra from the reactions Li/sup 6/(p,n)Be/sup 6/ and Li/sup 7/(p,n)Be/sup 7/ were measured, The neutron distribution and the reaction cross sections were also determined. For the Li/sup 6/ reaction Q/sub o/= 5.2 plus or minus 0.2 Mev. The width of the ground state was GAMMA < 0.3 Mev. The angular distribution of neutrons was sigma ( theta ) = 0.19 + 0.23 cos( theta ) + 0.70 cos/sup 2/( theta ) mb/ steradian. The mass defect of Be/sup 6/ was 20.3 < 0.2 Mev, and the reaction cross section for the ground state at a proton energy of 9 Mev was sigma = 5 plus or minus 1 mb. For the Li/sup 7/ reaction the neutrons corresponding to the ground state, the 0.43 Mev level, and the 4.65 Mev level was found. The angular distribution of the neutrons of the ground state and the first level was sigma ( theta ) = 6.8 + 2.4 cos/sup 2/( theta ) mb/ steradian. The total reaction cross section for the formation of the ground state and the first level at a proton energy of 9 Mev was sigma = 100 plus ormore » minus 20 mb. Neutrons were also observed from the Li/sup 6/(p,pn)Li/sup 5/ and Li/sup 6/(p,2pn) He/sup 4/ reactions. (J.S.R.)« less

The time-of-flight method has been used to study the neutron spectra from the reactions of 6Li and 7Li with 9 MeV protons. Neutron groups were observed corresponding to transitions to the ground state of 6Be and to the three lower states of 7Be, as well as a continuous distribution of low-energy neutrons due to more complex reactions. Observation of the group of neutrons from the reaction 6Li(p,n)6Be is the first experimental evidence of the existence of the 6Be nucleus. The Q-value of the reaction 6Li(p,n)6Be is equal to −5·2 MeV and the width of the ground state of 6Be is less than 0·3 MeV. The differential cross-sections for neutron formation were measured at angles of 0, 15, 30, 60 and 120°.

The time-of-flight neutron spectrometer used with the cyclotron opens up broad new possibilities of use of the cyclotron for the study of nuclear reactions. We shall enumerate several of them. The efficiency of the spectrometer can be brought up to several tens of percent, which permits the study with existing neutron fluxes of secondary processes (for example, the spectra of scattered neutrons entirely free from the background of γ-rays produced in the target. The spectrometer gives the possibility of studying neutron spectra on a background of harder and more intense groups, thanks to which the first works on the study of neutron spectra [20,21] already gave new physical results. The use of several counters, connected in the spectrometer circuit and in coincidence circuits with each other, allows the study of neutron spectra accompanied by a definite secondary particle, and also of the angular correlations of particles emitted by the target (for example, the angular correlation of γ-quanta with neutrons of definite energy).