S. E. Arnell

A 2π neutron and γ-ray multiplicity filter for the NORDBALL detection system

Abstract A description of the 2π neutron and γ-ray multiplicity filter designed as a part of the NORDBALL detection system is given. The filter consists of ten hexagon and six pentagon shaped detectors filled with BC501 liquid scintillator. Individual detector properties as well as system behaviour including neutron scattering are discussed and test results are presented. The properties of the n-γ pulse shape discriminators used for the system were studied. The discriminators, based on the zero-crossing principle, showed a very efficient separation in the 100:1 dynamic range of neutrons and γ-rays starting from 70 keV of recoil electron energy. Results from a use of the filter in a study of the 28 Si + 58 Ni reaction are presented.

States of high spin in 87Sr, 88Sr and 89Sr

Abstract The reactions 84 Kr( α , n), 86 Kr( α , 3n), 86 Kr( α , 2n) and 86 Kr( α , n) were used to excited states in 87 Sr, 88 Sr and 89 Sr. The de-excitation of these states was studied by in-beam γ-ray spectroscopy. A number of new high-spin states have been observed. Many 87 Sr and 89 Sr levels are interpreted as due to the coupling of a g 9 2 neutron hole and a d 5 2 neutron, respectively, to excited states of the core nucleus 88 Sr. Lifetime measurements have also been performed.

Particle identification by digital charge comparison method applied to CsI(Tl) crystal coupled to photodiode

Abstract The application of the high energy resolution technique to the digital charge comparison method of particle identification with a CsI(Tl)-photodiode assembly allowed to get a good α-proton separation down to about 2 MeV α particles.

Proton capture in A40

Abstract The A40(p, γ)K41 reaction has been studied in the range of proton energies from 700 keV to 1400 keV using electromagetic separated isotopes. Fifty-seven excited levels in K41 were observed. The target problem was given special attention.

High Spin States in 39K from the 36Ar(α,pγ) 39K Reaction

The decay properties of high-spin states in 39K have been investigated by means of the 36Ar(α,pγ)39K reaction at Eα=10-14 MeV. From measurements of the yield function and the angular distribution of the γ-transitions it can be concluded that the following states have been excited: 2 814 keV, 7/2-, 3 597 keV, 9/2-, 3 943 keV, 11/2-, 4 126 keV, 5/2(-), 4 521 keV, 9/2(-) (11/2-), 5 717 keV, 13/2 and 6 474 keV, (15/2). Multipole mixing ratios and transition strengths are given for some transitions. Comparisons are made with a recent shell-model calculation and with calculations involving collective features.

Low spin, negative parity states in the N = 103 isotones of 171Er, 173Yb and 175Hf identified by thermal neutron capture reactions

Abstract Energies and intensities of the γ-rays following thermal neutron capture in enriched samples of 170 Er, 172 Yb and 174 Hf have been measured using internal reactor targets and a three-crystal Ge(Li) pair and anti-Compton spectrometer. The reaction Q -values, excitation energies and intensity values have been deduced. Decay schemes of 171 Er, 173 Yb and 175 Hf are presented together with the spins and Nilsson assignments of the low-lying rotational bands populated from the capture states.

LOW SPIN STATES IN

The energies and intensities of gamma radiation from thermal neutron capture in an enriched sample of 180Hf have been determined by means of a Ge(Li) pair and anti-Compton spectrometer. An internal reactor target has been used. The reaction Q-value, the energies of the excited states and the decay scheme of 181Hf have been deduced. A large number of low K-value states are found in the range of excitation energy from 1 to 2 MeV.

sup 181

Abstract The reactions 82 Kr(α, n) and 84 Kr(α, 3n) were used to populate excited states in 85 Sr. The deexcitation of these states was studied by in-beam γ-ray spectroscopy. A number of new high-spin states have been observed. Lifetime measurements have also been performed. Some of the levels are interpreted as shell-model states.

Hf FROM THE THERMAL NEUTRON CAPTURE REACTION.

Abstract The half-lives of the positon emitters C11 N13 F17 Na21 Al25 and A188, P80 have been determined. The decay spectrum of Al25 has been investigated. No evidence for γ-rays indicating a complex decay was found. A plot of log T 1 2 against log A 2 3 is discussed in terms of shell effects. It is shown that individual lines can be drawn through the points belonging to successive proton subshells. The value for Ne19 falls below the line representing the d 5 2 subshell, which somewhat favours the proposal that the ground states of Ne19 and F19 are 2 s 1 2 -states From a plot of the β+-energies the pairing energy difference seems to have a value of about 0.1 MeV in the d 5 1 -subshell.

High-spin states of 85Sr

Abstract High-lying and high spin states of nuclei around N,Z=40 have studied using the ( 58 Ni + 28 Si) and ( 58 Ni + 32 S) reactions and NORDBALL Ge-Array equipped with a Silicon Ball for light charged particle detection. Simultaneously complementary experiment have been carried out using in-beam and β decay measurements to establish lifetimes and spin-party values of low-lying and ground states at Kyushu University. Some of results are reported.