Gamma-ray Coincidence Spectra Research Articles

Probing nuclear shapes close to the fission limit with the giant dipole resonance inRn216

The gamma-ray decay of the giant dipole resonance (GDR) in the compound nucleus {sup 216}Rn formed with the reaction {sup 18}O+{sup 198}Pt at the bombarding energy of 96 MeV was investigated. High-energy gamma-ray spectra in coincidence with both prompt and delayed low-energy transitions were measured. The obtained GDR width at the average temperature {approx_equal}1 MeV was found to be larger than that at T=0 MeV and to be approximately constant as a function of spin. The measured width value of 7 MeV is found to be consistent with the predictions based on calculations of the nuclear shape distribution using the newest approach for the treatment of the fission barrier within the liquid drop model. The present study is the first investigation of the giant dipole resonance width from the fusion-evaporation decay channel in this nuclear mass range.

Gamma decays of positive parity states in 45Sc

Levels in 45Sc have been investigated through the 42Ca(α, pγ) reaction. Gamma-ray spectra in coincidence with backscattered protons were recorded with a Ge(Li) detector positioned at angles 105° ≧ θ ≧ 0°. The data corresponding to the members of the proposed K π = 3 2 + band were analysed and led to the following results for excitation energies (keV), spins, parities and lifetimes (ps): 543.3, 5 2 +, 9.2 −3.3 +6.8; 974.8, 7 2 +, 3.2 −0.7 +0.8; 1433.8, 9 2 +, 7.8 −2.2 +4.3; 2031.6, 11 2 +, 1.6 −0.5 +0.8 and 2563.3, 9 2 +, 11 2 +, 13 2 +, 2.0 −0.6 +0.9 . Multipole mixing ratios and γ-ray branching ratios were also obtained from the data, and reduced electromagnetic transition matrix elements have been deduced. Results for other positive parity states are also presented.

Nuclear structure of 47Sc : (I). Gamma-ray correlations and lifetime measurements

Levels of 47Sc below an excitation energy of 2.7 MeV have been investigated through the 44Ca(α, pγ) 47Sc reaction. Gamma-ray spectra in coincidence with protons were recorded with a Ge(Li) detector positioned at several angles and at α-energies of 10.15 and 11.00 MeV. Level positions, lifetimes, decay modes and spin values were deduced from these measurements. This study was supplemented by a γ-γ coincidence measurement. The electromagnetic properties for the negative parity states are compared with intermediate coupling predictions. A classification of the positive parity states into several rotational bands is proposed.

A study of the decay scheme of 134I

The decay properties of 134I obtained from fission products have been investigated with NaI(Tl) and Ge(Li) detectors. Energies (and relative intensities) of the gamma rays determined from the Ge(Li) detector and NaI(Tl)-Ge(Li) coincidence studies are 136(5.0), 236(weak), 405(8.4), 433(4.2), 488(weak), 514(4.1), 541(9.8), 596(11.6), 622(10.3), 633(3.1), 644(weak), 677(7.7), 733(weak), 768(3.9), 848(100.0), 859(6.1), 873(weak), 885(69.1), 905(weak), 923(weak), 948(6.4), 976(5.4), 1041(3.2), 1073(17.1), 1103(2.3), 1138(11.8), 1458(4.3), 1615(4.7), 1743(3.0) and 1810(6.2) keV. Gamma-ray coincidence spectra with the Ge(Li) detector were obtained with six gates; the lower half, the upper half and the total peaks of gamma-ray at 0.87 and 1.80 MeV in the NaI(Tl) gamma-ray spectrum. Anisotropy measurements for the 885-848, 1073-848 and 1138-885 keV cascades were carried out, and the possible spin sequences were given. A decay scheme is proposed with energy levels (and spins) in 134Xe at 848(2 +), 1615(2 +), 1733(4 +), 1921(3,2), 2138, 2274, 2355, 2410, 2591, 2658, 2870(4.5), 3224and 3379 keV. The levels, which are populated by strong beta groups, are also confirmed by a summing spectrum measurement. The half-life of 134I was obtained to be 52.5 ± 0.1 min.

Decay ofAg103

Natural palladium foil was irradiated with 18-MeV protons to produce 1.1-h ${\mathrm{Ag}}^{103}$ by ($p,xn$) reactions. The target foil was placed directly into the ion source of the Princeton isotope separator, and the silver isotopes were volatilized, dispersed, and collected. Spectroscopic data were obtained using Ge(Li) gamma-ray detectors, an orange-type electron spectrometer, and permanent magnet spectrographs. Transitions were observed at 118.66, 148.26, 244.5, 266.9, 532.2, (555.9), 578.8, 741.9, 940.6, 1007.1, 1030.3, 1155.8, 1183.6, and 1274.6 keV. (Energies of doubtful transitions are mentioned in parentheses.) Gamma-ray spectra in coincidence with several conversion-electron lines, taken with a NaI(Tl) detector in conjunction with the orange spectrometer, gave evidence for levels in ${\mathrm{Pd}}^{103}$ at 0, 118.7, 244.5, 266.9, (532), (823), (1184), and 1274.4 keV.

Lifetimes of theN145.83-MeV and 6.44-MeV Levels

The lifetimes of the ${\mathrm{N}}^{14}$ 5.83- and 6.44-MeV levels were studied by the Doppler shift attenuation method using the ${\mathrm{C}}^{12}({\mathrm{He}}^{3}, p){\mathrm{N}}^{14}$ reaction to populate the levels. The shifts in energy of the 0.73-MeV 5.83\ensuremath{\rightarrow}5.10 transition and the 1.33-MeV 6.44\ensuremath{\rightarrow}5.10 transition were observed between two angles to the beam by recording gamma-ray spectra in coincidence with the ${\mathrm{N}}^{14}$ 5.10\ensuremath{\rightarrow}0 transition. From these measurements the mean lifetime of the ${\mathrm{N}}^{14}$ 5.83-MeV level was found to be greater than 2.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}12}$ sec, while the mean lifetime of the ${\mathrm{N}}^{14}$ 6.44-MeV level was found to be (5.9\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ sec.

Gamma-Ray Spectra from Neutron Capture in Resonances ofMn55

The Argonne fast chopper was used to select the energy of the incident neutrons on the basis of their time of flight. The gamma-ray spectra resulting from capture of these timed neutrons by Mn/sup 55/ were measured with two 4-in. NaI(Tl) scintillators using a fast-slow coincidence technique. The gamma-ray coincidence spectra associated with capture in the resonances at investigation of the low-lying excited state of Mn/sup 56/ was made by means of coincidence measurements on the gamma rays following capture of thermal neutrons. (W.D.M.)

LXI. The levels of19F from inelastic neutron scattering

Abstract The gamma-rays following inelastic neutron scattering in 19F have been studied as a function of neutron bombarding energy up to 2.2 Mev. The gamma-ray spectra in coincidence with radiation from the lowest excited levels, at 111 and 196 kev, have also been measured near the thresholds for excitation of the higher levels. The following gamma-rays have been found: 1.236±0.012 and 1.356±0.012 Mev, in coincidence with 111 kev radiation; 1.360±0.012 Mev, in coincidence with 196 kev radiation; 1.472±0.016 Mev corresponding to a ground-state transition. The results are interpreted in terms of 19F levels at 1.557, 1.466 and 1.346 Mev. Branching ratios for the decay of each level to the ground, 111 kev and 196 kev states have been examined. No other levels up to 2.0 Mev have been found.