Low-energy tail of the giant dipole resonance inMo98andMo100

Abstract

Dipole-strength distributions in the nuclides 98 Mo and 100 Mo up to the neutron-separation energies have been studied in photon-scattering experiments at the bremsstrahlung facility of the Forschungszentrum Dresden-Rossendorf. To determine the dipole-strength distributions up to the neutron-emission thresholds, statistical methods were developed for the analysis of the measured spectra. The measured spectra of scattered photons were corrected for detector response and atomic background by simulations using the code GEANT3. Simulations of γ -ray cascades were performed to correct the intensities of the transitions to the ground state for feeding from higher-lying levels and to determine their branching ratios. The photoabsorption cross sections obtained for 98 Mo and 100 Mo from the present (γ, γ ) experiments are combined with (γ, n) data from literature, resulting in a photoabsorption cross section covering the range from 4 to about 15 MeV of interest for network calculations in nuclear astrophysics. Novel information about the low-energy tail of the giant dipole resonance and its energy dependence is derived. The photoabsorption cross sections deduced from the present photon-scattering experiments are compared with existing data from neutron capture and 3 He-induced reactions.

Pygmy dipole strength inZr90

“…(4) 0.74 (9) (1 − ) [7] 0.93 (20) 154 (28) 884 (164) 8144(2) 20 (13) (8) 24 (14) 170(101) [8] 9034.0 (8) 35 (7) 247(50) [8] 9043. 6(4) 0.44(6) 1 71(10) 503(68) 9053.5 (7) 38 (7) 270 (49) (7) 107 (14) 778 (104)[8] 9177.5 (5) 162 (18) 1182(134) [8] 9187 (3) 45 (13) 329 (95)[8] 9196.5 (3) 0.72 (7) (1 − ) [7] 252 (25) 1849(186) 9260.5 (6) 0.67 (9) (7) 111 (21) 843 (161) (11) 71 (16) 543 (123)[8] 9424.3 (10) 79 (17) 608 (129) (7) 33 (6) 275(51) [8] 9754.0(6) 0.46 (29) 1 50(9) 413(7...…”

“…The remaining transitions, assumed as ground-state transitions, have been used to derive the corresponding level energies which are listed in Table I together with spin assignments deduced from angular distributions of the ground-state transitions, integrated scattering cross sections, and the quantities Γ 2 0 /Γ. (4) 0.74 (9) (1 − ) [7] 0.93 (20) 154 (28) 884 (164) 8144(2) 20 (13) (8) 24 (14) 170(101) [8] 9034.0 (8) 35 (7) 247(50) [8] 9043. 6(4) 0.44(6) 1 71(10) 503(68) 9053.5 (7) 38 (7) 270 (49) (7) 107 (14) 778 (104)[8] 9177.5 (5) 162 (18) 1182(134) [8] 9187 (3) 45 (13) 329 (95)[8] 9196.5 (3) 0.72 (7) (1 − ) [7] 252 (25) 1849(186) 9260.5 (6) 0.67 (9) (7) 111 (21) 843 (161) (11) 71 (16) 543 (123)[8] 9424.3 (10) 79 (17) 608 …”

“…I). [8] Value deduced under the assumption of J x = 1. [9] This transition is superimposed by a transition in 11 B.…”

“…The reliability of the simulation was tested by comparing simulated spectra with measured ones as described in Refs. [7,8]. The absolute efficiencies of the HPGe detectors were determined experimentally up to 1333 keV from measurements with 22 Na, 60 Co, 133 Ba, and 137 Cs calibration sources.…”

“…The bremsstrahlung facility [6] at the superconducting electron accelerator ELBE of the research center Dresden-Rossendorf opens up the possibility to study the dipole response of stable nuclei with even the highest neutron-separation energies in photon-scattering experiments. In the course of a systematic study of dipole-strength distributions for varying neutron and proton numbers in nuclei around A = 90 [7,8] we have investigated the N = 50 nuclide 90 Zr.…”