168
H. Utsunomiya et al.
The data newly acquired in the PHOENIX Collaboration are evaluated by the
Japan Atomic Energy Agency (JAEA), the Chinese Nuclear Data Center (CNDC),
and Korean Atomic Energy Research Institute (KAERI) and compiled in the IAEA
updated photonuclear data library. The data are also used to supplement the (γ, γ’)
and the Oslo method data to construct the photon strength function and compiled in
the IAEA reference database for photon strength functions.
4 γ-Ray Strength Function
Figure 1 shows the γ-ray strength function (γSF) for Ni isotopes constructed with
the γSF method [7] which has been devised to investigate systematically (γ, n) and
(n, γ) cross sections over an isotopic chain. The present (γ, n) data are used as
experimental constraints on the model E1 and M1 γSFs from the Hartree–Fock–
Bogolyubov plus quasi-particle random phase approximation based on the Gogny
D1M interaction. The recent systematics of the γSF [8] has been taken into account;
the γSF in de-excitation mode differs from that in excitation mode in the zerolimit behavior of both E1 and M1 strengths, the latter of which is referred to as
M1 upbend. In the figure, the M1 γSF is shown for two different zero-limit values,
3 × 10 −8 and 10 −7 MeV −3 .
The mean field plus QRPA calculations need some phenomenological corrections, which include a broadening of the QRPA strength to take the neglected
damping of collective motions into account as well as a shift of the strength to
lower energies due to the contribution beyond the one-particle–one-hole excitations
and the interaction between the single particle and low-lying collective phonon
degrees of freedom. As such phenomenological corrections [8], we have introduced
an E1 damping width of 4.5 MeV which is smaller than the systematics of
E1 = 7 − A/45 MeV [8] due to the closed proton shell in Ni isotope and M1
damping width of 2 MeV. As a consequence, a factor of 2/3 on the overall E1
strength is required to reproduce the present peak photoneutron cross section in
the GDR region. More details can be found in Ref. [7].
5 GDR Cross Section
5.1 209 Bi
Previously we published GDR cross sections for 209 Bi [12]. We found it necessary
to take into account the effect of the electromagnetic interaction (pair production,
Compton scattering, and photoelectric absorption) of high-energy γ-ray beams in
the thick (7 mm or 10 mm) 209 Bi target material on the (γ, xn) cross sections [13].
The interaction produces the secondary gamma rays which can induce the giant
H. Utsunomiya et al.
The data newly acquired in the PHOENIX Collaboration are evaluated by the
Japan Atomic Energy Agency (JAEA), the Chinese Nuclear Data Center (CNDC),
and Korean Atomic Energy Research Institute (KAERI) and compiled in the IAEA
updated photonuclear data library. The data are also used to supplement the (γ, γ’)
and the Oslo method data to construct the photon strength function and compiled in
the IAEA reference database for photon strength functions.
4 γ-Ray Strength Function
Figure 1 shows the γ-ray strength function (γSF) for Ni isotopes constructed with
the γSF method [7] which has been devised to investigate systematically (γ, n) and
(n, γ) cross sections over an isotopic chain. The present (γ, n) data are used as
experimental constraints on the model E1 and M1 γSFs from the Hartree–Fock–
Bogolyubov plus quasi-particle random phase approximation based on the Gogny
D1M interaction. The recent systematics of the γSF [8] has been taken into account;
the γSF in de-excitation mode differs from that in excitation mode in the zerolimit behavior of both E1 and M1 strengths, the latter of which is referred to as
M1 upbend. In the figure, the M1 γSF is shown for two different zero-limit values,
3 × 10 −8 and 10 −7 MeV −3 .
The mean field plus QRPA calculations need some phenomenological corrections, which include a broadening of the QRPA strength to take the neglected
damping of collective motions into account as well as a shift of the strength to
lower energies due to the contribution beyond the one-particle–one-hole excitations
and the interaction between the single particle and low-lying collective phonon
degrees of freedom. As such phenomenological corrections [8], we have introduced
an E1 damping width of 4.5 MeV which is smaller than the systematics of
E1 = 7 − A/45 MeV [8] due to the closed proton shell in Ni isotope and M1
damping width of 2 MeV. As a consequence, a factor of 2/3 on the overall E1
strength is required to reproduce the present peak photoneutron cross section in
the GDR region. More details can be found in Ref. [7].
5 GDR Cross Section
5.1 209 Bi
Previously we published GDR cross sections for 209 Bi [12]. We found it necessary
to take into account the effect of the electromagnetic interaction (pair production,
Compton scattering, and photoelectric absorption) of high-energy γ-ray beams in
the thick (7 mm or 10 mm) 209 Bi target material on the (γ, xn) cross sections [13].
The interaction produces the secondary gamma rays which can induce the giant