218
J. A Cizewski et al.
132 Sn(n,γ) cross section is expected to be dominated by DSD capture, for N < 82
isotopes the contribution from statistical capture, modeled in a Hauser–Feshbach
formalism, is expected to dominate over DSD processes [5]. Therefore a validated
surrogate for neutron capture is required to deduce the (n,γ) rate.
The neutron-transfer (d,pγ) reaction has recently been demonstrated to be a
valid surrogate for neutron capture [6]. The (d,p) reaction can also inform DSD
capture. To deduce the (n,γ) cross section, the γ-decay probabilities as a function
of excitation energy of several discrete gamma-ray transitions are measured. The
measured decay probabilities are fit with level density and gamma-ray strength
function models [7] with (d,p)-induced compound nucleus formation and spin-parity
weights calculated from non-elastic breakup of the deuteron [8]. Surrogate (d,pγ)
measurements require a radioactive ion beam of intensity >10 4 pps, a large solid
angle, segmented array of charged particle detectors, and a high-efficiency gammaray detector array.
2 GODDESS and 135 Xe
Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies
(GODDESS) [9] was commissioned in 2015 at Argonne National Laboratory.
Gamma radiation was measured with the 110-detector Gammasphere array
of Compton-suppressed HPGe detectors coupled to the Oak Ridge Rutgers
University Barrel Array (ORRUBA) of position-sensitive silicon-strip detectors
[10]. Accelerated beams of 134 Xe and 95 Mo from the ATLAS accelerator interacted
with CD 2 targets. Both charged particle singles and particle-gamma coincidence
events were recorded. The rectangular position-sensitive silicon-strip SX3 detectors
of the ORRUBA barrel were supplemented with pie-shaped, highly-segmented
QQQ5 detectors that formed annular arrays mounted at angles upstream and
downstream of the ORRUBA barrel. At forward angles both the QQQ5 and
many of the SX3 detectors were mounted in a E-E telescope to enable particle
identification.
Preliminary particle energy as a function of laboratory angle data with the 134 Xe
beam is displayed in Fig. 1. At the largest laboratory angles (that correspond to
the most forward center of mass (c.m.) angles for the (d,p) reaction), only (d,p)reaction protons are expected to be observed. Forward of 90 ◦ in the laboratory, the
spectrum is dominated by elastic scattering on the CD 2 target. Angular distributions
of reaction protons at smaller lab (larger c.m.) angles can be deduced from proton
particle identification with E-E telescopes. The red dotted lines are kinematic
curves expected for ground and new E x > 2.0 MeV states. The gap in counts between
the ground and E x > 2.0 MeV states in 135 Xe corresponds to the gap in excitations
below and above the N = 82 shell closure.
A preliminary, partial level scheme of 135 Xe is displayed in Fig. 1. The states at
2.04 and 2.40 MeV are likely 7/2 − and 3/2 − states with significant 2f 7/2 and 3p 3/2
J. A Cizewski et al.
132 Sn(n,γ) cross section is expected to be dominated by DSD capture, for N < 82
isotopes the contribution from statistical capture, modeled in a Hauser–Feshbach
formalism, is expected to dominate over DSD processes [5]. Therefore a validated
surrogate for neutron capture is required to deduce the (n,γ) rate.
The neutron-transfer (d,pγ) reaction has recently been demonstrated to be a
valid surrogate for neutron capture [6]. The (d,p) reaction can also inform DSD
capture. To deduce the (n,γ) cross section, the γ-decay probabilities as a function
of excitation energy of several discrete gamma-ray transitions are measured. The
measured decay probabilities are fit with level density and gamma-ray strength
function models [7] with (d,p)-induced compound nucleus formation and spin-parity
weights calculated from non-elastic breakup of the deuteron [8]. Surrogate (d,pγ)
measurements require a radioactive ion beam of intensity >10 4 pps, a large solid
angle, segmented array of charged particle detectors, and a high-efficiency gammaray detector array.
2 GODDESS and 135 Xe
Gammasphere ORRUBA: Dual Detectors for Experimental Structure Studies
(GODDESS) [9] was commissioned in 2015 at Argonne National Laboratory.
Gamma radiation was measured with the 110-detector Gammasphere array
of Compton-suppressed HPGe detectors coupled to the Oak Ridge Rutgers
University Barrel Array (ORRUBA) of position-sensitive silicon-strip detectors
[10]. Accelerated beams of 134 Xe and 95 Mo from the ATLAS accelerator interacted
with CD 2 targets. Both charged particle singles and particle-gamma coincidence
events were recorded. The rectangular position-sensitive silicon-strip SX3 detectors
of the ORRUBA barrel were supplemented with pie-shaped, highly-segmented
QQQ5 detectors that formed annular arrays mounted at angles upstream and
downstream of the ORRUBA barrel. At forward angles both the QQQ5 and
many of the SX3 detectors were mounted in a E-E telescope to enable particle
identification.
Preliminary particle energy as a function of laboratory angle data with the 134 Xe
beam is displayed in Fig. 1. At the largest laboratory angles (that correspond to
the most forward center of mass (c.m.) angles for the (d,p) reaction), only (d,p)reaction protons are expected to be observed. Forward of 90 ◦ in the laboratory, the
spectrum is dominated by elastic scattering on the CD 2 target. Angular distributions
of reaction protons at smaller lab (larger c.m.) angles can be deduced from proton
particle identification with E-E telescopes. The red dotted lines are kinematic
curves expected for ground and new E x > 2.0 MeV states. The gap in counts between
the ground and E x > 2.0 MeV states in 135 Xe corresponds to the gap in excitations
below and above the N = 82 shell closure.
A preliminary, partial level scheme of 135 Xe is displayed in Fig. 1. The states at
2.04 and 2.40 MeV are likely 7/2 − and 3/2 − states with significant 2f 7/2 and 3p 3/2