Upload
others
View
8
Download
0
Embed Size (px)
Citation preview
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
Investigation of radiative proton-capture reactions using high-resolution γ-ray spectroscopy
Philipp Scholz*, Felix Heim, Marvin Körschgen, Jan Mayer, Martin Müller, Julius Wilhelmy and Andreas Zilges
Institute for Nuclear Physics, University of Cologne
NUCLEAR PHYSICS IN STELLAR EXPLOSIONS WORKSHOP ´18
MTA Atomki, Debrecen, Hungary
Supported by the ULDETIS project within the UoC Excellence Initiative institutional strategy and by DFG (ZI 510/8-1, INST 216/544-1).
Supported by the Bonn-Cologne Graduate School of Physics and Astronomy.
γ-process nucleosynthesis
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
γ-process nucleosynthesis▪ Series of (γ,n), (γ,p), and (γ,α) reactions
▪ γ-ray induced reaction rates challenging to measure
▪ Measurement of (p,γ) and (α,γ) cross sections on heavy target nuclei
Hauser-Feshbach statistical model
▪ Optical-Model Potentials
▪ Nuclear Level Densities
▪ γ-strength functions
C
Target
Compound
T. R
ausc
her
et
al.,
Rep
. Pro
g. P
hys
. 76
(20
13
) 0
66
20
1
10 MV FN-Tandem accelerator
▪ Up to 1.5 µA protons and 500 nA α-particles
HORUS γ-ray spectrometer
▪ 14 HPGe detectors
▪ Efficiency ~ 2% @ 1.3 MeV
▪ FWHM ~ 2 keV @ 1.3 MeV
▪ Five different angles with respect to the
beam axis
▪ γγ-coincidence measurements
Target chamber
▪ Beam current read-out
▪ Cooling trap around the target position
▪ Build-in silicon detector for Rutherford
Backscattering spectrometry
In-Beam γ-ray spectroscopy at HORUS
L. Netterdon et al., Nucl. Inst. Meth. A 754 (2014) 94; F. Heim et al., to be published
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
HPGe
HPGe
RBS detector
Beam
Target withcooling trap
In-beam determination of total cross sections
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
Ecm
+ Q
AX
A+1Y
Detection of ground-state transitions
▪ Determine the yield of as many g.s. transitions as possible from angular distributions
▪ Sum of single yields provides the total yield▪ Measured cross sections are “lower” limits
▪ Not as sensitive as activation or 4π-summing▪ Complex analysis with increasing number of g.s. transitions
▪ Possible measurement of reactions with unstable, long livedand stable products
▪ Detailed γ-ray decay information
Cross section measurements @ HORUS
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
110Cd 111Cd 112Cd 113Cd 114Cd
115In113In
116Sn115Sn114Sn112Sn
108Cd
116Te
116Sb
107Ag 109Ag
L. Netterdon et al., PLB 744 (2015) 358 J. Mayer et al., Phys. Rev. C 93 (2016) 045809
L. Netterdon et al., Phys. Rev. C 91 (2015) 035801 P. Scholz et al., PLB 761 (2016) 247
85Rb 87Rb
86Sr 87Sr 88Sr
89Y
90Zr 91Zr 92Zr
92Nb 93Nb
94Mo92Mo
91Nb
93Tcpublished
to be published
other groups
F. Heim, to be published
L. Netterdon, to be published
107Ag(p,γ)108Cd cross section measurement
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
107Ag(p,γ)108Cd
▪ Measurement at six proton energies between 2.0 MeV and 5.0 MeV
▪ Target thicknesses ~ 3×1018 atoms/cm²
▪ Beam current ~ 1µA
F. Heim et al., to be published
107Ag(p,γ)108Cd – total cross sections
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
Total cross sections
▪ Disagreement with data from Khaliel et al.
▪ Good reproduction via TALYS using microscopical density models (HFB + combinatorial models)
▪ Small adjustment of ctable parameter needed
➢ Impact of the γ-ray strength function?
F. Heim et al., to be published
The γ-ray strength function
Philipp Scholz 8
100
101
102
30 40 50 60 70 80 90 100 110
<s
v>
(G
LO
-up
2)/
<s
v>
(G
LO
)
N
Fe
Mo
Cd
A.C. Larsen and S. Goriely, Phys. Rev. C 82 (2010) 014318
S. Goriely, Phys. Lett. B 436 (1998) 10
PDR
Upbend
▪ The γ-decay width depends on the nuclear level density and γ-ray strength functions
▪ Radiative capture reaction rates are very sensitive on the γ-decay width▪ Structures below particle separation thresholds enhance reaction rates
➢ How independent are these structures of excitation energy and mechanism?
Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
Partial cross sections and primary γ-ray transitions
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
Detection of primary γ-ray transitions
▪ Direct population of final states in the reaction product
▪ High energy γ-ray transitions in the single spectra of the HPGe detectors
▪ Intensity depends on the single γ-ray decay widths
▪ Can be used to study the γ-ray strength function in the reaction product
Ecm
+ Q
AX
A+1Y
107Ag(p,γ)108Cd – partial cross sections
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
F. Heim et al., to be published
Partial cross sections
▪ Measurement of eight partial cross sections at the highest beam energies
▪ Too low intensities at 2.0 MeV and 2.7 MeV
▪ Unsatisfying description within the statistical model
➢ Problem with γ-ray strength function in 108Cd?
▪ Assuming total decay widths, level densities, proton-OMP is well reproduced
➢ Real γ-strength can be obtained from cross section ratios:
𝑓𝑐𝑜𝑟𝑟 𝐸𝛾𝑖≈ 𝑓 𝐸𝛾𝑖
×𝜎𝑒𝑥𝑝
𝛾𝑖
𝜎𝑡ℎ𝑒𝑜
𝛾𝑖
γ-ray strength in Cd isotopes
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
F. Heim et al., to be published
▪ Determination of γ-ray strength values in 108Cd between ~ 10 MeV and 13.5 MeV
▪ Q-Value + low intensities in the single spectra deny access to lower γ-ray energies
▪ Visible fluctuations might be due to:▪ Influence of spin distribution?▪ Statistical fluctuations?▪ Imperfect description of other
nuclear physics input-parameter?
Primary γ-ray intensities from coincidence data
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
A+1Y
Ecm
+ Q
AX
Determining primary γ-ray intensities via coincidences
▪ Higher sensitivity via gates on secondary transitions
▪ Access to more transitions at one excitation energy
63,65Cu(p,γ) at 3.5 MeV/2.0 MeV
▪ One excitation energy below (p,n) thresholds➢ Constant total decay widths and level density
▪ Thick targets (1.5 and 2.5 mg/cm²)➢ Statistical approach to γ-decay widths
Two-step γ-ray cascades
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
▪ Sort coincident γ-rays according to their sum energy
▪ Gating in the sum-peak spectrum reveals TSC spectra ➢ Contains γ-rays participating in a TSC
population of level in the reaction product
Past: ▪ Statistical analysis of TSC spectra via, e.g.,
DICEBOX
New:▪ Extract primary intensities from the
depopulation of states via their absolute branching ratios
P. Scholz, PhD Thesis, to be published
Primary γ-ray intensities from radiative-proton captures
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
P. Scholz, PhD Thesis, to be published
Ratios of primary γ-ray intensities
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
▪ Ratios of primary γ-rays can be used to calculate relative strength▪ Focus on same spin and parities
➢ Reduce influence of spin distribution ➢ Strength function curves for different final states
▪ Different curves can be scaled towards each other at same γ-ray energies
𝒇(𝑬𝜸𝟏)
𝒇(𝑬𝜸𝟐)
≈𝑰𝜸𝟏
𝑬𝜸𝟏𝟑
𝑰𝜸𝟐𝑬𝜸𝟐
𝟑
P. Scholz, PhD Thesis, to be published
Results and conclusions
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
▪ Relative values need to be scaled/normalized
▪ Measurement of γ-strength values at energies below the separation thresholds possible
▪ Comparison to future Nuclear Resonance Fluorescence and Oslo-type experiments
▪ Testing the generalized Brink-Axel hypothesis
▪ Application to heavier target nuclei
P. Scholz, PhD Thesis, to be published
Summary & Outlook
Philipp Scholz, AG Zilges, IKP Investigation of radioactive proton-capture reactions using in-beam γ-ray spectroscopy
L. Netterdon et al., PLB 744 (2015) 358 L. Netterdon et al., Phys. Rev. C 91 (2015) 035801J. Mayer et al., Phys. Rev. C 93 (2016) 045809 P. Scholz et al., PLB 761 (2016) 247L. Netterdon, to be published F. Heim, to be published
▪ Combining cross section measurement with the investigation of nuclear physics input parameter
▪ Focus on the transition region between various processes for the nucleosynthesis of p nuclei
▪ N=50 isotones▪ Molybdenum and Cadmium
▪ Improving the predictions of reaction rates within the statistical model