7 research outputs found
Photodisintegration studies of astrophysically relevant p-nuclei: Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of ther-
monuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z>26) are
being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes.
There are 35 neutron de¯cient stable isotopes between Se and Hg which are shielded from the
rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive
stellar environments via photodisintegration reactions like (°,n), (°,p) and (°,®) on r- or s-
seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameteriza-
tions using statistical model calculations. At the bremsstrahlung facility of the superconducting
electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and
144Sm have been performed via the photoactivation technique. The residual nuclei resulting
from photoactivation were studied via °-ray spectroscopy. For the decay measurements of
short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and
144Sm(°,®) reactions, the activated samarium samples with very low counting statistics were
measured at the underground laboratory "Felsenkeller" in Dresden. The experimental activa-
tion yields for the 144Sm (°,n), (°,p) and (°; ®) and the 92Mo(°; ®) reactions were determined.
It is to be emphasized that the (°,p) and (°; ®) reactions were measured for the ¯rst time in a
laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of
the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(°,n)196Au
reaction has been established as an activation standard. The photoactivation yields for the
197Au(°,n) and 144Sm(°; n) reactions have been compared to the yield calculated using cross
sections from previous photoneutron experiments. A comparison of the two data sets leads to
a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the
activation experiments are very small except for the case of decay spectra with weak counting
statistics. The systematic uncertainties are mostly from the experimental determination of
photon °ux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have
been performed for all the concerned reactions. The experimental activation yields, in general,
agree within a factor of 2 to the simulated yields using statistical model predictions. The
sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear
level densities and °-ray strength functions has been tested
Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of thermonuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z>26) are being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes. There are 35 neutron deficient stable isotopes between Se and Hg which are shielded from the rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive stellar environments via photodisintegration reactions like (γ,n), (γ,p) and (γ,α) on r- or s-seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameterizations using statistical model calculations. At the bremsstrahlung facility of the superconducting electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and 144Sm have been performed via the photoactivation technique. The residual nuclei resulting from photoactivation were studied via γ-ray spectroscopy. For the decay measurements of short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and 144Sm(γ,α) reactions, the activated samarium samples with very low counting statistics were measured at the underground laboratory "Felsenkeller" in Dresden. The experimental activation yields for the 144Sm (γ,n), (γ,p) and (γ, α) and the 92Mo(γ,α) reactions were determined. It is to be emphasized that the (γ,p) and (γ,α) reactions were measured for the first time in a laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(γ,n)196Au reaction has been established as an activation standard. The photoactivation yields for the 197Au(γ,n) and 144Sm(γ,n) reactions have been compared to the yield calculated using cross sections from previous photoneutron experiments. A comparison of the two data sets leads to a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the activation experiments are very small except for the case of decay spectra with weak counting statistics. The systematic uncertainties are mostly from the experimental determination of photon flux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have been performed for all the concerned reactions. The experimental activation yields, in general, agree within a factor of 2 to the simulated yields using statistical model predictions. The sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear level densities and γ-ray strength functions has been tested
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Converting Treatment Plans From Helical Tomotherapy to L-Shape Linac: Clinical Workflow and Dosimetric Evaluation.
This work evaluated a commercial fallback planning workflow designed to provide cross-platform treatment planning and delivery. A total of 27 helical tomotherapy intensity-modulated radiotherapy plans covering 4 anatomical sites were selected, including 7 brain, 5 unilateral head and neck, 5 bilateral head and neck, 5 pelvis, and 5 prostate cases. All helical tomotherapy plans were converted to 7-field/9-field intensity-modulated radiotherapy and volumetric-modulated radiotherapy plans through fallback dose-mimicking algorithm using a 6-MV beam model. The planning target volume (PTV) coverage ( D1, D99, and homogeneity index) and organs at risk dose constraints were evaluated and compared. Overall, all 3 techniques resulted in relatively inferior target dose coverage compared to helical tomotherapy plans, with higher homogeneity index and maximum dose. The organs at risk dose ratio of fallback to helical tomotherapy plans covered a wide spectrum, from 0.87 to 1.11 on average for all sites, with fallback plans being superior for brain, pelvis, and prostate sites. The quality of fallback plans depends on the delivery technique, field numbers, and angles, as well as user selection of structures for organs at risk. In actual clinical scenario, fallback plans would typically be needed for 1 to 5 fractions of a treatment course in the event of machine breakdown. Our results suggested that <1% dose variance can be introduced in target coverage and/or organs at risk from fallback plans. The presented clinical workflow showed that the fallback plan generation typically takes 10 to 20 minutes per case. Fallback planning provides an expeditious and effective strategy for transferring patients cross platforms, and minimizing the untold risk of a patient missing treatment(s)
Photodisintegration studies of astrophysically relevant p-nuclei: Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of ther-
monuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z&gt;26) are
being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes.
There are 35 neutron de¯cient stable isotopes between Se and Hg which are shielded from the
rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive
stellar environments via photodisintegration reactions like (°,n), (°,p) and (°,®) on r- or s-
seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameteriza-
tions using statistical model calculations. At the bremsstrahlung facility of the superconducting
electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and
144Sm have been performed via the photoactivation technique. The residual nuclei resulting
from photoactivation were studied via °-ray spectroscopy. For the decay measurements of
short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and
144Sm(°,®) reactions, the activated samarium samples with very low counting statistics were
measured at the underground laboratory &quot;Felsenkeller&quot; in Dresden. The experimental activa-
tion yields for the 144Sm (°,n), (°,p) and (°; ®) and the 92Mo(°; ®) reactions were determined.
It is to be emphasized that the (°,p) and (°; ®) reactions were measured for the ¯rst time in a
laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of
the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(°,n)196Au
reaction has been established as an activation standard. The photoactivation yields for the
197Au(°,n) and 144Sm(°; n) reactions have been compared to the yield calculated using cross
sections from previous photoneutron experiments. A comparison of the two data sets leads to
a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the
activation experiments are very small except for the case of decay spectra with weak counting
statistics. The systematic uncertainties are mostly from the experimental determination of
photon °ux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have
been performed for all the concerned reactions. The experimental activation yields, in general,
agree within a factor of 2 to the simulated yields using statistical model predictions. The
sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear
level densities and °-ray strength functions has been tested
Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of thermonuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z>26) are being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes. There are 35 neutron deficient stable isotopes between Se and Hg which are shielded from the rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive stellar environments via photodisintegration reactions like (γ,n), (γ,p) and (γ,α) on r- or s-seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameterizations using statistical model calculations. At the bremsstrahlung facility of the superconducting electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and 144Sm have been performed via the photoactivation technique. The residual nuclei resulting from photoactivation were studied via γ-ray spectroscopy. For the decay measurements of short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and 144Sm(γ,α) reactions, the activated samarium samples with very low counting statistics were measured at the underground laboratory "Felsenkeller" in Dresden. The experimental activation yields for the 144Sm (γ,n), (γ,p) and (γ, α) and the 92Mo(γ,α) reactions were determined. It is to be emphasized that the (γ,p) and (γ,α) reactions were measured for the first time in a laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(γ,n)196Au reaction has been established as an activation standard. The photoactivation yields for the 197Au(γ,n) and 144Sm(γ,n) reactions have been compared to the yield calculated using cross sections from previous photoneutron experiments. A comparison of the two data sets leads to a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the activation experiments are very small except for the case of decay spectra with weak counting statistics. The systematic uncertainties are mostly from the experimental determination of photon flux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have been performed for all the concerned reactions. The experimental activation yields, in general, agree within a factor of 2 to the simulated yields using statistical model predictions. The sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear level densities and γ-ray strength functions has been tested
Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of thermonuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z>26) are being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes. There are 35 neutron deficient stable isotopes between Se and Hg which are shielded from the rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive stellar environments via photodisintegration reactions like (γ,n), (γ,p) and (γ,α) on r- or s-seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameterizations using statistical model calculations. At the bremsstrahlung facility of the superconducting electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and 144Sm have been performed via the photoactivation technique. The residual nuclei resulting from photoactivation were studied via γ-ray spectroscopy. For the decay measurements of short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and 144Sm(γ,α) reactions, the activated samarium samples with very low counting statistics were measured at the underground laboratory "Felsenkeller" in Dresden. The experimental activation yields for the 144Sm (γ,n), (γ,p) and (γ, α) and the 92Mo(γ,α) reactions were determined. It is to be emphasized that the (γ,p) and (γ,α) reactions were measured for the first time in a laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(γ,n)196Au reaction has been established as an activation standard. The photoactivation yields for the 197Au(γ,n) and 144Sm(γ,n) reactions have been compared to the yield calculated using cross sections from previous photoneutron experiments. A comparison of the two data sets leads to a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the activation experiments are very small except for the case of decay spectra with weak counting statistics. The systematic uncertainties are mostly from the experimental determination of photon flux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have been performed for all the concerned reactions. The experimental activation yields, in general, agree within a factor of 2 to the simulated yields using statistical model predictions. The sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear level densities and γ-ray strength functions has been tested
Photodisintegration studies of astrophysically relevant p-nuclei Photodisintegration studies of astrophysically relevant p-nuclei
The majority of the light elements up to iron (Fe) are formed by successive rounds of ther-
monuclear fusion burning in the stellar interiors. The nuclei heavier than iron (Z&gt;26) are
being synthesized mainly by neutron-capture reactions - the astrophysical r-and s-processes.
There are 35 neutron de¯cient stable isotopes between Se and Hg which are shielded from the
rapid neutron capture by stable isobars. These so-called p-nuclei are produced in explosive
stellar environments via photodisintegration reactions like (°,n), (°,p) and (°,®) on r- or s-
seed nuclei. The reaction rates of the p-nuclei are mostly based on theoretical parameteriza-
tions using statistical model calculations. At the bremsstrahlung facility of the superconducting
electron accelerator ELBE, photon-induced reactions of the p-nuclei are being studied.
In the scope of this thesis work, photodisintegration measurements of the p-nuclei 92Mo and
144Sm have been performed via the photoactivation technique. The residual nuclei resulting
from photoactivation were studied via °-ray spectroscopy. For the decay measurements of
short-lived nuclei, a pneumatic delivery system has been used. In the case of 144Sm(°,p) and
144Sm(°,®) reactions, the activated samarium samples with very low counting statistics were
measured at the underground laboratory &quot;Felsenkeller&quot; in Dresden. The experimental activa-
tion yields for the 144Sm (°,n), (°,p) and (°; ®) and the 92Mo(°; ®) reactions were determined.
It is to be emphasized that the (°,p) and (°; ®) reactions were measured for the ¯rst time in a
laboratory at astrophysically relevant energies.
In all the mentioned experiments, special care was taken to determine the endpoint energy of
the bremsstrahlung spectra by using the photodisintegration of deuteron. The 197Au(°,n)196Au
reaction has been established as an activation standard. The photoactivation yields for the
197Au(°,n) and 144Sm(°; n) reactions have been compared to the yield calculated using cross
sections from previous photoneutron experiments. A comparison of the two data sets leads to
a conclusion on the inaccuracies in previous data. The statistical uncertainties involved in the
activation experiments are very small except for the case of decay spectra with weak counting
statistics. The systematic uncertainties are mostly from the experimental determination of
photon °ux. A detailed discussion of the overall uncertainty is provided.
Hauser-Feshbach statistical model calculations using TALYS and NON-SMOKER codes have
been performed for all the concerned reactions. The experimental activation yields, in general,
agree within a factor of 2 to the simulated yields using statistical model predictions. The
sensitivity of the model codes to the nuclear physics inputs like optical-model potentials, nuclear
level densities and °-ray strength functions has been tested