.
Cross section measurements of (
p
,
γ
) reactions on the Mo isotopes have been performed at beam energies from 2 to 6.2 MeV that are relevant to the
p
-process. Partial cross sections and isomeric ...ratios were also determined for the
92
Mo case. Astrophysical S factors as well as reaction rates were derived from the experimental cross sections. Statistical model calculations were performed using the latest version (1.9) of the statistical model code TALYS and were compared with the new data. An overall good agreement between theory and experiment was found. In addition, the effect of different combinations of the nuclear input parameters entering the stellar reaction-rate calculations was investigated. It was found that, for certain combinations of optical-model potentials, nuclear level densities and
γ
-ray strength functions, the nuclear uncertainties propagated through the Hauser-Feshbach calculations are less than a factor of 2 which is well below the average discrepancies of the calculated
p
-nuclei abundances and the observations.
Neutron induced reaction cross-section measurements display special interest both for fundamental research in the Nuclear Physics field and many practical applications. The Institute of Nuclear and ...Particle Physics (INP) of the National Centre for Scientific Research Demokritos (N.C.S.R. “D”) hosts the 5.5 MV T11/25 Van de Graaff accelerator, which is the only accelerator used in Greece for research purposes. This accelerator recently underwent a major upgrade, including the installation of a new pelletron charging system, two new ion sources, a new gas stripper and beam optics. This neutron facility can produce quasi-monoenrgetic neutron beams in the energy range ∼16-19 MeV via the 3 H(d,n) 4 He (D-T) reaction, employing a tritiated Titanium target (TiT). The neutron induced cross sections of a total of nine reaction channels have been experimentally measured in the present work, via the activation technique, using enriched Ge targets. These targets produce more accurate cross-section results, in comparison with the - most commonly used in bibliography - nat Ge samples, since they do not suffer from contaminating reactions that produce the same residual nucleus. Monte Carlo simulations were also performed via the combined use of MCNP5 and NeuSDesc codes for the simulation of the neutron beam.
Several cross-section measurements of neutron-induced reactions on Ge found in literature, are performed utilizing natGe targets. The production of the same residual nucleus as the measured one might ...occur as a result of the unavoidable presence of neighboring isotopes in the same target, acting as a contamination. Corrections must be made based on theoretical calculations and models in order to resolve this problem. The accuracy and limits of a methodology for these "theoretical corrections" are investigated in this work using isotopically enriched targets, which can produce very accurate results without the need for such corrections. Experimental cross-section measurements have been made for the 76Ge(n,2n)75Ge, 72Ge(n,α)69mZn and 72Ge(n,p)72Ga reactions, via the activation technique, with the 27Al(n,α)24Na reaction used as reference, employing both a natGe and isotopically enriched Ge targets. The 3H(d,n)4He (D-T) reaction was used for producing the quasi-monoenergetic neutron beam in the 5.5 MV Tandem Accelerator Laboratory of the National Centre for Scientific Research "Demokritos" in Athens, Greece, at an incident deuteron beam energy of 2.9 MeV. Using HPGe detectors, γ-ray spectroscopy was applied to determine the induced γ-ray activity of the residual nuclei.
The fission cross section of
232
Th has been measured at fast neutron energies, using a setup based on Micromegas detectors. The experiment was performed at the 5.5 MV Van de Graaff Tandem ...accelerator in the neutron beam facility of the National Centre for Scientific Research “Demokritos”. The quasi-monoenergetic neutron beams were produced via the
3
H(p,n),
2
H(d,n) and
3
H(d,n) reactions, while the
238
U(n,f) and
235
U(n,f) reactions were used as references, in order to acquire cross-section data points in the energy range 2–18 MeV. The characterization of the actinide samples was performed via
α
-spectroscopy with a Silicon Surface Barrier (SSB) detector, while Monte Carlo simulations with the FLUKA code were used to achieve the deconvolution of the
232
Th
α
peak from the
α
background of its daughter nuclei present in the spectrum. Special attention was given to the study of the parasitic neutrons present in the experimental area, produced via charged particle reactions induced by the particle beam and from neutron scattering. Details on the data analysis and results are presented.
The aim of the present work was to study the cross-section of the (n,2n) reaction on 203Tl, by irradiating a natural TlCl pellet target with monoenergetic neutron beams at 16.4, 18.9 and 19.3 MeV. ...The cross section of the 203Tl(n,2n)202Tl reaction was measured via the activation method, with respect to the 197Au(n,2n)196Au and 27Al(n,α)24Na reference reactions. At the same time, the 203Tl(n,3n)201Tl was also measured at 18.9 and 19.3 MeV. The monoenergetic neutron beams were generated at the 5.5 MV Tandem accelerator of NCSR “Demokritos”, using the 3H(d,n)4He reaction. In addition, theoretical calculations with the EMPIRE code have been performed, in order to find a suitable model for the description of the experimental data of the present work along with the data from literature.
Experimental cross section measurements for the 176Hf(n,2n)175Hf and 174Hf(n,2n)173Hf reactions were carried out, using the activation technique. The neutron beam energy in the range of 15.3-20.3 MeV ...was produced via the 3H(d,n)4He reaction at the 5.5 MeV Tandem Van de Graaf accelerator laboratory of NCSR “Demokritos”. A thin metallic foil of natural Hf was used, while for the determination of the neutron flux at the target position, reference foils of Al were placed at the front and back of the Hf target. The irradiations were continuous for ~24-48 hours, leading to a total neutron fluence of 1010-1011 n/cm2 and a BF3 detector was used for monitoring the neutron flux during the irradiations. After the end of each irradiation, the activity of the Hf target and the Al reference foils were measured off-line by two HPGe detectors. The 176Hf(n,2n)175Hf reaction has been corrected for the contribution of the 177Hf(n,3n)175Hf and 174Hf(n,γ)175Hf reactions. Statistical model calculations based on the Hauser-Feshbach theory have also been performed using the EMPIRE 3.2.3 code. The predictions have been compared with the data of the present work as well as with data from literature.
Nine neutron induced reactions on Ge isotopes (
70
Ge(n,2n)
69
Ge,
76
Ge(n,2n)
75
Ge,
73
Ge(n,p)
73
Ga,
72
Ge(n,p)
72
Ga,
73
Ge(n,d/np)
72
Ga,
74
Ge(n,d/np)
73
Ga,
74
Ge(n,α)
71m
Zn,
72
Ge(n,α)
69m
...Zn,
73
Ge(n,nα)
69m
Zn) have been measured in this work at energies 16.4-18.9 MeV. For these reactions, most of the experimental datasets in literature were obtained with a
nat
Ge target. However, the residual nucleus produced by some reaction channels can also be produced from neighboring isotopes, acting as a contamination for the measured reactions. This contribution must be subtracted, based on theoretical calculations, bearing their own uncertainties. The use of enriched targets however, does not suffer from such contaminations, leading to accurate experimental results. In this scope, five highly isotopically enriched Ge samples have been used in this work. The quasi-monoenergetic neutron beams were produced via the
3
H(d,n)
4
He reaction at the 5.5 MV Tandem Van de Graaff accelerator of N.C.S.R. ‘Demokritos’. The cross section of these nine reactions were measured using the activation method, with respect to the
27
Al(n,α)
24
Na reference reaction.
Particle-Induced Gamma-ray Emission (PIGE) is a powerful analytical technique that exploits the interactions of rapid charged particles with nuclei located near a sample surface to determine the ...composition and structure of the surface regions of solids by measurement of characteristic prompt γ rays. The potential for depth profiling of this technique has long been recognized, however, the implementation has been limited owing to insufficient knowledge of the physical data and lack of suitable user-friendly computer codes for the applications. Although a considerable body of published data exists in the nuclear physics literature for nuclear reaction cross sections with γ rays in the exit channel, there is no up-to-date, comprehensive compilation specifically dedicated to IBA applications. A number of PIGE cross-section data had already been uploaded to the Ion Beam Analysis Nuclear Data Library (IBANDL) (http://www-nds.iaea.org/ibandl) by members of the IBA community by 2011, however a preliminary survey of this body of unevaluated experimental data has revealed numerous discrepancies beyond the uncertainty limits reported by the authors. Using the resources and coordination provided by the IAEA, a concerted effort to improve the situation was made within the Coordinated Research Project on the Development of a Reference Database for PIGE spectroscopy, from 2011 to 2015. The aim of the CRP was to create a data library for Ion Beam Analysis that contains reliable and usable data on charged particle γ-ray emission cross sections that would be made freely available to the user community. As the CRP has reached its completion, we shall present its main achievements, including the results of nuclear cross-section evaluations and the development of a computer code that will become available to the public allowing for the implementation of a standardless PIGE technique.
The
Tandem
Accelerator Laboratory of NCSR “Demokritos,” Athens, Greece, is presented. A technical description of the laboratory, the installed setups together with currently implemented upgrades and ...associated funded projects are given. A few highlights as well as future upgrade plans and access possibilities to external users are also presented.
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