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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.

Nine neutron induced reactions on Ge isotopes (70Ge(n,2n)69Ge, 76Ge(n,2n)75Ge, 73Ge(n,p)73Ga, 72Ge(n,p)72Ga, 73Ge(n,d/np)72Ga, 74Ge(n,d/np)73Ga, 74Ge(n,α)71mZn, 72Ge(n,α)69mZn, 73Ge(n,nα)69mZn) 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 natGe 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 3H(d,n)4He 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 27Al(n,α)24Na reference reaction.

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.

The 234U(n,f) reaction cross section was measured for three neutron energies 14.8, 16.5 and 17.8 MeV, relative to the238U(n,f) reference reaction. The in-beam measurements were carried out by using a set-up based on Micromegas detectors, while the quasi-monoenergetic neutron beams were produced by means of the 3H(d,n)4He reaction at the 5.5MV Tandem T11/25 Accelerator Laboratory of the National Center for Scientific Research "Demokritos" in Athens (Greece). Additionaly, α-spectroscopy measurements were performed in order to determine the active mass of the samples and the corresponding impurities. In order to estimate the fission-fragment detection efficiency, Monte Carlo simulations were carried out using the GEF and FLUKA codes. Furthermore, simulations were also performed by coupling the NeuSDesc and MCNP5 codes for the determination of the neutron energy distribution in all the irradiated samples and the results were used in order to correct for the contribution of low energy parasitic neutrons in the fission yield. The final cross section data are presented, along with the methodology adopted for the treatment of the parasitic neutrons.

Cross sections for the 70,76Ge(n,2n), 72,73Ge(n,p) and 72,74Ge(n, α) reactions have been measured at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR Demokritos, using the activation technique. Neutron beams have been produced in the ~16-20 MeV energy region, by means of the 3H(d,n)4He reaction. The maximum flux has been determined to be of the order of 105 n/cm2 s, while the flux variation of the neutron beam was monitored by using a BF3 detector. The cross section has been deduced with respect to the 27Al(n, α)24Na and 93Nb(n,2n)92mNb reference reactions. The contaminations from reactions induced on neighboring Ge isotopes and leading to the same residual nucleus, have been taken into account. After the end of the irradiations, the activity induced by the neutron beams at the targets and reference foils, has been measured by HPGe detectors. Statistical model calculations using the EMPIRE code were performed on the data measured in this work as well as on data reported in literature.

Accurate data on neutron-induced fission cross-sections of actinides are essential for the design of advanced nuclear reactors based either on fast neutron spectra or alternative fuel cycles, as well as for the reduction of safety margins of existing and future conventional facilities. The fission cross-section of 234U was measured at incident neutron energies of 560 and 660 keV and 7.5 MeV with a setup based on ‘microbulk’ Micromegas detectors and the same samples previously used for the measurement performed at the CERN n_TOF facility (Karadimos et al., 2014). The 235U fission cross-section was used as reference. The (quasi-)monoenergetic neutron beams were produced via the 7Li(p,n) and the 2H(d,n) reactions at the neutron beam facility of the Institute of Nuclear and Particle Physics at the ‘Demokritos’ National Centre for Scientific Research. A detailed study of the neutron spectra produced in the targets and intercepted by the samples was performed coupling the NeuSDesc and MCNPX codes, taking into account the energy spread, energy loss and angular straggling of the beam ions in the target assemblies, as well as contributions from competing reactions and neutron scattering in the experimental setup. Auxiliary Monte-Carlo simulations were performed with the FLUKA code to study the behaviour of the detectors, focusing particularly on the reproduction of the pulse height spectra of α-particles and fission fragments (using distributions produced with the GEF code) for the evaluation of the detector efficiency. An overview of the developed methodology and preliminary results are presented.

The 197Au(n,2n)196Au reaction cross section has been measured at two energies, namely at 17.1 MeV and 20.9 MeV, by means of the activation technique, relative to the 27Al(n,α)24Na reference reaction cross section. Quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR “Demokritos”, by means of the 3H(d,n)4He reaction, implementing a new Ti-tritiated target of ∼ 400 GBq activity. The induced γ-ray activity at the targets and reference foils has been measured with HPGe detectors. The cross section for the population of the second isomeric (12−) state m2 of 196Au was independently determined. Auxiliary Monte Carlo simulations were performed using the MCNP code. The present results are in agreement with previous experimental data and with theoretical calculations of the measured reaction cross sections, which were carried out with the use of the EMPIRE code.

The cross section of 191Ir(n,2n)190Irg+m1 and 191Ir(n,2n)190Irm2 reactions has been measured at 17.1 and 20.9 MeV neutron energies at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos”, using the activation method. The neutron beams were produced by means of the 3H(d,n)4He reaction at a flux of the order of 2 × 105 n/cm2s. The neutron flux has been deduced implementing the 27Al(n,α) reaction, while the flux variation of the neutron beam was monitored by using a BF3 detector. The 193Ir(n,2n)192Ir reaction cross section has also been determined, taking into account the contribution from the contaminant 191Ir(n,γ)192Ir reaction. The correction method is based on the existing data in ENDF for the contaminant reaction, convoluted with the neutron spectra which have been extensively studied by means of simulations using the NeusDesc and MCNP codes. Statistical model calculations using the code EMPIRE 3.2.2 and taking into account pre-equilibrium emission, have been performed on the data measured in this work as well as on data reported in literature.

The accurate determination of deuteron depth profile presents a strong analytical challenge for all the principal IBA (Ion Beam Analysis) techniques. As far as NRA (Nuclear Reaction Analysis) is concerned, the 2H(d,p) reaction, seems to be a promising candidate, especially in the case of complex matrices, or for the study of deep-implanted deuteron layers. In the present work differential cross-section values for the 2H(d,p) reaction have been determined at 140°, 160° and 170°, for Ed,lab=900-1600 keV, with an energy step of 50 keV, using a well-characterized, thin C:D target deposited on a polished Si wafer. The experimental results were analyzed using the R-matrix calculations code AZURE.

In this work we focus on properties in the quasi-continuum of light nuclei. Generally, both level density and γ-ray strength function (γ-SF) differ from nucleus to nucleus. In order to investigate this closer, we have performed particle-γ coincidences using the reactions (p, p'), (p, d) and (p, t) on a 46Ti target. In particular, the very rich data set of the 46Ti(p, p')46Ti inelastic scattering reaction allows analysis of the coincidence data for many independent data sets. Using the Oslo method, we find one common level density for all data sets. If transitions to well-separated low-energy levels are included, the deduced γ-SF may change by a factor of 2 – 3, due strong to Porter-Thomas fluctuations. However, a universal γ-SF with small fluctuations is found provided that only excitation energies above 3 MeV are taken into account. The nuclear structure of the titaniums is discussed within a combinatorial quasi-particle model, showing that only few Nilsson orbitals participate in building up the level density for these light nuclei.

We present preliminary results from a measurement of nuclear level densities and the γ-ray strength of light Sc and Ti isotopes using the Oslo Method.