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At the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" quasi-monoenergetic neutron beams can be produced in the energy ranges ∼15–21 MeV by means of the 3H(d,n)4He reaction, ∼4–11 MeV via the 2H(d,n)3He reaction, ∼2.0–5.3 MeV using the 3H(p,n)3He reaction and ∼120–650 keV via the 7Li(p,n)7Be reaction. The maximum flux has been determined to be of the order of 10 5 – 10 6 n/cm 2 s , implementing reference reactions, while the flux variation of the neutron beam is monitored using a BF3 detector and a BC501A scintillator. The neutron beams have been characterized using the multiple foil activation technique as well as extensive simulations and have been used for cross section measurements of neutron induced reactions implementing again the activation technique. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The measurement of the 236U(n, f) cross section was attempted with a new MicroMegas detector, based on the Microbulk technology. The incident quasi-monoenergetic neutron beams with energies in the range of 4-10 MeV were produced via the 2H(d, n) reaction at the neutron beam facility of the Institute of Nuclear and Particle Physics at the NCSR "Demokritos" and first results of the analysis are presented. [ABSTRACT FROM AUTHOR]

The 241Am(n,2n) 240Am reaction cross section has been measured at four energies, 10.0, 10.4, 10.8, and 17.1 MeV, by means of the activation technique, relative to the 27Al(n,α) 24Na reaction reference cross section. Quasi-monoenergetic neutron beams were produced via the ²H(d,n) ³He and the ³H(d,n) 4He reactions at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR "Demokritos". The high purity 241Am targets were provided by JRC-IRMM, Geel, Belgium. The induced γ -ray activity of 240Amwasmeasured with high-resolution high-purity germanium (HPGe) detectors. Auxiliary Monte Carlo simulations were performed with the MCNP code. The present results are in agreement with data obtained earlier and predictions obtained with the EMPIRE code. [ABSTRACT FROM AUTHOR]

Abstract: Quasi-monoenergetic neutron beams, in the energy range 7–11.5MeV, produced via the 2H(d,n) reaction, have been used at the 5.5MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos”. The flux variation of the neutron beam is monitored with a BF3 detector, while the absolute flux is obtained with respect to reference reactions. An investigation of the energy dependence of the neutron fluence has been carried out using two independent techniques: by a liquid scintillator BC501A detector and deconvolution of its recoil energy spectra performed by means of the DIFBAS code, as well as via the multiple foil activation technique in combination with the SULSA unfolding code. The neutron facility has also been characterized by means of Monte Carlo simulations with MCNP5. [Copyright &y& Elsevier]

The neutron facility at the 5.5 MV tandem T11/25 Accelerator of NCSR “Demokritos” can deliver monoenergetic neutron beams in the energy range from thermal to 450 keV, 4–11.5 MeV and 16–20.5 MeV via the 7Li(p,n), 2H(d,n) and 3H(d,n) reactions, respectively. The flux variation of the neutron beam is monitored by using a BF3 counter and a liquid scintillator BC501A detector. The 232Th(n,2n)231Th and 241Am(n,2n)240Am as well as (n,2n), (n,p) and (n,α) reactions on natural Ge and Hf isotopes, have been investigated from threshold up to 11.5 MeV, by using the activation method. The cross section values have been determined relative to the 197Au(n,2n)196Au, 27Al(n,α)24Na and 93Nb(n,2n) reference reaction cross sections. [ABSTRACT FROM AUTHOR]

The measurement of the cross section of the reaction 241Am(n,2n)240Am has been performed at neutron energies from 8.8 to 11.1 MeV, implementing the activation technique. The neutron beam was produced at the TANDEM accelerator of NCSR “Demokritos” by the 2H(d,n)3He reaction, using a deuterium gas target. During the 5-day long irradiation, the neutron beam fluctuations were monitored in 100 seconds intervals by a BF3 counter connected with a multiscaling unit. The radioactive target consisted of a 37 GBq 241Am source enclosed in a Pb container. A natural Au foil, a 27Al foil and a 93Nb foil were used as reference materials for the neutron flux determination. After the end of the irradiation the activity induced at the target and the reference foils, was measured off-line by a 56% HPGe detector. [ABSTRACT FROM AUTHOR]

The cross section of the 193Ir(n, 2n)192Ir reaction has been determined by means of the activation technique, relative to the 27Al (n, α ) and 197Au(n, 2n) reference reactions cross sections, at neutron beam energies ranging from 10 to 21 MeV. The quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" via the 2H(d, n) and 3H(d, n) reactions. The induced γ -ray activity of the irradiated target and reference foils was measured with high resolution HPGe detectors. In order to correct for the contribution of the 191Ir(n, γ )192Ir reaction, which is open to low energy parasitic neutrons, a recently developed analysis method was implemented and it is presented in great detail. Furthermore, cross section theoretical calculations were carried out using the EMPIRE and TALYS codes over a wide energy range. [ABSTRACT FROM AUTHOR]

The cross sections of the 191 Ir (n, 2 n) 190 Ir and 191 Ir (n, 3 n) 189 Ir reactions have been determined by means of the activation technique, relative to the 27 Al (n, a) 24 Na reaction, at neutron beam energies higher than 15 MeV. The quasi-monoenergetic neutron beams were produced at the 5.5 MV Tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" by implementing the 3 H (d, n) 4 He reaction. The induced γ -ray activity of the irradiated target and reference foils was measured with high resolution, high purity germanium (HPGe) detectors. The cross section for the high-spin isomeric state (11 -) of the 190 Ir nucleus was determined along with the sum of the ground (4 -), the first (1 -), and the second (11 -) isomeric states. Moreover, the cross section for the production of the ground state of the residual nucleus of (n, 3 n) reaction, 189 Ir, was also estimated. Additionally, cross section theoretical calculations were carried out using the empire 3.2.2 and talys 1.8 codes, in which the input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the (n, 2 n), (n, 3 n), (n, p), (n, a), and (n, total) ones. Similar combination of theoretical model parameters had also been successfully used in the case of the neighboring 197 Au nucleus, and this constitutes an encouraging confirmation of how accurately the theoretical models can reproduce the experimental results in this mass region. [ABSTRACT FROM AUTHOR]

The cross section of the 197Au(n,2n)196Au reaction has been determined at six energies ranging from 15.3-20.9 MeV by means of the activation technique, relative to the 27Al(n,α)24Na reaction. Quasimonoenergetic neutron beams were produced via the ³H(d,n)4He reaction at the 5.5 MV Tandem T11/25 accelerator laboratory of NCSR "Demokritos". After the irradiations, the induced γ-ray activity of the target and reference foils was measured with high-resolution HPGe detectors. The cross section for the high spin isomeric state (12-) was determined along with the sum of the ground (2-), the first (5+), and second (12-) isomeric states. Theoretical calculations were carried out with the codes empire 3.2.2 and talys 1.8. Optimum input parameters were chosen in such a way as to simultaneously reproduce several experimental reaction channel cross sections in a satisfactory way, namely the (n,elastic), (n,2n), (n,3n), (n,p), (n,α), and (n,total) ones. [ABSTRACT FROM AUTHOR]

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. • Cross section measurements with natural Ge targets need to be corrected for contaminations from neighboring isotopes • A methodology is proposed for the correction of the contribution from parasitic channels • The accuracy and limits of the methodology are investigated with two sets of measurements • Enriched and natural Ge targets were employed for cross-section measurements via the activation technique [ABSTRACT FROM AUTHOR]

The 162Er(n,2n)161Er reaction cross section (Eth=9.26MeV) was measured at six incident neutron beam energies by means of the activation technique. Two energy regions were covered in the present work: the near-threshold energies between 10.7 and 11.3 MeV, as well as the higher energies from 17.1 up to 19.0 MeV. In this way, the energy range from the reaction threshold up to 19 MeV was experimentally mapped, considering also the existing experimental information around 14 MeV. The quasi-monoenergetic neutron beam at near-threshold energies was produced via the ²H(d,n)³He reaction, while the higher neutron beam energies were achieved by using the ³H(d,n)4He reaction. The primary deuteron beam was delivered in both cases by the 5.5 MV Tandem Van de Graaff accelerator of NSCR "Demokritos." Statistical model calculations were performed and compared with all the available experimental data. [ABSTRACT FROM AUTHOR]