28 research outputs found
Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF
This article presents a few selected developments and future ideas related to the measurement of (n,Îł) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with Îł-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area
Advances and new ideas for neutron-capture astrophysics experiments at CERN n_TOF
This article presents a few selected developments and future ideas related to the measurement of (n,Îł) data of astrophysical interest at CERN n_TOF. The MC-aided analysis methodology for the use of low-efficiency radiation detectors in time-of-flight neutron-capture measurements is discussed, with particular emphasis on the systematic accuracy. Several recent instrumental advances are also presented, such as the development of total-energy detectors with Îł-ray imaging capability for background suppression, and the development of an array of small-volume organic scintillators aimed at exploiting the high instantaneous neutron-flux of EAR2. Finally, astrophysics prospects related to the intermediate i neutron-capture process of nucleosynthesis are discussed in the context of the new NEAR activation area
Pushing the high count rate limits of scintillation detectors for challenging neutron-capture experiments
One of the critical aspects for the accurate determination of neutron capture
cross sections when combining time-of-flight and total energy detector
techniques is the characterization and control of systematic uncertainties
associated to the measuring devices. In this work we explore the most
conspicuous effects associated to harsh count rate conditions: dead-time and
pile-up effects. Both effects, when not properly treated, can lead to large
systematic uncertainties and bias in the determination of neutron cross
sections. In the majority of neutron capture measurements carried out at the
CERN n\_TOF facility, the detectors of choice are the CD
liquid-based either in form of large-volume cells or recently commissioned sTED
detector array, consisting of much smaller-volume modules. To account for the
aforementioned effects, we introduce a Monte Carlo model for these detectors
mimicking harsh count rate conditions similar to those happening at the CERN
n\_TOF 20~m fligth path vertical measuring station. The model parameters are
extracted by comparison with the experimental data taken at the same facility
during 2022 experimental campaign. We propose a novel methodology to consider
both, dead-time and pile-up effects simultaneously for these fast detectors and
check the applicability to experimental data from Au(,),
including the saturated 4.9~eV resonance which is an important component of
normalization for neutron cross section measurements
Activation Cross Section Measurement of the (n,2n) Reaction on
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
Isomeric cross section study of neutron induced reactions on Ge isotopes
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
Isomeric cross section study of neutron induced reactions on Ge isotopes
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
Study of the H(p,n)He neutron producing reaction at N.C.S.R. “Demokritos” – Application on the Th(n,f) reaction
In the present work, the neutron beams produced via the H(p,n) He reaction, were studied at N.C.S.R. “Demokritos”. For detecting and monitoring the neutrons, the following reference reactions U(n,f), U(n,f) and Np(n,f) were used. Furthermore, a systematic study of the parasitic neutrons, produced via reactions on the target constituents, was performed. At the same time, the cross sections of the Th(n,f) reaction were deduced, in the energy range from 2 to 5.5 MeV. Seven actinide targets were used, coupled with seven Micromegas detectors, one for each target, for the detection of the fission fragments. The target-detector assembly was placed in an aluminum chamber filled with Ar:CO (90:10) in atmospheric pressure and room temperature. Monte Carlo simulations with the MCNP6 code, coupled with the NeuSDesc and SRIM-2013 codes, were used for the estimation of the neutron beam incident at each target. Additional Monte Carlo simulations were carried out using the codes FLUKA and GEF, in order to determine the exact masses of the Th targets and the energy deposition of the fission fragments in the detector gas
Measurement of the 234U(n,f) cross section in the energy range between 14.8 and 17.8 MeV using Micromegas detectors
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
Measurement of the
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 Section Measurements and Theoretical Study of the
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