First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

First Results of the 140^{140}Ce(n,γ)141^{141}Ce Cross-Section Measurement at n_TOF

An accurate measurement of the $^{140}$Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the $^{140}$Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in $^{140}$Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the $^{140}$Ce Maxwellian-averaged cross-section

Experimental and theoretical study of the isomeric cross section of the 197Au(n,2n) reaction

65 σ.Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές”Στην παρούσα εργασία, η ενεργός διατομή της αντίδρασης 197Au(n,2n) προσδιορίστηκε πειραματικά σχετικά με την ενεργό διατομή της αντίδρασης 27Al(n,α)24Na σε ενέργειες προσπιπτόντων νετρονίων μεταξύ 9.0 και 10.5 MeV μέσω της τεχνικής ενεργοποίησης. Η σχεδόν μονοενεργειακή δέσμη νετρονίων παρήχθη μέσω της αντίδρασης 2H(d,n)3He στον επιταχυντή Tandem van de Graaff 5.5 MV του ΕΚΕΦΕ `` Δημόκριτος '' και μελετήθηκε ως προς τη συνεισφορά ``παρασιτικών'' νετρονίων χρησιμοποιώντας την τεχνική πολλαπλής ενεργοποίησης και τον κώδικα αποσυνέλιξης SULSA. Οι ενεργές διατομές τροφοδότησης της δεύτερης ισομερούς κατάστασης (12-) του 196Au και το άθροισμα των ενεργών διατομών τροφοδότησης της θεμελιώδους (2-) και πρώτης ισομερούς στάθμης (5-) προσδιορίστηκαν ανεξάρτητα. Βοηθητικές προσομοιώσεις Monte Carlo πραγματοποιήθηκαν με τον κώδικα MCNP. Θεωρητικοί υπολογισμοί των ανωτέρω ενεργών διατομών στην ενεργειακή περιοχή 8 με 25 MeV πραγματοποιήθηκαν με τους κώδικες STAPRE-F, EMPIRE και TALYS, οι οποίοι συγκρίθηκαν και ως προς την υλοποίηση του Γενικευμένου Μοντέλου Υπερρευστού (Generalised Superfluid Model). Τα θεωρητικά αποτελέσματα συγκρίθηκαν με παλαιότερα αποτελέσματα στην ίδια περιοχή μαζών αποκαλύπτοντας την ισχυρή εξάρτηση από το ενεργειακό διάγραμμα των συμμετεχόντων πυρήνων.In the present work, the 197Au(n,2n) reaction cross section is experimentally determined relative to the 27Αl(n,a)24Na reaction at incident neutron energies of 9.0 to 10.5 MeV by means of the activation technique. The quasi-monoenergetic fast neutron beam was produced via the 2H(d,n)3He reaction at the 5.5 MV Tandem Van de Graaff accelerator at the NCSR ``Demokritos'' and was studied to determine the contribution of background ``parasitic'' neutrons using the multiple foil activation technique and the SULSA unfolding code. The cross sections for the population of the second isomeric state (12-) of 196Au and the sum of the ground (2-) and first isomeric state (5-) population cross sections were independently determined. Auxiliary Monte Carlo simulations were performed with the MCNP code. Theoretical calculations of the above cross sections in the 8 to 25 MeV region were carried out with the use of the STAPRE-F, EMPIRE and TALYS codes, which were also compared in their implementation of the Generalised Superfluid Model (GSM). The theoretical results are compared with previous work in the same mass region and the strong dependence on the level scheme of the nuclei involved was revealed.Ανδρέας Ι. Τσιγγάνη

Characterisation of the radiation hardness of cryogenic bypass diodes for the HL-LHC inner triplet quadrupole circuit

The powering layout of the new HL-LHC Nb$_3$Sn triplet circuits is the use of cryogenic bypass diodes, where the diodes are located inside an extension to the magnet cryostat, operated in superfluid helium and exposed to radiation. Therefore, the radiation hardness of different type of bypass diodes has been tested at low temperatures in CERN’s CHARM irradiation facility during the operational year 2018. The forward characteristics, the turn on voltage and the reverse blocking voltage of each diode were measured weekly at 4.2 K and 77 K, respectively, as a function of the accumulated radiation dose. The diodes were submitted to a dose close to 12 kGy and a 1 MeV equivalent neutron fluence of $2.2 \times 10^{14}$ n/cm$^2$. After the end of the irradiation campaign the annealing behaviour of the diodes was tested by increasing the temperature slowly to 300 K. This paper describes the experimental setup, the measurement procedure and discusses the results of the measurements

First Results of the 140Ce(n,g)141Ce Cross-Section Measurement at n_TOF

The cerium oxide material for this measurement was provided by T. Katabuchi of the Tokyo Institute of Technology.An accurate measurement of the 140Ce(n,g) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged cross-section

Measurement and analysis of 241Am(n,gamma) cross sections with C6D6 detectors at the n_TOF facility at CERN

The 241Am(n,gamma) cross sections have been measured at the n TOF facility at CERN using C6D6 liquid scintillators and time of flight spectrometry. The results in the resolved resonance range bring new constraints to evaluations below 150 eV, and the energy upper limit can be extended from 150 eV to 320 eV. The analysis goes from thermal energy to 150 keV, and the unresolved resonance range cross section turns out to be larger than expected by evaluations or otherwise measured by previous works. The thermal cross section is found to be σth = 740 ± 74 barns, which is larger than expected by evaluations and most previous measurements.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Measurements of neutron cross sections for advanced nuclear energy systems at n_TOF (CERN)

The n_TOF facility operates at CERN with the aim of addressing the request of high accuracy nuclear data for advanced nuclear energy systems as well as for nuclear astrophysics. Thanks to the features of the neutron beam, important results have been obtained on neutron induced fission and capture cross sections of U, Pu and minor actinides. Recently the construction of another beam line has started; the new line will be complementary to the first one, allowing to further extend the experimental program foreseen for next measurement campaigns

Spin measurements of n+87Sr for level density studies

We have used the 4π BaF2 gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n+87Sr by measuring the gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Neutron cross-sections for advanced nuclear systems: the n_TOF project at CERN

The study of neutron-induced reactions is of high relevance in a wide variety of fields, ranging from stellar nucleosynthesis and fundamental nuclear physics to applications of nuclear technology. In nuclear energy, high accuracy neutron data are needed for the development of Generation IV fast reactors and accelerator driven systems, these last aimed specifically at nuclear waste incineration, as well as for research on innovative fuel cycles. In this context, a high luminosity Neutron Time Of Flight facility, n_TOF, is operating at CERN since more than a decade, with the aim of providing new, high accuracy and high resolution neutron cross-sections. Thanks to the features of the neutron beam, a rich experimental program relevant to nuclear technology has been carried out so far. The program will be further expanded in the near future, thanks in particular to a new high-flux experimental area, now under construction