In this review we will present the results of recent $$\beta $$ β -decay studies using the total ... more In this review we will present the results of recent $$\beta $$ β -decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain $$\beta $$ β -decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the $$\gamma $$ γ cascades that follow the initial $$\beta $$ β decay. For this reason the technique requires the use of calorimeters with very high $$\gamma $$ γ detection efficiency. The measurements presented and discuss...
The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya... more The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U while the part dominated by the fission of 239Pu was in good agreement with the conversion model. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. These measurements allow the correction of the nuclear data for the Pandemonium effect, thus making an important contribution to calculating the antineutrino spectra. The impact of these ten years of measurement from our collaboration on the predicted antineutrino energy spectrum and f...
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI), 2011
26 Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in nova... more 26 Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in novae outbursts is still uncertain mainly due to the lack of nuclear information concerning the 25 Al(p,γ) 26 Si reaction. We report here on a neutron-gamma coincidence measurement of the 24 Mg(3 He,nγ) 26 Si reaction performed at the Orsay TANDEM facility aiming at the spectroscopic * Speaker.
Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities... more Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities to perform background rejection by scintillation pulse shape discrimination is generally limited in large detectors. This paper describes a novel approach for a pulse shape based event classification developed in the context of the Double Chooz reactor antineutrino experiment. Unlike previous implementations, this method uses the Fourier power spectra of the scintillation pulse shapes to obtain event-wise information. A classification variable built from spectral information was able to achieve an unprecedented performance, despite the lack of optimization at the detector design level. Several examples of event classification are provided, ranging from differentiation between the detector volumes and an efficient rejection of instrumental light noise, to some sensitivity to the particle type, such as stopping muons, ortho-positronium formation, alpha particles as well as electrons and positrons. In combination with other techniques the method is expected to allow for a versatile and more efficient background rejection in the future, especially if detector optimization is taken into account at the design level.
Journal of Cosmology and Astroparticle Physics, 2017
A study on cosmic muons has been performed for the two identical near and far neutrino detectors ... more A study on cosmic muons has been performed for the two identical near and far neutrino detectors of the Double Chooz experiment, placed at ∼120 and ∼300 m.w.e. underground respectively, including the corresponding simulations using the MUSIC simulation package. This characterization has allowed us to measure the muon flux reaching both detectors to be (3.64 ± 0.04) × 10 −4 cm −2 s −1 for the near detector and (7.00 ± 0.05) × 10 −5 cm −2 s −1 for the far one. The seasonal modulation of the signal has also been studied observing a positive correlation with the atmospheric temperature, leading to an effective temperature coefficient of α T = 0.212 ± 0.024 and 0.355 ± 0.019 for the near and far detectors respectively. These measurements, in good agreement with expectations based on theoretical models, represent one of the first measurements of this coefficient in shallow depth installations.
For the first time, the summation method has been coupled with a complete reactor model, in order... more For the first time, the summation method has been coupled with a complete reactor model, in order to predict the antineutrino emission of a research reactor. This work, discussed in the first part of this paper, allows us to predict the low energy part of the antineutrino spectrum, evidencing the important contribution of actinides to the antineutrino emission. Experimental conditions at short distance from research reactors are challenging, because the reactor itself produces huge gamma background that induce accidental and correlated backgrounds in an antineutrino target. The understanding of this background is of utmost importance and triggered the second part of the work presented here.
Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017
Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission... more Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission from neutron-unbound states populated in the β-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission a constraint on the (n,γ) cross section for highly unstable neutron-rich nuclei can be deduced. A surprisingly large γ branching was observed for a number of isotopes which might indicate the need to increase by a large factor the Hauser-Feshbach (n,γ) cross-section estimates that impact on r process abundance calculations.
During the commissioning of the first of the two detectors of the Double Chooz experiment, an une... more During the commissioning of the first of the two detectors of the Double Chooz experiment, an unexpected and dominant background caused by the emission of light inside the optical volume has been observed. A specific study of the ensemble of phenomena called Light Noise has been carried out in-situ, and in an external laboratory, in order to characterize the signals and to identify the possible processes underlying the effect. Some mechanisms of instrumental noise originating from the PMTs were identified and it has been found that the leading one arises from the light emission localized on the photomultiplier base and produced by the combined effect of heat and high voltage across the transparent epoxy resin covering the electric components. The correlation of the rate and the amplitude of the signal with the temperature has been observed. For the first detector in operation the induced background has been mitigated using online and offline analysis selections based on timing and light pattern of the signals, while a modification of the photomultiplier assembly has been implemented for the second detector in order to blacken the PMT bases.
Dipole strength distributions were determined for the neutron-rich nuclei 129-132Sn and 133,134Sb... more Dipole strength distributions were determined for the neutron-rich nuclei 129-132Sn and 133,134Sb from electromagnetic excitation in an experiment using the FRS-LAND setup. For all nuclei, a sizeable fraction of ``pygmy'' dipole strength at excitation energies well below the giant dipole resonance was observed. The integrated low-lying dipole strength of the nuclei with low neutron separation energies can be compared to
The IS419 experiment at the ISOLDE facility at CERN dedicated to the measurement of production an... more The IS419 experiment at the ISOLDE facility at CERN dedicated to the measurement of production and release rates of volatile elements from an irradiated Pb/Bi target by a proton beam of 1/1.4 GeV has been completed. The release of He, Ne, Ar, Br, Kr, Cd, I, Xe, Hg, Po and At isotopes was investigated at different target temperatures, ranging from 250 • C to 600 • C. Three experimental methods were used for the mass-separated, ionized beams: i) implantation of short-and medium-lived isotopes in a tape and on-line detection with a HPGe γ detector; ii) implantation of longer-lived isotopes in Al foils and off-line detection with a HPGe detector; iii) a Faraday Cup used mainly for stable nuclides. The results were compared with predictions from the FLUKA and MCNPX codes using different options for the intra-nuclear cascades and evaporation/fission models. Results show good agreement with calculations for Hg and for noble gases. For other elements such as iodine it is apparent that only a fraction of the produced isotopes is released. The results from FLUKA and MCNPX with the INCL4/ABLA models are in general more satisfactory than those obtained using MCNPX with the standard Bertini/Dresner model combination. Interestingly also significant yields of 204−210 At isotopes were observed. At isotopes are produced either by (p, π − xn) charge exchange reactions on 209 Bi or by secondary reactions involving 3 He and 4 He. Despite the non-release of polonium from Pb/Bi targets at typical operation temperatures, a smaller amount of highly radiotoxic Po isotopes can actually be liberated indirectly as decay daughters of the released astatine.
Applications of Nuclear Techniques: Eleventh International Conference, 2011
Numerous domains, in fundamental research as well as in applications, require the study of reacti... more Numerous domains, in fundamental research as well as in applications, require the study of reactions induced by neutrons with energies from few MeV up to few tens of MeV. Reliable measurements also are necessary to improve the evaluated databases used by nuclear transport codes. This energy range covers a large number of topics like transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors. A new facility called Neutrons For Science (NFS) is being built for this purpose on the GANIL site at Caen (France). NFS is composed of a pulsed neutron beam for time-of-flight facility as well as irradiation stations for cross-section measurements. Neutrons will be produced by the interaction of deuteron and proton beams, delivered by the SPIRAL-2 linear accelerator, with thick or thin converters made of beryllium or lithium. Continuous and quasi-mono-energetic spectra will be available at NFS up to 40 MeV. In this fast energy region, the neutron flux is expected to be up to 2 orders of magnitude higher than at other existing time-of-flight facilities. In addition, irradiation stations for neutron-, proton-and deuteron-induced reactions will allow performing cross-section measurements by the activation technique. After a description of the facility and its characteristics, the experiments to be performed in the short and medium term will be presented.
Inelastic scattering of 40 Ca on 40 Ca at 50 MeV/A has been measured at the GANIL facility in coi... more Inelastic scattering of 40 Ca on 40 Ca at 50 MeV/A has been measured at the GANIL facility in coincidence with light charged particles. For the first time, the SPEG spectrometer was associated with 240 CsI(Tl) scintillators of the INDRA 4π array. The missing energy method, successfully used in previous experiments to study the nucleon decay of collective states is applied to the study of alpha-particle decay of the GQR. A significant direct decay branch by alpha-particles of the GQR in 40 Ca is measured for the first time.
The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nucle... more The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nuclei impinging on targets of high nuclear charge with energies of 500-700 MeV/nucleon. New experimental data are presented for 136 Xe and 238 U together with further analysis of earlier data on 208 Pb. Differential cross sections d/dE* and d/d for electromagnetic excitations were deduced. Depending on the isotope, cross sections appear to be enhanced in comparison to those expected from a purely harmonic nuclear dipole response. The cumulative effect of excitations of two-phonon states composed of one dipole and one quadrupole phonon, of predicted anharmonicities in the double-phonon dipole response, and of damping of the dipole resonance during the collision may account for the discrepancy. In addition, decay properties of two-phonon resonances were studied and compared to that of a statistical decay.
ABSTRACT Double-differential cross sections for neutron production were measured in 96-MeV neutro... more ABSTRACT Double-differential cross sections for neutron production were measured in 96-MeV neutron-induced reactions at The Svedberg Laboratory in Uppsala, Sweden. Measurements for Fe and Pb targets were performed using two independent setups: DECOI-DEMON, time-of-flight telescope dedicated to the detection of emitted neutrons with energies between a few and 50 MeV and CLODIA-SCANDAL device devoted to measuring emitted neutrons with energies above 40 MeV. Double-differential cross sections were measured for an angular range between 15 and 98 deg and with low-energy thresholds (≈2 MeV). Angular and energy distributions and total neutron emission cross sections have been obtained from those measurements. Results have been compared with predictions given by different models included in several transport codes (MCNPX, GEANT, TALYS, PHITS, and DYWAN) and with other experimental data (the EXFOR database).
The near detector of Double Chooz will provide the most accurate measurement of the spectrum and ... more The near detector of Double Chooz will provide the most accurate measurement of the spectrum and the flux of the electronic anti-neutrinos (νe) emitted by a nuclear power plant. This enables the collaboration to address certain safeguards issues for the International Atomic Energy Agency's(IAEA) benefit.
In this letter, we show that the non-linearities of large amplitude motions in atomic nuclei indu... more In this letter, we show that the non-linearities of large amplitude motions in atomic nuclei induce giant quadrupole and monopole vibrations. As a consequence, the main source of anharmonicity is the coupling with configurations including one of these two giant resonances on top of any state. Two-phonon energies are often lowered by one or two MeV because of the large matrix elements with such three phonon configurations. These effects are studied in two nuclei, 40 Ca and 208 Pb.
In this review we will present the results of recent $$\beta $$ β -decay studies using the total ... more In this review we will present the results of recent $$\beta $$ β -decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain $$\beta $$ β -decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the $$\gamma $$ γ cascades that follow the initial $$\beta $$ β decay. For this reason the technique requires the use of calorimeters with very high $$\gamma $$ γ detection efficiency. The measurements presented and discuss...
The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya... more The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U while the part dominated by the fission of 239Pu was in good agreement with the conversion model. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. These measurements allow the correction of the nuclear data for the Pandemonium effect, thus making an important contribution to calculating the antineutrino spectra. The impact of these ten years of measurement from our collaboration on the predicted antineutrino energy spectrum and f...
Proceedings of 11th Symposium on Nuclei in the Cosmos — PoS(NIC XI), 2011
26 Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in nova... more 26 Al was the first cosmic radioactivity ever detected in the galaxy. Its nucleosynthesis in novae outbursts is still uncertain mainly due to the lack of nuclear information concerning the 25 Al(p,γ) 26 Si reaction. We report here on a neutron-gamma coincidence measurement of the 24 Mg(3 He,nγ) 26 Si reaction performed at the Orsay TANDEM facility aiming at the spectroscopic * Speaker.
Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities... more Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities to perform background rejection by scintillation pulse shape discrimination is generally limited in large detectors. This paper describes a novel approach for a pulse shape based event classification developed in the context of the Double Chooz reactor antineutrino experiment. Unlike previous implementations, this method uses the Fourier power spectra of the scintillation pulse shapes to obtain event-wise information. A classification variable built from spectral information was able to achieve an unprecedented performance, despite the lack of optimization at the detector design level. Several examples of event classification are provided, ranging from differentiation between the detector volumes and an efficient rejection of instrumental light noise, to some sensitivity to the particle type, such as stopping muons, ortho-positronium formation, alpha particles as well as electrons and positrons. In combination with other techniques the method is expected to allow for a versatile and more efficient background rejection in the future, especially if detector optimization is taken into account at the design level.
Journal of Cosmology and Astroparticle Physics, 2017
A study on cosmic muons has been performed for the two identical near and far neutrino detectors ... more A study on cosmic muons has been performed for the two identical near and far neutrino detectors of the Double Chooz experiment, placed at ∼120 and ∼300 m.w.e. underground respectively, including the corresponding simulations using the MUSIC simulation package. This characterization has allowed us to measure the muon flux reaching both detectors to be (3.64 ± 0.04) × 10 −4 cm −2 s −1 for the near detector and (7.00 ± 0.05) × 10 −5 cm −2 s −1 for the far one. The seasonal modulation of the signal has also been studied observing a positive correlation with the atmospheric temperature, leading to an effective temperature coefficient of α T = 0.212 ± 0.024 and 0.355 ± 0.019 for the near and far detectors respectively. These measurements, in good agreement with expectations based on theoretical models, represent one of the first measurements of this coefficient in shallow depth installations.
For the first time, the summation method has been coupled with a complete reactor model, in order... more For the first time, the summation method has been coupled with a complete reactor model, in order to predict the antineutrino emission of a research reactor. This work, discussed in the first part of this paper, allows us to predict the low energy part of the antineutrino spectrum, evidencing the important contribution of actinides to the antineutrino emission. Experimental conditions at short distance from research reactors are challenging, because the reactor itself produces huge gamma background that induce accidental and correlated backgrounds in an antineutrino target. The understanding of this background is of utmost importance and triggered the second part of the work presented here.
Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017
Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission... more Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of γ emission from neutron-unbound states populated in the β-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission a constraint on the (n,γ) cross section for highly unstable neutron-rich nuclei can be deduced. A surprisingly large γ branching was observed for a number of isotopes which might indicate the need to increase by a large factor the Hauser-Feshbach (n,γ) cross-section estimates that impact on r process abundance calculations.
During the commissioning of the first of the two detectors of the Double Chooz experiment, an une... more During the commissioning of the first of the two detectors of the Double Chooz experiment, an unexpected and dominant background caused by the emission of light inside the optical volume has been observed. A specific study of the ensemble of phenomena called Light Noise has been carried out in-situ, and in an external laboratory, in order to characterize the signals and to identify the possible processes underlying the effect. Some mechanisms of instrumental noise originating from the PMTs were identified and it has been found that the leading one arises from the light emission localized on the photomultiplier base and produced by the combined effect of heat and high voltage across the transparent epoxy resin covering the electric components. The correlation of the rate and the amplitude of the signal with the temperature has been observed. For the first detector in operation the induced background has been mitigated using online and offline analysis selections based on timing and light pattern of the signals, while a modification of the photomultiplier assembly has been implemented for the second detector in order to blacken the PMT bases.
Dipole strength distributions were determined for the neutron-rich nuclei 129-132Sn and 133,134Sb... more Dipole strength distributions were determined for the neutron-rich nuclei 129-132Sn and 133,134Sb from electromagnetic excitation in an experiment using the FRS-LAND setup. For all nuclei, a sizeable fraction of ``pygmy'' dipole strength at excitation energies well below the giant dipole resonance was observed. The integrated low-lying dipole strength of the nuclei with low neutron separation energies can be compared to
The IS419 experiment at the ISOLDE facility at CERN dedicated to the measurement of production an... more The IS419 experiment at the ISOLDE facility at CERN dedicated to the measurement of production and release rates of volatile elements from an irradiated Pb/Bi target by a proton beam of 1/1.4 GeV has been completed. The release of He, Ne, Ar, Br, Kr, Cd, I, Xe, Hg, Po and At isotopes was investigated at different target temperatures, ranging from 250 • C to 600 • C. Three experimental methods were used for the mass-separated, ionized beams: i) implantation of short-and medium-lived isotopes in a tape and on-line detection with a HPGe γ detector; ii) implantation of longer-lived isotopes in Al foils and off-line detection with a HPGe detector; iii) a Faraday Cup used mainly for stable nuclides. The results were compared with predictions from the FLUKA and MCNPX codes using different options for the intra-nuclear cascades and evaporation/fission models. Results show good agreement with calculations for Hg and for noble gases. For other elements such as iodine it is apparent that only a fraction of the produced isotopes is released. The results from FLUKA and MCNPX with the INCL4/ABLA models are in general more satisfactory than those obtained using MCNPX with the standard Bertini/Dresner model combination. Interestingly also significant yields of 204−210 At isotopes were observed. At isotopes are produced either by (p, π − xn) charge exchange reactions on 209 Bi or by secondary reactions involving 3 He and 4 He. Despite the non-release of polonium from Pb/Bi targets at typical operation temperatures, a smaller amount of highly radiotoxic Po isotopes can actually be liberated indirectly as decay daughters of the released astatine.
Applications of Nuclear Techniques: Eleventh International Conference, 2011
Numerous domains, in fundamental research as well as in applications, require the study of reacti... more Numerous domains, in fundamental research as well as in applications, require the study of reactions induced by neutrons with energies from few MeV up to few tens of MeV. Reliable measurements also are necessary to improve the evaluated databases used by nuclear transport codes. This energy range covers a large number of topics like transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors. A new facility called Neutrons For Science (NFS) is being built for this purpose on the GANIL site at Caen (France). NFS is composed of a pulsed neutron beam for time-of-flight facility as well as irradiation stations for cross-section measurements. Neutrons will be produced by the interaction of deuteron and proton beams, delivered by the SPIRAL-2 linear accelerator, with thick or thin converters made of beryllium or lithium. Continuous and quasi-mono-energetic spectra will be available at NFS up to 40 MeV. In this fast energy region, the neutron flux is expected to be up to 2 orders of magnitude higher than at other existing time-of-flight facilities. In addition, irradiation stations for neutron-, proton-and deuteron-induced reactions will allow performing cross-section measurements by the activation technique. After a description of the facility and its characteristics, the experiments to be performed in the short and medium term will be presented.
Inelastic scattering of 40 Ca on 40 Ca at 50 MeV/A has been measured at the GANIL facility in coi... more Inelastic scattering of 40 Ca on 40 Ca at 50 MeV/A has been measured at the GANIL facility in coincidence with light charged particles. For the first time, the SPEG spectrometer was associated with 240 CsI(Tl) scintillators of the INDRA 4π array. The missing energy method, successfully used in previous experiments to study the nucleon decay of collective states is applied to the study of alpha-particle decay of the GQR. A significant direct decay branch by alpha-particles of the GQR in 40 Ca is measured for the first time.
The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nucle... more The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nuclei impinging on targets of high nuclear charge with energies of 500-700 MeV/nucleon. New experimental data are presented for 136 Xe and 238 U together with further analysis of earlier data on 208 Pb. Differential cross sections d/dE* and d/d for electromagnetic excitations were deduced. Depending on the isotope, cross sections appear to be enhanced in comparison to those expected from a purely harmonic nuclear dipole response. The cumulative effect of excitations of two-phonon states composed of one dipole and one quadrupole phonon, of predicted anharmonicities in the double-phonon dipole response, and of damping of the dipole resonance during the collision may account for the discrepancy. In addition, decay properties of two-phonon resonances were studied and compared to that of a statistical decay.
ABSTRACT Double-differential cross sections for neutron production were measured in 96-MeV neutro... more ABSTRACT Double-differential cross sections for neutron production were measured in 96-MeV neutron-induced reactions at The Svedberg Laboratory in Uppsala, Sweden. Measurements for Fe and Pb targets were performed using two independent setups: DECOI-DEMON, time-of-flight telescope dedicated to the detection of emitted neutrons with energies between a few and 50 MeV and CLODIA-SCANDAL device devoted to measuring emitted neutrons with energies above 40 MeV. Double-differential cross sections were measured for an angular range between 15 and 98 deg and with low-energy thresholds (≈2 MeV). Angular and energy distributions and total neutron emission cross sections have been obtained from those measurements. Results have been compared with predictions given by different models included in several transport codes (MCNPX, GEANT, TALYS, PHITS, and DYWAN) and with other experimental data (the EXFOR database).
The near detector of Double Chooz will provide the most accurate measurement of the spectrum and ... more The near detector of Double Chooz will provide the most accurate measurement of the spectrum and the flux of the electronic anti-neutrinos (νe) emitted by a nuclear power plant. This enables the collaboration to address certain safeguards issues for the International Atomic Energy Agency's(IAEA) benefit.
In this letter, we show that the non-linearities of large amplitude motions in atomic nuclei indu... more In this letter, we show that the non-linearities of large amplitude motions in atomic nuclei induce giant quadrupole and monopole vibrations. As a consequence, the main source of anharmonicity is the coupling with configurations including one of these two giant resonances on top of any state. Two-phonon energies are often lowered by one or two MeV because of the large matrix elements with such three phonon configurations. These effects are studied in two nuclei, 40 Ca and 208 Pb.
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Papers by Muriel Fallot