Littérature scientifique sur le sujet « Neutrino ma »

ABSTRACT Axions, if realized in nature, can be copiously produced in the early universe via thermal processes, contributing to the mass-energy density of thermal hot relics. In light of the most recent cosmological observations, we analyse two different thermal processes within a realistic mixed hot dark matter scenario which includes also massive neutrinos. Considering the axion–gluon thermalization channel, we derive our most constraining bounds on the hot relic masses ma < 7.46 eV and ∑mν < 0.114 eV both at 95 per cent CL; while studying the axion–pion scattering, without assuming any specific model for the axion–pion interactions, and remaining in the range of validity of the chiral perturbation theory, our most constraining bounds are improved to ma < 0.91 eV and ∑mν < 0.105 eV, both at 95 per cent CL. Interestingly, in both cases, the total neutrino mass lies very close to the inverted neutrino mass ordering prediction. If future terrestrial double beta decay and/or long-baseline neutrino experiments find that the nature mass ordering is the inverted one, this could rule out a wide region in the currently allowed thermal axion window. Our results therefore, strongly support multi messenger searches of axions and neutrino properties, together with joint analyses of their expected sensitivities.

205 Tl in the lorandite (TiAsS 2 ) mine of Allchar (Majdan, FYR Macedonia) is transformed to 205 Pb by cosmic ray reactions with muons and neutrinos. At depths of more than 300 m, muogenic production would be sufficiently low for the 4.3 Ma old lorandite deposit to be used as a natural neutrino detector. Unfortunately, the Allchar deposit currently sits at a depth of only 120 m below the surface, apparently making the lorandite experiment technically infeasible. We here present 25 erosion rate estimates for the Allchar area using in situ produced cosmogenic 36 Cl in carbonates and 10 Be in alluvial quartz. The new measurements suggest long-term erosion rates of 100–120 m Ma −1 in the silicate lithologies that are found at the higher elevations of the Majdanksa River valley, and 200–280 m Ma −1 in the underlying marbles and dolomites. These values indicate that the lorandite deposit has spent most of its existence at depths of more than 400 m, sufficient for the neutrinogenic 205 Pb component to dominate the muon contribution. Our results suggest that this unique particle physics experiment is theoretically feasible and merits further development.

We estimate Majorana CP phases for a simple flavor neutrino mixing matrix which has been reported by Qu and Ma. Sizes of Majorana CP phases are evaluated in the study of the neutrinoless double beta decay and a particular leptogenesis scenario. We find the dependence of the physically relevant Majorana CP phase on the mass of lightest right-handed neutrino in the minimal seesaw model and the effective Majorana neutrino mass which is related with the half-life of the neutrinoless double beta decay.

Abstract For the sterile neutrino experiment IsoDAR (Isotope Decay-At-Rest), we have developed a compact particle accelerator system delivering a 10 mA, continuous wave (cw) proton beam at 60 MeV to a neutrino production target. The accelerator comprises a compact isochronous cyclotron, an RFQ embedded in the cyclotron yoke, and an ion source. To reduce space charge effects during injection and acceleration, we are accelerating H+ 2 instead of protons. To produce the needed cw H+ 2 beam current of 10 mA (nominal) at the required purity and quality, we have built a new filament driven, multicusp ion source (MIST-1). Here we report commissioning results for long-time running at reduced power, demonstrating the feasibility of the design. Highlights include an H+ 2 beam current density of ≈ 10 mA/cm2, ≈ 80% H+ 2 fraction, and extrapolated emittances of 0.05 π-mm-mrad (RMS, normalized) after extraction. We also present high fidelity simulations that are in good qualitative and quantitative agreement with emittance measurements in our test beam line.

Abstract We revisit the joint constraints in the mixed hot dark matter scenario in which both thermally produced QCD axions and relic neutrinos are present. Upon recomputing the cosmological axion abundance via recent advances in the literature, we improve the state-of-the-art analyses and provide updated bounds on axion and neutrino masses. By avoiding approximate methods, such as the instantaneous decoupling approximation, and limitations due to the limited validity of the perturbative approach in QCD that forced to artificially divide the constraints from the axion-pion and the axion-gluon production channels, we find robust and self-consistent limits. We investigate the two most popular axion frameworks: KSVZ and DFSZ. From Big Bang Nucleosynthesis (BBN) light element abundances data we find for the KSVZ axion ΔN eff < 0.31 and an axion mass bound ma < 0.53 eV (i.e., a bound on the axion decay constant fa > 1.07 × 107 GeV) both at 95% CL. These BBN bounds are improved to Δ N eff < 0.14 and ma < 0.16 eV (fa > 3.56 × 107 GeV) if a prior on the baryon energy density from Cosmic Microwave Background (CMB) data is assumed. When instead considering cosmological observations from the CMB temperature, polarization and lensing from the Planck satellite combined with large scale structure data we find Δ N eff < 0.23, ma < 0.28 eV (fa > 2.02 × 107 GeV) and ∑ mν < 0.16 eV at 95% CL. This corresponds approximately to a factor of 5 improvement in the axion mass bound with respect to the existing limits. Very similar results are obtained for the DFSZ axion. We also forecast upcoming observations from future CMB and galaxy surveys, showing that they could reach percent level errors for ma ∼ 1 eV.

It is now clear that the masses of the neutrino sector are much lighter than those of the other three sectors. Canonial seesaw model would be the most famous for the above explanation. But one must introduce heavy particles that will not be able to observed with present scientific technologies. On the other hand, there are many attempts to explain the neutrino masses radiatively by means of inert Higgses, which do not have the vacuum expectation values. Then one can discuss cold dark matter candidates, because of no needing so heavy particles. The most famous work would be the Zee model17. Recently a new type model (hep-ph/0601225)4 along this line of thought was proposed by E. Ma. We adopted this idea, and then we introduced a new flavor symmetry to constrain the Yukawa sector. So our model might be more predictive, and can be investigated at LHC. I will present how we can obserb the particular signal at LHC, and what we can predict about the neutrino sector.

In an improved application of the tetrahedral symmetry A4 first introduced by Ma and Rajasekaran, supplemented by the discrete symmetry Z3 as well as supersymmetry, a two-parameter form of the neutrino mass matrix is derived which exhibits the tribimaximal mixing of Harrison, Perkins and Scott. This form is the same as the one obtained previously by Altarelli and Feruglio, and the inverse of that obtained by Babu and He. If only A4 is used, then corrections appear, making tan2 θ12 different from 0.5, without changing significantly sin22θ23 from one or θ13 from zero.

Abstract Interest in high intensity generators of neutrons for basic and applied science has been growing, and thus the demand for an economical neutron generator has been growing. A major driver for the development of high intensity neutron generators are studies of neutron disturbance in integrated circuits, for which a compact generator that can be easily accommodated in an ordinary size lab would be highly desirable. We have investigated possible designs for neutron generators based on the D-D fusion reaction, which produce direction dependent mono-energetic neutrons with carry-off energy larger than 2.45 MeV. Specifically, we find a negative deuterium ion beam most attractive for this application, and plan to construct such a system with a negative deuterium ion beam of 200 keV energy and 100 mA current as a prototype of this concept.

I neutrini sono le particelle meno conosciute di tutto il modello standard. Da quando Pauli ha postulato la loro esistenza nella lettera 1930 sono stati compiuti molti progressi nello studio dei neutrini, ma tutt'ora ci sono delle caratteristiche fondamentali che non conosciamo: non sappiamo la scala di massa dei neutrini, e non sappiamo se sono particelle di Majorana o particelle di Dirac, infine, non abbiamo ancora risolto il problema della gerarchia. Negli ultimi due decenni, grazie alle misure degli esperimenti Super-Kamiokande, SNO, Daya Bay e Reno che hanno confermato l'oscillazione dei neutrini, è stato stabilito il fatto che i neutrini abbiano una massa non nulla. Le oscillazioni dei neutrini però dipendono soltanto dalla differenza di massa al quadrato tra gli autostati massa, quindi non possono fornire alcuna informazione circa la scala di massa assoluta. I metodi più comuni per misurare la massa del neutrino sono il decadimento doppio decadimento beta senza neutrini, osservazioni cosmologiche e la misura diretta della massa del neutrino dallo spettro di un decadimento beta o di una cattura elettronica. La misura diretta è l'unico metodo che permette di misurare la massa senza dipendenze da alcun modello dal momento che si tratta di una misura puramente cinematica e si basa unicamente sul principio di conservazione dell'energia. Il tema affrontato in questa tesi è la descrizione di Holmes, un esperimento iniziato nel 2015 che mira a misurare la massa del neutrino in maniera diretta analizzando lo spettro di cattura elettronica dell'isotopo 163-Ho. Per poter raggiungere una sensibilità sulla massa del neutrino minore di 1 eV è necessario disporre di un'elevata quantità di dati nella regione finale dello spettro, che è la regione dove è evidente l'effetto della massa non nulla del neutrino; 163-Ho è un ottimo isotopo per effettuare una misura simile, data la sua bassa energia di transizione, che si trova inoltre vicino all'energia del livello orbitale M1 da cui gli elettroni vengono catturati, aumentando così il tasso di decadimenti nella regione finale. HOLMES utilizzerà calorimetri a bassa temperatura in cui l'Olmio verrà impiantato, al fine di eliminare le incertezze sistematiche che derivano dall'utilizzo di una sorgente esterna tipica degli spettrometri. Nella sua configurazione finale HOLMES misurerà una matrice di 1000 rivelatori che saranno mantenuti ad una temperatura di funzionamento attorno a 60 mK in un refrigeratore a diluizione. La mia tesi è composta da due parti; nella prima descriverò brevemente lo status delle misure per la determinazione della massa dei neutrini, inquadrando in questo ambito gli obiettivi dell'esperimento HOLMES, mentre nella seconda parte mi limiterò a descrivere tutte le misure effettuate e ancora da effettuare prima di poter misurare la matrice di 1000 rilevatori, concentrandomi sullo sviluppo del sistema di lettura multiplexato e sulla caratterizzazione dei rivelatori di HOLMES descrivendo le sfide intraprese per raggiungere ​​le prestazioni necessarie in termini di risposta temporale e di risoluzione energetica per poter raggiungere la sensisbilità di 1 eV sulla massa neutrino.
Neutrinos are the most elusive particle in the Standard model. Since their existence has been proposed by Pauli in the 1930 letter, we have made important steps towards the understanding of neutrinos, yet there are important pieces of information missing: we don't know neutrinos absolute mass scale, nor we know whether they are Majorana or Dirac particles, finally we have not yet solved the so called hierarchy problem. In the last two decades, measurements performed at the Super-Kamiokande, SNO, Daya-Bay and RENO neutrinos observatories have shed light on the neutrino oscillation phenomena and have firmly established the fact that neutrinos do have a non zero mass. Neutrino oscillations experiments are sensible to the square mass difference of neutrino mass eigenstates and they can not provide any information about the absolute mass scale. The most common methods to assess neutrino mass are measurement of the neutrinoless double beta decay rate, cosmological observations and surveys and the direct measurement of the neutrino mass from single beta or electron capture decay spectrum. The latter is the one and only that can provide a model independent measurement since it is purely kinematic and relies solely on the energy conservation principle. The topic of this dissertation is the description of HOLMES, an experiment started in 2015, aiming at performing a direct measruement of neutrino mass from the electron capture spectrum of 163-Ho. In order to be able to reach the desired sub-eV sentivity on neutrino mass, very high statistics have to be gathered at the end point, which is the sensitive part of the spectrum to a non zero neutrino mass; 163-Ho is a very suitable isotope for this purpouse since its low transition value is close to the energy of the M1 orbital from which electrons are captured, enhancing the event rate close to the end point. HOLMES will use low temperature calorimeters with Holmium embedded in the detector itself in order to eliminate the systematics uncertainties arising from the use of an external beta emitting source, typical of spectrometeres. In its final configuration HOLMES will deploy a 1000 detectors array operated at temperatures as low as 60 mK in a dilution refrigerator. The dissertation will be separated in two parts; in the former I will briefly describe the status of neutrino mass direct measurements focusing in detail on the goals of HOLMES experiment, while in the latter I will describe all the necessary steps taken and yet to be taken for operating the final 1000 detectors array, focusing on the development of the multiplexed readout and the characterization of the single HOLMES detector with the related challenges for achieveing the requiered performances in terms of time and energy resolution for being able to probe the neutrino mass.

Gli unici metodi per misurare la massa del neutrino che non siano dipendente dal modello teorico sono quelli basati sullo studio cinematico del decadimento beta o per cattura elettronica, poiché assumono solo la conservazioni di energia e momento. Holmes è un progetto ERC che è iniziato nel 2014 e che è portato avanti nei laboratori di criogenia dell’università di Milano-Bicocca. Il suo obiettivo è quello di effettuare una misura diretta della massa del neutrino con una sensibilità statistica dell’ordine dell’elettronvolt. Inoltre, proverà anche la fattibilità di questa tecnica per una futuro esperimento che mirerà a superare la sensibilità attuale di KATRIN, che rappresenta lo stato dell’arte delle misure dirette. Per raggiungere la sensiblità di 1 eV. Holmes farà una misura calorimetrica, adottando 1000 microcalorimeteri a basse temperature, ognuno dei quali verrà impiantato con una attività di 300 Bq di 163 Ho. In una misura calorimetrica del decadimento per cattura elettronica dell’Ho, tutta l’energia viene misurata eccetto quella del neutrino. Anche se il neutrino non viene rivelato, il valore della sua massa altera la forma dello spettro di diseccitazione, riducendo anche il valore dell’end-point di un eguale valore. Questa distorsione dello spettro è misurabile solo in una regione vicino all’end-point, dove il rate di conteggi è basso e il background può facilmente nascondere il segnale. Il 163 Ho rappresenta il miglior candidato per una misura calorimetrica della massa del neutrino in termini di sensibilità statistica, dato che ha un Q valore basso di 2833 eV. Inoltre ha anche una vita media relativamente breve (4570 anni), che permette di inserire una piccola quantità di nuclei in un piccolo volume contenitivo. Ogni singolo rivelatore di Holmems è composto da un assorbitore in oro con l’olmio impiantato, termicamente accoppiato a un Transition Edge Sensor (TES), il quale è un termometro molto sensibile, costituito da un bilayer superconduttivo di Mo/Cu. I rivelatori di Holmes devono produrre dei segnali sia dal veloce tempo di salita, per ridurre il pile-up, sia con un veloce tempo di discesa, per ridurre il tempo morto della misura. Il tempo di salita è però limitato dalla massima frequenza di campionamento data dalla banda del sistema di acquisizone, che a sua volta è fissata dal numero di rivelatori che devono essere letti in contemporanea. Dato il numero previsto di rivelatori e di attività, sia i TES che il sistema di lettura microwave multiplexing saranno spinti al loro limite per soddisfare i requisiti dell’esperimento. Durando il mio dottorato, mi sono occupato di vari compiti, sia software che hardware. Ho testato i processi che portano alla fabbricazione finale dei rivelatori TES e ho misurato le loro performance con il sistema di lettura a microonde usando una sorgente di raggi X esterna. Ho inoltre studiato il background atteso dovuto ai raggi cosmici e alla radioattività naturale. Allo stesso tempo, ho sviluppato un software modulare per l’analisi del segnale e dei dati, assieme a innovativi algoritmi per la discriminazione del pile-up, la fonte di background più importante per Holmes. Nel capitolo 1 presento brevemente il panorama sperimentale sulla misura della massa del neutrino, mentre nel capitolo 2 parlerò in particolare dell’esperimento Holmes. Nel capitolo 3 introduco la fisica che sta alla base della risposta dei rivelatori TES, per poi concentrarmi sul design di quelli adottati da Holmes. Nel capitolo 4 presento le routine di analisi che ho sviluppato per produrre uno spettro calibrato a partire dai dati grezzi. Il capitolo 5 finalmente presenta le performance che ho misurato dei rivelatori di Holmes. Nell’ultima parte di questo elaborato presenterò invece i risultati ottenuti nella campagna di misure atta a stimare il rate atteso di background.
The absolute mass of neutrinos is one of the most important riddles yet to be solved, since it has many implications in Particle Physics and Cosmology. The only model independent method of measuring the neutrino mass is based on the kinematic analysis of the beta or the electron capture (EC) decay, which only assumes momentum and energy conservation. Holmes is an ERC project started in 2014, which is currently being set up in the cryogenic laboratory of the University of Milano Bicocca. It will perform a direct measurement of the neutrino mass with a sensitivity of the order of 1 eV. In addition, it will prove the scalability of this technique to a next generation experiment that might go beyond the current expected sensitivity of the state of the art experiment, KATRIN. In order to reach its goal sensitivity, Holmes will use 1000 low temperature microcalorimeters, each implanted with an activity of 300 Bq of 163 Ho, performing thus a calorimetric measurement. In a calorimetric measurement of the electron capture (EC) decay of 163Ho, all the energy is measured except for the fraction carried away by the neutrino. Although the neutrino is not detected, the value of its mass affects the shape of the de-excitation spectrum, reducing also the end-point of the spectrum by an amount equal to m_nu. The spectrum distortion is statistically significant only in a region close to the end-point, where the count rate is lowest and background can easily hinder the signal. In terms of achievable statistical sensitivity, 163 Ho is one of the best candidate, given the combined effect of its low Q-value (2.833 keV) and the proximity of the highest energy peak to the end-point of the spectrum. 163 Ho also has a relatively short half life of 4570 years, which allows to embed a small number of nuclei in a small absorbing volume. Each single Holmes detector is composed of a 163 Ho ion-implanted gold absorber thermally coupled to a Transition Edge Sensor (TES). A TES is a sensitive thermometer, consisting of a superconductor Mo/Cu bi-layer film. The Holmes detectors not only need a fast recovery time to reduce the amount of dead time but also a quick time response to discriminate between two nearly coincident interactions. The latter is limited by the maximum sampling frequency set by the bandwidth of the acquisition system, which in turn is set by the number of detectors that need to be readout at the same time. Given the target number of detectors and the single pixel activity, the detectors and the microwave multiplexing readout system will be pushed to their limits to meet the Holmes requirements. During my PhD work I took care of various tasks, both hardware and software related. I tested the detector fabrication process and measured the resulting detector performances with the microwave multiplexing readout using external X-ray sources. I also studied the expected background due to cosmic rays and environmental radioactivity. At the same time, I developed a modular and robust software for signal processing and data analysis, alongside new algorithms for the pile-up discrimination, the Holmes expected main source of background. Chapter one briefly reviews the experimental efforts on the neutrino mass determination, with a spotlight on the state of the art experiments, while chapter two presents the Holmes experiment with its expected statistical sensitivity. Chapter 3 firstly introduces the physics behind the behavior of a Transition Edge Sensors, then focuses on the specific design and fabrication process of the Holmes detectors. Chapter 4 presents the analysis routines required to produce a clean calibrated spectrum from a raw dataset. Chapter 5 finally shows the measured detectors performances. The last part of the dissertation presents the expected background rate after the studies conducted with a dedicate measurements campaign.

Neutrons produced deuterium Z-pinch plasmas are widely acknowledged to be a consequence of highly accelerated deuterons undergoing nuclear fusion with relatively stationary deuterons. The acceleration is thought to occur in intense fields created in the MHD instabilities that punctuate the plasma column. Interestingly, the energies of the accelerated ions exceed the applied voltage across the electrode gap. We use the 1 MA Zebra pulsed-power generator at the Nevada Terawatt Facility (NTF) to explore this poorly understood fast neutron production mechanism by creating deuterium Z-pinches in three distinct types of target loads. The loads are a cylindrical shell of deuterium gas, the far less explored deuterided palladium wire arrays, and a deuterium-carbon ablated laser plume target, which is unique to the NTF.

The pinch dynamics vary considerably in these three targets and provide the opportunity to explore the ion acceleration mechanism. We infer the characteristics of the accelerating fields from a wide range of diagnostic data including the neutron yield, energy spectrum and angular distribution, and the properties of the matching electron beams that are accelerated in the same field, and the energetic X-rays they produce on stopping. The plasma and the instabilities were recorded on several high-speed imaging diagnostics along with time-integrated soft (<10 keV) X-ray pinhole images. The three load types produced total neutron yields in the 10⁸–10¹⁰ n/pulse range. The synchronization we observe between the ion and electron beams and the development of instabilities leads us to conrm the acceleration hypothesis. We also present the characteristics of the fields and ion beams in these varied pinches.

The advanced fuels investigated in this thesis comprise fuels non− conventional in their design/form (TRISO), their composition (high content of plutonium and minor actinides) or their use in a reactor type, in which they have not been used before (e.g. nitride fuel in BWR). These fuels come with a promise of improved characteristics such as safe, high temperature operation, spent fuel transmutation or fuel cycle extension, for which reasons their potentialis worth assessment and investigation. Their possible use also brings about various challenges, out of which some were addressed in this thesis. TRISO particle fuels with their superior retention abilities enable safe, high−temperature operation. Their combination with molten salt in the Advanced High Temperature Reactor (AHTR) concept moreover promises high operating temperature at low pressure, but it requires a careful selection of the cooling salt and the TRISO dimensions to achieve adequate safety characteristic, incl. a negative feedback to voiding. We show that an AHTR cooled with FLiBe may safely operate with both Pu oxide and enriched U oxide fuels. Pu and Minor Actinides (MA) bearing fuels may be used in BWR for transmutation through multirecycling; however, the allowable amounts of Pu and MA are limited due to the degraded feedback to voiding or low reactivity.We showed that the main positive contribution to the void effect in the fuelswith Pu and MA content of around 11 to 15% consist of the decreased thermalcapture probability in Pu-240, Pu-239 and Am-241 and increased fast and resonance fission probability of U-238, Pu239 and Pu-240. The total void worthmoreover increases during multirecycling, limiting the allowable amount ofMA to 2.45% in uranium−based fuels. An alternative, thorium−based fuel allows for 3.45% MA without entering the positive voiding regime at any point of the multirecycling. The increased alpha−heating associated with the use of transmutation fuels, is at level 24−31 W/kgFUEL in the uranium based fuels and 32−37 W/kgFUEL in the thorium−based configurations. The maximum value of the neutron emission, reached in the last cycle, is 1.7·106 n/s/g and 2·106 n/s/g for uranium and for thorium−based fuels, respectively. Replacing the standard UO2 fuel with higher−uranium density UN orUNZrO2 fuels in BWR shows potential for an increase of the in-core fuelresidence time by about 1.4 year. This implies 1.4% higher availability of the plant. With the nitride fuels, the total void worth increases and the efficiency of the control rods and burnable poison deteriorates, but no major neutronics issue has been identified. The use of nitride fuels in the BWR environment is conditioned by their stability in hot steam. Possible methods for stabilizing nitride fuels in water and steam at 300◦ C were suggested in a recent patentapplication.

QC 20121004

AbstractIntegral experiments on critical irradiation of neuptium-237 (237Np) and americium-241 (241Am) foils are carried out in a hard spectrum core at KUCA with the use of the back-to-back fission chamber, and Monte Carlo calculations together with a reference nuclear data library are conducted for confirming the precision of numerical simulations. Subcritical irradiation of minor actinide (MA) by ADS is a very important step, before operating actual ADS facilities, in a critical assembly at zero power, such as KUCA, which is an exclusive facility for ADS that comprises a uranium-235 (235U) fueled core and a 100 MeV proton accelerator. The first significant attempt is made to demonstrate the principle of nuclear transmutation of MA by ADS through the injection of high-energy neutrons into the KUCA core at a subcritical state. Here, the main targets of nuclear transmutation of MA by the ADS experiments are fission reactions of 237Np and 241Am, and capture reactions of 237Np.

In the paper a possibility of using a lead isotope, pure Pb-208, as a coolant for a subcritical core of 80 MW thermal capacity of the PDS-XADS type facility is considered. Calculations of neutronic characteristics were performed using Monte Carlo technique. The following initial data were chosen: an annular core with a target, as a neutron source, at its centre; the core coolant — Pb-208 (100%); a fuel — a mix of mono nitrides of depleted uranium and power plutonium with a small share of neptunium and americium; the target coolant — a modified lead and bismuth eutectic, Pb-208(80%)-Bi(20%); proton beam energy — 600 MeV; effective multiplication factor of the core under operation — Keff = 0.97; thermal capacity of the core — N = 80 MW. From calculations performed it follows that in using Pb-208 as the core coolant the necessary intensity of the external source of neutrons to deliver 80 MW thermal capacity is equal to S = 2.29−1017 n/s that corresponds to proton beam current Ip = 2.8 mA and beam capacity Pp = 1.68 MW. In using natural lead instead of Pb-208 as the core coolant, effective multiplication factor of the core in normal operating regime falls down to the value equal to Keff = 0.95. In these conditions multiplication of external neutrons in the core and thermal capacity of the subcritical core are below nominal by 1.55 times. For achievement the rated core power N = 80 MW it is required on ∼20–30% to increase the fuel loading and volume of the core, or by 1.55 times to increase intensity of the external source of neutrons. In the last case, the required parameters of the neutron source and of the corresponding proton beam are following: intensity of the neutron source S = 3.55·1017 n/s., beam current Ip = 4.32 mA, beam capacity Pp = 2.59 MW. To exploit the accelerator with the reduced proton beam current it will be required about 56 tons of Pb-208, as a minimum, for the core coolant. Charges for its obtaining can be recovered at the expense of the economy of the proton accelerator construction cost. In this case, the acceptable price of the lead isotope Pb-208 must be less than $2,860/kg.

Abstract This study proposes to make effective use of plutonium transmuted from minor actinides (MA) by fusion reactors as fertile fuel in a light water reactor (LWR). The plutonium transmuted from MA, particularly Pu-238, has a large neutron capture cross section and becomes fissile Pu-239 by the reaction. If the plutonium transmuted from MA is loaded into LWR appropriately, there is a possibility to maintain a constant effective multiplication factor. This study evaluated the effects of the plutonium transmuted from MA on a full MOX boiled water reactor (BWR) core by Monte Carlo-based neutron transport and burnup calculation. We revealed that some fuel assemblies achieved the effective multiplication factor is greater than 1.0 and its decrease was significantly small (−0.013) during 400 days operation. However, under this condition, the power peaking factor was 1.4, which should be unacceptable from the viewpoint of thermal design. Inventories of heavy nuclides in fuel cycles was evaluated using a simple diagram and its result indicated that the accumulation of MA in the fuel cycle was reduced by introducing the MA transmutation and the Pu recycle system. Furthermore, the amount of MA production and MA transmutation are balanced by introducing two fusion reactors with 3 GW thermal output into the fuel cycle, and the MA inventory was equilibrated.

Pursuing a high minor actinide (MA) transmutation rate, this paper proposes a neutronics concept design of lead-bismuth (LBE) cooled accelerator-driven system (ADS) with burnup reactivity swing less than 1% and proton beam current smaller than 17mA. After a comparison with other types of fuels, Uranium-free metallic dispersion fuel (TRU-10Zr)-Zr* is selected to obtain a harder neutron spectrum to transmute MA. With a MA initial loading, the suitable proportion of initial Plutonium to transuranium element (TRU) is found around 33% to make sure that the burnup reactivity swing is less than 1%. The location of the spallation target is optimized to guarantee high external spallation neutron source efficiency and to lower proton beam current. For the subcritical system, initial effective multiplication factor is 0.97, and the thermal power is 1000 MW. For the accelerator, proton with energy of 1.5GeV and a parabolic spatial profile is provided by proton linac. It is demonstrated by the numerical results that the transmutation rate of MA is about 28% after 600 effective full power days (EFPD) while the support ratio for LWR units with the same power is about 46.

Minor actinides in the spent fuel have strong radiotoxicity and very long half-life, the the properly dispose of spent fuel is indispensible to the development of nucler energy. Generally,we dispose the spent fuel by geological burying. But it can not compeletly solve the problem. Neutron transmutation is the only way to shorten the half-life of radioactive nuclides, under the irradiation of neutron MA nuclide will capture neutron or fission, and translate into the short lived nuclide or something valued nuclide. Reactivity temperature coefficient is an improtant safety parameter in nuclear reactor physics.In the reactor design, for the safely operation of reactor, reactivity temperature coefficient must be be negative. The introduction of MA in the PWR must have interference to the temperature coefficient. This paper mainly studied the influence of PWR transmutation minor actinide on the temperature coefficient.

The new radiation source ELBE at Research Center Rossendorf uses the high brilliance electron beam from a superconducting LINAC to produce various secondary beams. Electron beam intensities of up to 1 mA at energies between 12 MeV and 40 MeV can be delivered with a wide variability in the electron pulse structure. The maximum pulse frequency is 13 MHz with a pulse width less than 10 ps. The small emittance of the electron beam permits the irradiation of very small volumes. These main beam parameters led to the idea to convert the intense picosecond electron pulses into sub-ns neutron pulses by stopping the electrons in a heavy (high atomic number) radiator and to produce neutrons by bremsstrahlung photons through (γ,n)-reactions. In order to enable measurements of energy resolved neutron cross sections like (n,p), (n,α) and (n,f) with a time-of-flight arrangement with a short flight path of only a few meters, it is necessary to keep the volume of the radiator for neutron production as small as possible to avoid multiple scattering of the emerging neutrons which would broaden the neutron pulses. It is the primary physics objective of this neutron source to determine neutron cross sections firstly for construction materials of fusion and fission reactors, for which it is important to select radiation hard materials, and secondly for the handling of waste from such reactors, especially in order to find processes which transmute long-lived radioactive nuclides into short-lived and finally stable ones. In addition, the distribution of fragments can be analyzed which are produced by neutron-induced transmutation of long-lived radioactive nuclides. Furthermore experiments can be performed which address problems of nuclear astrophysics. The energy deposition of the electron beam in the small neutron radiator is that high that any solid material would melt. Therefore, the neutron radiator consists of liquid lead flowing through a channel of 11.2×11.2 mm2 cross section. From the thermal and mechanical point of view molybdenum turned out to be the most suited channel wall (thickness 0.5 mm) material. Depending on the electron energy and current up to 20 kW power will be deposited into a radiator volume of 3 cm3. This heating power is removed through the heat exchanger in the liquid lead circuit. Typical flow velocities of the lead are in the range of 2 m/s in the radiator section. The electrons that are not stopped in the radiator and the secondary radiation are dumped in an aluminum beam dump. To reduce the radiation back-ground in the measuring direction, the neutrons are decoupled from the radiator at an angle of 90° with respect to the impinging electrons. Particle transport calculations were carried out using the Monte Carlo codes MCNP and FLUKA. These calculations predict a neutron source strength of 7.88·1012 and 2.67·1013 n/s for electron energies between 20 and 40 MeV. At the measuring place 362 cm away from the radiator, neutron fluxes of 1.7·107 n/(cm2 s) will be obtained. The mentioned time-of-flight distance allows for an energy resolution better than 1%. The maximum usable neutron energy is about 7 MeV.

The Minor Actinides (MA) generated by nowadays PWRs fleet has significant impact on environment and biosphere. Inert Matrix Fuels (IMF) is a possible way to reduce the production and hazard of MA in recent. From neutronic aspect, using the MCNP code with temperature related continuous neutron data, the present paper analyses the isotopic contributions to the Doppler Coefficients of certain types IMF fuels. It is concluded that, the Doppler Coefficients of Al2O3+ZrO2+MgO and ZrO2 based IMF fuels are much smaller than those containing ThO2, since the low neutron absorptions and lacking of resonance broadening of Al, Zr, Mg and O elements. For the same Inert Matrix, Reactor Grade Plutonium (RG-Pu) IMF fuels have more negative Doppler Coefficients than Weapon Grade Plutonium (WG-Pu) IMF fuels, which induce by the more abundance of resonance isotopes 240Pu, 242Pu in RG-Pu. Since the different neutron absorption cross-section profiles, the Er2O3 burnable poison has negative contribution to the Doppler Coefficient, however 10B, a typical 1/v absorber, is on the contrary way.