The main sources of neutrons - PDF Free Download

1.Introduction 2.High neutron fluxes 3.The drive for Multi-MW beams: a) Spallation neutron sources b) Accelerator driven sources-transmutation c) IFMIF-Testing materials for ITER d) Radioactive Ion Beams e) Beta beams for focussed neutrino beams 4.Radioactive Ion Beams:Why do we need them? How can we make them? 5.The challenges-an example. The next generation of gamma ray arrays-agata 6.Conclusions

1. Spallation The main sources of neutrons There are many ways to produce neutrons There are three ways to produce very high, controlled fluxes of neutrons 2. Nuclear reactors 3.Breakup reactions with loosely bound nuclei -most obviously deuterons[binding energy 2.23 MeV] Neutron sources are important because 1. They have many uses studies of condensed matter - biological studies - astrophysics 2. We need to shield against the neutrons produced in our applications and we need good sources to understand their interactions and we need good neutron detectors.

Spallation Reactions [10 fast neutrons per proton at 500 MeV]

Neutrons from Deuteron Breakup graphite deuterons 40MeV,5mA neutrons UCx Either we use the neutrons directly behind the target. This happens in IFMIF to test how materials in a fusion reactor (ITER) withstand constant bombardment by 10 15 ncm 2 s -1, Or we can use the neutrons to induce fission in a uranium carbide target. The resulting fission products can then be extracted, ionised, accelerated and used in experiments. This is the basis of the SPIRAL-2 project at GANIL in France.

Why do we need Multi-MW Beams? The drive comes from several areas: 1) Spallation neutron sources 2) Accelerator Driven sources for Transmutation 3) Testing materials for fusion reactors 4) Creating Radioactive Ion Beams 5) Creating Beta beams( Focussed beams of low energy neutrinos) 1,2 & 3) all involve the creation of high fluxes of neutrons either by Spallation or by breakup of deuterons. 4 & 5) may or may not involve the creation of a high neutron flux. In general we need beams of intensity 2-5 ma or more. In spallation the beam usually consists of 0.5-1.5 GeV protons.

The need for Nuclear Power One could debate the need for a new fleet of nuclear generation stations endlessly Building such a fleet is inhibited/prohibited by public perception of problems/risks associated with a)storage of long-lived toxic waste b)weapons proliferation c)chernobyl-style accidents In principle one could create systems which essentially eliminate all these problems One such system advocated in Europe and the U.S. is the so-called Accelerator Driven System (ADS) for the transmutation of nuclear waste. In this proposal one builds a fleet of ADS systems alongside the new set of reactors. In essence one has a system to destroy actinides and fission fragments when they are withdrawn from the reactor. Basic idea-high energy protons on a heavy solid/liquid target to produce high neutron flux. The target is surrounded by a sub-critical core and then by a blanket of liquid waste. This requires front end partitioning but not exit partitioning. At the end the waste can go directly to storage.

Criteria for ADS Design and Development Should not increase the cost Should reduce infrastructure complexity Overall operational safety improved Must reduce access to weapons material No new class of nuclear weapons No single national storage site needed Reduce need for strong International oversight -reduce weapons material as much as possible -possible further bonus of complete energy recovery Needs to be seen as major advance Transition from startup should not be characterised by unsafe conditions or any negative aspects

Accelerator Driven Sources for Transmutation Basic Idea:- A sub-critical assembly driven critical by the neutrons from spallation induced by a high intensity 1.0 GeV proton beam. It can be used to transmute waste such as Pu and other long-lived actinides or it can be used to generate power or a combination of the two. The process is complicated and involves chemical partitioning as a vital step(s)

IFMIF Intense Neutron Source 40 MeV 2 x 125mA Deuteron Beam Medium Flux Low Flux ~1x10 17 n/s over 4π Liquid Li Jet average neutron energy ~11 MeV High Flux Beam Spot (20x5cm 2 ) ~1x10 15 n/(s cm 2 ) on the back side of Li U. Fischer, Fast Neutron Physics Workshop, Dresden, 5-7 September, 2002

Neutron flux spectra: IFMIF/fusion/fission 10 7 Neutron flux density [10 10 /cm 2 /MeV/s] 10 6 10 5 10 4 10 3 10 2 10 1 ITER first wall IFMIF high flux test module HFR Petten 10 0 0,01 0,1 1 10 100 Neutron energy [MeV] U. Fischer, Fast Neutron Physics Workshop, Dresden, 5-7 September, 2002

SPIRAL-2 project (France) graphite > 10 13 fiss s -1 deuterons 40MeV; 5mA neutrons UCx Courtesy of M.Lewitowicz

Energy spectra of neutrons IFMIF-like neutron flux available at SPIRAL-2 IFMIF: on the back of the converter 5cm x 20cm ~1x10 15 n/(s cm 2 ) SPIRAL: on the back of the converter 1cm x 4cm ~1x10 14 n/(s cm 2 ) d+c compared to d+li gives harder neutron spectrum

Super Heavies Fewer than 300 nuclei Proton Drip Line Neutron Drip Line

Outline and motivation One of the most interesting question in nuclear astrophysics is how and where the heavy isotopes were produced. ABUNDANCE BB Fusion H, He C N O Fe Neutron capture How and where are the heavy isotopes produced? MASS NUMBER Nucleosynthesis of the heavy elements by neutron capture processes (s process and r process) Nuclear data needs for s and r process Can one use neutrons from SPIRAL 2 to measure neutron capture cross sections?

Overview s and r process p-only s-only r-only s process terminates at 209 Bi r process produces also the heaviest elements like uranium p process produces about 30 isotopes on the proton rich side which cannot be produced by s or r process

The r process r-process abundances of old stars match solar abundance pattern at high atomic numbers (Z>55). This implies that there is a unique, very robust r-process mechanism (main component). However, there are discrepancies between data and solar abundance pattern for light elements below Ba. This indicates that there is at least one other component (weak component). from J.J. Cowan and C. Sneden

Neutrons for Science at SPIRAL-2 Proposal: production of neutrons for a new ToF facility at GANIL N-tof : CERN, spallation GELINA : Geel, electrons Spiral-2 neutrons: Reaction: d(40mev)+c xn E n : from 100keV to 40 MeV High intensities available Neutron flux: 2 orders higher than n-tof E n resolution: better than 1% Excellent beam time structure Available in parallel with RNB production interest CEA/DSM&DAM international n-tof community ADS and fusion community X. Ledoux, D. Ridikas

Current Schemes for producing beams of radioactive nuclei A)The classic ISOLDE scheme B)The ISOL plus post-accelerator C)Fragmentation -In Flight (GSI,MSU,GANIL,RIKEN) D)The Hybrid-An IGISOL to replace the ISOL in B) -The basis of RIA

92 Mo fragmentation on nat Ni target 76 Rb 69 Se 67 Ge C. Chandler et al. Phys. Rev. C61 (2000) 044309

The need for improved Gamma-ray Detectors Ge detectors are the workhorse of γ-ray spectroscopy. -Good energy resolution and reasonable efficiency(0.01-10mev) They are limited by a) photo-peak eff.--best arrays have 10-20% at 1.3MeV b) Peak to Compton ratio c) Doppler spreading for moving sources due to finite opening angle Radioactive Ion Beams will place new demands on such detectors. a) Greater efficiency- since beams are weak. b) Better peak to background because of radioactivity of beam. c) Higher counting rate capabilities d) Better position resolution for first interaction( θ) important for high velocity beams from fragmentation and for reactions such as (p,γ) where we have no particle coincidences. [ E = E 1 - β2 ] 0 (1 - βcosθ) Beam Recoil γ θ Det.

D C 60 x 90mm B Tests at Surrey-Fixing the Interaction position Detector-HpGe-n-type,Outer p + contact divide into 6 segments in rad. and long t directions.inner contact not segmented to give total E.All signals digitised. A Segmentation Risetimes Slice 1 Slice 3 E F Radial pos n -risetime of pulse Azimuthal pos n -Mirror charges Two pulses from section E3:- 1-200 kev 2-430 kev

Defining the Interaction position Approaches rely on methods from artificial intelligence, genetic algorithms, artificial neural networks and discrete wavelet transform. Interaction energy provides vital information for tracking. Moving Window Deconvolution Method is used to obtain the deposited energy with high resolution from the digitised signals. Figure shows MWD used to give spectra from B1 (front edge). We get 3.1 and 3.5 kev for 122 and 1332 kev.

Conclusions There are strong reasons for us to develop MW beams of charged particles. Some of these applications will mean intense new neutron sources. Among the applications is the production of intense beams of radioactive ions -Nuclear Physics -Nuclear astrophysics These applications will require new detection systems e.g. AGATA- the european gamma ray tracking array

n_tof at CERN

(n,γ) binding energy TOF technique BaF 2 : 100% efficiency fast timing low neutron sensitivity

n_tof beam Flight path: 185 m energy resolution: <10-3 Proton pulse width: 6 ns Neutron energy range: 0.1 ev 10 GeV Repetition rate: < 0.5 Hz Neutron intensity: >1.5 10 4 dn/dlne/pulse

Neutron flux characteristics at SPIRAL-2 irradiation zone ( 56 Fe at 50%) C converter (0.8 cm thick) 40MeV d-beam ( 4.00 or 2.83cm) 3cm Representative energy spectrum Neutron flux: > 5x10 13 n/( s cm 2 ) Damage rates: > 3dpa/fpy Useful volume: ~10 cm 3 Variable temperature: 500-1000 C 6cm Beam axis (cm) interest 6 5 4 3 2 1 3,2E13 5,7E13 4,4E13 6,9E13 9,3E13 8,1E13 Neutron flux (n s -1 cm -2 ) 2E13 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 Radius r (cm) 7,5E12 2E13 3,2E13 4,4E13 5,7E13 6,9E13 8,1E13 9,3E13 1,1E14 1,2E14 1,3E14 CEA Cadarache, DSM/DRFC CEA Saclay, DEN/DMN/SRMA IFMIF collaboration, EURATOM

900 800 700 T m a x ( C ) 600 500 Thermal conditions at SPIRAL-2 donn401 donn402 donn403 donn404 donn405 Container Irradiation sample (iron foils) Heater 400 300 0 5 10 15 20 25 30 35 900 700 500 300 N of foil Max. T, C Optional material D-beam Container cooling Graphite target-converter Possibility to stabilize the temperature at a desired level!

Summary: material irradiations Necessary conditions for successful material irradiations dedicated plug for irradiations with automatic extraction of samples neutron flux detectors & sample temperature monitors dedicated storage and handling hall for irradiated samples transport permission for irradiated samples should be requested Beam availability: at least 3 months/year at full power!

Physics with intense neutron beams from 1 to 40 MeV Cross section measurements Fission, (n, xn), (n, xlcp), Astrophysics Studies related to hybrid reactors (ADS) Validation of codes Measurements with actinides (very small quantities) Studies of the reaction D(n,2n)p 3-body system (forces) Measurements of the n-n scattering length

Neutron beams provided by SPIRAL-2 Neutron production Energy Beam definition Experimental hall reaction d(40 MeV) + C neutrons between 0 and 40 MeV determined by ToF beam line, collimation, moderation (?), shielding, at 0 (with respect to the d-beam) Beam characteristics: Flux Energy resolution Energy domain f( E, flight path, beam frequency, ) f( flight path, time resolution of beam, ) f( flight path, beam frequency, )

Energy resolution 2 2 E t L + E t L t t L L neutron ToF - time resolution - flight path - uncertainty of flight path At 40 MeV : L= 5 m E/E ~ 1 % L=10 m E/E ~ 0.5 %

Beam repetition rate Requirement: differentiation of 2 neutrons with the ToF t and t+t With L=10 m and T~ 2 µs no overlapping of low and high energy neutrons F ~ 500kHz, i.e. by a factor 200 smaller than the original beam frequency

Summary: neutron beams Conditions to fulfill for neutron beams Experimental hall at 0 Flight path (beam line) at least of 5 m long Accelerator time structure - pulsation 100 ps - frequency 500 khz (use in parallel with RIB production) Expected performances Energy resolution < 1% up to 40 MeV Average neutron energy ~14 MeV Flux : ~100 times higher than at CERN between 5 and 40 MeV Other work in progress Signal to noise ratio (neutrons & gammas) Definition of the experimental hall (size, shielding, ) Moderation of neutrons (C, Be, D 2 O, ) use of other targets (D, T, Li, Be, ) & lower energy deuterons

Summary: NFS at SPIRAL-2 Material irradiations: report with facility characteristics is finished and published budget request is made at EURATOM Neutron beams: report with facility characteristics is nearly finished physics case report still to be done Outlook: organization of potential users meeting by the end of this year