1.Introduction

3.The drive for Multi-MW beams:a) Spallation neutron sourcesb) Accelerator driven sources-Transmutationc) IFMIF-Testing materials for ITERd) Radioactive Ion Beamse) Beta beams for focussed neutrino beams

2.High neutron fluxes

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

The main sources of neutrons

1. Spallation

2. Nuclear reactors

3.Breakup reactions with loosely bound nuclei-most obviously deuterons[Binding energy 2.23 MeV]

There are many ways to produce neutrons

There are three ways to produce very high, controlled fluxes of neutrons

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 applicationsand we need good sources to understand their interactions and weneed good neutron detectors.

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

neutrons UCxdeuterons

graphite

40MeV,5mA

Neutrons from Deuteron Breakup

• Either we use the neutrons directly behind the target. This happens inIFMIF to test how materials in a fusion reactor (ITER) withstand constant bombardment by 1015 ncm2s-1,

• Or we can use the neutrons to induce fission in a uranium carbidetarget. 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 sources2) Accelerator Driven sources for Transmutation3) Testing materials for fusion reactors 4) Creating Radioactive Ion Beams5) 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 breakupof deuterons. 4 & 5) may or may not involvethe 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/risksassociated with a)Storage of long-lived toxic wasteb)Weapons proliferationc)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-calledAccelerator 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 neutronflux. 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 thewaste 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 intensity1.0 GeV proton beam.

•It can be used to transmute waste such as Pu and other long-lived actinides

orit can be used to generatepower

ora combination of the two.

•The process is complicatedand involves chemicalpartitioning as a vital step(s)

U. Fischer, Fast Neutron Physics Workshop, Dresden, 5-7 September, 2002

IFMIF Intense Neutron Source

Beam Spot(20x5cm2)

High Flux

Low FluxMedium Flux

LiquidLi Jet

DeuteronBeam

~1x1017n/s over 4π

~1x1015 n/(s cm2) on the back side of Liaverage neutron energy ~11 MeV

40 MeV2 x 125mA

U. Fischer, Fast Neutron Physics Workshop, Dresden, 5-7 September, 2002

Neutron flux spectra: IFMIF/fusion/fission

0,01 0,1 1 10 100100

101

102

103

104

105

106

107

ITER first wall IFMIF high flux test module HFR Petten

Neu

tron

flu

x de

nsit

y [1

010/c

m2 /M

eV/s

]

Neutron energy [MeV]

SPIRAL-2 project (France)

40MeV; 5mAdeuterons neutrons

graphite

UCx

Courtesy of M.Lewitowicz

> 1013 fiss s-1

IFMIFIFMIF--like neutron fluxlike neutron flux available at SPIRALavailable at SPIRAL--22

IFMIF: on the back of the converter5cm x 20cm

~1x1015 n/(s cm2)

SPIRAL: on the back of the converter1cm x 4cm

~1x1014 n/(s cm2)

d+C compared to d+Ligives harder neutron spectrum

Energy spectra of neutrons

Proton Drip Line

Neutron Drip Line

Super Heavies

Fewer than 300 nuclei

Outline and motivationOne of the most interesting question in nuclear astrophysics is how and where the heavy isotopes were produced.

MASS NUMBER

AB

UN

DA

NC

E How and where are the heavy isotopes produced?

Fe

BB Fusion Neutron captureH, HeC N O

• 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

s-only

r-only

• s process terminates at 209Bi• 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

p-only

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

Proposal: production of neutrons for a new ToF facility at GANIL

• Neutron flux: 2 orders higher than n-ToF• En resolution: better than 1%• Excellent beam time structure• Available in parallel with RNB production

• CEA/DSM&DAM• international n-ToF community• ADS and fusion community

interest

N-tof : CERN, spallationGELINA : Geel, electrons

Spiral-2 neutrons:• Reaction: d(40MeV)+C xn• En: from 100keV to 40 MeV• High intensities available

Neutrons for Science at SPIRAL-2

X. Ledoux, D. Ridikas

Current Schemes for producingbeams 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

C. Chandler et al. Phys. Rev. C61 (2000) 044309

67Ge

69Se

76Rb

92Mo fragmentation on natNi target

E = E0 [√ 1 - β2

(1 - βcosθ)]

• 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 1.3MeVb) Peak to Compton ratioc) Doppler spreading for moving sources due to finite opening angle

BeamRecoil

γ

θ

• Radioactive Ion Beams will place newdemands 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 fromfragmentation and for reactions such as (p,γ)where we have no particle coincidences.

The need for improved Gamma-ray Detectors

Det.

Tests at Surrey-Fixing the Interaction positionDetector-HpGe-n-type,Outer p+ contact divide into 6segments in rad. and longt directions.Inner contact notsegmented to give total E.All signals digitised.

SegmentationSlice 1 Slice 3

Risetimes

60 x 90mm

•Radial posn-risetime of pulse•Azimuthal posn-Mirror charges

Two pulses from sectionE3:-1-200 keV2-430 keV

A

C

D

E F

B

Defining the Interaction position• Approaches rely on methods from artificial intelligence, genetic

algorithms, artificial neural networks and discrete wavelet transform.

Interaction energy providesvital information fortracking. Moving WindowDeconvolution Method isused to obtain the depositedenergy 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 ofcharged particles.

▪ Some of these applications will mean intense new neutron sources.

▪ Among the applications is the production of intense beams ofradioactive 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

TOF technique

BaF2:• 100% efficiency• fast timing• low neutron sensitivity

(n,γ) binding energy

n_TOF beamFlight path: 185 m Proton pulse width: 6 nsNeutron energy range: 0.1 eV – 10 GeVRepetition rate: < 0.5 HzNeutron intensity: >1.5·104 dN/dlnE/pulse

energy resolution: <10-3

Neutron flux characteristics at SPIRAL-2

40MeV d-beam(∅ 4.00 or 2.83cm)

C converter(0.8 cm thick)

irradiation zone (56Fe at 50%)

6cm

3cm

40MeV d-beam(∅ 4.00 or 2.83cm)

C converter(0.8 cm thick)

irradiation zone (56Fe at 50%)

6cm

3cm

• Representative energy spectrum• Neutron flux: > 5x1013 n/( s cm2) • Damage rates: > 3dpa/fpy • Useful volume: ~10 cm3

• Variable temperature: 500-1000°C

• CEA Cadarache, DSM/DRFC• CEA Saclay, DEN/DMN/SRMA • IFMIF collaboration, EURATOM

interest

9,3E13 8,1E13

6,9E135,7E13 4,4E13

3,2E13

2E13

0,0 0,5 1,0 1,5 2,0 2,5 3,00

1

2

3

4

5

6Neutron flux (n s-1 cm-2)

Radius r (cm)B

eam

axi

s (c

m)

7,5E122E133,2E134,4E135,7E136,9E138,1E139,3E131,1E141,2E141,3E14

Irradiation sample(iron foils)

Container

Graphite target-converter

D-beam

Optional material Container cooling

HeaterIrradiation sample(iron foils)

Container

Graphite target-converter

D-beam

Optional material Container cooling

Heater

300

400

500

600

700

800

900

0 5 10 15 20 25 30 35

N° of foil

Tmax

(°C

)

donn401donn402donn403donn404donn405

Max. T, C°

Thermal conditions at SPIRAL-2

Possibility to stabilize the temperature at a desired level!

900 700 500 300

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

Summary: material irradiations

Beam availability: at least 3 months/year at full power!

Physics with intense neutron beams from 1 to 40 Physics with intense neutron beams from 1 to 40 MeVMeV

Cross section measurementsFission, (n, xn), (n, xlcp), …AstrophysicsStudies related to hybrid reactors (ADS)Validation of codesMeasurements with actinides (very small quantities)

Studies of the reaction D(n,2n)p3-body system (forces)Measurements of the n-n scattering length

Neutron beams provided by SPIRALNeutron beams provided by SPIRAL--22

Neutron production reaction d(40 MeV) + CEnergy neutrons between 0 and 40 MeV determined by ToFBeam definition beam line, collimation, moderation (?), shielding, …Experimental hall at 0° (with respect to the d-beam)

Beam characteristics:Flux f( E, flight path, beam frequency, …)Energy resolution f( flight path, time resolution of beam, …)Energy domain f( flight path, beam frequency, …)

Energy resolutionEnergy resolution

2 2E t LE t L∆ ∆ ∆ +

t – neutron ToF∆t - time resolution L - flight path ∆L - uncertainty of flight path

At 40 MeV :L= 5 m ∆E/E ~ 1 %L=10 m ∆E/E ~ 0.5 %

Beam repetition rate 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

Proposal: production of neutrons for a new ToF facility at GANIL

• Neutron flux: 2 orders higher than n-ToF• En resolution: better than 1%• Excellent beam time structure• Available in parallel with RNB production

• CEA/DSM&DAM• international n-ToF community• ADS and fusion community

interest

N-tof : CERN, spallationGELINA : Geel, electrons

Spiral-2 neutrons:• Reaction: d(40MeV)+C xn• En: from 100keV to 40 MeV• High intensities available

Neutrons for Science at SPIRAL-2

Summary: neutron beamsSummary: neutron beamsConditions 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 progressSignal to noise ratio (neutrons & gammas)Definition of the experimental hall (size, shielding, …)Moderation of neutrons (C, Be, D2O, ) use of other targets (D, T, Li, Be, …) & lower energy deuterons

Material irradiations:

• report with facility characteristics is finished and published• budget request is made at EURATOM

Summary: NFS at SPIRAL-2

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

Accelerator Driven Sources for Transmutation

Basic Idea:- A sub-critical assembly driven critical by the neutrons from spallation induced by a high intensity1.0 GeV proton beam.

•It can be used to transmute waste such as Pu and other long-lived actinides

orit can be used to generatepower

ora combination of the two.

•The process is complicatedand involves chemicalpartitioning as a vital step(s)