Laser driven nuclear reaction

studies: recent successes and

new unique opportunities for

future research

Klaus M Spohr

SUPA collaboration

University of the West of Scotland

&

University of Strathclyde

Overview

• Laser driven Nuclear Physics: Introductory remarks

– Development of high power laser systems

– History and milestone achievements in laser-nuclear research

• Laser induced nuclear photo-proton reaction studies

– Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes

– Methodology and setup of IOQ Jena multi TW laser system

– Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes

– Conclusions, opportunities and future challenges

• Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision

– The principle of ‘Laser Induced Compton Backscattering’

– Motivation

– LICB experiment on resonant photoabsorption of Mößbauer nuclei

– Some final thoughts: induced nuclear emission (lasing)

– Summary

Introductory remarks

Development of high power laser systems

HiPER

NIF

Development of high power laser systems

• Chirped Pulse Amplification (CPA) by Strickland and Mourou allowed

intensities I > 1015 Wcm-2

– CPA (Strickland D and Mourou G, Opt. Comm. 56 (3) 219 (1985))

• Ultrashort laserpulse up to the petawatt level with the laser pulse being

stretched out temporally and spectrally prior to amplification

– CPA is the current state-of-the-art technique for all of the highest power lasers

>100 TW

• Currently strongest civilian systems

– NIF @ LLNL, I > 1022 Wcm-2

– 2009 ASTRA/GEMINI @ CLF RAL I ~1022 Wcm-2

– Vulcan @ CLF RAL, I > 1021 Wcm-2

• HiPER project I ~ 5 ×1024 Wcm-2 (2020)

‘game-changers’

NYT, March 2009

• Concept of Chirped Pulse Amplification (CPA)

Chirped Pulse Amplification

History and milestone achievements in laser-nuclear research

• 1996 Femtosecond quasi-monoenergetic keV-pulses (atomic physics)

– Schoenlein R et al., Science 274 236 (1996)

• 2000 Laser-induced nuclear fission of 238U

– Ledingham K et al.,PRL 84 899 (2000), Cowan T et al.,PRL 84 903 (2000)

• 2003 Laser-induced fusion evaporation reactions

– McKenna P et al., PRL 91 (7) 075006 (2003)

• 2006 GeV electron beams from a centimetre-scale 40 TW laser

accelerator

– Leemans W et al., Nature Physics 2 (10) 696 (2006)

• 2007/08 Proton acceleration to 60 MeV and proton focussing

– Robson L et al., Nature Physics 3 (1) 58 (2007), Schollmeier M et al., PRL 101 055004 (2008)

• 2007 High order harmonic keV radiation (HOHG) of high brightness

– Dromey B et al., PRL 99 085001 (2007)

• 2009 Highest density of antimatter in solids (e+) (20 MeV) via Bethe-Heitler process n(e+)=1016cm-3

– Chen H et al., PRL 102 105001 (2009)

Laser induced nuclear photo-proton reaction studies

The measurement of integral photonuclear cross-sections such

as sint(γ, p) using nuclear activation is ideally suited for

modern high power multi-TW laser systems

• Table-top Laser systems as competitive tool for nuclear

studies

– High intensity and hot bremsstrahlung spectra kT>2 MeV

– Bremsstrahlung spectra spans over GDR regime ~8 - 35 MeV

– Multi-TW Ti:Sapphire Laser system at the IOQ Jena, Germany

Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes

• Nuclear Theory: cross-sections for p-emission and capture in

plasma conditions, need to extend astrophysical data sets for low-Z

isotopes: 25Mg,48,49Ti, 68Zn and 97,98Mo (feasible with method)

– Hauser-Feshbach code

• Applied: GDR-regime of interest for technological R&D work

– nuclear power, shielding, radiation transport, radiotherapy, reactor

development (transmutation studies) & medical applications

– IAEA: encourages experiments esp. to retrieve reaction data in the

region of the Giant Dipole Resonance (GDR) esp. for ~40 isotopes

• Limitations and ‘old’ age of measurements

– Values of sint(g, p) for only 40 different stable isotopes are published

– Ratios: sint(g, n)/sint(g, p) for Z=12-42 needed!

– Accuracy of old measurements

• Probing and enhancement of nuclear models and reaction codes

– EMPIRE, GNASH

Methodology and setup of IOQ Jena multi-TW laser system

• Harvest the bremsstrahlung radiation of high-intensity laser generated

relativistic electrons to induce reaction

– Quasi-Maxwellian distribution: Tγ Te , McCall G,J Phys D 15 823 (1982)

– Energy distribution of γ-radiation for temperatures achievable with multi-

TW lasers extends over the full GDR-region

• Measure the activity of the decay of the radioactive daughter nucleus

• Characteristic g-rays of decay: intensity of photopeaks allows yield

determination of original daughter products, hence sint(g, p)

– Efficient Ge-detector system

– Adjustments for: branching, detection efficiency (system, geometry), self-

absorption, abundances; irradiation-, handling- and decay-time;

contaminating reaction channels, target impurities and electro-

disintegration

• Introduced for laser nuclear physics by Stoyer et al.

– Stoyer M et al., Rev Sci Inst 72 767 (2001)

Activation

Liesfeld B et al., J Phys D 79 1047 (2004)

Schwörer H et al., PRL 86 2317 (2001)

Schematic setup of IOQ Jena multi-TW laser system

E0laser pulse ~ 600 mJ

tlaser pulse ~ 80 fs

λ = 800 nm

P ~ 7.5 TW

ne per pulse ~ 2 - 5 ×109

(Elaser / Ee) ~ 0.6 - 1.5%

~5m

Activation

targets: MgF2,Ti,Zn,Mo

thicknesses~2-4 mm

p~ 80 bar

Setup of target chamber

Target chamber

Target & radiator

holder

f/2-mirror

He gas-jet nozzle Laser-room

university-scale system!

Relativistic electrons from 10TW Laser-Gas Interaction

Spatial confinement of e-

(measured, E=18 MeV)

Simulated e- density Simulated e- momentum distribution for different depths

Energy of e- (measured)

from Guiletti A et al., PRL 101 105002 (2008)

2×106

1×106

0250 mrad

PIC simulations, Pukov A and Meyer-ter-Veen, PRL 76 (21) 3975 (1996)

Simulated γ-distribution after Ta-radiator and Mo-target

(GEANT4)

Experimental considerations & limitations

• Extraction & detection limit: 5 min ≲ t1/2 ≲ 200 days

• kT measurement necessary with activation method

• Bulk targets with natural abundances

• Analysis:

– Uncertainty from kT & Ge-efficiency

– Activity is weighted with photon distribution and needs to be referenced

to well known (g, n) channel in probe

– To extract sint(g, p) the three parameters determining the GDR have to

be assumed based on models: sres, res(i), Eres(I)

kT measurement via Ta-activation

fitted kT=2.73(22)MeV

Activation spectra: MgF2-, Ti- and Zn-probes

~only 8 min of laser activation, 5000 pulses with 3-5 x1019 Wcm-2

Observed photo-proton channels

Measured and simulated photo-reaction channels in 25Mg

sint (g, p) deduced from

EMPIRE calculation is fully

reproducing measured sint (g, p)

Experimental data &

EMPIRE calculations

Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes

• TRK Dipole Sum Rule:

• TRK=Thomas Reiche Kuhn Sum rule 1925

– A standard benchmark for E1-strengths

• Aligned with data from Wyckoff J et al., PR 137 576 (1965)

─ Values of sint up to 35 MeV relative to the classical dipole sum rule show a

monotonic increase with atomic weight

– Correction factor ~ 0.85 - 1.25

)(60~35

0MeVmb

A

NZ s

Agreement with TRK sum-rule

Agreement with TRK sum-rule

only s(g,n)

Total σint values ~ σint (g,sn) + σint (g,p) show good to excellentagreement with the TRK-sum rule. For 97Mo no σint (g,n) known

0

500

1000

1500

2000

2500

25Mg 48Ti 49Ti 68Zn 69Zn 98Mo

Isotope

s in

t [M

eV

mb

]σ(γ,sn) from Lit. + σ(γ,p) Exp.

TRK (folded with Wyckoff)

only σint(g,n) known

0

50

100

150

200

250

1 2 3

Reaction

sin

t [M

eV

mb

]this work

Literature

Agreement with known σint-values

64Zn (g, 2n)62Cu 70Zn (g, n)69mZn

Aligned acc. to branching

No errors given in

Literature values

Ivanchenko V et al.,

P.ZHETF 11 452 (1966)

Carlos P et al.,

NP A258 365 (1976)

Goryachev A et al.,

Yad.Fiz. 8 121 (1982)

All three measured σint-values for different targets and particle channelsthat can be benchmarked with known data show good agreement

Known σint(g,n)/ σint(g,p) ratios (IAEA)

Experiment added 15%

towards all existing data!

σin

t (g,

n)/

σin

t (g,

p)

this work

• We measured a total of 6 new sint (g,p) values and

hence deduced six new sint (g,n)/sint (g,p) ratios for light

nuclei

– First time laser driven research adds new data to nuclear physics

– almost 15% of previously published data

– Spohr K et al., New J Phys 10 043037 (2008) & New J Phys Best

of 2008 collection

• Conclusively proven that nuclear reactions can be

produced and cross-section can be measured using

table-top Laser systems

– data agrees with TRK-sum rule

– data agrees with EMPIRE calculations

– data agrees with three previously known data-sets

• A good base for a more extensive research investigation

Conclusions, opportunities and future challenges

• Opportunity for extended campaign:

– Determination of >110 new sint (g, p) measurable with university-

scale multi-TW laser systems is possible

• ~90 lifetimes 5 min < t1/2 < 300 days (feasible)

• Challenge ~25 lifetimes t1/2 < 5 min

• Challenges:

– Use of isotopic enriched targets

– Rapid transport mechanism (@ e.g. ELBE)

– On-line measurement of prompt g-radiation

– Deflection of electrons, separation with small Halbach magnets

– Lowering the uncertainties of kT measurement

– Multi-Ge-system in coincidence

– Particle detectors in coincidence, radiation resistant detectors

Conclusions, opportunities and future challenges

• Conjoined ELBE/Laser @ FZ-Dresden Rossendorf

– SUPA has allocated beam-time quota

– Elinac (40MeV) and 150 TW laser system (mid-2009)

• We could use both systems and compare

• 150 TW laser ~ E(e-) = ~80-90 MeV endpoint

– Proposal to study sint (g,p) reaction of stable p-nuclei:

• p-nuclei are neutron deficient (except 176Lu) nuclei that are shielded by

their isobaric neighbours from production via the r-process and can not

be produced by the s-process either

• p-nuclei of astrophysical interest: 96Ru, 120Te, 130Ba, 156Dy, 162Er, 168Yb

and 176Lu are feasible to study, yield improvement with new system ~103

• Understand formation of p-nuclei and support Hauser-Feshbach

calculations

• Higher power will give laser competitive edge over Elinacs

Conclusions, opportunities and future challenges

Using different kT for evaluation of s(E)

Unfold cross-sectionby using differentkT values, 1 MeV <kT <10 MeV

K. Spohr

J.J. Melone

R. Chapman

M. Shaw

K. Ledingham

W. Galster

L. Robson

P. McKenna

T. McCanny

K-U. Amthor

B. Liesfeld

R. Sauerbrey

H. Schwoerer

J. Yang

Collaborators

Photonuclear reaction studies

using laser induced Compton

backscattering (LICB): proposed

studies & vision

The future strategy: harvest the

unique capabilities

of newly developed laser driven

accelerator systems

Photonuclear reaction studies using laser induced

Compton backscattering (LICB): proposed studies & vision

• Laser Inverse Compton Backscattering (LICB)

– Cobald/ERLP system @ Daresbury (May 2009) & ELBE(40MeV)/150TW Laser (Spring 2010)

– High brightness, ultra short, energy tunable source for low-lying quasi coherent, polarised gamma-radiation <30 keV (2009)

– Proof of concept: Schoenlein R et al., Science 274 236 (1996)

– Brightness:

– Total Photons:

– Brightness comparable to proposed 4th generation light sources (only approched by SPring8 in the moment)

– Comparison with synchrotrons

• + Much smaller (cheaper) systems

• + Better time resolution

• - lower repetition rate 10 Hz and hence total yield 10 to 100 lower

– Cobald/ERLP: Priebe G, Spohr K et al., Las Part Beams 26 (4) 201 (2008)

Photonuclear reaction studies using laser induced

Compton backscattering (LICB): proposed studies & vision

• Motivation:

– ‘Finest’ g-source available

• Highest intensity & shortest steerable pulse duration

– A new class of (g, g’) reactions allowing precise study of nuclear

transitions (as of 2009: E<40 keV)

• Population of isomeric states

• Nuclear spectroscopy with high energy resolution

• Nuclear lifetime measurements (direct measurements of fs-lifetimes and below!) ,

spectroscopic information

– Coherent ensembles of gamma excitations in nuclei (excitons)

• New quantum phenomena (quantum beats), ‘coherent nuclear physics’

• Enhancement of decay width

– Resonance reactions to probe for existence of materials in probes

The principle of Laser Induced Compton Backscattering

Superconducting Elinac

Cobald/ERLP @ DaresburyELBE/150TW system is similar

Cobald @ Daresbury

LICB photons: the principle

• Laser light works like undulator on electrons

• Electrons are deflected ~ 104 more often than in

conventional magnetic undulators

• LICB scattered photons remain partially

coherent

Principle of SCAPA

(SUPA2) project

from Priebe G, …, Spohr K et al., Laser and Particle Beams 26 (4) 201 (2008)

Laser/e-beam collision geometry

Normalised vector potential of the laser field

~undulator deflection parameter of static field

0

100

200

300

-2

0

2

0

10

20

30

0

100

200

300

Eγ

[kev

]

collision angle Φ [] scat

tere

d an

gle θ

[

]keV15

22

g

g

EE

transverse configuration

keV304 2 LEE gg

head on configuration

Spatial distribution of photon-energy

Photon-energy vs scattered angle

θ = π

Simulation

Motivation for studying isomers with LICB

• Laser inverse Compton Backscattering present an unique opportunity for

studies into the laser induced pumping of nuclear states

– Ideal cases: short lived Möβbauer isomers:161Dy, 57Fe,181Ta

– Questions: feasibility and efficiency, new coherent phenomena?

Baldwin G and Solem J, Rev Mod Phys 69 (4) 1085 (1995)

Einstein A, Phys Zeit 18 121 (1917)

161Dy

LICBE1

|2>

|1>

LICB experiment on resonant photoabsorption of Mößbauer nuclei

• High brightness of impacting pulsed photon-beam complicates detection of

resonant absorbed and re-emitted γ-radiation

– Target spins within ultra-fast rotating spindle, mapping of time into spatial domain

– Röhlsberger R et al., PRL 87 (4) 047601 (2001) Nuclear Lighthouse Effect

LICB - γ

fast rotor

e.g.161Dy

Avalanche Photo Diode

Rotors up to 70kHz

LICB experiment on resonant photoabsorption of Mößbauer nuclei

• Will reveal insight into new coherent nuclear physics phenomena– Ensemble (>1000) of coupled nucleons in the same state of excitation

(excitons)

– Exciton stationary or migrates through the probe with slow speeds (polaritons)

• E.g. Nuclear Lighthouse effect

• Quantum beats as different hyperfine components interfere

– Decay rate is increases, hence the absorption line-width

– Even more so, if an ensemble of polaritons is created

– Estimate: 161Dy ~ 2 x 108 detectable 25.7 keV g-rays in 5 days experiment, 181Ta ~5000 detectable 6.2 keV g-rays in 5 days

• Based on natural and measured line-widths, conversion coefficients, resonant excitation cross-section, mass attenuation coefficient, recoilless f-fraction of Mossbauer nuclei, brightness and spatial beam distribution

• Cobald functional May 2009, Future in STFC? ....

A word on controlled amplification

nuclear systems

• Cross section at resonance:

• Radiative width |2> -> |1> into stable g.s.:

– For lasing: problem population inversion, many nuclei in g.s. level

– Small for long lived isomers! Never feasible for bulk targets

• Decay from unstable state |2> into unstable state |1>:

– Inversion population if N(|2>) > N(|1>)

• Possible for T2 > T1

• Favourable ‘pumping reaction’ to enhance population of |2>

• Favourable branching b=1 and low conversion a small

– Decay times are somewhat similar, as for T2 >> T1, ss is small

– Resembles Four-level pumping scheme of optical lasers

Some final thoughts: induced nuclear emission (lasing)

Some final thoughts: induced nuclear emission (lasing)

Pumping nuclear reaction

e.g. photonuclear type

Laser induced!

High energetic levels

|2>

|1>

g.s.

LICB

g

Some final thoughts: induced nuclear emission (lasing)

• Stedile generated population inversion via NRF in stable 103Rh – |2> = 357 keV, (5/2-) t=107 ps and |1> = 295 keV, (3/2-) t=9.8 ps

– ‘Generating an inversion on a nuclear transition - Photopumping of 103Rh’, Stedile F, Hyper Inter. 143 (1-4) 133 (2002)

• A thought… for something new: Use bremsstrahlung radiation to create population inversion via NRF with high yields (high rep rate) and then impinge quasi-monochromatic matching γ-energy from LICB on target!– For the moment: yields by far to small

– Need effective high yield pump (high power and repitition laser accelerator) and LICB laser system

– Identification of favourable isotope

• 103Rh not ideal, Eγ=62 keV too high …,

– 2 high power laser systems: MBI Berlin (~2011)

Summary• Laser Nuclear physics offers promising research into new phenomena at the

interface of two very diverse areas of research

– Will it become a mainstream field in Nuclear Physics in the UK?

– As of March 2009: 4 researchers (Strathclyde & UWS)

• Laser driven nuclear physics has just begun to deliver the goods for applied

and fundamental new nuclear research

– Integrated cross-section measurements

– Ability to reach high kT values and hence to derive effective photodisintegration

rates in high temperature plasma

• Though facing tremendous challenges, British-led efforts could be crucial for

the exploitation of new systems using Laser Inverse Compton backscattering

– LICB systems have the potential to add a new unique quality to nuclear research

– Study of resonant photoabsorption is ideally suited to harvest these systems

– Something really new and challenging

In Memory of Dr Wilfred Galster 1948-2009

The next generation IOQ Jena multi-TW laser system

Single diode pump station of

150TW-system (5 total) @IOQ

Start: 04/2008

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 1 2 3 4 5 6 7 8 9 10

Energy(MeV)

Flu

x(M

eV

/cm

^2

)

kT=2.91MeV kT=5MeV kT=7MeV kT=4MeV

Simulated bremsstrahlung-spectra in Ta-radiator (MCNPX)

kT measurement

• First to be determined: kTg

– By activation method

– Very well known cross-sections allow best-fit of kTg

– Two independent measurements

• 181Ta(γ,n)180Ta and 181Ta(γ,3n)178Ta

– Intensities: I103keV with t1/2=8.15 hrs and I426keV with t1/2=2.36 hrs

– N (178Ta) / N (180Ta) = 3.06(48) x 10-4, with Ge-detector

– Uncertainty: I103keV, literature value, influence of electro-disintegrationreactions (e,e’) was ~20% (no e--rejection)

– Measured kT=2.73(33) MeV

• 12C(γ,n)11C and 63Cu(γ,n)62Cu

– Both β+ giving rise to 511 keV annihilation

• Influence of electro-disintegration (e,e’) dramatically reduced

– N (11C) / N (62Cu) = 8.58(13) x 10-3, with NaI coincidence system

– Uncertainty: low intensity in 11C, ~ 2 counts/s

– Measured kT=3.09(23) MeV

• Accepted result: kT=2.90(23) MeV

Measured and simulated photo-reaction channels in 66,67Zn

Experimental data &

EMPIRE calculations

sint (g, p) deduced from EMPIRE

calculations are reproducing

measured sint (g, p)

-20

-15

-10

-5

0

5

10

15

20

-30 -20 -10 0 10 20 30

Y (

mra

d)

X (mrad)

Backscattering angular distribution; each colour is a 1 keV energy band with 20-

21 keV on outside and 30-31 keV at centre

Spatial distribution of photons

Photon brightness vs photon energy

Simulation