Helmholtz -Zentrum-Dresden RossendorfSeptember 2011

Nuclear Excitation in Plasmas- NEET/NEEC

Ken Ledingham

SUPA, Dept of Physics, University of Strathclyde, Glasgow G4 0NG, Scotland & AWE plc Aldermaston, Reading, RG7 4PR, UK ,

Helmholtz -Zentrum - Dresden, Rossendorf

Vacancy in an inner shell will be immediately filled by electron jumping from an outer orbit

• If emission of a real photon takes place then we have X-ray emission

• If we have emission of a virtual photon then two further processes can take place

• Absorption by an outer electron of the virtual photon leads to Auger electron emission

• Absorption of the virtual photon by the nucleus (usually in heavier nuclei) can take place leaving the nucleus excited

Definitions• Internal Conversion (IC) Nuclear de-excitation

resulting in the emission of an orbital electron to the continuum

• Bound Internal conversion (BIC) Same as IC but electron is promoted to a bound state

• NEEC (Nuclear excitation following electron capture from continuum) inverse of IC

• NEET (Nuclear Excitation following an electronic de-excitation inverse of BIC

Cartoon of NEET/NEECKritcher et al LLNL

Why are NEET/NEEC Experiments so difficult to perform?

• Electron beam, laser induced and synchrotron produced plasmas produce huge numbers of energetic electrons and photons as well as vacancies in electronic shells

• The energetic electrons excite the nuclear transition by inelestic scattering

• The photons excite the nuclear levels by direct photon interactions

• The nuclear transitions are of course also excited by NEET/NEEC

• The nuclear de-excitation for all methods of excitation has the same signature

Feynman diagrams for Nuclear Excitation in Plasmas

Production of 235Um in a CO2 laser produced plasma - Izawa 1979

Here the mismatch between electronic and nuclear transitions is considerable

Recent experiments have not excited the isomer

181Ta Excitation – A.V Andreev

Excitation of 181Ta in a Fs Dye Laser Plasma Andreev et al J.Exp.Theor.Phys. 91, 1163

2000

Half life 7± 3 µs in agreement with accepted value. No other group has

replicated this including mine.

One of the few accepted experiments which measures NEET – 197 Au

Monoenergetic x-rays from a synchrotron were used to ionize the K-shell of gold (81 keV) A similar technique could be used on X-FEL for transitionsThe NEET probability was determined by comparing the number of de-excitation conversion electrons per photon at photon irradiation above the K-edge and at the nuclear resonance (77.351keV)and was determined to be 5x10-8

NEET/NEEC Programme at Omega Rochester

They intend to use a high resolution crystal spectrometer to detect nuclear photons

The theory is now sufficiently well understood that competing nuclear excitation by scattered electrons and direct photons can easily be calculated leaving NEET/NEEC experimental comparisons with theory meaningful

Can NEET/NEEC excitation from excited states reduce nuclear lifetimes

The answer is in principle yes if the half-lives from the upper states are shorter

than the isomeric states

169Tm half life decreases with plasma temperature and with mass density

According to Gosselin, Meot and Morel half life is predicted to decrease from ns to ps

Proposed EBIT measurement of 242mAm NEEC(Electron Beam Ion Trap)

This is the only proposed NEEC experiment

Ross Marrs LLNL UCRL-PRES-427008

Scaling of NEET & NEEC signal to NIF

According to plasma theorists NEET/NEEC nuclear transitions

are among the most important transitions at high temperature and very few cross sections are

known

Can these experiments be done at XFEL/PW laser?

The PW laser can produce proton beams which can excite NEET isotopes by e.g. (p,n) reactions.

The XFEL can create K shell vacancies using monochromatic gamma rays and also measure the direct nuclear photon reaction from which the NEET mcross section can be calculated

Thank you

Proposed Spohr, Ledingham Experiment at NIF

What do we intend to do at NIF – modification of the half life of 26Al

using the high temps of the multiple laser beams – 108K - 100 times

hotter than present lasers.

Motivation• 26Al in the astrophysical context using a gamma

camera• • 1809 keV line in Galaxy

Interstellar abundance

Level scheme

Evolution of stellar abundance

Skelton R et. al., Phys.Rev. C35(1),45,1987

NASA Compton Gamma Ray observatory (COMPTEL) 1991-2000 & Plüschke S et al., arXiv:astro-ph/0104047v1

Voss R et al., Astronomy & Astrophysics, 504, 531, 2009

Al26 Decay scheme

How could NEET/EEC affect the half lives of 26Al

• Increase the number of prompt 418 keV γ rays by NEET/NEEC excitation from the ground state

• Increase the number of 0.511/1.81 MeV coincidences by NEET/NEEC excitation from the 6 sec isomeric state at 229 keV

How do we make the Al26 -use the PW short pulse laser to

generate a proton beam and then use a

Mg26(p,n)Al26reaction

Schematic of laser plasma nuclear 26Al experiment

Edriver~15J

Use the NIF PW laser at 1022 W/cm2

ShieldingCanvas

DiamondTarget

26Mg

Plasma medium e.g. Al

adjustable

p

TSNAI~1018-20 Wcm-2

'p-productionpulse'

'Plasma production pulse'

All within a hohlraum

The experiment entails measuring the 511 keV coincident counting rate

or the 511keV and 1.8 MeV coincident counting rate or the 418

prompt counting rate as a function of plasma temperature with

semiconductor or scintillation counter systems like the ORGAM

system after a rapid transfer of target

ORGAM Detector System

Particle induced Fission

Could the no of fragments detected change as a function of temperature because change of half life?

Laser Induced Proton Fission of 238U and Nuclear Fission Yields as a Fn of Temp

Front Al-sheet 1thickness: 10μmisochoric heated

Back Al-sheet 2thickness:10μm

depleted 238Uthickness: 8μmencapsulated by Al-foilsProton beam

0-40μmvariable

Laser

Al-production target

~200μm

isochoric heated volume

Fission products & trajectories

Cu-stack

Al-U-Al sandwich target

This was an experiment to be carried out using short pulse laser isochoric heating but could be done by NIF heating. The Al was hot when distance was 40µ and cold at 0µ

ORGAM Detector system

Ross Marrs LLNL UCRL-PRES-427008

First Measure the 26Mg(p,n)26Al cross section (Fazia Hannachi)

Precision measurement of 26Mg(p,n)26Al, with 'ORGAM & Neutron Detection system' 4.9-25 MeV

Nuclear exercise to allow laser plasma driven nuclear investigations in the future

i) total neutron yield 26Mg(p,n0)26Al

ORGAM in coincidence with neutron array (neutron wall (GANIL?)) Ip(max)= 6 x 1012 pps , σ~100mb, dtarget~40μg/cm2 estimation of:

ii) β+ delayed yield from the isomeric 0+ (T1/2=6.3 s) state at 228 keV: 26Mg(p,n1)

26mAl

Bombard and count cycles: 6s/24s, 24s to measure delayed 511 keV radiation For each Ei:20 cycles of 30s each: ORGAM (Phase I) ε=4.2%, no n-coincidence required

For Ep>16.1 MeV, correction for 2n channel leading to 25Al must be taken

iii) prompt yield of 417 keV

26Mg(p,n)26Al

ii) 411 keV

iii) del. 511 keV

i) total neutrons

g.s. calc.

Norman: total γ-yield

No measurement of neutrons

OPTMISE the NUCLEAR datato ALLOW the LASER PLASMA Nuclear endeavour on 26Al

Outlook on future laser nuclear experiments with 100TW e.g DRACO or LULI and the few PW ELI system (2014)

Prima facie study at 100 TWFirstly, production of 26Al and exposure to hot photon gas and MeV electrons.

How does production of 26mAl scale as beam parameters Challenge: characterisation of plasma, shot-to-shot fluctuations of pulsed proton energy spectra (1 per 20 mins), deconvolution of proton energy spectra, Delayed 511 keV radiation servers as the measurement

Secondly, exposure of 26Al to WDM matter conditions of ~1 × 106 K = 100eV

A long long, long way from GK, but we have to start!

Preparation for ELI (2014/15)

Intense pulses of mono-energetic protons up to GeV

Creation of GK environments possible, foreseen implementation of a mass separator

Radiation Pressure Acceleration (RPA) regime for ions → Quasi monoenergetic, solid-density bulks of accelerated ions! ~1kJ of laser pulse ≈ n~1013 @ GeV and n~ 1016 @MeV protons, in μm 'sheets', rep. Rate: 1 Hz; implementation of spectrometer & neutron detectors (ELI White book)

The 'ideal' astrophysical laboratory