Helmholtz -Zentrum-Dresden Rossendorf September 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/NEEC Kritcher 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 235 U m in a CO 2 laser produced plasma - Izawa 1979 Here the mismatch between electronic and nuclear transitions is considerable Recent experiments have not excited the isomer

181 Ta Excitation – A.V Andreev

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

169 Tm 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 242m Am NEEC (Electron Beam Ion Trap) This is the only proposed NEEC experiment

Ross Marrs LLNL UCRL-PRES

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 26 Al using the high temps of the multiple laser beams – 10 8 K times hotter than present lasers.

Motivation 26 Al 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) & Plüschke S et al., arXiv:astro-ph/ v1 Voss R et al., Astronomy & Astrophysics, 504, 531, 2009

Al 26 Decay scheme

How could NEET/EEC affect the half lives of 26 Al 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 Al 26 -use the PW short pulse laser to generate a proton beam and then use a Mg 26 (p,n)Al 26 reaction

Schematic of laser plasma nuclear 26 Al experiment E driver ~15J Use the NIF PW laser at W/cm 2 Shielding Canvas Diamond Target 26 Mg Plasma medium e.g. Al adjustable p TSNA I ~ Wcm -2 'p-production pulse' '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 238 U and Nuclear Fission Yields as a Fn of Temp Front Al-sheet 1 thickness: 10μm isochoric heated Back Al-sheet 2 thickness:10μm depleted 238 U thickness: 8μm encapsulated by Al-foils Proton beam 0-40μm variable 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

First Measure the 26 Mg(p,n) 26 Al cross section (Fazia Hannachi) Precision measurement of 26 Mg(p,n) 26 Al, with 'O RGAM & Neutron Detection system' MeV Nuclear exercise to allow laser plasma driven nuclear investigations in the future i) total neutron yield 26 Mg(p,n 0 ) 26 Al O RGAM in coincidence with neutron array (neutron wall (G ANIL ?)) I p (max)= 6 x pps, σ ~100mb, d target ~40 μg/cm 2 estimation of: ii) β + delayed yield from the isomeric 0 + (T 1/2 =6.3 s) state at 228 keV: 26 Mg(p,n 1 ) 26m Al Bombard and count cycles: 6s/24s, 24s to measure delayed 511 keV radiation For each E i :20 cycles of 30s each: O RGAM (Phase I) ε =4.2%, no n-coincidence required For E p >16.1 MeV, correction for 2n channel leading to 25 Al must be taken iii) prompt yield of 417 keV

26 Mg(p,n) 26 Al ii) 411 keV iii) del. 511 keV i) total neutrons g.s. calc. Norman: total γ-yield No measurement of neutrons OPTMISE the NUCLEAR data to ALLOW the LASER PLASMA Nuclear endeavour on 26 Al

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 TW Firstly, production of 26 Al and exposure to hot photon gas and MeV electrons. How does production of 26m Al 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 26 Al to WDM matter conditions of ~1 × 10 6 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~10 GeV and n~ 10 protons, in μm 'sheets', rep. Rate: 1 Hz; implementation of spectrometer & neutron detectors (ELI White book) The 'ideal' astrophysical laboratory