Nuclear isomers excitation and triggering via autoionization states (NEET via AS)

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Nuclear isomers excitation and triggering via
autoionization states (NEET via
AS) I.N.Izosimovizig_at_mail.ru
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Autoionization states (AS) are unstable related
to ionization of atomic state (escape of
electron) with two or more excited electrons
(two or more holes in inner electron shells) . AS
are the quasi stationary states and were observed
as a resonances.
Because of electron-electron interaction at the
AS decay simultaneously one electron escape from
atom (ionization) and the other one go to the
ground state by photon emission (electron shell
transition). At a suitable conditions instead of
photon emission the nuclear excitation by an
electron transition (NEET) may take place.
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For NEET via AS decay the excitation energy is
distributed between emitted electron and NEET .
Emission of e- may compensate the difference in
the energy and multipolarity for NEET and it is
not necessary to have the precise coincidence
between energy and multipolarity of electron
shell transition and nuclear transition.
For external electron shells excitation AS are
well known and were observed practically for all
elements up to Pu.
AS for internal electron shells excitation
practically were not studied.
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The energy of such states (EAS,n2-Z2/4) is
higher than the energy of single charged ion
(E-Z2/2) and nlnl states with n2 are the
unstable AS states.
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For electron configuration 2s2 we will have 1S
autoionization state, for 2s2p configuration
1,3P- AS states and for 2p2 1S, 1D, 3P AS
states. Electron-electron interaction mixed 1S
states from 2s2 and 2p2 configurations and one of
1S (with more weight of 2s2 configuration) AS
will have the lowest energy and other 1S ( with
more weight of 2p2 configuration) AS will have
the highest energy. The decay width ? is
different for different AS and weekly depend on
Z. For lowest 1S AS state 1D and 1P- AS states
?0.2eV. For highest 1S and 3P- AS states
?(0.02-0.005)eV. Decay of 3P AS states to 1s
state is forbidden as E1 and its decay width may
be much smaller compare to other AS. So the width
and half-life for AS may change in wide range
and ? 0.2eV, T1/210-14s.
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Emission of e- compensate the difference in
angular momentum (multipolarity) and in energy
between electron shell transition and nuclear
transition.
Wide range of AS energies       Wide range of
energies for NEET and intermediate states
excitation from eV up to 100 keV.
 
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NEET via AS in eV region (229mTh 3.5eV isomer
excitation)
Ionization potential (IP) for Th is 6.08eV. Using
three step excitation scheme (h?1 h?2 h?3
12eV) it is possible to study NEET via AS for
nuclear isomers with excitation energy E6eV.
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For NEET via AS the energy of emitted electron
(Ee), AS excitation energy (EAS), ionization
potential (IP), electron energy (Ee) when instead
NEET photon with energy Eh? is emitted and
isomer excitation energy (ENEET) are connected
as   EAS IP Ee ENEET,
(1)   Eh? (Ee Ee) ENEET.
(2)   Due to electron emission for NEET the
differences between Eh? and ENEET may be
compensated. Also electron emission may
compensate the differences in multipolarity
between electron shell transition and nuclear
transition. For M1 nuclear transition (229mTh) it
is not necessary to compensate multipolarity,
because for NEET the proper AS (for which E1
transition is forbidden, similar to 3P AS) may
be used.
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NEET via AS in keV region ( nuclear isomer
triggering)
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Now there is no detail experimental data on AS
excitation in internal electron shells and the
finding of effective mechanism of such AS
excitation may allow to make the next step in
triggered gamma emission processes. One of the
way is the multiple-electron transfer-capture in
collisions of highly charged ions with atoms and
molecules.
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• Collision energy (1.-100)q eV cross section
  significantly depending on the collision energy
  and projectile species.
• 2. Collision energies keV/u cross section
  do not depend greatly on the collision energy and
  are nearly the same for the projectile species
  with the same q. Type of electron shell
  configuration involved in process depend on q,
  type of species and collision energy.
• 3. Single and double capture of the outermost
  target electrons are seen to be the dominant
  processes.

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the string (j)(l 0 1 0 0 0 0 0)
characterises a process in which the electron of
index 1-this is the electron with binding energy
I1 on the target-and the electron of index 3-i.e.
the electron with binding energy I3 are captured
by A, while the other electrons remain on the
target B. Within the model, the string (j)
characterises the process uniquely. I1 lt I2 lt I3

There are in general CNr different processes
in which r electrons are captured out of the N
available target electrons. These processes lead
to different electron configurations on A and B.
The unresolved cross section for capture of r
electrons is where the sum runs over the
different strings, (j)
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Processes q , k, s q5 Ar5 Ar Ark Ars.
E1.8q keV
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Processes q , k, s in collisions q5 Ar5 Ar
Ark Ars. E1.8q keV
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Single and double capture of the outermost target
electrons are seen to be the dominant processes.
. Autoionisation of the projectile following
double capture starts around q 5, additional
contribution arises around q 7 .
Autoionisation following triple capture has a
similar threshold to autoionisation following
double capture.
the principal quantum number of the captured
electrons increases with q.
Projectile autoionisation is much more probable
than target autoionisation. Target autoionisation
is predicted for recapture of the two outermost
electrons and loss of at least two or three
electrons by the target atom for instance, for
(j )(0, 0, 1, 1, 1,0,0,0) in collisions with q gt
4. The corresponding cross sections are of the
order of 10-16 cm2
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Usual NEET PNEET less than 410-10 per created
K-hole
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Usual NEET PNEET less than 410-10 per created
K-hole
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We propose to measure the AS excitation cross
sections (sAS) and cross sections for 189mOs
(E30.8 keV, T1/25.8h) isomer excitation (sEX)
and triggering (sTG) using the nuclear excitation
by an electron transition (NEET) via AS in
collisions of highly charged (q5 - 15) Arq and
Xeq ions with Os (natural) metal target. The
levels of 69.5keV and 97.4keV in 189Os are the
most convenient for excitation and triggering of
189mOs isomer. The most suitable AS for 189mOs
isomer triggering in Os ions will have the
energies about 39 keV and 67 keV. The most
suitable AS for 189mOs (E30.8 keV, T1/25.8h)
isomer excitation in Os ions will have the
energies about 100 keV , 70 keV and 31 keV.
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For simple NEET via K-hole excitation PNEET lt
410-10 per created K-hole for 189mOs
(experiment).
For NEET via AS the ?E compensation may take
place and we may observed much more PNEET value
than for NEET via K-hole. From PNEET value one
may conclude about mechanism of NEET.
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• The corresponding autoionisation states cross
  sections are of the order of 10-16 cm2
• Beam 1012 ions/s
• Target 1013 atoms
• Efficiency of NEET via AS 10-7
• Will have about 100 excitation/triggering/s of
  nuclear level/isomer
• Conclusion
• Nuclear excitation by an electron transition
  (NEET) via autoionization states may be an
  effective instrument for both nuclear isomers
  excitation and for triggering of ?-ray emission
  and depopulation of isomers driven by NEET via
  AS.

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Gamma and X-ray radiation
Gamma and X-ray radiation31-yr 178-Hf
Energy (keV)
Intensity
Energy (keV)
Intensity
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