Experimental techniques and equipment

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Lecture 4 Experimental techniques and equipment

• studies with RIBs
• reaction types
• direct approach
• indirect approach
• some selected examples

http//www.univie.ac.at/strv-astronomie/unterhaltu
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RIB production methods

• Isotope Separation on Line (ISOL) (CERN, LLN,
  ORNL, TRIUMF)
• Projectile Fragmentation (PF) (GANIL, GSI, MSU,
  RIKEN)
• in-flight production (ANL, Notre Dame, TAMU)
• batch mode production (suitable for long-lived
  species)

? excellent quality high purity
high intensities
? independent from chemical properties no
limitations on t½ (fast separation)
? typical beam energies too high for NA
poorer beam quality (energy, size)
possible beam contaminations
? limited number of species different
production for different species limited to
nuclei with t½ 1s (allow for diffusion)
M.S. Smith and K.E. Rehm, Ann. Rev. Nucl. Part.
Sci, 51 (2001) 91-130
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targets
? ?
H targets
solid CH2 target (plastic material)
simple to handle hydrogen depletion dx 50 -
1000 ?g cm-2 non uniformity melting
problems deuterium contamination
He targets
solid implanted target
simple to handle low concentration
(n 1015 - 1017 atoms cm-2)
window-confined gas target
higher concentration background
reactions (depending on pressure) (e.g. on
window materials)
windowless gas target
higher concentration
differential-pumping system almost background
free high pumping speeds no physical
degradation
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NUCLEAR DATA NEEDS
reactions involving A lt 30 A gt 30
knowledge required
cross-section dependence individual
resonances nuclear properties statistical
properties Hauser-Feshbach calculations
excitation energies spin-parity widths decay
modes
masses level densities part. separation energy

• very large amount of reactions in various
  astrophysical sites
• not feasible to study all reactions involved
• experimental constraints wherever possible

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experimental approaches
reaction types and experimental techniques

• DIRECT APPROACHES
• radiative capture reactions
• transfer reactions
• INDIRECT APPROACHES
• resonant elastic scattering
• transfer reactions
• time-inverse reactions
• coulomb dissociation
• ...

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DIRECT APPROACHES
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X(p,?)Y X(?,?)Y
among the most common reactions in nuclear
astrophysics
RADIATIVE CAPTURE

• heavy recoil detection

inverse kinematics ? forward peaked emission
(? 1o) ? detection efficiency 100
BUT high suppression factors required
(1010-1015)
RIB intensities 107 ions/s
examples 21Na(p,?)22Mg, 15O(?,?)19Ne _at_
DRAGON TRIUMF
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low efficiency ? 4? coverage needed ?-ray
background induced by ? beam decay

• ?-ray detection

gammasphere
courtesy D. Jenkins
100 HPGe detector array absolute efficiency 9
for 1.33 MeV g ray
example 22Na(p,?)23Mg _at_ ANL

• delayed decay measurements

example 19Ne(p,?)20Na(?)20Ne(?)16O _at_
Louvain-la-Neuve
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TRANSFER REACTIONS
mainly X(p,?)Y and X(?,p)Y

• light-heavy nuclei coincidence

silicon strip detector arrays ? large solid
angle coverage (e.g. LEDA see later)
RIB intensities 105 ions/s
examples 18Ne(?,p)21Na _at_ LLN Groombridge
et al. Phys Rev C 66 (2002) 55802(10)
TRIUMF (planned) TUDA
collaboration 18F(p,a)15O _at_ ORNL Bardayan
et al. Phys Rev C 63 (2001) 65802(6) Bardayan
et al. Phys Rev Lett 89 (2002)
262501(4) 14O(?,p)17F _at_ LLN
(planned) Aliotta et al.
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INDIRECT APPROACHES
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RESONANT ELASTIC SCATTERING
typically X(p,p)X
? investigate resonance properties of
compound nucleus
the method
inverse kinematics suitably thick target (eg
(CH2)n) proton detection
proton spectrum
excitation function
target thickness ?E
high beam energy loss
high-energy protons
low-energy protons
low beam energy loss
energy
protons undergo little energy loss, little
kinematics variation, little straggling
retain information on resonance shape
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a real case
19Ne(p,p)19Ne resonant elastic scattering
excitation function
19Ne p
target thickness DE
20Ne
Coszach et al. Phys Rev C 50 (1994) 1695
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resonant elastic scattering
relevance
useful approach when

• resonance energy not known
• partial widths not known
• very weak resonance(s) dominate(s) reaction rate

fit to experimental data (e.g. by R-matrix
analysis) to determine resonance properties
advantage
RIB intensities 103 ions/s
typically enough thanks to high elastic
scattering cross sections
limitations
requirement proton width Gp 1 keV due to
current limits in detection energy resolution
progressively harder at lower energies due to
increase in Rutherford cross section and decrease
in resonance widths because of penetrability
effects
examples 11C(p,p) 7Be(p,p) _at_ LLN
21Na(p,p) _at_ TUDA - TRIUMF
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TRANSFER REACTIONS
e.g. X(d,p)Y ? investigate (n,?)
reactions for s- (or r-)process
RIB intensities 104 ions/s
TIME-INVERSE REACTIONS
e.g. Coulomb dissociation ? investigate
(x,?) radiative capture reactions
MASS LIFETIME MEASUREMENTS
and much more
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SELECTED EXAMPLES

• the 21Na(p,p) resonant elastic scattering
• the 21Na(p,g)22Mg reaction
• the 22Na(p,g)23Mg reaction

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the 21Na(p,p)21Na reaction
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considerations
in A 21 mass region and for nova (T9 0.4)
and X-ray burst temperatures (T9 2) nuclear
level densities are low ? proton capture
reactions dominated by capture into narrow,
isolated resonances
recall from Lecture 1
Breit-Wigner cross section
fold in with Maxwell-Boltzmann distribution and
integrate to get
reaction rate
resonant strength
with
stellar reaction rate
(cm3 s-1mol-1)
need knowledge of resonance energy and
properties of state
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the 21Na(p,p) reaction
first measurement with RIB _at_ TRIUMF Canada
TUDA (TRIUMF UK Detector Array) multipurpose
scattering chamber
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LEDA system Louvain-Edinburgh Detector Array
CD Compact Detector
8 sectors x 16 strips 128 individual channels

• large area ? larger solid angle coverage
• high segmentation ? reduced sensitivity to
  background (i.e. beam b-decay)
• good modularity ? different configurations
  possible

T. Davinson et al. NIM A 454 (2000) 350-358
(for details on LEDA detector array)
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astrophysical motivation
investigate states in 22Mg of astrophysical
relevance for 21Na(p,g)22Mg reaction

• novae explosions
• synthesis of 22Na
• onset of rp-process?

the experiment
21Na 5x107 pps Ecm 0.45 1.40
MeV (CH2)n 50 mg cm-2 250 mg cm-2
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the results
determined resonance energies, widths and
spin-parity assignments
C. Ruiz et al Phys. Rev C65 (2002) 42801 (R)
6.813
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more recently
20Na(p,p)20Na
resonant elastic scattering with TUDA _at_ TRIUMF
investigate states in 21Mg of astrophysical
relevance for 20Na(p,g)21Mg reaction
evidence for a new resonance at E 4.44 MeV
courtesy A. Murphy
data analysis still in progress
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• the 21Na(p,g)22Mg reaction
• the 22Na(p,g)23Mg reaction

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astrophysical motivation
novae explosion rate 30-40 y-1 Galaxy lifetime
1010 y mass ejected 2x10-5 Msun /
nova novae scarcely contribute to Galactic
abundances BUT produce key isotopes (e.g. 7Be,
22Na and 26Al) which provide clear signature of
novae explosion via characteristic g-ray emission
José Hernanz, ApJ 494 (1998) 680
idea observe g-ray signature to test nova models
22Na the fingerprint of a nova outburst
Clayton Hoyle, ApJ L101 (1974) 187
why 22Na?

• novae are thought to be principal galactic site
  for 22Na
• 22Na decay has conveniently short half-life
• ? hence spatial and temporal limits to its
  detection

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• theoretical models of novae indicate that
  measurable g-ray fluxes should be observed
• from novae explosions within few kilo-parsecs
  from the Sun (1pc 3.26 ly)

• from COMPTEL data on 5 ONe-type novae
• (Nova Her 1991, Nova Sgr 1991, Nova Sct
  1991, Nova Pup 1991, and Nova Cyg 1992)
• data from CO-type novae
• ? only upper limit 3x10-8 Msun of 22Na
  ejected by any nova in the Galactic disk

A. F. Iyudin et al., AA 300 (1995) 422
WHY?

• over-production predicted by models? (e.g. 10-4
  Msun for ONe novae)
• too low g-ray detection sensitivity?
• unclear (nuclear) inputs?

reduce uncertainties affecting reaction rates for
production and destruction of 22Na
important constraints on models and observations
(i.e. distance and epoch)
compare with observations g-ray detection by
INTEGRAL mission
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22Na production and destruction processes
in Ne-enriched envelopes of ONe novae
José arXivastro-ph/0407558 v1 27 Jul 2004
production of 22Na

• 20Ne(p,g)21Na(b)21Ne(p,g)22Na (cold NeNa)
• 20Ne(p,g)21Na(p,g)22Mg(b)22Na (hot NeNa)

• destruction of 22Na
• 22Na(p,g)23Mg (mainly)

• first direct measurement of the 21Na(p,g)22Mg
  rate
• recently performed with DRAGON recoil
  separator _at_ TRIUMF
• also indirect determination of the 22Na(p,g)23Mg
  rate
• carried out with the Gamma-sphere array _at_ ANL

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the 21Na(p,?)22Mg reaction (the 22Na production
process)
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the experiment
first direct measurements of 21Na(p,g)22Mg _at_
TRIUMF Canada
S. Bishop et al. Phys Rev Lett 90 (2003)
162501(4)
J.M. DAuria et al. Phys Rev C 69 (2004)
65803(16)
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the DRAGON facility
Detector of Recoils And Gammas Of Nuclear
reactions
differentially pumped window-less gas target (
12cm)
30 BGO g-ray detector array 90 of 4p
two-stage recoil separator (magnetic and electric
dipoles)
(start)
(stop)
DSSSD double sided silicon strip detectors for
recoil detection
see J.M. DAuria et al., Nucl Phys A 701 (2002)
625 and D. Hutcheon et al., NIM A 498 (2003) 190
for details
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aim of the measurements direct determination of
the resonant strengths wg for key resonances in
22Mg the method thick-target yield measurement
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effects of target thickness in cross section
measurements
consider resonance with width G and target
with thickness D
if D ltlt G thin-target case ? yield
measurement proportional to resonance profile
if D gtgt G thick-target case ? yield
measurement integrated Breit-Wigner cross
section smooth step function
D ? ?
yield measurement gives directly wg
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example
9Be(p,g)10B
ER 1.017 MeV
G 4 keV
rule for thick-target yield applicability D 6G
see Rolfs Rodney, Cauldrons in the Cosmos
(1988) for details
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the results
S. Bishop et al. Phys Rev Lett 90 (2003)
162501(4)
wg measured for state at Ex 5.714 MeV

• thick-target yield measurement
• Ecm 202 -221 keV
• 21Na beam 109 s-1 (t½ 22.5 s)
• P (H2) 4.6 Torr

22Mg
wg 1.03 0.16stat 0.14sys meV
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astrophysical implications
S. Bishop et al. Phys Rev Lett 90 (2003)
162501(4)
stellar reaction rate
reduced uncertainties on previous estimates
higher rate ? lower 22Na abundance ?
lower detection limits confirmed maximum g-ray
detection distance 1 kpc (with INTEGRAL)
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the results
J.M. DAuria et al. Phys Rev C 69 (2004)
65803(16)
measured wg for seven resonances of astrophysical
relevance in Ecm 200-1103 keV

• thick-target yield measurement
• Ecm 0.2 1.1 MeV
• 21Na beam 109 s-1 (t½ 22.5 s)
• P (H2) 5 Torr

note little agreement on spin-parity values of
excited states, except for Ex 5.714 MeV
also, state at Ex 5.837 MeV observed once
but not confirmed by other experiments
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astrophysical implications
stellar reaction rate
J.M. DAuria et al. Phys Rev C 69 (2004)
65803(16)
novae
X-ray bursts
dominant contribution from state at Ex 5.714
MeV up to T9 1.1
novae same conclusions as in Bishop et
al. (2003) X-ray bursts two nova models,
using present rate and rate 0 for 21Na(p,g)
evolution of explosion is the same
alternative routes to heavier nuclei are possible
? 21Na(p,g) not critical
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the 22Na(p,?)23Mg reaction (the 22Na destruction
process)
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heavy-fusion reaction to investigate properties
of relevant states in 23Mg
measurement at Argonne National Laboratory
12C(12C,n)23Mg
D.G. Jenkins et al., Phys Rev Lett 92 (2004)
031101(4)
12C 10 pnA Elab 22 MeV 12C target 40 mg
cm-2 detector Gammasphere

• new states observed
• accuracy in excitation energies improved
• several spin-parity uncertainties resolved

newly discovered level at Ex 7.769 MeV in 23Mg
(189 keV above proton threshold) may have a
non-negligible contribution to stellar rate if
spin-parity confirmed ? need for new
investigation
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astrophysical implications
22Na(p,?)23Mg
stellar reaction rate
new limits
previous limits from NACRE
D.G. Jenkins et al., Phys Rev Lett 92 (2004)
031101(4)
C. Angulo et al., Nucl Phys A 656 (1999) 3
factor 3 less 22Na ejected in novae
?
limits detection to within 0.6 kpc from the Sun
instead of 1 kpc from previous rate
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summary and outlook
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overview of main astrophysical processes
M.S. Smith and K.E. Rehm Ann. Rev. Nucl. Part.
Sci, 51 (2001) 91-130
nuclear reactions involving UNSTABLE nuclei are
take place in a many astrophysical sites
Radioactive Ion Beams (will) play dominant role
in understanding these processes
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summary and outlook
much has already been achieved since first RIBs
available at LLN (1990)
for example

• better knowledge of explosive H-burning
  processes
• better understanding of key reactions ?
  constraints on physical conditions
• in astrophysical sites
• first measurements ever on structure and
  properties of highly exotic nuclei
• (proton-rich and neutron-rich)

however

• at present limitations on
• species which can be produced at current
  facilities
• intensities of available RIBs

future projects (e.g. RIA, EURISOL, upgraded GSI)
aimed at overcoming present limitations will open
up new and exciting avenues in experimental
Nuclear Astrophysics
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planned future facilities
The EURISOL Report published by GANIL, 2003
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the RIA facility
RIA Rare Isotope Accelerator facility
ISOL
fragmentation
RIA Physics White Paper
objectives

• nature of nucleonic matter
• origin of the elements and energy generation in
  stars
• tests of the Standard Model and of fundamental
  conservation laws

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yield estimates available at RIA
RIA Physics White Paper
enormous discovery potential !
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the EURISOL project
LINAC
RFQ
1 GeV 5 mA proton beam
The EURISOL Report published by GANIL, 2003
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With special thanks to Hendrik Schatz
Michael Heil for permission to use and readapt
some of their material and to Rene
Reifarth for unknowingly providing me with one
of his slides
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further reading
BOOKS
W.D. Arnett and J.W. Truran Nucleosynthesis The
University of Chicago Press, 1968 J. Audouze
and S. Vauclair An introduction to Nuclear
Astrophysics D. Reidel Publishing Company,
Dordrecth, 1980 E. Böhm-Vitense Introduction
to Stellar Astrophysics, vol. 3 Cambridge
University Press, 1992 D.D. Clayton Principles
of stellar evolution and nucleosynthesis The
University of Chicago Press, 1983 H.
Reeves Stellar evolution and Nucleosynthesis G
ordon and Breach Sci. Publ., New York, 1968 C.E.
Rolfs and W.S. Rodney Cauldrons in the
Cosmos The University of Chicago Press, 1988
(the Bible)
copies of these lectures at
www.ph.ed.ac.uk/maliotta/teaching