Diapositiva 1

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Study of nuclei far from stability by using the
CHIMERA 4p detector and radioactive beams at LNS
G.Cardella for the CHIMERA collaboration
Dubrovnik May 3-9 2009
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The Detector built for multifragmentation -
useful for many other thinks
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The kinematical coincidences method cleaning
background
The 95 efficiency of CHIMERA and the low
detection threshold allow to detect both reaction
partners in binary reaction reducing very much
the background - one of the main problems with
radioactive beams
A simple example can be provided by the study of
the reaction 7Lip (52 MeV) using a plastic
target we have large background due to the
reaction on 12C
Take two detectors with Df180
p(7Li,7Li)p II sol.
p(7Li,6Li)d II sol.
Select only events in coincidence
Tel 40 (q3.1) silicon energy
Tel 178 (q7.8) CsI(Tl) energy
4 order of magnitude background rejection
spectra backgroud free further background
rejection considering fast-slow pd discrimination
mass charge measurements with TOF and Pulse
shape analysis of silicon detector
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The kinematical coincidences method too
large coincidence angles?
Looking to more backward angles we see also the I
kinematical solution of elastic scattering
We select again two detectors with Df180
Select only coincidences

Tel 117 (q6.4) silicon energy
Tel 802 (q58) Silicon energy
In this case peaks are large tel 802 is in the
sphere and has an opening angle of 4 can we do
better? What is the bump near the main peak at
58? Lets look to E7Li-Ep plots to better
understand
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The kinematical coincidences method excited
level discrimination
We can very simply calculate the excitation
energy subtracting to the beam energy the energy
of detected particles
This is the E7Li-Ep plot
And these are the expected kinematical
correlations
E (MeV)

Selecting both p and 7Li stopped in our silicon
detectors we have a quite good energy resolution
- we see very well the p, p reactions at the
first excited level of 7Li ( 0.47 MeV )
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The kinematical coincidences method
improving angular resolution
We can now use kinematics to improve our angular
resolution
We can select a narrow angular range using
appropriate cuts on the detected particle energies

Further analysis is in progress to extract
complete p,p - p,p - p,d angular distributions
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The kinematical coincidences method
detecting neutrons
It is very interesting to see the reaction
p(7Li,7Be)n
Our detector is not able to detect and identify
neutrons however we have quite thick CsI(Tl)
detectors and neutrons can do reactions inside
them producing g, p, a
We select again two detectors with Df180

Select only coincidences
Tel 624 (q25.5) CsI(Tl) energy
Tel 117 (q6.4) silicon energy
Further work is in progress to verify efficiency
that can reach 5-10
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Next steps use the EXCYT beams
At LNS are available radioactive beams at tandem
energy produced by EXCYT
The beam delivered is 8Li from few MeV to 54 MeV
during last experimental campaign 7x104
nuclei/s where delivered on target
9Li is also produced inside the source with a
factor 10-20 smaller intensity so we expect about
2-3 kHz beam intensity
We have an approved proposal for the study of
10Li resonance using this beam the experiment
will be performed October this year
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Next steps Rex-Isolde results
We will use the 9Li(d,p)10Li reaction at 52 MeV
(5.8 MeV/A) - The same reaction has been already
measured at 2.36 MeV/A at Rex-Isolde H.B.
Jeppesen et al., Phys. Lett. B 642 (2006) 449--
Nucl. Phys. A 748 (2005) 374
Despite the low statistics and the small angular
range they are able to calculate the spectra for
s ½ and p ½ contributions
Higher energy (1.5 MeV) levels were not seen
because of low beam energy In our experiment we
can search for higher energy resonances and
larger angular momenta
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Next steps tagging system for radioactive beams
EXCYT beam is a continuous beam we need a time
reference to measure the TOF of fragments and to
have a good stable reference signal for our
gates.
In 2006 we had a good experience with a MCP
detector used to get the timing of the beam in
one experiment with Zoran Basrak
Therefore we decided to built a new MCP it
works at very high rate we measured 100
efficiency with a beam of 106 p/s (7Li 52 MeV)
(LiF enriched foil)
Obtaining at the same time a good time resolution
(better than 300 ps)
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Next steps FRAGMENTATION BEAMS FRIBS at LNS
Since 2004 we are able to produce at LNS
fragmentation beams using the standard beam lines
Final focus of the Fragment Separator
Raciti et al. DOI10.1016/J.NIMB.2008.05.153
Fragment Separator
Production Target
EXCYT
Slide of G.Raciti
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With 18Ne beam we studied 2He decay
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Next steps FRAGMENTATION BEAMS FRIBS at LNS
We recently tested the production of 11Be and
other nuclei in its surroundings Obtaining a
relatively good and clean beam at about 48 MeV/A
produced via fragmentation of a 13C primary beam
55 MeV/A
DE (ch)
12Be
11Be
10Be
9Li
8Li
7Li
4He
6He
TOF (ch)
The 11Be was about 50 of the total beam
transported on the CHIMERA chamber - with a
current of 700 nA (5) currently available from
the cyclotron we can get a yield of about 15 kHz
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Next steps tagging system with fragmentation
beams
Because the fragmentation beam is not pure we
need to identify it event-by-event measuring its
mass - charge - energy and impinging position
We measure the energy loss arrival time - and
position of the beam with a silicon strip
detector (140mm thick ), placed at the entrance
of the scattering chamber
We measure the start of our time of flight using
a large size (4060 mm2) MCP detector with mylar
aluminized emitting foil
It is placed along the beam line at around 13 m
from the tagging strip. The long flight path
allows to measure the beam energy
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Next steps scheduled measurements - July
Using p and d target, well be able to measure
elastic scattering -transfer/pick-up reactions
with all the beams we are able to produce, for
instance 11Be(p,d)10Be - 10Be(d,p)11Be -
13B(p,3He)11Be - 12B(d,3He)11Be
40 MeV/A
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Summary
We are going to use CHIMERA to investigate on
exotic light nuclei around the drip lines
We will use kinematical coincidences in order to
clean from background, select excited levels and
improve the angular resolution
We will benefit of the LNS radioactive beams
where some new beams for EXCYT are going to be
developed and A rebuilding of the FRIBS beam
line is going to be done next year with a
foreseen beam increase of 10-40 times for
details look to the user group web site of
lns http//www.lns.infn.it/index.php?optioncom_co
ntentviewarticleid247catid31Itemid53
In the future we can also move the detector to
other laboratories (SPES SPIRAL2) to profit of
the radioactive beams that will be available
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CHIMERA-EXOCHIM collaboration
Lanzhou
Rochester