exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

Charge identification
Most of the heavy fragments produced in nuclear
reactions at 35 AMeV, were stopped in the second
silicon.
For this detector, we show in figure 1 a bidimensional-map
representing the energy of the particle,
calculated through digital filtering, versus the risetime
of the signal at the charge output of the PACI
preamplifier (taken at 10-90% of the maximum amplitude).
The full range of the PACI for these detectors
corresponds to 2 GeV. The signal is digitized
with a 14-bit, 100MS ADC. A very clear Z-
identification is visible in the figure, up to the xenon
projectile charge, Z=54. It is also obvious that this
value is not an upper limit and that heavier nuclei
can be identified. Conversely there is an energy
threshold for this identification, estimated at 30 μm
of silicon. Such a highly efficient identification, obtained
for the first time in the world, comes from
the excellent resolution due to the FEE, and to the
characteristics of the silicon mentioned above.
Mass identification with the ΔE-E technique
We have also examined how the high qualities of
the detectors and of the electronics influence a
standard ΔE-E R map constructed with the energy
lost in the first silicon, ΔE, and the residual energy
deposited in the second one, E R . The PACI con-
Mass identification in a single silicon
The mass identification shown in figure 2 suffers
the drawback of the ΔE-E technique, namely the
threshold introduced by the necessity for the particles
to punch through the first silicon detector,
equal to 25 AMev for heavy ions. The particles
identified by this technique provide however a large
and continuous range (in Z, A, E) of nuclei
which will be used to test algorithms of mass identification
through pulse shape in the second silicon.
References :
[1] C. A. J. Ammerlaan et al. , Nucl. Inst. Meth. 22 , 189, 1963.
[2] M. Mutterer et al., IEEE tr. on nucl. Sci. 47,756, 2000.
[3] http://fazia2.in2p3.fr/spip/
[4] L. Bardelli et al. Nucl. Instr. Meth. A602, 501, 2009.
[5] H. Hamrita, thèse, Orsay, http://tel.archives-ouvertes.fr/
tel-000010145, 2005.
[6] L. Bardelli et al. Nucl. Instr. Meth. A605 , 353, 2009.
[7] H. Hamrita et al., Nucl. Inst. Meth. A531, 607, 2004.
Figure 2: Energy lost in the first silicon
detector vs the residual energy deposited
in the second one. Both are in
channel. Right part: full spectrum; left
part: zoom on the region of Z=20.
nected to the first silicon detector has a full
range of 3.5 GeV, and the same sampling conditions
as the second member. Again extremely
good performances have been observed. Besides
the trivial (but very clean) Z-identification (figure 2,
right part), mass identification is visible up to isotopes
of chromium or manganese (Z=24, 25), see
left panel of figure 2.
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