First First Radioactive Radioactive Beam Beam Experiment Experiment
Mustafa Rajabali , Melanie Evanger , Ramsey Turner , Bryan Luther , Thomas Baumann , Yao Lu , Michael Thoennessen b,c,, Erik
University ,, East
MoNA, a small version of MoNA consisting of 8 MoNA bars, was used to study the feasibility of detecting 7He which decays in flight into 6He and a neutron. A secondary beam of 8Li at 85 MeV/u bombarded a 5.6 mm and a
3.3 mm carbon target in two different runs. States in 7He were populated via the single proton stripping reaction. The subsequent 6He fragments were detected at zero degrees with a E-E detector arrangement consisting of a 1-E-E detector arrangement consisting of a 1cm-thick plastic scintillator and 10-cm-thick BaF2 detector. The corresponding neutron from the 7He decay was detected with MoNA, which was configured in two rows of four detectors above and below the BaF 2 detector. From
the energy of the 6He and the position and time-of-flight of the neutron, it should be possible to kinematically reconstruct the populated states of 7He. The experimental setup and some preliminary data from the study is presented
The 1D plots below show our neutron detection on the MoNA bars.
The plots below are 2D plots of the time of flight
The position of the particle deposition on the horizontal axis is
E-E detector arrangement consisting of a 1E
The Modular neutron array (MoNA) is a large-area
detector. (Units displayed are channel number. Time
neutron detector to be located at the NSCL for the
( which corresponds to position along the bar) and
investigation of neutron-rich nuclei [1,2].
has the particle counts (in logarithmic
scale). 1 Raw position graph.
MoNA will have a front face area of 2 m x 1.6 m
Position with cut
and will consist of 144 individual detector modules (see
from veto bar
rendering at left). Each independent module consists of
a BC-408 plastic scintillator bar, 2 m long and 10 x 10
Position with cut
This was to see
cm2 in cross section, with light guides and phototubes at
From E-E detector arrangement consisting of a 1-E TOF.
each end .
Position with cuts
constituents of the
from veto TOF
beam fell in the
Singles trigger, without a
2001 T. Baumann
and E-E detector arrangement consisting of a 1-E TOF.
Position with cuts
The neutron position on a module is found from
from E-E detector arrangement consisting of a 1-E TOF, E-E detector arrangement consisting of a 1-E
the timing difference between light arrival at the two
We identified the
phototubes. Energy is deduced by the neutron time of
large peak in the
flight from the start detector to the individual module.
above graph as
left (5) when all cuts
MoNA (a small version of MoNA) consisting of
carbon and boron.
are applied (No
eight detector modules was used for neutron detection
This run was done to
target to produce
in this experiment.
No target, Carbon & Boron tuned by
The 5.6 mm target
was used since it has
a higher crossThe Experiment
section than the 3.3
A 36Ar primary beam on a beryllium target was
mm. The thicker
used to make a secondary 8Li rich beam which was
target was expected
the large peak at
bombarded onto a carbon target under two different
to give us a larger
~channel 150 (energysituations. One was with the target being 5.6 mm
number of neutron
horizontal axis) is 8Li
thick and the second with the target 3.3 mm thick.
and the smaller peak at
(Impurities found in the beam included carbon and
3.3mm Carbon target
boron, whose identification will be discussed later.)
Li p He
On hitting the carbon target, the reaction
From the results of the experiment we were able to detect
fragment with highest population is expected to be
He 6He + n
neutrons in correlation with 6He. The energy resolution, however,
He which decays instantaneously to 6He giving off a
Another run was made
was not good enough to kinematically reconstruct the states of 7He.
this time with a thicker
He comes off in a narrow cone while neutrons
target (5.6 mm) to
break up into 7He by detecting the 6He and neutron from the 7He
come off at a significantly larger cone.
improve the count rate
with the full MoNA detector. MoNAs large active area allows for a
of the 6He. As we can
longer flight path hence better energy resolution.
see, The smaller peak
Members of the MoNA collaboration have proposed repeating
at ~channel 20 has
5.6mm Carbon target
the experiment on a larger scale using the completed MoNA
To receive the He and for the identification of
now slightly more
detector with large veto paddles and an improved central E-E detector arrangement consisting of a 1-E-E
other charged fragments or particles, a E-E detector arrangement consisting of a 1-E-E
arrangement was placed along the beam axis. The E-E detector arrangement consisting of a 1-E
E-E detector arrangement consisting of a 1-E-E arrangement
detector was a 1-cm-thick plastic scintillator wrapped
with black tape for light tightness. It was placed in
front of the E detector, which was a 10-cm-thick
cylindrical BaF2 crystal.
To accommodate the E-E detector arrangement consisting of a 1-E-E telescope and to
measure the neutrons, the eight MoNA bars were
separated into two layers of four bars. The layers
were placed above and below the E-E detector arrangement consisting of a 1-E-E arrangement
so that a neutron coming off at an angle from a
decaying 7He (along beam axis) could be detected by
one of the four bars in either of the layers.
Experimental Setup Diagram
Not to scale
 T. Baumann et al., Nucl. Instr and Meth. B, 192 (2002) 339-344.
 B. Luther et al. Nucl. Instr and Meth. B, in press.
 P.J. Van Wylen et al., Poster 5P1.071 presented at this conference.
This work supported in part
by grants from the National
Science Foundation and the
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