First First Radioactive Radioactive Beam Beam Experiment Experiment

First First Radioactive Radioactive Beam Beam Experiment Experiment

First
First Radioactive
Radioactive Beam
Beam Experiment
Experiment
With
With the
the Modular
Modular Neutron
Neutron Array
Array
MoNA
MoNA
aa
aa
aa
aa
cc
bb
b,c
Mustafa
Rajabali
,
Melanie
Evanger
,
Ramsey
Turner
,
Bryan
Luther
,
Thomas
Baumann
,
Yao
Lu
,
Michael
Thoennessen
Mustafa Rajabali , Melanie Evanger , Ramsey Turner , Bryan Luther , Thomas Baumann , Yao Lu , Michael Thoennessen b,c,, Erik
Erik
cc
Tryggestad
Tryggestad
aa
Concordia
Concordia College,
College, Moorhead,
Moorhead, MN
MN
bb
Michigan
Michigan State
State University
University ,, East
East Lansing,
Lansing, MI
MI
cc
National
National Superconducting
Superconducting Cyclotron
Cyclotron Laboratory,
Laboratory, East
East Lansing,
Lansing, MI
MI

Abstract
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
here.
Neutron detection
Helium
Detection
MoNA
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
(vertical
axis)
and
energy
(horizontal
axis)
of
the
E-E detector arrangement consisting of a 1E
The Modular neutron array (MoNA) is a large-area
channel number
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
the
vertical
axis
Key
to
graphs:
to
channel
conversion
is
0.089
ns/ch.)
investigation of neutron-rich nuclei [1,2].
has the particle counts (in logarithmic
scale). 1 Raw position graph.
Single
trigger,
MoNA will have a front face area of 2 m x 1.6 m
2
no target
Position with cut
This
run
was
taken
and will consist of 144 individual detector modules (see
8
from veto bar
with
the
Li beam,
4
rendering at left). Each independent module consists of
3
3
2
TOF.
without
a
target.
a BC-408 plastic scintillator bar, 2 m long and 10 x 10
1
Position with cut
This was to see
cm2 in cross section, with light guides and phototubes at
4
From E-E detector arrangement consisting of a 1-E TOF.
were
the
5
each end [3].
Position with cuts
constituents of the
from veto TOF
beam fell in the
Singles trigger, without a
5
target
2001 T. Baumann
5.6mm
and E-E detector arrangement consisting of a 1-E TOF.
spectrum.
Carbon target
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
4
the timing difference between light arrival at the two
3
We identified the
energy
and veto
2
The
single-trigger
1
phototubes. Energy is deduced by the neutron time of
large peak in the
energy
plot
has
no
neutrons
flight from the start detector to the individual module.
above graph as
left (5) when all cuts
5
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.
verify our
neutrons).
identification.
3.3mm
No target, Carbon & Boron tuned by
The 5.6 mm target
A1900
Carbon
was used since it has
target
4
3
a higher crossThe Experiment
2
1
section than the 3.3
A
3.3
mm
carbon
target
A 36Ar primary beam on a beryllium target was
mm. The thicker
was
placed
in
the
pod,
used to make a secondary 8Li rich beam which was
target was expected
6
8
the large peak at
He
Li
5
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
6
thick and the second with the target 3.3 mm thick.
events
and
He
and the smaller peak at
(Impurities found in the beam included carbon and
6
counts.
~channel
20
is
the
He.
3.3mm Carbon target
boron, whose identification will be discussed later.)
Conclusion
8
+
7
Li p He
On hitting the carbon target, the reaction
From the results of the experiment we were able to detect
7
fragment with highest population is expected to be
He 6He + n
neutrons in correlation with 6He. The energy resolution, however,
7
He which decays instantaneously to 6He giving off a
Another run was made
was not good enough to kinematically reconstruct the states of 7He.
neutron.
this time with a thicker
8
We
conclude
therefore
that
it
is
feasible
to
observe
the
Li
6
8
He
6
Li
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
Experimental setup
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
6
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
intensity.
telescope.
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
E detector
Veto paddles

Window
Carbon Target

Thin scintilator
(start) detector
8

MoNA Bars

BaF2 detector

470 cm

Li Beam

64.5 cm

Not to scale

References
[1] T. Baumann et al., Nucl. Instr and Meth. B, 192 (2002) 339-344.
[2] B. Luther et al. Nucl. Instr and Meth. B, in press.
[3] 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
NSCL

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