Enter The DRAGON

1
Enter The DRAGON

• Investigating the
• 13C(p,?)14N reaction

ISAC talk 24th November 2003
Aaron M. Bebington (University Of Surrey,
Guildford, Surrey, England)
2
Enter The DRAGON
Aaron
Bebington
1) The Importance of the 13C(p,?)14N reaction

• 13N(p,?)14O reaction important in our
  understanding of explosive astrophysical sites.
• It determines the conditions for breakout from
  the CNO cycle to the Hot CNO cycle.
• When temperatures become hot enough 13N captures
  a proton before it has chance to beta decay.

• Beta decay of 14O (t1/2 70.6 secs) is much
  quicker than beta decay of 13N (t1/2 9.97 mins)
  ? HCNO cycle produces energy much faster.
• DRAGON plans to measure the cross-section of the
  13N(p,?)14O reaction at energies around the Gamow
  window.
• Problem due to closeness in mass between 13N
  and 13C (a difference of 0.002383 amu), a pure
  13N beam cannot be produced.
• Studying the 13C(p,?)14N reaction means that its
  contribution can be compensated for when studying
  the 13N(p,?)14O reaction.

3
Enter The DRAGON
Aaron
Bebington
2) DRAGON

• Essentially a 21m recoil mass spectrometer,
  which creates elements via proton or alpha
  captures, and then separates them in a two stage
  mass separation(QQMSQQQSE)(QQSMQSEQQ)

• Windowless gas target box, surrounded by 30 BGO
  gamma detectors.
• Pumps either side of target box, keep entrance
  and exit in vacuum (10-7 Torr).

M magnetic dipole, Q magnetic quadrupole, S
magnetic sextupole, E electrostatic dipole
4
Enter The DRAGON
Aaron
Bebington
2.1) DRAGONs CCD Camera
Nicknamed the Dragon Breathalyzer, it is
placed, looking upstream, through an alignment
port at MD1. Beam passes through target and emits
light, which is seen by the CCD camera.
CCD image is sent to PC, and 2-D plot is
made. Width and intensity of the beam, can be
measured.
5
Enter The DRAGON
Aaron
Bebington
3) Data Analysis
DRAGONs data analyzer is a MIDAS program, which
looks at runs online and offline.
Passing the same run through the analyzer, we can
make changes to the ODB to look at data not
available online.
Shows a typical coincidence gamma energy spectrum
for a 13C(p,?)14N reaction run with the DRAGON
Energy spectrum of the final recoils. Shows a dip
in the low energy side. Possible cause
clipping due to large cone angle.
6
Enter The DRAGON
Aaron
Bebington
3.1) Calculation of the cone angle for the
13C(p,?)14N reaction
Therefore, some recoils will not make it through
the gas target box, or through the beam tubes,
but will be clipped, preventing them from
reaching the end detector.
To find out what percentage of recoils were not
making it to the end detector, we needed to
create a simulation of DRAGON and this reaction.
7
Enter The DRAGON
Aaron
Bebington
4) GEANT
- A program that simulates the way in which
particles pass through matter.

• Originally designed for High Energy Physics, is
  today used in medical and biological sciences,
  and also astronautics, aswell.

• Main Applications of GEANT
• Tracking of particles through experimental setup
• Simulation of detector response
• Graphical illustration of setup and particle
  trajectories

Created by Peter Gumplinger. Modified by Chris
Ruiz.
i.e. Perfect for simulating the DRAGON!
8
Enter The DRAGON
Aaron
Bebington
4.1) BGO detector array simulations
Q How do we define a neighbouring BGO? A The
simulation uses a volume of a cuboid technique.
BGO array only covers 92 of the solid angle of
the gas target.
9
Enter The DRAGON
Aaron
Bebington
4.2) Initial 13C(p,?)14N reaction simulations
Input File Includes all relevant data, including
energy levels, their lifetimes, and possible
gamma decays.
Initial simulation showed Recoil Energy 6.55
MeV Analysis showed Recoil Energy 5
MeV Difference? because the IC not in
simulation. IC contains a Mylar foil. Recoils
lose 1.5 MeV through it.
cont..
10
Enter The DRAGON
Aaron
Bebington
4.3) DRAGONs Ionization Chamber
-One of two end detectors for DRAGON -Parallel
plate arrangement of a single cathode and five
anodes, creating E field between plates
11
Enter The DRAGON
Aaron
Bebington
4.4) Motivations for creating an Ionization
Chamber in the DRAGON simulation
- Compare to the real data, and estimate the
acceptance loss - To get a proper estimate of
energy straggling - Find out which anode the
recoil ions stop in - Simulate the correct
geometry features of the energy loss - Test
recoils in different pressure within the
ionization chamber
12
Enter The DRAGON
Aaron
Bebington
5) Creating an ionization chamber in GEANT
Once one problem was fixed, along came
another. One of the main problem with the IC
simulation, even for Peter The GEANT Wizard
Gumplinger, was the Mylar foil. Eventually
discovered that the foil was just too small in
thickness ( lt 1µm ) to be recognised by
GEANT. Solution make the window 30 times
thicker, so that GEANT sees it, and reduce the
density by 30 times. Will this produce the same
amount of energy loss? Test them both, using SRIM.
13
Enter The DRAGON
Aaron
Bebington
5) Creating an ionization chamber in GEANT
Using SRIM, place the ion and target data, and
the number of events. SRIM then goes through
simulation, and the output is put into a text
file. This text was imported into Excel, and
histograms were plotted.
14
Enter The DRAGON
Aaron
Bebington
5) Creating an ionization chamber in GEANT
15
Enter The DRAGON
Aaron
Bebington
5) Creating an ionization chamber in GEANT
16
Enter The DRAGON
Aaron
Bebington
6) Current Work
6.1) Further simulations of the 13C(p,?)14N
reaction
With the simulation proven to work, went ahead
with mistuning the reference tune within the
simulation. Tune could be mistuned in position,
angle, and energy.
Results so far show
Position offsets, show that reference tune gives
highest acceptance. However, for energy offsets,
a mistune of -0.5 gives the highest acceptance.
17
Enter The DRAGON
Aaron
Bebington
6) Current Work
6.1) Further simulations of the 13C(p,?)14N
reaction
Results so far show (cont.)
For angular offsets, results are showing that the
highest acceptance is when the reference tune is
mistuned at -1.5 mrad in x and -0.5 mrad in
y. However, I feel more data points are needed
for the energy and angular offset graphs.
(Position offsets showed steep peaks, and result
is conclusive). Also, highest acceptance my not
be a peak, but rather a plateau.
18
Enter The DRAGON
Aaron
Bebington
6) Current Work
6.2) Initial simulations of the 12C(12C,?)24Mg
reaction

• - York experiment
• Replacing the gas target with a solid target
• Changing pumping tubes and collimators to accept
  very large cone angle
• Create a simple simulation, making all exit
  collimators out of vacuum, and placing 12C target
  within old gas box.

19
Enter The DRAGON
Aaron
Bebington
6) Current Work
6.2) Initial simulations of the 12C(12C,?)24Mg
reaction

• Two input files, to look at gamma data.
• Initial results show that in both cases, the
  crown BGO detectors receive the majority of gamma
  data.

Shows the Compton tail of the 12 MeV gamma, and
the 10 MeV peak added on top.
20
Enter The DRAGON
Aaron
Bebington
7) Conclusions

• Comparisons between the actual data and the
  simulation of the 13C(p,?)14N reaction, show the
  same energy loss from the recoils, through the
  DRAGON.
• The addition of an ionization chamber into the
  DRAGON simulation, means that future reactions
  requiring the IC can be done before DRAGON starts
  new experiments.
• SRIM simulations proved that the two ways to
  simulate the Mylar foil, yield the same energy
  loss.
• The simulations of the 13C(p,?)14N reaction,
  have shown that there is a large acceptance loss,
  and that our data from this reaction (and the
  future 13N(p,?)14O reaction) will need to be
  corrected, for it to be used. (i.e. more
  simulation work is needed).
• If a plateau is found for the highest acceptance
  for mistunes of the beam, this means that DRAGON
  is not sensitive to small changes in the tune of
  the beam.

21
Enter The DRAGON
Aaron
Bebington
Acknowledgements
I would like to thank Dr Chris Ruiz, Dr Alison
Laird, Dr Sabine Engel, Dario Gigliotti, and Mike
Lamey, for their close help and support,
throughout this project, and their friendship
during my year at TRIUMF. Also, I like to thank
Professor John DAuria for giving me this
excellent opportunity to come to this facility,
and experience nuclear astrophysics outside of
the classroom.
The End.