Enter The DRAGON Investigating the 13 C(p,γ) 14 N reaction Aaron M. Bebington (University Of Surrey, Guildford, Surrey, England) ISAC talk – 24 th November 2003

Enter The DRAGON Aaron Bebington 1) The Importance of the 13 C(p,γ) 14 N reaction - 13 N(p,γ) 14 O 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 13 N captures a proton before it has chance to beta decay. - Beta decay of 14 O (t 1/2 = 70.6 secs) is much quicker than beta decay of 13 N (t 1/2 = 9.97 mins)  HCNO cycle produces energy much faster. - DRAGON plans to measure the cross-section of the 13 N(p,γ) 14 O reaction at energies around the Gamow window. - Problem: due to closeness in mass between 13 N and 13 C (a difference of amu), a pure 13 N beam cannot be produced. - Studying the 13 C(p,γ) 14 N reaction means that its contribution can be compensated for when studying the 13 N(p,γ) 14 O reaction.

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 ]

Enter The DRAGON Aaron Bebington 2.1) DRAGON’s 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.

Enter The DRAGON Aaron Bebington 3) Data Analysis DRAGON’s data analyzer is a MIDAS program, which looks at runs online and offline. Shows a typical coincidence gamma energy spectrum for a 13 C(p,γ) 14 N reaction run with the DRAGON Passing the same run through the analyzer, we can make changes to the ODB to look at data not available online. Energy spectrum of the final recoils. Shows a dip in the low energy side. Possible cause: “clipping” due to large cone angle.

Enter The DRAGON Aaron Bebington 3.1) Calculation of the cone angle for the 13 C(p,γ) 14 N reaction 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. 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.

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 i.e. Perfect for simulating the DRAGON! Created by Peter Gumplinger. Modified by Chris Ruiz.

Enter The DRAGON Aaron Bebington 4.1) BGO detector array simulations BGO array only covers 92% of the solid angle of the gas target. Q: How do we define a neighbouring BGO? A: The simulation uses a volume of a cuboid technique.

Enter The DRAGON Aaron Bebington 13 C(p,γ) 14 N reaction simulations 4.2) Initial 13 C(p,γ) 14 N reaction simulations 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….. Input File Includes all relevant data, including: energy levels, their lifetimes, and possible gamma decays.

Enter The DRAGON Aaron Bebington 4.3) DRAGON’s Ionization Chamber -One of two end detectors for DRAGON -Parallel plate arrangement of a single cathode and five anodes, creating E field between plates

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

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 ( < 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.

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.

Enter The DRAGON Aaron Bebington 5) Creating an ionization chamber in GEANT

Enter The DRAGON Aaron Bebington 5) Creating an ionization chamber in GEANT

Enter The DRAGON Aaron Bebington 6) Current Work 6.1) Further simulations of the 13 C(p,γ) 14 N 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.

Enter The DRAGON Aaron Bebington 6) Current Work 6.1) Further simulations of the 13 C(p,γ) 14 N 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.

Enter The DRAGON Aaron Bebington 6) Current Work 6.2) Initial simulations of the 12 C( 12 C,γ) 24 Mg 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 12 C target within old gas box.

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

Enter The DRAGON Aaron Bebington 7) Conclusions - Comparisons between the actual data and the simulation of the 13 C(p,γ) 14 N 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 13 C(p,γ) 14 N reaction, have shown that there is a large acceptance loss, and that our data from this reaction (and the future 13 N(p,γ) 14 O 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.

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 D’Auria for giving me this excellent opportunity to come to this facility, and experience nuclear astrophysics outside of the classroom. The End.