NUCLEAR ASTROPHYSICS AT ISAC WITH DRAGON
The DRAGON Facility: Status Report
Nov. 1, 2002
I. SUMMARY
This brief report provides a summary of the status of the DRAGON facility including
activities in 2002 and near term plans for the facility. A summary of results obtained from
E824 will also be given. In addition beam time is requested for E811 and E805, which
could not run in 2002 because of the unavailability of the ISAC ECR source.
Figure 1: Schematic view of DRAGON
II. INTRODUCTION
The primary purpose of the DRAGON (Detector of Recoils And Gammas Of Nuclear
reactions) facility is to measure the astrophysical S-factor or resonance strengths in
radiative proton and alpha capture reactions. These reactions will be studied using inverse
kinematics with gaseous targets of hydrogen or helium, and heavy ions with center of
mass energies from 0.15 to 1 MeV/u. Since the facility is located at TRIUMF-ISAC,
these heavy ions will consist primarily of short-lived radioactive species and the reactions
are of interest to increasing our understanding of the process of explosive nucleosynthesis
in nova, supernova, and x-ray bursts. Funding for the DRAGON Facility was received
April 1998 and DRAGON began operations taking data for E824 in Oct. 2001. The
purpose of this report is to give the TRIUMF Experimental Evaluation Committee a
report on the status of the facility, improvements and commissioning completed in 2002,
results of any experiments performed in 2002 and other relevant information. Included
will be an overview of both stable beams and radioactive beams to be requested in 2003
for the previously EEC approved experiments.
III. THE FACILITY
A. Background
Figure 1 is a schematic representation of the DRAGON facility. It is composed of a
windowless gas (hydrogen or helium) target surrounded with a gamma detection (30
BGO units) array, a multi-unit electromagnetic separator (EMS) and a recoil detection
system. The separator will accept heavy recoil products of radiative capture reactions and
their momentum is essentially the same as the beam itself. The philosophy of the EMS is
to first allow only one charge state of the beam and reaction products to pass through slits
located after the first magnetic dipole. Beam and reaction products are then separated in
the first electrostatic dipole, taking advantage of the difference in kinetic energy.
Additional separation is achieved in the second stage. In the focal plane detection system
the main detector used has been DSSSD (double sided silicon strip detector), which
provided both energy and spatial information both singly and in coincidence with the
gamma system.
B. Synopsis of Facility Changes in 2002
A number of hardware improvements were made in 2002. These included
1. installation and testing of a segmented ionization chamber for detection and
identification of the recoil products at the exit of the EMS;
2. installation and testing of the microchannel plate system to be used
at the focal plane for timing and positional information;
3. testing of a novel optical viewing system to allow tuning of the
beam while it is intercepting the gas in the target;
4. improvements in the EPICS based, DRAGON separator tuning program;
5. ordering replacements of several older model power supplies;
6. construction and installation of safety fence around the complete facility;
7. installation of lead-filled shields around mass and charge slit chambers.
C. Commissioning in 2002
Considerable time was devoted in the past year using stable beams of 14N, 20Ne, 21Ne, and
24
Mg with a wide range of energies to understand and improve the operation of the
facility. Approximately 125 shifts in total, with runs in every month except March were
delivered to DRAGON. In particular these studies were devoted to:
1. calibration of the technique of measuring the incident beam energy;
2. calibration of the overall absolute efficiency of the DRAGON;
3. studying the response of DRAGON for a wide resonance;
4. testing focal plane detection systems;
1. Beam energy
Beam energy at DRAGON is measured using the first dipole, MD1. Without gas in the
system, the beam is initially tuned through the system by ISAC operations. It is then
centered through a 2 mm opening in the slits at a focus after MD1. An NMR probe then
measures the field setting. This approach was calibrated using three well-known
resonances in two different experimental approaches (Table 1). Such studies will
continue.
Table 1: Reaction Resonances Used for Energy Calibration Studies
21
Ne(p,)22Na at
21
Ne(p,)22Na at
20
Ne(p,)21Na at
24
Mg(p,)25Al at
Ecm
Ecm
Ecm
Ecm
= 259.3  0.4 keV
= 732.7  0.5 keV
= 1113  1 keV
= 213.97  0.08 keV
2. Efficiency
Since the DRAGON is used to measure the absolute resonance strength of unknown
reactions involving radioactive reactants, studies were performed to understand the
operation (transmission, etc) under different settings (e.g. slit settings, tuning, etc). The
wobbler magnet was used to study transmission and a number of well-known resonance
strengths using stable beams were measured (Table 2). Such studies will continue.
Table 2: Efficiency Calibration Studies
Reaction E_cm
keV
20
1113
Ne(p,)
21
Ne(p,) 259.4
21
Ne(p,) 732.7
24
Mg(p,) 214
24
Mg(p,) 420.2

lit
mrad
eV
3.8
1.13
14.9 0.0825
9.4
3.95
5.2 0.0127
4
0.0416
 
eV
0.07
0.0125
0.79
0.0009
0.0026
meas
eV
1.41
0.1495
3.6
0.0114
0.042
 
eV
0.13
0.0173
0.5
0.0023
0.009
3. Wide resonance
DRAGON was designed specifically to study resonance whose width was much less than
the energy loss in the gas target chamber. However there is interest in broad resonances
and non-resonant capture reactions also, and beam time was devoted to explore and
measure the response of DRAGON in those cases.
4. Focal plane detectors
The specially designed ionization chamber for detecting reaction products at the end of
DRAGON was tested (for E811) using the 21Ne(p,)22Na reaction. Excellent separation
was noted between neon and sodium ions at 0.5 MeV/u both singly and in coincidence
with the gamma array.
III. Science with DRAGON
A. E824
Radioactive 21Na beam was delivered to DRAGON for E824 for 2.5 weeks in April/May
in 2002. Studies were attempted of resonances in the 21Na(p, )22Mg reaction at Ecm =
212, 336, 460, 545 and 822 keV. Fig. 2 presents some of these results for the most
important resonance at 212 keV and data on the broad resonance at 822 keV. Beam time
will be used in Nov. of 2002 to complete this study for the astrophysically significant
resonances around 500 keV.
B. Outlook for 2003
Beam time (both stable and radioactive) will be requested for approved experiments
E811 (U.Greife, Spokesperson), the study of the 19Ne(p ,)20Na reaction, and E805
(J.King/J. D’Auria, spokespersons), the 13N(p ,)14O reaction. Both of these require the
use of the ISAC ECR ion source, which is expected to be operational by April 2003.
Fig. 2 Preliminary data for E824
In addition, several new experiments, if approved by the EEC, could run in 2003, with, at
most, minor changes to the DRAGON facility. These include studies of the 17F(p ,)18Ne,
12
C( ,)16O, and 12C(12C, )24Mg reactions. Some longer-term proposals, requiring more
extensive changes to the BGO array or gas target include a revised 8Li(,n)11B study or
phase II of 12C(,)16O. In addition, studies are in progress to explore the feasibility of
producing a sufficient amount of 15O (for E813) with the TR13 cyclotron using a (p,n)
reaction, with an on-line gas transfer (of C15O) to OLIS for the production of an
accelerated beam.
IV. Summary
The DRAGON facility is now operational with the completion of the first study, E824
expected by the end of the year; a number of commissioning studies have also been
performed. In addition to presentation at conferences and several manuscripts submitted
or accepted for publication on DRAGON related studies, one M.Sc. thesis has been
completed and 4 other thesis projects (2-Ph.D., 2-M.Sc.) are essentially completed.
J.D’Auria
D.Hutcheon