- Email: [email protected]
Measurements with DRAGON on resonances in the 21Na(p, γ)22Mg reaction with a radioactive ion beam
Nuclear
ELSEVIER
Physics
A7 19 (2003)
107c-110~ www.elsevier.com/locate/npe
Measurements reaction with
with DRAGON on resonances a radioactive ion beam
in the ‘lNa(p,
y)“A!Ig
S. Engel”lb, S. Bishopc, L. Buchmann”, M.L. Chatterjeed, A. Chen”, J.M. D’AuriaC, D. Gigliottif, U. Greifeg, D. HunterC, A. Husseinf, R. Lewish, W. Liuc, A. Olin”, D. Ottewell”, P. Parkerh, J. Rogers”, F. Striederb and C. WredeC “TRIUMF,
Vancouver Canada
bRuhr-Universit&,
Bochum, Germany
‘Simon Fraser University, Burnaby, Canada dSaha Institute of Nuclear Physics, Calcutta, India eMcMaster University, Hamilton, Canada fUniversity of Northern British Columbia, Prince George, Canada “Colorado School of Mines, Golden, USA hYale University, New Haven, USA In the modelling of nucleosynthesis in nova explosions, temperature and density are important parameters to describe the hydrodynamics. Those parameters are not easy to observe, but specific gamma-ray emitters produced in the explosion provide constrains on the models, such as “Na, produced via 21Na(p, y)22Mg(P+)22Na. The new DRAGON recoil separator facility, designed and built to measure directly the rates of radiative proton and alpha capture reactions, important for nuclear astrophysics, is now operational. Experiments have been conducted on the 21Na(p, y)221Mg reaction using a radioactive 21Na beam incident onto a windowless hydrogen gas target. Yield measurements have been performed detecting the prompt gamma and the reaction recoils at EC, M 821 keV and 204 keV.
1. INTRODUCTION A site for explosive nucleosynthesis are so called ONeMg-novae. In the present understanding such an explosion occurs on the surface of a white dwarf that already underwent carbon burning, so that proton and alpha capture reactions on 0, Ne and Mg seeds lead to a thermonuclear runaway. In the modelling of nucleosynthesis in nova explosions, observables, like the beta decay of 22Na with a half life of 2.6 years, are needed to constrain parameters such as temperature and density. 0375-9474/03/$ - see front matter doi:lO.l016/S0375-9474(03)00976-X
0 2003 Elsevier
Science
B.V.
All rights
reserved.
108~
S. Engel et al. /Nuclear
Physics A719 (2003j 107c-110~
The concept of the DRAGON experiment is to measure reactions with astrophysical relevance in the explosive nucleosynthesis, starting with 21NaCp,y)22Mg leading to 22Na via 22Mg(p+). S’mce May 2001, commissioning experiments with stable beams have been conducted, while the astrophysical program has been launched with studies on the 21Na(p,y)22Alg c ro s s section at the recently discovered E,, z 821 keV resonance [I], preparing for the weaker resonance at E,, z 204 keV. 2. EXPERIMENTAL
SET-UP
The measurements were conducted at the DRAGON facility in the new ISAC radioactive beams facility at TRIUMF, Canada [a]. Stable beams are available from on off-line 2.5 GHz ion source, while the radioactive 21Na was produced with the ISOL method with intensities of up to 5 10’ ions per second in a pulsed beam having 86 ns between pulses. The DRAGON [3] consists of a windowless, recirculating, differentially pumped gas target with typical central pressures of 4.5 torr over a geometrical length of 11 cm, which contains 89% of the total amount of gas [4]. Inside the target cell Si-detectors at 30 and 55 degrees monitor the elastically scattered protons. The target is surrounded by an array of 30 BGO detectors and followed by a double stage recoil mass separator, where the beam energy can be measured to 0.2% with the first magnetic bender [4]. Each stage of the DRAGON separator consists of a combination of one magnetic and one electric dipole, and an arrangement of steerers, quadrupoles and sextupoles. Beam monitor devices, slits and Faraday cups are positioned along the beam axis to establish a separator tune ahead of every run. A double-sided silicon strip detector DSSSD at the final focus distinguishes the recoils of interest from leaky beam ions due to their energy and position. 3. OVERALL
EFFICIENCY
To test the detection efficiency of the system several cross section with various energies, recoil cone angles @r/s, resonance widths P and resonance strengths wy of well studied stable beam reactions were measured with the DRAGON. From the results listed in table 1 it was concluded that the DRAGON properties are sufficiently well known and the systematic errors are in the order of the statistical uncertainties.
Table 1 Preliminary
results
Reaction
of the commissioning Em
[51
studies
with well known
reactions.
%/a
Wpubl
WYdra
beV1
[mrad]
bV1
[mevl
21Ne(p, yy
1113 259.3
3.8 15
1130 zlc 70 82.5 xt 12.5
1410 f 130 149.5 & 17.3
‘lNe(p,
y)L51
732.7
9.4
3950 i 790
3600 i 500
%Wg(p,
“iy
214.0
5.2
12.7 31 0.9
11.4 f
402.2
4
41.6 f 2.6
42 i 9
20Ne(p,y)L61
2i112;rg(p, yysl
2.1
S. Engel et al. /Nuclear
Physics A719 (2003) 107c-110~
4. ‘lNa(p, y)22&‘g AT EC,, = 821 AND
109c
204 keV
Two resonances have been scanned with radioactive ‘rNa beam impinging onto a Hz target. Cuts on the recoils of interest were applied on their energy and position in the DSSSD spectrum to establish full separation from the beam ions leaking through the recoil mass separator. For the first resonance the energy in the center-of-mass frame was measured to be 821.2 f 2.0 keV with a preliminary strength 251-l
.rprr
wy= (2&+1)(2J2+1)
(1)
r
of wy = 491 Z!Z62 meV. Compared to earlier publications [l], the total width f’ appears to be broader than expected. Further analysis will be done. For the second resonance visited, additional coincidence requirements with the prompt reaction gammas were necessary to dist,inguish the much weaker recoil yield from background. The resonance strength was measured to be approximately 1.2 meV at an energy zz 204 keV. Careful tests on the energy calibration confirm a disagreement with E eir?ier results that place the resonance at 212 keV [9].
21NMp,#%&l/ i
I&; 821 keVi
i
T 2.5 ton
a 4.6 ton
0.0 820
840
860 Beam
200
880 Energy
(keVb)
Figure 1. Two resonances were observed in the Z1Na(p,y)22Mg keV and 204 keV.
205
210
215
220
C. M. Energy
ReVj
regime at E,,
NN 821.2
S. Engel et al. /Nuclear Physics A719 (2003) 107~~110~
1lOc
5. DISCUSSION
AND
OUTLOOK
Based on the commissioning reactions and the first results on radioactive beams periment,s DRAGON has proven to function reliably. The strengths and energies of resonances in the 21Na(p, y)22Mg reaction at Ecn M 821 and 204 keV were measured preliminary results are presented in this paper. Their analysis as well as studies on intermediate resonances will be continued.
Table 2 Preliminary
results
of the studies
on “iNa(p,
-%&eV 21Na(p, y)22A4-g
extwo and the
y)221Mg.
821.2 Zt 2.0
we [meV] 491 & 62
204.0 zt 1.0
-1.2
Acknowledgements The DRAGON group would like to thank Bob Laxdal and the ISAC operators for their help and support in providing the ion beam as well as the TRIUMF technical staff that brought the DRAGON to life. The work was done with the financial support of NSERC and the DOE. REFERENCES 1. 2.
3. 4.
5. 6. 7. 8. 9.
C. Ruiz et al., Phys. Rev. C 65 (2001) 042861(R). R.E. Laxdal, “Acceleration of Radioactive Ions”, proceedings of the 14th EMIS (ElectroMagnetic Isotope Separators and techniques related to their applications) Conference; Victoria, British Columbia, Canada on May 6-10, 2002. D.A. Hutcheon at al., “The DRAGON Facility for Nuclear Astrophysics at TRIUMFISAC: Design, Construction and Operation” submitted to Nucl. Instr. & Meth. 2002 S. Engel et al., “Commissioning and Operation of the DRAGON”, proceedings of the 14th EMIS (ElectroMagnetic Isotope Separators and techniques related to their applications) Conference, Victoria, British Columbia, Canada on May B-10, 2002. NACRE compilation (C. Angulo et al., Nucl. Phys. A 656 (1999) 3.) R. Bloch et al., Nucl. Phys. A 123 (1969) 129. J. Gijrres et al., Nucl. Phys. A 385 (1982) 57. C. Iliadis et al., Nucl. Phys. A 660 (1999) 349. P.M. Endt, Nucl. Phys. A 521 (1990) 1.
ELSEVIER
Physics
A7 19 (2003)
107c-110~ www.elsevier.com/locate/npe
Measurements reaction with
with DRAGON on resonances a radioactive ion beam
in the ‘lNa(p,
y)“A!Ig
S. Engel”lb, S. Bishopc, L. Buchmann”, M.L. Chatterjeed, A. Chen”, J.M. D’AuriaC, D. Gigliottif, U. Greifeg, D. HunterC, A. Husseinf, R. Lewish, W. Liuc, A. Olin”, D. Ottewell”, P. Parkerh, J. Rogers”, F. Striederb and C. WredeC “TRIUMF,
Vancouver Canada
bRuhr-Universit&,
Bochum, Germany
‘Simon Fraser University, Burnaby, Canada dSaha Institute of Nuclear Physics, Calcutta, India eMcMaster University, Hamilton, Canada fUniversity of Northern British Columbia, Prince George, Canada “Colorado School of Mines, Golden, USA hYale University, New Haven, USA In the modelling of nucleosynthesis in nova explosions, temperature and density are important parameters to describe the hydrodynamics. Those parameters are not easy to observe, but specific gamma-ray emitters produced in the explosion provide constrains on the models, such as “Na, produced via 21Na(p, y)22Mg(P+)22Na. The new DRAGON recoil separator facility, designed and built to measure directly the rates of radiative proton and alpha capture reactions, important for nuclear astrophysics, is now operational. Experiments have been conducted on the 21Na(p, y)221Mg reaction using a radioactive 21Na beam incident onto a windowless hydrogen gas target. Yield measurements have been performed detecting the prompt gamma and the reaction recoils at EC, M 821 keV and 204 keV.
1. INTRODUCTION A site for explosive nucleosynthesis are so called ONeMg-novae. In the present understanding such an explosion occurs on the surface of a white dwarf that already underwent carbon burning, so that proton and alpha capture reactions on 0, Ne and Mg seeds lead to a thermonuclear runaway. In the modelling of nucleosynthesis in nova explosions, observables, like the beta decay of 22Na with a half life of 2.6 years, are needed to constrain parameters such as temperature and density. 0375-9474/03/$ - see front matter doi:lO.l016/S0375-9474(03)00976-X
0 2003 Elsevier
Science
B.V.
All rights
reserved.
108~
S. Engel et al. /Nuclear
Physics A719 (2003j 107c-110~
The concept of the DRAGON experiment is to measure reactions with astrophysical relevance in the explosive nucleosynthesis, starting with 21NaCp,y)22Mg leading to 22Na via 22Mg(p+). S’mce May 2001, commissioning experiments with stable beams have been conducted, while the astrophysical program has been launched with studies on the 21Na(p,y)22Alg c ro s s section at the recently discovered E,, z 821 keV resonance [I], preparing for the weaker resonance at E,, z 204 keV. 2. EXPERIMENTAL
SET-UP
The measurements were conducted at the DRAGON facility in the new ISAC radioactive beams facility at TRIUMF, Canada [a]. Stable beams are available from on off-line 2.5 GHz ion source, while the radioactive 21Na was produced with the ISOL method with intensities of up to 5 10’ ions per second in a pulsed beam having 86 ns between pulses. The DRAGON [3] consists of a windowless, recirculating, differentially pumped gas target with typical central pressures of 4.5 torr over a geometrical length of 11 cm, which contains 89% of the total amount of gas [4]. Inside the target cell Si-detectors at 30 and 55 degrees monitor the elastically scattered protons. The target is surrounded by an array of 30 BGO detectors and followed by a double stage recoil mass separator, where the beam energy can be measured to 0.2% with the first magnetic bender [4]. Each stage of the DRAGON separator consists of a combination of one magnetic and one electric dipole, and an arrangement of steerers, quadrupoles and sextupoles. Beam monitor devices, slits and Faraday cups are positioned along the beam axis to establish a separator tune ahead of every run. A double-sided silicon strip detector DSSSD at the final focus distinguishes the recoils of interest from leaky beam ions due to their energy and position. 3. OVERALL
EFFICIENCY
To test the detection efficiency of the system several cross section with various energies, recoil cone angles @r/s, resonance widths P and resonance strengths wy of well studied stable beam reactions were measured with the DRAGON. From the results listed in table 1 it was concluded that the DRAGON properties are sufficiently well known and the systematic errors are in the order of the statistical uncertainties.
Table 1 Preliminary
results
Reaction
of the commissioning Em
[51
studies
with well known
reactions.
%/a
Wpubl
WYdra
beV1
[mrad]
bV1
[mevl
21Ne(p, yy
1113 259.3
3.8 15
1130 zlc 70 82.5 xt 12.5
1410 f 130 149.5 & 17.3
‘lNe(p,
y)L51
732.7
9.4
3950 i 790
3600 i 500
%Wg(p,
“iy
214.0
5.2
12.7 31 0.9
11.4 f
402.2
4
41.6 f 2.6
42 i 9
20Ne(p,y)L61
2i112;rg(p, yysl
2.1
S. Engel et al. /Nuclear
Physics A719 (2003) 107c-110~
4. ‘lNa(p, y)22&‘g AT EC,, = 821 AND
109c
204 keV
Two resonances have been scanned with radioactive ‘rNa beam impinging onto a Hz target. Cuts on the recoils of interest were applied on their energy and position in the DSSSD spectrum to establish full separation from the beam ions leaking through the recoil mass separator. For the first resonance the energy in the center-of-mass frame was measured to be 821.2 f 2.0 keV with a preliminary strength 251-l
.rprr
wy= (2&+1)(2J2+1)
(1)
r
of wy = 491 Z!Z62 meV. Compared to earlier publications [l], the total width f’ appears to be broader than expected. Further analysis will be done. For the second resonance visited, additional coincidence requirements with the prompt reaction gammas were necessary to dist,inguish the much weaker recoil yield from background. The resonance strength was measured to be approximately 1.2 meV at an energy zz 204 keV. Careful tests on the energy calibration confirm a disagreement with E eir?ier results that place the resonance at 212 keV [9].
21NMp,#%&l/ i
I&; 821 keVi
i
T 2.5 ton
a 4.6 ton
0.0 820
840
860 Beam
200
880 Energy
(keVb)
Figure 1. Two resonances were observed in the Z1Na(p,y)22Mg keV and 204 keV.
205
210
215
220
C. M. Energy
ReVj
regime at E,,
NN 821.2
S. Engel et al. /Nuclear Physics A719 (2003) 107~~110~
1lOc
5. DISCUSSION
AND
OUTLOOK
Based on the commissioning reactions and the first results on radioactive beams periment,s DRAGON has proven to function reliably. The strengths and energies of resonances in the 21Na(p, y)22Mg reaction at Ecn M 821 and 204 keV were measured preliminary results are presented in this paper. Their analysis as well as studies on intermediate resonances will be continued.
Table 2 Preliminary
results
of the studies
on “iNa(p,
-%&eV 21Na(p, y)22A4-g
extwo and the
y)221Mg.
821.2 Zt 2.0
we [meV] 491 & 62
204.0 zt 1.0
-1.2
Acknowledgements The DRAGON group would like to thank Bob Laxdal and the ISAC operators for their help and support in providing the ion beam as well as the TRIUMF technical staff that brought the DRAGON to life. The work was done with the financial support of NSERC and the DOE. REFERENCES 1. 2.
3. 4.
5. 6. 7. 8. 9.
C. Ruiz et al., Phys. Rev. C 65 (2001) 042861(R). R.E. Laxdal, “Acceleration of Radioactive Ions”, proceedings of the 14th EMIS (ElectroMagnetic Isotope Separators and techniques related to their applications) Conference; Victoria, British Columbia, Canada on May 6-10, 2002. D.A. Hutcheon at al., “The DRAGON Facility for Nuclear Astrophysics at TRIUMFISAC: Design, Construction and Operation” submitted to Nucl. Instr. & Meth. 2002 S. Engel et al., “Commissioning and Operation of the DRAGON”, proceedings of the 14th EMIS (ElectroMagnetic Isotope Separators and techniques related to their applications) Conference, Victoria, British Columbia, Canada on May B-10, 2002. NACRE compilation (C. Angulo et al., Nucl. Phys. A 656 (1999) 3.) R. Bloch et al., Nucl. Phys. A 123 (1969) 129. J. Gijrres et al., Nucl. Phys. A 385 (1982) 57. C. Iliadis et al., Nucl. Phys. A 660 (1999) 349. P.M. Endt, Nucl. Phys. A 521 (1990) 1.