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Production and use of post-accelerated radioactive nuclear beams
Nuclear Physics A553 (1993) 837c-840c North-Holland, Amsterdam
NUCLEAR PHYSICS A
Production and Use of Post-Accelerated Radioactive Nuclear Beams P. Van Duppena, P. Decrocka, Th. Delbarb, P. Duhamelc, M. Gaelensa, W. Galsterb, M. Huyse a, P. Leleuxb, I. Lieotb, P. Lipnikb, E. Li~nardb, M. Loiseletb, C. Miehotteb, G. Ryckewaert b, G. Vancraeynesta, J. Vanhorenbeecke and J. Vervierb Instituut voor K e r n - en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium a
b Institut de Physique Nucl~aire et Centre de Recherches du Cyclotron, U.C.L., Chemin du Cyclotron 2, B-1348 Louvain--la-Neuve, Belgium c Institut d'Astronomie et d'Astropbysique, U.L.B., Avenue F.D. Roosevelt 50, B-1050 Bruxelles, Belgium
Abstract The production and acceleration of radioactive beams using two cyclotrons coupled by an electron cyclotron resonance ion source is described• Pure beams of aN(T1/2=996 m) and tgNe(T112=lTs) with an energy between 0.5 and 4.OMe~'/amu are obtained. The first experiments using these energetic radioactive beams are discussed and the ARENAS3 project is very briefly outlined.
1. INTRODUCTION The production of radioactive beams at energies enabling nuclear reaction studies, • ~ " . ". the so-called "radioactive nuclear beams " ( RNB), ]s a topic of great current interest. Possible applications for such beams can be found m nuclear astrophysics, sohd state physics and nuclear structure physics [1]. At Louvain-la-Neuve (Belgium), a project to produce and post-accelerate radioactive ion beams was initiated in 1987. By coupling two cyclotrons with an Electron Cyclotron Resonance (ECR) ion source, medium-energy beams of light radioactive dements have been produced• In this contribution we will present details on the production of 1aN(T1/2=9.96 m) and 19Ne(T1/2=17 s) beams and discuss some experiments that have been performed with these beams. Finally we will briefly outline the future plans for further production aria use of radioactive beams in Belgium. 0375-9474/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved.
838c
P, Van Duppcn ctal. / Post-accelerated radioactive mlclear herons
2. PRODUCTION AND POST-ACCELERATION OF RADIOACTIVE BEAMS The general layout of the production cycle used at Louvain-la-Neuve is shown in figure I.
9o deg: RNRLYZ-!N~ MRCNET 7
TARGET OURORUPOLE ~00UBLET --
90 deq. BENOINE | LENS ---// -] i MRENET : , / EXCLONE
i
I J~
~: Ii
,
I
Figure I. General layout of the radioactive ion beam facility.
I
gO dec]. BENDINI; / HR~NET
The radioactive atoms are produced with a 30 MeV proton beam delivered by the first cyclotron, CYCLONE30. This fixed-field, fixed-frequency cyclotron accelerates Hions from an external source to a maximum energy of 31.5 MeV and a maximum intensity of 500 pA. The proton beam is deflected by a 900 dipole magnet, at the same time tilted upwards by 30% and sent towards the target situated in the concrete wall separating the vaults of the two cyclotrons. A graphite target, enriched in tsC, was used for the production of tan via the ~sC(p,n) reaction (yield -- 1.6,I0-3 taN atoms per incident proton [2]). The target consists out of a pellet (thickness II ram, diameter 27 mm) containing 50% of tsC [3]. The taN atoms leave the target as nitrogen molecules and an overall extract]on efficiency of ~20% is routinely achieved. A LiF target is used to produce tSNe and tsO via the tSF(p,n) and the tSF(p,ml) reaction respectively. A B203 target is used to produce tiC via the ttB(p,n) reaction. The LiF (B2Os) target consists out of LiF (B203) powder embedded in a graphite container. Due to the power deposited by the proton beam in the target, the powder is liquefied. The maximum proton-beam intensity that can be handled by these liquid targets is ~150 #A. Between the target and the ion source a liquid nitrogen trap or - in the case of tSNe - a cryogenic trap working at 20 K, is installed in order to reduce the gas load for the ion source. A dedicated ECR source was developed for efficient, low-charge state ionization of light elements [4]. For t3N an efficiency of about 8% was obtained. The low-energy
P. Van Duppen et al. / Post-accelerated radioactive nuclear beams
839c
mass 13 beam (~8 keV) is sent towards the CYCLONE cyclotron and is axially injected. Apart from the tON atoms, the mass 13 beam contains large amounts of t3C atoms and IsCH molecules: the s-~C/t0N and nCH/t0N ratios are over 1000. In the case of tONe, only the q>2+ charge states can be accelerated by the CYCLONE cyclotron. A tONe ionization efficiency close to 10 % for the 2+ charge state was obtained.. For the first experiments the beam was accelerated to energzes around 1 MeV/amn. The overall acceleration efficiency was 6% and due to the high mass resolution of the cyclotron the t2C/t0N ratio was reduced by more then five orders of magnitude. Table 1 summarizes the beams that have been produced and their characteristics. More details on the project can be found in references [5,6] Table 1 Radioactive beams produced with the Belgian RIB project Isotope
Half life
tON
9.96 m
tONe
17.2 s
Charge state +1 +2 +2 +2 +4
Energy (MeV)
Intensity (atoms/s)
(ppA)
8.2 10.2 12.0 19.2 88.0
4.0-100 1.9x10 ° 1.6=10 s 1.6.10 s 6.0. l0 s
70 30 250 250 10
3. FIRST EXPERIMENTS USING POST ACCELERATED RNB's The first experiment using the 13N beam was the determination of the cross section of the proton-c~pture reaction on t3N't3N(p,*)')140. This reaction of astrophysical interest is a key reaction in the so-called CNO--cycle. The 8.2 MeV taN beam was sent onto a polyethylene (CH2) foil. The 5.15 MeV 7--rays deexciting the 5.15 MeV level in t40 were detected by the use of two large volume Ge detectors. Figure 2.a shows part of the prompt 7-ray spectrum. From these data a gamma width of 3.8~1.2 eV was deduced for the 5.15 MeV level [7]. A second measurement that has been carried out is a cross-section measurement of the nN(d,n)t40 reaction. In this case the reaction rate is measured through the detection of the ~ decay of t40. An example of a 7--ray spectrum is shown in figure 2.b. From the results obtained, we will get information about the direct capture contribution of the t3N(p,'y)140 reaction. Other experiments like proton scattering on t3N and tgNe atoms, elastic scattering of t3N on I2C and t3C targets, and coulomb excitation of tgNe have been performed. The proton scattering on tONe revealed information on the resonance parameters of the ~2.65 MeV ~V < 1 keV), the 2.980 MeV (P=33.6,0.3 keV, Jw=l +) and the 3.068 MeV (V=38.7i0.6 keV, Jx=0+) levels in 20Na.
I
5000
1
t
MOO Ener)y
9000 IkeVl
Figure 2. a) Part of the prompt +y-ray spectrum resulting from the lsN(p,@*O reaction. T6 e full-energy, first and second escape peaks of the 5.15 MeV y ray are clearly visible. (b) Part of the y-ray singles spectrum obtained during the %I(lsN,n)l*O measurement (E(‘sN)=l 2 MeV). The inset shows the intensity of the 2.313 MeV r_line form the p decay of 140 as a function of time. The curve is a fit through the data with the half life equal to the half life of 140. Note the 2.615 MeV background line from the decay chain of ss2Th. 4. THE ARENAS3 PROJECT Future plans for radioactive beams are guided by the demand for energetic RNB of other isotopes produced in a wider energy range, and by the growing interest in lowenergy 50 keV and more), high-intensity, polarized beams of light elements for solidstate p6.ysxs studies. Therefore the ARENAS, project (Acceierated Radioactive Elements for Nuclear, Astrophysical and Solid State Studies) was initiated. With this project that covers the existing LISOL [S] and CYCLONES&CYCLONE facilities, an upgrade of both facilities (installation of an efficient high-charge state ECR ion source) as well as the construction of a new post-accelerator are planned. 5. REFERENCES Th. Delbar (ed.), Proc. of the Second International Conference on Radioactive Nuclear Beams (Adam Ailger) (1992) Wa Kitwanga et al., Phys. Rev. C40 (1989) 35 D. Darquennes et al., Nucl. Instrum. and Meth. B47 (1990) 311 P. Decrock et al., Nucl. Instrum. and Meth. B58 (1991) 252 D. Darquennes et al., Phys. Rev. C42 (1990) R804 P. Van Duppen et ai., Nucl. Instrum. and Meth. in press P. Decrock et al., Phys. Rev. Lett. 67 (1991) 808 M. Huyse et al., Nucl. Instrum. and Meth. in press
NUCLEAR PHYSICS A
Production and Use of Post-Accelerated Radioactive Nuclear Beams P. Van Duppena, P. Decrocka, Th. Delbarb, P. Duhamelc, M. Gaelensa, W. Galsterb, M. Huyse a, P. Leleuxb, I. Lieotb, P. Lipnikb, E. Li~nardb, M. Loiseletb, C. Miehotteb, G. Ryckewaert b, G. Vancraeynesta, J. Vanhorenbeecke and J. Vervierb Instituut voor K e r n - en Stralingsfysica, K.U.Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium a
b Institut de Physique Nucl~aire et Centre de Recherches du Cyclotron, U.C.L., Chemin du Cyclotron 2, B-1348 Louvain--la-Neuve, Belgium c Institut d'Astronomie et d'Astropbysique, U.L.B., Avenue F.D. Roosevelt 50, B-1050 Bruxelles, Belgium
Abstract The production and acceleration of radioactive beams using two cyclotrons coupled by an electron cyclotron resonance ion source is described• Pure beams of aN(T1/2=996 m) and tgNe(T112=lTs) with an energy between 0.5 and 4.OMe~'/amu are obtained. The first experiments using these energetic radioactive beams are discussed and the ARENAS3 project is very briefly outlined.
1. INTRODUCTION The production of radioactive beams at energies enabling nuclear reaction studies, • ~ " . ". the so-called "radioactive nuclear beams " ( RNB), ]s a topic of great current interest. Possible applications for such beams can be found m nuclear astrophysics, sohd state physics and nuclear structure physics [1]. At Louvain-la-Neuve (Belgium), a project to produce and post-accelerate radioactive ion beams was initiated in 1987. By coupling two cyclotrons with an Electron Cyclotron Resonance (ECR) ion source, medium-energy beams of light radioactive dements have been produced• In this contribution we will present details on the production of 1aN(T1/2=9.96 m) and 19Ne(T1/2=17 s) beams and discuss some experiments that have been performed with these beams. Finally we will briefly outline the future plans for further production aria use of radioactive beams in Belgium. 0375-9474/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved.
838c
P, Van Duppcn ctal. / Post-accelerated radioactive mlclear herons
2. PRODUCTION AND POST-ACCELERATION OF RADIOACTIVE BEAMS The general layout of the production cycle used at Louvain-la-Neuve is shown in figure I.
9o deg: RNRLYZ-!N~ MRCNET 7
TARGET OURORUPOLE ~00UBLET --
90 deq. BENOINE | LENS ---// -] i MRENET : , / EXCLONE
i
I J~
~: Ii
,
I
Figure I. General layout of the radioactive ion beam facility.
I
gO dec]. BENDINI; / HR~NET
The radioactive atoms are produced with a 30 MeV proton beam delivered by the first cyclotron, CYCLONE30. This fixed-field, fixed-frequency cyclotron accelerates Hions from an external source to a maximum energy of 31.5 MeV and a maximum intensity of 500 pA. The proton beam is deflected by a 900 dipole magnet, at the same time tilted upwards by 30% and sent towards the target situated in the concrete wall separating the vaults of the two cyclotrons. A graphite target, enriched in tsC, was used for the production of tan via the ~sC(p,n) reaction (yield -- 1.6,I0-3 taN atoms per incident proton [2]). The target consists out of a pellet (thickness II ram, diameter 27 mm) containing 50% of tsC [3]. The taN atoms leave the target as nitrogen molecules and an overall extract]on efficiency of ~20% is routinely achieved. A LiF target is used to produce tSNe and tsO via the tSF(p,n) and the tSF(p,ml) reaction respectively. A B203 target is used to produce tiC via the ttB(p,n) reaction. The LiF (B2Os) target consists out of LiF (B203) powder embedded in a graphite container. Due to the power deposited by the proton beam in the target, the powder is liquefied. The maximum proton-beam intensity that can be handled by these liquid targets is ~150 #A. Between the target and the ion source a liquid nitrogen trap or - in the case of tSNe - a cryogenic trap working at 20 K, is installed in order to reduce the gas load for the ion source. A dedicated ECR source was developed for efficient, low-charge state ionization of light elements [4]. For t3N an efficiency of about 8% was obtained. The low-energy
P. Van Duppen et al. / Post-accelerated radioactive nuclear beams
839c
mass 13 beam (~8 keV) is sent towards the CYCLONE cyclotron and is axially injected. Apart from the tON atoms, the mass 13 beam contains large amounts of t3C atoms and IsCH molecules: the s-~C/t0N and nCH/t0N ratios are over 1000. In the case of tONe, only the q>2+ charge states can be accelerated by the CYCLONE cyclotron. A tONe ionization efficiency close to 10 % for the 2+ charge state was obtained.. For the first experiments the beam was accelerated to energzes around 1 MeV/amn. The overall acceleration efficiency was 6% and due to the high mass resolution of the cyclotron the t2C/t0N ratio was reduced by more then five orders of magnitude. Table 1 summarizes the beams that have been produced and their characteristics. More details on the project can be found in references [5,6] Table 1 Radioactive beams produced with the Belgian RIB project Isotope
Half life
tON
9.96 m
tONe
17.2 s
Charge state +1 +2 +2 +2 +4
Energy (MeV)
Intensity (atoms/s)
(ppA)
8.2 10.2 12.0 19.2 88.0
4.0-100 1.9x10 ° 1.6=10 s 1.6.10 s 6.0. l0 s
70 30 250 250 10
3. FIRST EXPERIMENTS USING POST ACCELERATED RNB's The first experiment using the 13N beam was the determination of the cross section of the proton-c~pture reaction on t3N't3N(p,*)')140. This reaction of astrophysical interest is a key reaction in the so-called CNO--cycle. The 8.2 MeV taN beam was sent onto a polyethylene (CH2) foil. The 5.15 MeV 7--rays deexciting the 5.15 MeV level in t40 were detected by the use of two large volume Ge detectors. Figure 2.a shows part of the prompt 7-ray spectrum. From these data a gamma width of 3.8~1.2 eV was deduced for the 5.15 MeV level [7]. A second measurement that has been carried out is a cross-section measurement of the nN(d,n)t40 reaction. In this case the reaction rate is measured through the detection of the ~ decay of t40. An example of a 7--ray spectrum is shown in figure 2.b. From the results obtained, we will get information about the direct capture contribution of the t3N(p,'y)140 reaction. Other experiments like proton scattering on t3N and tgNe atoms, elastic scattering of t3N on I2C and t3C targets, and coulomb excitation of tgNe have been performed. The proton scattering on tONe revealed information on the resonance parameters of the ~2.65 MeV ~V < 1 keV), the 2.980 MeV (P=33.6,0.3 keV, Jw=l +) and the 3.068 MeV (V=38.7i0.6 keV, Jx=0+) levels in 20Na.
I
5000
1
t
MOO Ener)y
9000 IkeVl
Figure 2. a) Part of the prompt +y-ray spectrum resulting from the lsN(p,@*O reaction. T6 e full-energy, first and second escape peaks of the 5.15 MeV y ray are clearly visible. (b) Part of the y-ray singles spectrum obtained during the %I(lsN,n)l*O measurement (E(‘sN)=l 2 MeV). The inset shows the intensity of the 2.313 MeV r_line form the p decay of 140 as a function of time. The curve is a fit through the data with the half life equal to the half life of 140. Note the 2.615 MeV background line from the decay chain of ss2Th. 4. THE ARENAS3 PROJECT Future plans for radioactive beams are guided by the demand for energetic RNB of other isotopes produced in a wider energy range, and by the growing interest in lowenergy 50 keV and more), high-intensity, polarized beams of light elements for solidstate p6.ysxs studies. Therefore the ARENAS, project (Acceierated Radioactive Elements for Nuclear, Astrophysical and Solid State Studies) was initiated. With this project that covers the existing LISOL [S] and CYCLONES&CYCLONE facilities, an upgrade of both facilities (installation of an efficient high-charge state ECR ion source) as well as the construction of a new post-accelerator are planned. 5. REFERENCES Th. Delbar (ed.), Proc. of the Second International Conference on Radioactive Nuclear Beams (Adam Ailger) (1992) Wa Kitwanga et al., Phys. Rev. C40 (1989) 35 D. Darquennes et al., Nucl. Instrum. and Meth. B47 (1990) 311 P. Decrock et al., Nucl. Instrum. and Meth. B58 (1991) 252 D. Darquennes et al., Phys. Rev. C42 (1990) R804 P. Van Duppen et ai., Nucl. Instrum. and Meth. in press P. Decrock et al., Phys. Rev. Lett. 67 (1991) 808 M. Huyse et al., Nucl. Instrum. and Meth. in press