- Email: [email protected]
Accelerator mass spectrometry with completely stripped 41Ca and 53Mn ions at the Munich tandem accelerator
Nuclear Instruments and Methods North-Holland, Amsterdam
in Physics
Research
ACCELERATOR MASS SPECTROMETRY WITH COMPLETELY IONS AT THE MUNICH TANDEM ACCELERATOR G. KORSCHINEK, and A. URBAN
H. MORINAGA,
67
B29 (1987) 67-71
E. NOLTE,
E. PREISENBERGER,
STRIPPED
4’Ca AND =Mn
U. RATZINGER
Fachbereich Physik, Technische Universitiit Miinchen, 8046 Garching, FRG
P. DRAGOVITSCH
and S. VOGT
Abtlg. Nuklearchemie am Institut ftirBiochemie der Universitiit Kiiln, 5000 Kiiln, FRG
Accelerator mass sepctrometry (AMS) experiments with completely stripped 41Ca and 53Mn ions have been performed at the Munich tandem laboratory. It is the first time that 53Mn has been detected by AMS. The necessary high beam energies of 5.5 MeV/nucleon were provided by the recently installed second linear postaccelerator cavity. Negative ion beams of CaF- and MnOin the CA range were provided by an improved Middleton high current source. Sensitivities of 41Ca/Ca = 9~ lo-l3 and of “Mn/Mn = 3 x lo-” were achieved. 41Ca was measured in samples from a meteorite and from Hiroshima granite exposed to the A-bomb, “Mn in samples from a meteorite and a CERN-SC beam dump.
1. Introduction Following our very good experiences with accelerator mass spectrometry with fully stripped 36C1 ions and the use of a macroscopic guide beam (here 36S) during the last years [l], we have undertaken first measurements with 41Ca and 53Mn, applying the same technique. 41Ca has been proposed for AMS dating by Raisbeck and Yiou [2]. They also proposed the elegant method of separating the interfering ion 41K by means of fully stripped ions where 41K’9+ and 41Ca20+ can be separated magnetically. 41Ca has been measured in meteorites [3,4] and natural samples of terrestrial origin [5,6]. Still measurements of 41Ca are not simple, which is mainly due to: (i) the low natural abundance of 41Ca; (ii) the low intensities for a Ca beam by using a tandem; (iii) the rather low efficiency for producing a Ca beam. Therefore, a successful measurement of 41Ca down to the natural level demands a suitable ion source with a high yield of Ca ions. In addition, using the method of totally stripped ions, sufficient beam energy is needed. For achieving a high yield we have studied a Middleton high current sputter source in order to optimize the ionizer-target geometry and to find the appropriate target material. The recently finished second stage of our postaccelerator [7] was used for the first time to increase the beam energy. 53Mn (Ti,* = 3.7 x lo6 yr) has been measured at first by Millard [8] by thermal neutron activation analyses. There was not much de0168-583X/87/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
mand till now for measuring 53Mn by AMS, as neutron activation analysis achieves already a sensitivity down to 10mi3. But neutron activation analysis is not possible in the presence of 54Mn ions as in the beam dump samples 191. Additionally in the course of improving our AMS system it seemed worthwhile to evaluate the feasibility of performing AMS measurements with bare stripped s3Mn ions.
2. Experimental setup and calibration standards
2.1. Ion source A very critical part for ams is the ion source, especially in the case of 41Ca where the production of a high yield is a difficult task. We have performed therefore a detailed study [lO,ll] for optimizing a Middleton high current sputter source. We followed similar ideas for optimizing the geometry as it is discussed in ref. [12] and shown in [11,13]. The result of our calculations can be seen in fig. 1. The main advantage is an improved optics for the primary Cs ions and the sputtered secondary negative ions. The best choice for the production of a Ca beam was a target mixture of CaF, + KF + Ag (weight ratio of 1: 1: 1). Such a target delivered a typical current of 1.6 p A @CaF- and at the same time a 41KF- yield of 3.6 nA (measured on a 90 o testbench) which is enough for slit stabilization of the tandem. For the production of the Mn beam a typical target mixture I. ADVANCES
IN AMS
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions
68
the dead line stripper had to be used in order to obtain these energies. The tandem voltage was stabilized with the slit currents behind the analysing magnet via the auxiliary beams 41K9+ and 53Mn13+, respectively. The ions were stripped to the charge states 16 + for 41Ca and 41K and to 19 + for 53Cr and 53Mn, postaccelerated by the two linear RF booster cavities [7] to an energy of 5.5 MeV/nucleon, analysed, stripped completely, analysed again and injected into the detection chamber, a Bragg-curve spectroscopy detector [17]. By the technique of complete stripping and subsequent magnetic analysis the auxiliary beams were suppressed to a degree that they did not disturb the detection of the ions 41CaZo+ and s3Mn2’+, respectively. Fig. 1. The modified high current sputter source with the sphericalionizer.
was: 20 mg (Mn,O,), 15 mg (Ag) and 0.22 mg (Cr,O,). Such a target delivers a 55MnO- yield of more than 1 PA. The 53CrO- beam is sufficient for the slit stabilization. 2.2. Beam line system The beam line and analysing system is shown in fig. 2. The ions, 41CaF-, 41KF- and 53CrO-, 53Mn0respectively were injected into the tandem and accelerated to an energy of 2.4 MeV/nucleon. Because of the low tandem voltage during these runs. in the case of Mn
2.3. Calibration standards The calibration standard 41Ca was produced by irradiation of an enriched 40Ca target with thermal neutrons in the Munich research reactor. The neutron dose was determined by means of gold foils. Calibration standards with concentrations for 41Ca/Ca of 0.95 X 10e9 and 0.88 x lo-” were produced. The calibration standard 53Mn was produced through the reaction “Al( 28Si, 2p)53Mn by the irradiation of an aluminum target with 28Si ions from the Munich MP tandem. By calculating the production rate for 53Mn and adding 55Mn we have achieved after chemistry a calibration sample with a concentration of 53Mn/55Mn = 1.3 x 10e9. As this target-projectile combination
133 MeV
103MeV LlK9’,LlC,9’
dead
line
termanal
strlpperiused
for 53Mnl
stripper
MP-TANDEM 10 m
IOIl source
L, KFm,L’C,F53Cr0-,
Fig. 2. The beam
line and analysing
53Mr,0-
system.
The AMS ions and the corresponding experiments.
pilot ions are indicated
as used during
these
69
G. Korschinek et al. / AMS with compleiely stripped 4’Ca and 53Mn ions does not yield s4Mn, we are able to determine an accurate concentration by neutron activation analysis. This measurement is presently done. For the production of stronger standards the reaction 54Fe(p, 2~)~~Mn was used. The proton beam was delivered by the Munich AEG-compact cyclotron, the target enrichment was 99%. The final concentration of the standard was 53Mn/ 55Mn = 2 x lo-‘.
3. Measurements 3.1. Probabilities for complete stripping For the production of completely stripped ions, a 120 pg/cm*, carbon foil was used in the symmetry plane of the achromatic analysing system behind the postaccelerator. At beam energies of 5.5 MeV/nucleon, the probability for complete stripping was 5.7 X lo-’ for 41Ca20+ and 9 X 10e4 for 53Mn25+. At a beam energy of 4.3 MeV/nucleon only 1.3% of the 41Ca ions were completely stripped. These values together with measurements obtained in Munich for Cl”+ ions at 4.3 MeV/nucleon [14] and 2.6 MeV/nucleon [15] and in Argonne for Cl”+, CaZo+, Co2’+ and Ni2*+ ions are shown in fig. 3. The values are plotted versus (Uion/uea)2
=
=
0.L
0.5
0.6 0.7 0.6
E,,,/A[MeVlnucleonl 22 xLo,L
Fig. 3. The probability for bare stripped ions plotted versus 40.4(E,,/A)/Z2. The values are experimentalresults, marked by A (Argonne data [16]) and M (own Munich data).
(Eion/Mion)/(EeK/Me)
EiO,,/A [ MeV/nucleon]
x 40.4
22
with ion velocity, classical velocity of the electron in K shell, mass of the ion, m ion mass of electron, m, E&A MeV/nucleon. All measured values can be described by one functional dependence of ( E,,/A)/Z2. “ion
V
0.3
=K
3.2. Measured samples and discussion 41Ca was measured in a sample of the iron meteorite Boxbole and in a sample from the surface of a granite stone exposed to the Hiroshima A-bomb at a distance of 107 m to the hypocenter. The aim of the last measurement is the determination of the RBE factor (Relative Biological Effectiveness) for fast neutrons. Measurements for the determination of the 36Cl/C1 concentration in this granite stone performed at different depths were reported in an earlier paper [l]. In these first 41Ca measurements, only 4 and 34 events were detected, respectively. The corresponding ratios of 41Ca/ 40Ca are: Boxhole: (1 + 0.6) x 10-12, (5.3 f 1.4) X 10-12. Hiroshima:
With the known ratio of Ca/(Fe + Co + Ni) in the meteorite a value 41Ca/(Fe + Co + Ni) = (1.5 f 0.8) x lo-l4 was deduced. This corresponds to an activity of 2.1 + 1.3 dpm/kg of Fe, Co, Ni. 53Mn was measured in a sample from the meteorite Jilin and in a beam dump sample from the 600 MeV proton synchrocyclotron in CERN. On the basis of our preliminary determined concentration of 53Mn/Mn = 1.3 x 10e9, the following ratios of 53Mn/Mn were deduced: J&n VI: (9 + 3) x lo-to, (8 & 3) x 10e9. Beam dump: For the Jilin VI sample, an activity of about 780 dpm/kg of Fe, Co, Ni was derived. A preliminary 54Mn analysis for the SC beam dump gives a ratio of 53Mn/54Mn of about 4. Fig. 4 shows the measured 41Ca spectrum for the Hiroshima sample and a blank, and fig. 5 shows the 53Mn spectrum for the beam dump. The 41Ca/40Ca ratio measured in the grave stone is higher than that calculated from a 36Cl/Cl determination by multiplying the 36C1/35Cl value of (1.5 + 0.2) x lo-” [l] with the ratio of the cross sections for thermal neutron capture, a(40Ca(n,,, v))/a(35Cl(n,,, y)) = l/108. This discrepancy reflects the fact that the granite was irradiated not only by thermal neutrons and that in the case of 40Ca which has a small cross section for thermal neutron capture compared to 35C1, the reacLADVANCESINAMS
70
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions
SC
beam dumo
41c,20+
. . 0
u
.
.
0.
.
. I
mewyE
.
Fig. 5. The 53Mn spectrum from the beam dump.
. .
....D.
I -
I
I
I
1 1. D
and also the tandem-postaccelerator system, the following limits are expected: 41Ca/Ca = lo-l4 and 53Mn/Mn = lo-‘*.
t 41&O+ /
4. Conclusions All values measured were obtained in first experiments and are not final results. The results for the meteorites are in the range expected from other measurements [9]. The 53Mn content in the beam dump sample was measured in the presence of 54Mn. 54Mn does not disturb the AMS measurement of 53Mn but would not allow a neutron activation analysis for 53Mn.
00000 0000 000~ 0
References
.
f energy
E -
Fig. 4. Measured 41Ca spectra: upper for a blank, lower for the Hiroshima sample. tions with higher energetic neutrons are more important than in the case of Cl. No background or cross talk events could be detected during the measurements. A strong proof was undertaken by running a lo-* (41Ca/Ca) calibration sample for 50 min and looking for 41Ca events (40 min) after replacing by a blank sample. No events were detected. The following detection limits, defined as one event detected per hour were obtained: 41Ca/Ca 53Mn/Mn
= 9 X 10-13, = 3 X 10-l’.
By optimizing the use of the stripping foils and the injector (presently is a 90 o injector under construction)
[l] G. Haberstcck, J. Heinzl, G. Korschinek, H. Morinaga, E. Nolte, U. Ratzinger, K. Kato and M. Wolf, Raclicarbon 28 (2A) (1986) 204. [2] G.M. R&beck and F. Yiou, Nature 277 (1979) 42. [3] P.W. Kubik, D. Elmore, N.J. Conard, K. Nishiizurni and J.R. Arnold, Nature 319 (1986) 568. [4] D. Fink, M. Paul, G. HOBOS,S. Theis, P. Englert, S. Vogt, P. Stueck and R. Michel, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hall, p. 183. (51 W. Henning, P.J. Billquist, B. Glagola, Z. Liu, H.F. Lucas, K.E. Rehm, J.L. Yntema, W. Kutschera, M. Paul, W.A. Bell, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hall, p. 127. [6] A. Steinhoff, W. Henning, M. Miiller, E. R&&l, D. S&till, G. Korschinek, E. Nolte and M. Paul, these Proceedings (AMS ‘87) Nucl. Instr. and Meth. B29 (1987) 59. [7] U. Ratzinger, Dissertation TU Munich (1986); U. Ratzinger, N. Gitner, R. Geier, E. Nolte and H. Morinaga to be published in IEEE Trans. Nucl. Sci. [8] H. Millard Jr., Science 147 (1965) 503.
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions [9] R. Michel,
P. Dragovitsch, P. Englert, F. Pfeiffer, R. Stuck, S. Theis, F. Begemann, H. Weber, P. Signer, R. Wieler, D. F&es and P. Cloth, Nucl. Instr. and Meth. B16 (1986) 61. [lo] A. Urban, Diplomthesis TU Munich (1986); G. Korschinek, J. Sehmair, A. Urban and M. MtiIler, Proc. Int. Conf. on Solar Neutrino Detection with 205Tl and Related Topics, Duprovnik (1986). [ll] A. Urban, G. Korschinek and E. Nolte, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hail, p. 108. [12] N.R. White, Proc. Symp. on AMS, Argonne (1981) ed., W. Kutschera, p. 373.
71
[13] R. Middleton, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hall, p. 82. [14] P.W. Kubik, G. Korschinek and E. Nolte, Nucl. Instr. and Meth. Bl (1984) 51. [15] H. Mtinzer, private communication. [16] W. Henning, W. Kutschera, B. Myslek-Lamikainen, R.C. Pardo, R.K. Smither and J.L. Yntema, Proc. Symp. on AMS, Argonne (1981) ed., W. Kutschera, p. 320. [17] Ch. Schiessl, W. Wagner, K. Hartel, H.J. Korner, W. Mayer and K.E. Rehm, Nucl. Instr. and Meth. 192 (1982) 291.
I. ADVANCES
IN AMS
in Physics
Research
ACCELERATOR MASS SPECTROMETRY WITH COMPLETELY IONS AT THE MUNICH TANDEM ACCELERATOR G. KORSCHINEK, and A. URBAN
H. MORINAGA,
67
B29 (1987) 67-71
E. NOLTE,
E. PREISENBERGER,
STRIPPED
4’Ca AND =Mn
U. RATZINGER
Fachbereich Physik, Technische Universitiit Miinchen, 8046 Garching, FRG
P. DRAGOVITSCH
and S. VOGT
Abtlg. Nuklearchemie am Institut ftirBiochemie der Universitiit Kiiln, 5000 Kiiln, FRG
Accelerator mass sepctrometry (AMS) experiments with completely stripped 41Ca and 53Mn ions have been performed at the Munich tandem laboratory. It is the first time that 53Mn has been detected by AMS. The necessary high beam energies of 5.5 MeV/nucleon were provided by the recently installed second linear postaccelerator cavity. Negative ion beams of CaF- and MnOin the CA range were provided by an improved Middleton high current source. Sensitivities of 41Ca/Ca = 9~ lo-l3 and of “Mn/Mn = 3 x lo-” were achieved. 41Ca was measured in samples from a meteorite and from Hiroshima granite exposed to the A-bomb, “Mn in samples from a meteorite and a CERN-SC beam dump.
1. Introduction Following our very good experiences with accelerator mass spectrometry with fully stripped 36C1 ions and the use of a macroscopic guide beam (here 36S) during the last years [l], we have undertaken first measurements with 41Ca and 53Mn, applying the same technique. 41Ca has been proposed for AMS dating by Raisbeck and Yiou [2]. They also proposed the elegant method of separating the interfering ion 41K by means of fully stripped ions where 41K’9+ and 41Ca20+ can be separated magnetically. 41Ca has been measured in meteorites [3,4] and natural samples of terrestrial origin [5,6]. Still measurements of 41Ca are not simple, which is mainly due to: (i) the low natural abundance of 41Ca; (ii) the low intensities for a Ca beam by using a tandem; (iii) the rather low efficiency for producing a Ca beam. Therefore, a successful measurement of 41Ca down to the natural level demands a suitable ion source with a high yield of Ca ions. In addition, using the method of totally stripped ions, sufficient beam energy is needed. For achieving a high yield we have studied a Middleton high current sputter source in order to optimize the ionizer-target geometry and to find the appropriate target material. The recently finished second stage of our postaccelerator [7] was used for the first time to increase the beam energy. 53Mn (Ti,* = 3.7 x lo6 yr) has been measured at first by Millard [8] by thermal neutron activation analyses. There was not much de0168-583X/87/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
mand till now for measuring 53Mn by AMS, as neutron activation analysis achieves already a sensitivity down to 10mi3. But neutron activation analysis is not possible in the presence of 54Mn ions as in the beam dump samples 191. Additionally in the course of improving our AMS system it seemed worthwhile to evaluate the feasibility of performing AMS measurements with bare stripped s3Mn ions.
2. Experimental setup and calibration standards
2.1. Ion source A very critical part for ams is the ion source, especially in the case of 41Ca where the production of a high yield is a difficult task. We have performed therefore a detailed study [lO,ll] for optimizing a Middleton high current sputter source. We followed similar ideas for optimizing the geometry as it is discussed in ref. [12] and shown in [11,13]. The result of our calculations can be seen in fig. 1. The main advantage is an improved optics for the primary Cs ions and the sputtered secondary negative ions. The best choice for the production of a Ca beam was a target mixture of CaF, + KF + Ag (weight ratio of 1: 1: 1). Such a target delivered a typical current of 1.6 p A @CaF- and at the same time a 41KF- yield of 3.6 nA (measured on a 90 o testbench) which is enough for slit stabilization of the tandem. For the production of the Mn beam a typical target mixture I. ADVANCES
IN AMS
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions
68
the dead line stripper had to be used in order to obtain these energies. The tandem voltage was stabilized with the slit currents behind the analysing magnet via the auxiliary beams 41K9+ and 53Mn13+, respectively. The ions were stripped to the charge states 16 + for 41Ca and 41K and to 19 + for 53Cr and 53Mn, postaccelerated by the two linear RF booster cavities [7] to an energy of 5.5 MeV/nucleon, analysed, stripped completely, analysed again and injected into the detection chamber, a Bragg-curve spectroscopy detector [17]. By the technique of complete stripping and subsequent magnetic analysis the auxiliary beams were suppressed to a degree that they did not disturb the detection of the ions 41CaZo+ and s3Mn2’+, respectively. Fig. 1. The modified high current sputter source with the sphericalionizer.
was: 20 mg (Mn,O,), 15 mg (Ag) and 0.22 mg (Cr,O,). Such a target delivers a 55MnO- yield of more than 1 PA. The 53CrO- beam is sufficient for the slit stabilization. 2.2. Beam line system The beam line and analysing system is shown in fig. 2. The ions, 41CaF-, 41KF- and 53CrO-, 53Mn0respectively were injected into the tandem and accelerated to an energy of 2.4 MeV/nucleon. Because of the low tandem voltage during these runs. in the case of Mn
2.3. Calibration standards The calibration standard 41Ca was produced by irradiation of an enriched 40Ca target with thermal neutrons in the Munich research reactor. The neutron dose was determined by means of gold foils. Calibration standards with concentrations for 41Ca/Ca of 0.95 X 10e9 and 0.88 x lo-” were produced. The calibration standard 53Mn was produced through the reaction “Al( 28Si, 2p)53Mn by the irradiation of an aluminum target with 28Si ions from the Munich MP tandem. By calculating the production rate for 53Mn and adding 55Mn we have achieved after chemistry a calibration sample with a concentration of 53Mn/55Mn = 1.3 x 10e9. As this target-projectile combination
133 MeV
103MeV LlK9’,LlC,9’
dead
line
termanal
strlpperiused
for 53Mnl
stripper
MP-TANDEM 10 m
IOIl source
L, KFm,L’C,F53Cr0-,
Fig. 2. The beam
line and analysing
53Mr,0-
system.
The AMS ions and the corresponding experiments.
pilot ions are indicated
as used during
these
69
G. Korschinek et al. / AMS with compleiely stripped 4’Ca and 53Mn ions does not yield s4Mn, we are able to determine an accurate concentration by neutron activation analysis. This measurement is presently done. For the production of stronger standards the reaction 54Fe(p, 2~)~~Mn was used. The proton beam was delivered by the Munich AEG-compact cyclotron, the target enrichment was 99%. The final concentration of the standard was 53Mn/ 55Mn = 2 x lo-‘.
3. Measurements 3.1. Probabilities for complete stripping For the production of completely stripped ions, a 120 pg/cm*, carbon foil was used in the symmetry plane of the achromatic analysing system behind the postaccelerator. At beam energies of 5.5 MeV/nucleon, the probability for complete stripping was 5.7 X lo-’ for 41Ca20+ and 9 X 10e4 for 53Mn25+. At a beam energy of 4.3 MeV/nucleon only 1.3% of the 41Ca ions were completely stripped. These values together with measurements obtained in Munich for Cl”+ ions at 4.3 MeV/nucleon [14] and 2.6 MeV/nucleon [15] and in Argonne for Cl”+, CaZo+, Co2’+ and Ni2*+ ions are shown in fig. 3. The values are plotted versus (Uion/uea)2
=
=
0.L
0.5
0.6 0.7 0.6
E,,,/A[MeVlnucleonl 22 xLo,L
Fig. 3. The probability for bare stripped ions plotted versus 40.4(E,,/A)/Z2. The values are experimentalresults, marked by A (Argonne data [16]) and M (own Munich data).
(Eion/Mion)/(EeK/Me)
EiO,,/A [ MeV/nucleon]
x 40.4
22
with ion velocity, classical velocity of the electron in K shell, mass of the ion, m ion mass of electron, m, E&A MeV/nucleon. All measured values can be described by one functional dependence of ( E,,/A)/Z2. “ion
V
0.3
=K
3.2. Measured samples and discussion 41Ca was measured in a sample of the iron meteorite Boxbole and in a sample from the surface of a granite stone exposed to the Hiroshima A-bomb at a distance of 107 m to the hypocenter. The aim of the last measurement is the determination of the RBE factor (Relative Biological Effectiveness) for fast neutrons. Measurements for the determination of the 36Cl/C1 concentration in this granite stone performed at different depths were reported in an earlier paper [l]. In these first 41Ca measurements, only 4 and 34 events were detected, respectively. The corresponding ratios of 41Ca/ 40Ca are: Boxhole: (1 + 0.6) x 10-12, (5.3 f 1.4) X 10-12. Hiroshima:
With the known ratio of Ca/(Fe + Co + Ni) in the meteorite a value 41Ca/(Fe + Co + Ni) = (1.5 f 0.8) x lo-l4 was deduced. This corresponds to an activity of 2.1 + 1.3 dpm/kg of Fe, Co, Ni. 53Mn was measured in a sample from the meteorite Jilin and in a beam dump sample from the 600 MeV proton synchrocyclotron in CERN. On the basis of our preliminary determined concentration of 53Mn/Mn = 1.3 x 10e9, the following ratios of 53Mn/Mn were deduced: J&n VI: (9 + 3) x lo-to, (8 & 3) x 10e9. Beam dump: For the Jilin VI sample, an activity of about 780 dpm/kg of Fe, Co, Ni was derived. A preliminary 54Mn analysis for the SC beam dump gives a ratio of 53Mn/54Mn of about 4. Fig. 4 shows the measured 41Ca spectrum for the Hiroshima sample and a blank, and fig. 5 shows the 53Mn spectrum for the beam dump. The 41Ca/40Ca ratio measured in the grave stone is higher than that calculated from a 36Cl/Cl determination by multiplying the 36C1/35Cl value of (1.5 + 0.2) x lo-” [l] with the ratio of the cross sections for thermal neutron capture, a(40Ca(n,,, v))/a(35Cl(n,,, y)) = l/108. This discrepancy reflects the fact that the granite was irradiated not only by thermal neutrons and that in the case of 40Ca which has a small cross section for thermal neutron capture compared to 35C1, the reacLADVANCESINAMS
70
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions
SC
beam dumo
41c,20+
. . 0
u
.
.
0.
.
. I
mewyE
.
Fig. 5. The 53Mn spectrum from the beam dump.
. .
....D.
I -
I
I
I
1 1. D
and also the tandem-postaccelerator system, the following limits are expected: 41Ca/Ca = lo-l4 and 53Mn/Mn = lo-‘*.
t 41&O+ /
4. Conclusions All values measured were obtained in first experiments and are not final results. The results for the meteorites are in the range expected from other measurements [9]. The 53Mn content in the beam dump sample was measured in the presence of 54Mn. 54Mn does not disturb the AMS measurement of 53Mn but would not allow a neutron activation analysis for 53Mn.
00000 0000 000~ 0
References
.
f energy
E -
Fig. 4. Measured 41Ca spectra: upper for a blank, lower for the Hiroshima sample. tions with higher energetic neutrons are more important than in the case of Cl. No background or cross talk events could be detected during the measurements. A strong proof was undertaken by running a lo-* (41Ca/Ca) calibration sample for 50 min and looking for 41Ca events (40 min) after replacing by a blank sample. No events were detected. The following detection limits, defined as one event detected per hour were obtained: 41Ca/Ca 53Mn/Mn
= 9 X 10-13, = 3 X 10-l’.
By optimizing the use of the stripping foils and the injector (presently is a 90 o injector under construction)
[l] G. Haberstcck, J. Heinzl, G. Korschinek, H. Morinaga, E. Nolte, U. Ratzinger, K. Kato and M. Wolf, Raclicarbon 28 (2A) (1986) 204. [2] G.M. R&beck and F. Yiou, Nature 277 (1979) 42. [3] P.W. Kubik, D. Elmore, N.J. Conard, K. Nishiizurni and J.R. Arnold, Nature 319 (1986) 568. [4] D. Fink, M. Paul, G. HOBOS,S. Theis, P. Englert, S. Vogt, P. Stueck and R. Michel, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hall, p. 183. (51 W. Henning, P.J. Billquist, B. Glagola, Z. Liu, H.F. Lucas, K.E. Rehm, J.L. Yntema, W. Kutschera, M. Paul, W.A. Bell, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hall, p. 127. [6] A. Steinhoff, W. Henning, M. Miiller, E. R&&l, D. S&till, G. Korschinek, E. Nolte and M. Paul, these Proceedings (AMS ‘87) Nucl. Instr. and Meth. B29 (1987) 59. [7] U. Ratzinger, Dissertation TU Munich (1986); U. Ratzinger, N. Gitner, R. Geier, E. Nolte and H. Morinaga to be published in IEEE Trans. Nucl. Sci. [8] H. Millard Jr., Science 147 (1965) 503.
G. Korschinek et al. / AMS with completely stripped 4’Ca and 53Mn ions [9] R. Michel,
P. Dragovitsch, P. Englert, F. Pfeiffer, R. Stuck, S. Theis, F. Begemann, H. Weber, P. Signer, R. Wieler, D. F&es and P. Cloth, Nucl. Instr. and Meth. B16 (1986) 61. [lo] A. Urban, Diplomthesis TU Munich (1986); G. Korschinek, J. Sehmair, A. Urban and M. MtiIler, Proc. Int. Conf. on Solar Neutrino Detection with 205Tl and Related Topics, Duprovnik (1986). [ll] A. Urban, G. Korschinek and E. Nolte, Proc. Workshop on Techniques in AMS, Oxford (1986) eds., R.E.M. Hedges and E.T. Hail, p. 108. [12] N.R. White, Proc. Symp. on AMS, Argonne (1981) ed., W. Kutschera, p. 373.
71
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I. ADVANCES
IN AMS