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Precision measurements of γ-rays in the decay of 161Tb
512
Nuclear Instruments and Methods in Physics Research 227 (1984) 512-514 North-Holland, Amsterdam
PRECISION MEASUREMENTS OF -y-RAYS IN THE DECAY OF
161
Tb §
G. DE CHAMBRIER, B . AAS, W. BEER, I . BELTRAMI, Th . v. LEDEBUR, H.J . LEISI, W. RUCKSTUHL, G. STRASSNER and A . VACCHI Institut fur Milherenergiephysek der ETHZ, c/o SIN, CH-5234 Villigen, Switzerland
U. KIEBELE and R. WEBER Physikdepartement der Universitat Fribourg, CH-1700 Fribourg, Switzerland
Received 10 May 1984 We have measured the transition wavelengths of the 74 .6 keV, 48 .9 keV and 25 .7 keV -y-lines in the 1`Tb decay with a curved-crystal spectrometer. The precision reached are 1 .7 ppm, 1 .7 ppm and 6 .8 ppm, respectively .
1. Introduction The wavelengths of a number of y-rays (and electronic X-rays) have been related to the optical wavelength standard in a program carried out at the US National Bureau of Standards (NBS) during the past ten years [1]. As a result of this work a set of y-ray standards in the energy range E > 63 keV (169Yb) is now available whose wavelengths are known to about 1 ppm. These standards are widely used in all fields of precision spectroscopy . In particular, they form the basis for the precision measurement of muonic and pionic X-rays being done at SIN with curved-crystal spectrometers [2,3]. In the course of our experiments with muonic and pionic X-rays it became necessary to extend the calibration region towards smaller energies . An interesting way to achieve this is to measure the y-rays of 48 .9 and 25 .7 keV in the decay of "' Tb because they have an intense cross-over transition of 74.6 keV which is inside the NBS calibration region . We report here on the results of these y-ray measurements. The precise knowledge of the three -y-lines in '6'Tb should serve a useful purpose in many fields of -y-ray precision spectroscopy ** .
[2]. The spectrometer was operated in the continuous scanning mode [4]. The Tb -y-ray measurements were performed following the muonic X-ray experiments described to ref. [5]. The experimental set-up was kept exactly the same . The experimental details (crystals, detectors etc.) are described in ref. [5]. The wavelength reference for this work is the '7° Tm -y-line of 84 .3 keV measured in runs 27 and 28 of ref. [5]. The Tb y-lines (as well as the Tin line) were measured with the "shadow" technique [2]. An extended 16'Tb source (10 mm high) was placed 65 cm behind the focal position of the instrument. A cylindrical wire of jewelry silver (80% silver and 20% copper), flattened to about 0.25 mm, served as an absorber at the focal position . The absorbers for the Tb measurements and the Tm (reference) measurement were displaced by about 2 mm, giving rise to a small "zero-angle correction" [2]. The Tb-lines were analysed by fits of Gaussian func-
2. Experimental procedure The measurements were carried out with the curvedcrystal spectrometer designed for muonic X-ray work § Thus work is supported in part by SIN. ** In crystal-spectrometer experiments electronic X-rays are generally not suitable as calibration lines because of their large natural width. 0168-9002/84/$03 .00 © Elsevier Science Publishers B.V . (North-Holland Physics Publishing Division)
Fig. 1 . Angular spectrum of crystal 1 for 48 .9 keV transition as a function of the interferometer reading R (in optical units) . Lines at positive and negative Bragg angle are shown.
of
G. de Chambrier et al. / Precision measurements tions to the angular spectra, including parameters to
t 6t Tb y-rays
513
Bragg angles were allowed to be different. This data
Table 2 Wavelengths of the three -y-lines m 161Tó, in pin. The entries for the two crystals contain the statistal errors ; the average values are with total errors .
of-gravity method which has a firm basis theoretically
Energy (keV)
Crystal l (pin)
75 49 26
16 .627338(23) 16.627347(25) 16.627342(29) 1.7 25 .346772(33) 25 .346762(36) 25 .346767(43) 1.7 48 .334135(61) 48.334317(68) 48 .33422(33) 6.8
account for a linearly sloping background (see fig. 1) .
The line width and -intensity for positive and negative
analysis procedure was compared in detail to the center[2,5]. The two methods are found to agree within 0.7 ppm. More
details on
the experment and the data
analysis can be found in ref. [6].
3. Results The difference between the position of the diffrac-
Crystal 2 (pin)
Error
(Pp-)
Table 3 Energies (without recoil corrections) of the three -y-lines of t61-1-ó, in eV.
tion peaks for positive and negative Bragg angle (twice
the "T-value") is proportional to the transition wavelength . The T-values together with their statistical errors are given in table 1 for both bent crystals used in the
Average
Error (ppm)
Ref.
75 keV
74567.06(23) 74577(9)
3.1 121
this work ref. [7]
experiment . With the measured wavelength of the Tm line [1] *,
49 keV
48915.59(15) 48918(4)
3.1 82
this work ref. [7]
A84= 14 .715430(13) pin,
26 keV
25 651.64(19) 25 655(3)
7.3 117
this work ref. [7]
the wavelengths of the three Tb lines can be derived from the corresponding T-value ratios from table 1 . Applying a zero-angle correction of +0 .6(2) ppm we obtain the wavelength values of table 2.
In order to check the cross-over relation between the
three Tb energies we define D = E26+E49 - E-t5*
(2)
Taking into account experimental uncertainties in addition to statistics we find D = 0.17 +_ 0.11 eV . A non-zero
value for D could arise experimentally because of the different focal distances used for the three y-ray energies : Slightly different crystal areas with small local differences in crystal properties are exposed to the three Table 1 T-values (defined to be half the distance between the positions of the right and the left diffraction peak) in optical units [2]. Statistical errors are given. Isotope 161Tb
170T
m
y-transition [keV]
Crystal l
Crystal 2
74 .6 48 .9 25 .7 25 .7 at
638423 .46(52) 973 214.96(58) 1855 838.1(11) 1855 837.2(32)
638414 .45(53) 973 200.30(67) 1855 817.4(13) 1855 821.2(37)
b)
565 014.16(65)
565005.88(70)
84 .3
at From run 28 of ref. [5]. b) From runs 27 and 28 of ref. [5].
* Part of the NBS -y-ray calibration procedure has been repeated by Becker et al. [8]. There appears to be a significant difference between the two measurements of 1.5±0 .5 ppm [9] which is further investigated by the NBS group.
-y-rays, due to the lamella structure in the collimator
tube [5]. We therefore add an additional uncertainty of 0.17 eV to the 26 keV transition . The errors quoted in table 2 contain, apart from statistics, uncertainties due to the error in eq . (1) (0 .9 ppm), temperature instabili ties (0 .8 ppm) and the line-position analysis (0.7 ppm) . With the energy-wavelength conversion factor [1], 1 .2398520(32) x 10 -6 eV - m, we obtain from table 2 the transition energies listed in table 3.
For relative calibration purposes the uncertainties are considerably lower than those given in table 3. The errors assigned to the conversion factor (3) and to the Tin wavelength eqs. (1) can be removed. This is equivalent to removing quadractically the 0.9 ppm uncertainty of eq . (1) from the errors given in table 2.
References [1] R.D . Deslattes, E.G . Kessler, W.C . Sauder and A. Henins, Ann. Phys . (NY) 129 (1980) 378; E.G . Kessler, Jr, R.D. Deslattes, D. Girard, W. Schwitz, L. Jacobs and O. Renner, Phys . Rev. A26 (1982) 2696 . [2] B. Aas, W. Beer, I. Beltrami, P. Ebersold, R. Eichler, Th . v. Ledebur, H.J. Leisi, W. Ruckstuhl, W.W . Sapp, A. Vacchi, J. Kern, J.-A. Pinston, W. Schwitz and R. Weber, Nucl . Phys . A375 (1982) 405. [3] W. Ruckstuhl, B. Aas, W. Beer, I. Beltrami, F.W .N . de Boer, K. Bos, P.F .A . Goudsmit, U. Kiebele, H.J . Leist, G. Strassner, A. Vacchi and R. Weber, Phys. Rev. Lett . 49 (1982) 859.
514
G. de Chambrier et al / Precision measurements of "'Tb y-rays
[4] W. Beer, Th . v. Ledebur and W. Schops, Nucl . Instr. and Meth . 156 (1978) 493. [5] 1 . Beltrami et al ., to be published. [61 1. Beltrami, LHE-report, ETH Zürich (1982) unpublished . [7] Table of isotopes, 7th ed ., eds., C.M . Lederer and V.S . Shirley (Wiley, New York, 1978) .
[81 P. Becker, K. Dorenwendt, G. Ebelmg, R. Laner, W. Lucas, R. Probst, H.-J. Rademacher, G. Reim, P. Syfned and H. Siegert, Phys . Rev. Lett . 46 (1981) 1540 ; P, Becker, P. Seyfried and H. Siegert, Z. Physik B48 (1982) 17 . [9] R.D . Deslattes, private communication (1983) .
Nuclear Instruments and Methods in Physics Research 227 (1984) 512-514 North-Holland, Amsterdam
PRECISION MEASUREMENTS OF -y-RAYS IN THE DECAY OF
161
Tb §
G. DE CHAMBRIER, B . AAS, W. BEER, I . BELTRAMI, Th . v. LEDEBUR, H.J . LEISI, W. RUCKSTUHL, G. STRASSNER and A . VACCHI Institut fur Milherenergiephysek der ETHZ, c/o SIN, CH-5234 Villigen, Switzerland
U. KIEBELE and R. WEBER Physikdepartement der Universitat Fribourg, CH-1700 Fribourg, Switzerland
Received 10 May 1984 We have measured the transition wavelengths of the 74 .6 keV, 48 .9 keV and 25 .7 keV -y-lines in the 1`Tb decay with a curved-crystal spectrometer. The precision reached are 1 .7 ppm, 1 .7 ppm and 6 .8 ppm, respectively .
1. Introduction The wavelengths of a number of y-rays (and electronic X-rays) have been related to the optical wavelength standard in a program carried out at the US National Bureau of Standards (NBS) during the past ten years [1]. As a result of this work a set of y-ray standards in the energy range E > 63 keV (169Yb) is now available whose wavelengths are known to about 1 ppm. These standards are widely used in all fields of precision spectroscopy . In particular, they form the basis for the precision measurement of muonic and pionic X-rays being done at SIN with curved-crystal spectrometers [2,3]. In the course of our experiments with muonic and pionic X-rays it became necessary to extend the calibration region towards smaller energies . An interesting way to achieve this is to measure the y-rays of 48 .9 and 25 .7 keV in the decay of "' Tb because they have an intense cross-over transition of 74.6 keV which is inside the NBS calibration region . We report here on the results of these y-ray measurements. The precise knowledge of the three -y-lines in '6'Tb should serve a useful purpose in many fields of -y-ray precision spectroscopy ** .
[2]. The spectrometer was operated in the continuous scanning mode [4]. The Tb -y-ray measurements were performed following the muonic X-ray experiments described to ref. [5]. The experimental set-up was kept exactly the same . The experimental details (crystals, detectors etc.) are described in ref. [5]. The wavelength reference for this work is the '7° Tm -y-line of 84 .3 keV measured in runs 27 and 28 of ref. [5]. The Tb y-lines (as well as the Tin line) were measured with the "shadow" technique [2]. An extended 16'Tb source (10 mm high) was placed 65 cm behind the focal position of the instrument. A cylindrical wire of jewelry silver (80% silver and 20% copper), flattened to about 0.25 mm, served as an absorber at the focal position . The absorbers for the Tb measurements and the Tm (reference) measurement were displaced by about 2 mm, giving rise to a small "zero-angle correction" [2]. The Tb-lines were analysed by fits of Gaussian func-
2. Experimental procedure The measurements were carried out with the curvedcrystal spectrometer designed for muonic X-ray work § Thus work is supported in part by SIN. ** In crystal-spectrometer experiments electronic X-rays are generally not suitable as calibration lines because of their large natural width. 0168-9002/84/$03 .00 © Elsevier Science Publishers B.V . (North-Holland Physics Publishing Division)
Fig. 1 . Angular spectrum of crystal 1 for 48 .9 keV transition as a function of the interferometer reading R (in optical units) . Lines at positive and negative Bragg angle are shown.
of
G. de Chambrier et al. / Precision measurements tions to the angular spectra, including parameters to
t 6t Tb y-rays
513
Bragg angles were allowed to be different. This data
Table 2 Wavelengths of the three -y-lines m 161Tó, in pin. The entries for the two crystals contain the statistal errors ; the average values are with total errors .
of-gravity method which has a firm basis theoretically
Energy (keV)
Crystal l (pin)
75 49 26
16 .627338(23) 16.627347(25) 16.627342(29) 1.7 25 .346772(33) 25 .346762(36) 25 .346767(43) 1.7 48 .334135(61) 48.334317(68) 48 .33422(33) 6.8
account for a linearly sloping background (see fig. 1) .
The line width and -intensity for positive and negative
analysis procedure was compared in detail to the center[2,5]. The two methods are found to agree within 0.7 ppm. More
details on
the experment and the data
analysis can be found in ref. [6].
3. Results The difference between the position of the diffrac-
Crystal 2 (pin)
Error
(Pp-)
Table 3 Energies (without recoil corrections) of the three -y-lines of t61-1-ó, in eV.
tion peaks for positive and negative Bragg angle (twice
the "T-value") is proportional to the transition wavelength . The T-values together with their statistical errors are given in table 1 for both bent crystals used in the
Average
Error (ppm)
Ref.
75 keV
74567.06(23) 74577(9)
3.1 121
this work ref. [7]
experiment . With the measured wavelength of the Tm line [1] *,
49 keV
48915.59(15) 48918(4)
3.1 82
this work ref. [7]
A84= 14 .715430(13) pin,
26 keV
25 651.64(19) 25 655(3)
7.3 117
this work ref. [7]
the wavelengths of the three Tb lines can be derived from the corresponding T-value ratios from table 1 . Applying a zero-angle correction of +0 .6(2) ppm we obtain the wavelength values of table 2.
In order to check the cross-over relation between the
three Tb energies we define D = E26+E49 - E-t5*
(2)
Taking into account experimental uncertainties in addition to statistics we find D = 0.17 +_ 0.11 eV . A non-zero
value for D could arise experimentally because of the different focal distances used for the three y-ray energies : Slightly different crystal areas with small local differences in crystal properties are exposed to the three Table 1 T-values (defined to be half the distance between the positions of the right and the left diffraction peak) in optical units [2]. Statistical errors are given. Isotope 161Tb
170T
m
y-transition [keV]
Crystal l
Crystal 2
74 .6 48 .9 25 .7 25 .7 at
638423 .46(52) 973 214.96(58) 1855 838.1(11) 1855 837.2(32)
638414 .45(53) 973 200.30(67) 1855 817.4(13) 1855 821.2(37)
b)
565 014.16(65)
565005.88(70)
84 .3
at From run 28 of ref. [5]. b) From runs 27 and 28 of ref. [5].
* Part of the NBS -y-ray calibration procedure has been repeated by Becker et al. [8]. There appears to be a significant difference between the two measurements of 1.5±0 .5 ppm [9] which is further investigated by the NBS group.
-y-rays, due to the lamella structure in the collimator
tube [5]. We therefore add an additional uncertainty of 0.17 eV to the 26 keV transition . The errors quoted in table 2 contain, apart from statistics, uncertainties due to the error in eq . (1) (0 .9 ppm), temperature instabili ties (0 .8 ppm) and the line-position analysis (0.7 ppm) . With the energy-wavelength conversion factor [1], 1 .2398520(32) x 10 -6 eV - m, we obtain from table 2 the transition energies listed in table 3.
For relative calibration purposes the uncertainties are considerably lower than those given in table 3. The errors assigned to the conversion factor (3) and to the Tin wavelength eqs. (1) can be removed. This is equivalent to removing quadractically the 0.9 ppm uncertainty of eq . (1) from the errors given in table 2.
References [1] R.D . Deslattes, E.G . Kessler, W.C . Sauder and A. Henins, Ann. Phys . (NY) 129 (1980) 378; E.G . Kessler, Jr, R.D. Deslattes, D. Girard, W. Schwitz, L. Jacobs and O. Renner, Phys . Rev. A26 (1982) 2696 . [2] B. Aas, W. Beer, I. Beltrami, P. Ebersold, R. Eichler, Th . v. Ledebur, H.J. Leisi, W. Ruckstuhl, W.W . Sapp, A. Vacchi, J. Kern, J.-A. Pinston, W. Schwitz and R. Weber, Nucl . Phys . A375 (1982) 405. [3] W. Ruckstuhl, B. Aas, W. Beer, I. Beltrami, F.W .N . de Boer, K. Bos, P.F .A . Goudsmit, U. Kiebele, H.J . Leist, G. Strassner, A. Vacchi and R. Weber, Phys. Rev. Lett . 49 (1982) 859.
514
G. de Chambrier et al / Precision measurements of "'Tb y-rays
[4] W. Beer, Th . v. Ledebur and W. Schops, Nucl . Instr. and Meth . 156 (1978) 493. [5] 1 . Beltrami et al ., to be published. [61 1. Beltrami, LHE-report, ETH Zürich (1982) unpublished . [7] Table of isotopes, 7th ed ., eds., C.M . Lederer and V.S . Shirley (Wiley, New York, 1978) .
[81 P. Becker, K. Dorenwendt, G. Ebelmg, R. Laner, W. Lucas, R. Probst, H.-J. Rademacher, G. Reim, P. Syfned and H. Siegert, Phys . Rev. Lett . 46 (1981) 1540 ; P, Becker, P. Seyfried and H. Siegert, Z. Physik B48 (1982) 17 . [9] R.D . Deslattes, private communication (1983) .