TY - JOUR
T1 - 41Ca in iron falls, Grant and Estherville
T2 - production rates and related exposure age calculations
AU - Fink, D.
AU - Klein, J.
AU - Middleton, R.
AU - Vogt, S.
AU - Herzog, G. F.
N1 - Funding Information:
We thank J. Birck for permission to quote unpublished data, B. Zanda for releasing calculations prior to publication and Mr. Harry White for assistance in sample preparation and measurement on the accelerator. We also thank F. Bege-mann and two anonymous reviewers for their thorough and thoughtful comments. This work was supported in part by NASA grant 9-26 and we gratefully acknowledge the National Science Foundation for their continued support of our tandem accelerator facility at the University of Pennsylvania.
PY - 1991/10
Y1 - 1991/10
N2 - Recent technical developments in accelerator mass spectrometry have enabled us to measure routinely and with a precision of 5-7% the 41Ca (T 1 2 = 104 ky) contents of extraterrestrial samples weighing approximately 100 mg. In essence, these advances have elevated 41Ca to the role of a new and potent cosmogenic radioisotope with wide-ranging applications. We present here the results from the first phase of our 41Ca cosmogenic studies program, aimed at establishing baseline concentrations and trends in selected meteorites and the use of 41Ca in estimating exposure ages and pre-atmospheric meteorite radii. The average 41Ca saturation activity recorded in four small iron falls is 24 ± 1 dpm/kg. This result, together with measurements at the center and surface of the large iron Grant, indicates that production of 41Ca from spallation on iron is weakly dependent on shielding to depths as large as 250 g/cm2. We estimate the 41K41Ca exposure age of Grant to be 330 ± 50 My, and an upper limit to its terrestrial age of 43 ± 15 ky. A comparison of the 41Ca contents of stony and metallic material separated from the mesosiderite Estherville identifies low-energy neutron capture on native Ca as a second important channel of production. We find that the 41Ca signal in the stone phase from three meteorites correlates with their size, and that the inferred low-energy neutron fluxes vary by a factor of at least 20.
AB - Recent technical developments in accelerator mass spectrometry have enabled us to measure routinely and with a precision of 5-7% the 41Ca (T 1 2 = 104 ky) contents of extraterrestrial samples weighing approximately 100 mg. In essence, these advances have elevated 41Ca to the role of a new and potent cosmogenic radioisotope with wide-ranging applications. We present here the results from the first phase of our 41Ca cosmogenic studies program, aimed at establishing baseline concentrations and trends in selected meteorites and the use of 41Ca in estimating exposure ages and pre-atmospheric meteorite radii. The average 41Ca saturation activity recorded in four small iron falls is 24 ± 1 dpm/kg. This result, together with measurements at the center and surface of the large iron Grant, indicates that production of 41Ca from spallation on iron is weakly dependent on shielding to depths as large as 250 g/cm2. We estimate the 41K41Ca exposure age of Grant to be 330 ± 50 My, and an upper limit to its terrestrial age of 43 ± 15 ky. A comparison of the 41Ca contents of stony and metallic material separated from the mesosiderite Estherville identifies low-energy neutron capture on native Ca as a second important channel of production. We find that the 41Ca signal in the stone phase from three meteorites correlates with their size, and that the inferred low-energy neutron fluxes vary by a factor of at least 20.
UR - http://www.scopus.com/inward/record.url?scp=0026289949&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0026289949&partnerID=8YFLogxK
U2 - 10.1016/0012-821X(91)90048-M
DO - 10.1016/0012-821X(91)90048-M
M3 - Article
AN - SCOPUS:0026289949
SN - 0012-821X
VL - 107
SP - 115
EP - 128
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 1
ER -