Accounting for Overcounting Induced by 222Rn Contamination in 14C Measurements Performed with Liquid Scintillation Counting

Maksymilian Jędrzejowski; Danuta J. Michczyńska; Adam Michczyński; Marzena Kłusek; Konrad Tudyka

doi:10.2478/geochr-2023-0007

Figures & Tables

Alpha and beta particle spectra of radioactive nuclides in a Quantulus 1220™ liquid scintillation counter with counting windows used at the Gliwice Laboratory (Poland). In most cases, peak from 210Pb would not be observed in radiocarbon dating due to its low probability.

Counts spectra for the GdS-4657 sample with counting windows used at the Gliwice Laboratory.

Exponential function fitted into (A) – radon and daughter products window, (B) – combined 14C and radon and daughter products window. Fitted functions are shown with a 68.3% confidence band.

The results of the solved system of equations for the GdS-4657 sample. (A) – Equation corresponding to the radon and daughter products window. (B) – Equation corresponding to the combined 14C and radon and daughter products window. The fitted functions for both equations are shown with a 68.3% confidence band.

Evolution of determined count rate, with a χ2 value versus χcrit2 \chi _{crit}^2 at α = 0.05. Each data point represents a hypothetical scenario where measurements were terminated after a specific cycle, starting from the 10th cycle for the first point, the 11th cycle for the second point, the 12th cycle for the third point, and so on. (A) – Subtraction approach. (B) – System of equations approach.

Subsequent decays of the uranium series from 226Ra to 210Pb_

Parent isotope	Decay mode	Daughter isotope	Percentage of decay mode (%)	Half-life T_1/2	Weighted mean β⁻ decay energy, keV	Q value (max energy), keV	Major decay branches (>0.5%)

							Mean β⁻energy, keV	End-point energy, keV	Branching percentages (%)
¹⁴C	β⁻	¹⁴N	100	5700(30) year	49.47(10)	156.475(4)	49.47(10)	156.475(4)	100
²²⁶Ra	α	²²²Rn	100	1600(7) year	–	4870.62(25)	4601(1)	–	6.16(3)
²²⁶Ra	α	²²²Rn	100	1600(7) year	–	4870.62(25)	4784.34(25)	–	93.84(11)
²²²Rn	α	²¹⁸Po	100	3.8222(9) day	–	5590.4(3)	5489.48(30)	–	99.920(10)
²¹⁸Po	α	²¹⁴Pb	99.980(2)	3.097(12) min	–	6114.75(9)	6002.55(10)	–	99.9789(20)
²¹⁸Po	β⁻	²¹⁸At	0.020(2)	3.097(12) min	–	259(12)	–	–	–
²¹⁸At	α	²¹⁴Bi	99.95(5)	1.27(6) s	–	6876.1(26)	6654(5)	–	6.90(10)
²¹⁸At	α	²¹⁴Bi	99.95(5)	1.27(6) s	–	6876.1(26)	6693(3)	–	92.7(5)
²¹⁸At	β⁻	²¹⁸Rn	0.05(5)	1.27(6) s	–	2883(12)	–	–	–
²¹⁸Rn	α	²¹⁴Po	100	33.75(15) ms	–	7262.5(19)	7129.1(19)	–	99.870(4)
²¹⁴Pb	β⁻	²¹⁴Bi	100	27.06(7) min	224(5)	1018(11)	48.0(32)	179(11)	2.75(8)
							142.8(37)	484(11)	1.063(18)
							205.1(39)	666(11)	44.5(7)
							225.3(40)	723(11)	39.0(5)
							334.5(42)	1018(11)	12.7(9)

²¹⁴Bi	β⁻	²¹⁴Po	99.9790(13)	19.71(2) min	641(6)	3269(11)	161.4(38)	540(11)	0.542(22)
							247.8(40)	787(11)	1.28(4)
							260.5(41)	821(11)	2.78(6)
							317.8(42)	976(11)	0.563(16)
							351.8(42)	1065(11)	5.56(5)
							356.1(43)	1076(11)	0.866(12)
							384.7(43)	1150(11)	4.33(4)
							424.2(44)	1252(11)	2.459(15)
							426.7(44)	1258(11)	1.433(11)
							433.1(44)	1274(11)	1.192(21)
							474.5(44)	1379(11)	1.589(17)
							491.6(44)	1422(11)	8.16(5)
							524.9(43)	1504(11)	16.90(11)
							539.0(45)	1539(11)	17.55(10)
							566.8(45)	1608(11)	0.57(5)
							614.9(46)	1726(11)	3.09(4)
							667.6(46)	1854(11)	0.90(5)
							683.3(46)	1891(11)	7.22(8)
							1007.1(47)	2660(11)	0.55(8)
							1268.4(48)	3269(11)	19.2(4)
²¹⁴Bi	α	²¹⁰Tl	0.0210(13)	19.9(4) min	–	5621(3)	5273(9)	–	5.8(5) ^a
							5452(3)		54(4) ^a
							5516(3)		39(3) ^a
²¹⁴Po	α	²¹⁰Pb	100	163.6(3) µs	–	7833.46(6)	7686.82(7)	–	99.9895(6)
²¹⁰Tl	β⁻	²¹⁰Pb	100	1.30(3) min	1.18(16)∙10³	5482(12)	477(13)	1380(30)	2.0(10)
							568(14)	1600(30)	7.0(20)
							674(10)	1860(24)	24(5)
							743(11)	2020(30)	10(3)
							877.1(69)	2413(17)	10(3)
							1635(18)	4210(40)	30(6)
							1762.6(54)	4386(12)	20.0(20)

²¹⁰Pb	β⁻	²¹⁰Bi	100	22.20(22) year	6.1(6)	63.5(5)	4.16(13)	17.0(5)	84(3)
²¹⁰Pb	β⁻	²¹⁰Bi	100	22.20(22) year	6.1(6)	63.5(5)	16.16(13)	63.5(5)	16(3)
²¹⁰Pb	α	²⁰⁶Hg	1.9(3)∙10⁻⁶	22.20(22) year	–	3792(20)	3720(20)	–	–

The measurement results for sample without correction, with both methods of exponential corrections, and after aging process_

Sample ID	as+bC, min-1 ⋅ g-1 {\boldsymbol {a}}_{\boldsymbol {s + b}}^\boldsymbol {C}\boldsymbol {,}\,{{\bf{min}}^{{\bf{ - 1}}}}\,{\bf{ \cdot }}\,{{\bf{g}}^{{\bf{ - 1}}}}	SQP(E)	F¹⁴C	Radiocarbon age, ¹⁴C year
GdS-4657	6.420(18)	806.35(30)	0.8318(45)	1480(43)
Immediate, without correction	6.420(18)	806.35(30)	0.8318(45)	1480(43)
GdS-4657	6.272(55)	806.35(30)	0.8120(79)	1673(78)
Exponential correction
Subtraction approach
GdS-4657	6.275(24)	806.35(30)	0.8124(48)	1669(48)
Exponential correction
System of equations approach
GdS-4684	6.345(31)	809.89(44)	0.8115(54)	1678(53)
After aging process	6.345(31)	809.89(44)	0.8115(54)	1678(53)

Accounting for Overcounting Induced by 222Rn Contamination in 14C Measurements Performed with Liquid Scintillation Counting

Figures & Tables

Fig 1.

Fig 2.

Fig 3.

Fig 4.

Fig 5.

Subsequent decays of the uranium series from 226Ra to 210Pb_

The measurement results for sample without correction, with both methods of exponential corrections, and after aging process_

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