碳的同位素

**主要的碳同位素**
標準原子質量 (Ar, 標準)	[12.0096, 12.0116][1]; 傳統: 12.011;
←B（5）	N（7）→

碳（原子量：12.0107(8)）共有15個已知同位素，其中有2個（¹²C與¹³C）是穩定的，其他都具有放射性。¹⁴C是碳唯一的天然放射性同位素，在宇宙線作用下發生¹⁴N + ¹n → ¹⁴C + ¹H反應而產生，半衰期為5700年。

常見的碳同位素

碳-11是碳的一個放射性同位素，會衰變為硼-11，半衰期約20.334分鐘。絕大多數的碳-11會透過β⁺衰變衰變為硼-11，其過程會發射出正子，而有少部分的(約0.19–0.23%)的碳-11會透過電子捕獲衰變為硼-11[2][3]。

11
C → 11
B + e+
+ ν
e + 0.96 MeV

11
C + e−
→ 11
B + ν
e + 1.98 MeV

碳-11可以利用氮透過粒子加速器以下列反應制備：

14
N + p → 11
C + 4
He

正电子发射计算机断层扫描中的放射線標記分子通常會使用含有放射性碳同位素碳-11的放射性分子，例如[11
C]DASB[4]和[11
C]Cimbi-5[5][6]。

符號	Z（p ）	N（n ）	同位素質量（u）	半衰期	衰變方式[7]	衰變產物[n 1]	原子核自旋	相對豐度（莫耳分率）	相對豐度的變化量（莫耳分率）
⁸C	6	2	8.037675(25)	2.0(4) × 10⁻²¹ s [230(50) keV]	2p	6 Be[n 2]	0+
⁹C	6	3	9.0310367(23)	126.5(9) ms	β⁺ (60%)	9 B[n 3]	(3/2−)
					β⁺, p (23%)	8 Be[n 4]
					β⁺, α (17%)	5 Li[n 5]
¹⁰C	6	4	10.0168532(4)	19.290(12) s	β⁺	10 B	0+
11 C[n 6]	6	5	11.0114336(10)	20.334(24) min	β⁺ (99.79%)	11 B	3/2−
11 C[n 6]	6	5	11.0114336(10)	20.334(24) min	ε (.21%)[2][3]	11 B	3/2−
12 C	6	6	12 確定的整數[n 7]	稳定			0+	0.9893(8)	0.98853–0.99037
13 C[n 8]	6	7	13.0033548378(10)	穩定			1/2−	0.0107(8)	0.00963–0.01147
14 C[n 9]	6	8	14.003241989(4)	5,730 years	β⁻	14 N	0+	痕量[n 10]或天然放射性	<10⁻¹²
¹⁵C	6	9	15.0105993(9)	2.449(5) s	β⁻	15 N	1/2+
¹⁶C	6	10	16.014701(4)	0.747(8) s	β⁻, n (97.9%)	15 N	0+
¹⁶C	6	10	16.014701(4)	0.747(8) s	β⁻ (2.1%)	16 N	0+
¹⁷C	6	11	17.022586(19)	193(5) ms	β⁻ (71.59%)	17 N	(3/2+)
¹⁷C	6	11	17.022586(19)	193(5) ms	β⁻, n (28.41%)	16 N	(3/2+)
¹⁸C	6	12	18.02676(3)	92(2) ms	β⁻ (68.5%)	18 N	0+
¹⁸C	6	12	18.02676(3)	92(2) ms	β⁻, n (31.5%)	17 N	0+
¹⁹C[n 11]	6	13	19.03481(11)	46.2(23) ms	β⁻, n (47.0%)	18 N	(1/2+)
					β⁻ (46.0%)	19 N
					β⁻, 2n (7%)	17 N
²⁰C	6	14	20.04032(26)	16(3) ms [14(+6-5) ms]	β⁻, n (72.0%)	19 N	0+
²⁰C	6	14	20.04032(26)	16(3) ms [14(+6-5) ms]	β⁻ (28.0%)	20 N	0+
²¹C	6	15	21.04934(54)#	<30 ns	n	20 C	(1/2+)#
²²C[n 12]	6	16	22.05720(97)#	6.2(13) ms [6.1(+14-12) ms]	β⁻	22 N	0+

備註：畫上#號的數據代表沒有經過實驗的証明，只是理論推測而已，而用括號括起來的代表數據不確定性。

←	同位素列表	→
硼的同位素	碳的同位素	氮的同位素

Bold for stable isotopes
Subsequently decays by double proton emission to ⁴He for a net reaction of ⁸C -> ⁴He + 4¹H
Immediately decays by proton emission to ⁸Be, which immediately decays to two ⁴He atoms for a net reaction of ⁹C -> 2⁴He + ¹H + e⁺
Immediately decays into two ⁴He atoms for a net reaction of ⁹C -> 2⁴He + ¹H + e⁺
Immediately decays by proton emission to ⁴He for a net reaction of ⁹C -> 2⁴He + ¹H + e⁺
Used for labeling molecules in 正电子发射计算机断层扫描
The 原子质量单位 is defined as 1/12 the mass of an unbound atom of carbon-12 at ground state
Ratio of ¹²C to ¹³C used to measure biological productivity in ancient times and differing types of 光合作用
Has an important use in 放射性定年法 (see 放射性碳定年法)
Primarily cosmogenic, produced by 中子s striking atoms of ¹⁴N (¹⁴N + ¹n -> ¹⁴C + ¹H)
Has 1 halo neutron
Has 2 halo neutrons

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