Isotopes of neptunium (₉₃Np)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 235Np synth 396.1 d α 231Pa ε 235U 236Np synth 1.54×105 y ε 236U β− 236Pu α 232Pa 237Np trace 2.144×106 y α 233Pa 239Np trace 2.356 d β− 239Pu

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Neptunium (₉₃Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be synthesized and identified was ²³⁹Np in 1940, produced by bombarding ²³⁸
U
with neutrons to produce ²³⁹
U
, which then underwent beta decay to ²³⁹
Np
.

Trace quantities are found in nature from neutron capture reactions by uranium atoms, a fact not discovered until 1951.^[2]

Twenty-five neptunium radioisotopes have been characterized, with the most stable being ²³⁷
Np
with a half-life of 2.14 million years, ²³⁶
Np
with a half-life of 154,000 years, and ²³⁵
Np
with a half-life of 396.1 days. All of the remaining radioactive isotopes have half-lives that are less than 4.5 days, and the majority of these have half-lives that are less than 50 minutes. This element also has five meta states, with the most stable being ^236m
Np
(t_1/2 22.5 hours).

The isotopes of neptunium range from ²¹⁹
Np
to ²⁴⁴
Np
, though the intermediate isotope ²²¹
Np
has not yet been observed. The primary decay mode before the most stable isotope, ²³⁷
Np
, is electron capture (with a good deal of alpha emission), and the primary mode after is beta emission. The primary decay products before ²³⁷
Np
are isotopes of uranium and protactinium, and the primary products after are isotopes of plutonium. Neptunium is the heaviest element for which the location of the proton drip line is known; the lightest bound isotope is ²²⁰Np.^[3]

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[4] [n 2][n 3]	Half-life	Decay mode [n 4]	Daughter isotope [n 5]	Spin and parity [n 6][n 7]	Isotopic abundance
	Excitation energy[n 7]
219 Np [5][n 8]	93	126	219.03162(9)	0.15+0.72 −0.07 ms	α	215Pa	(9/2−)
220 Np [3]	93	127	220.03254(21)#	25+14 −7 μs	α	216Pa	1−#
222 Np [6]	93	129		380+260 −110 ns	α	218Pa	1-#
223 Np [7]	93	130	223.03285(21)#	2.15+100 −52 μs	α	219Pa	9/2−
224 Np [8]	93	131	224.03422(21)#	38+26 −11 μs	α (83%)	220m1Pa	1−#
					α (17%)	220m2Pa
225 Np	93	132	225.03391(8)	6(5) ms	α	221Pa	9/2−#
226 Np	93	133	226.03515(10)#	35(10) ms	α	222Pa
227 Np	93	134	227.03496(8)	510(60) ms	α (99.95%)	223Pa	5/2−#
					β+ (.05%)	227U
228 Np	93	135	228.03618(21)#	61.4(14) s	β+ (59%)	228U
					α (41%)	224Pa
					β+, SF (.012%)	(various)
229 Np	93	136	229.03626(9)	4.0(2) min	α (51%)	225Pa	5/2+#
					β+ (49%)	229U
230 Np	93	137	230.03783(6)	4.6(3) min	β+ (97%)	230U
					α (3%)	226Pa
231 Np	93	138	231.03825(5)	48.8(2) min	β+ (98%)	231U	(5/2)(+#)
					α (2%)	227Pa
232 Np	93	139	232.04011(11)#	14.7(3) min	β+ (99.99%)	232U	(4+)
					α (.003%)	228Pa
233 Np	93	140	233.04074(5)	36.2(1) min	β+ (99.99%)	233U	(5/2+)
					α (.001%)	229Pa
234 Np	93	141	234.042895(9)	4.4(1) d	β+	234U	(0+)
234m Np				~9 min[9]	IT	234Np	5+
					EC	234U
235 Np	93	142	235.0440633(21)	396.1(12) d	EC	235U	5/2+
					α (.0026%)	231Pa
236 Np [n 9]	93	143	236.04657(5)	1.54(6)×105 y	EC (87.3%)	236U	(6−)
					β− (12.5%)	236Pu
					α (.16%)	232Pa
236m Np	60(50) keV			22.5(4) h	EC (52%)	236U	1
					β− (48%)	236Pu
237 Np [n 10]	93	144	237.0481734(20)	2.144(7)×106 y	α	233Pa	5/2+	Trace[n 11]
					SF (2×10−10%)	(various)
					CD (4×10−12%)	207Tl 30Mg
238 Np	93	145	238.0509464(20)	2.117(2) d	β−	238Pu	2+
238m Np	2300(200)# keV			112(39) ns
239 Np	93	146	239.0529390(22)	2.356(3) d	β−	239Pu	5/2+	Trace[n 11]
240 Np	93	147	240.056162(16)	61.9(2) min	β−	240Pu	(5+)	Trace[n 12]
240m Np	20(15) keV			7.22(2) min	β− (99.89%)	240Pu	1(+)
					IT (.11%)	240Np
241 Np	93	148	241.05825(8)	13.9(2) min	β−	241Pu	(5/2+)
242 Np	93	149	242.06164(21)	2.2(2) min	β−	242Pu	(1+)
242m Np	0(50)# keV			5.5(1) min			6+#
243 Np	93	150	243.06428(3)#	1.85(15) min	β−	243Pu	(5/2−)
244 Np	93	151	244.06785(32)#	2.29(16) min	β−	244Pu	(7−)
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Zdroj:https://en.wikipedia.org?pojem=Neptunium-235
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