Isotopes of neptunium: Difference between revisions

Content deleted Content added

Inline

Revision as of 12:24, 18 May 2011

Neptunium (Np) has no stable isotopes. A standard atomic mass cannot be given.

19 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 lifes that are less than 50 minutes. This element also has 4 meta states, with the most stable being ^236m
Np
(t_½ 22.5 hours).

The isotopes of neptunium range in atomic weight from 225.0339 u (²²⁵
Np
) to 244.068 u (²⁴⁴
Np
). 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 element 92 (uranium) isotopes (alpha emission produces element 91, protactinium, however) and the primary products after are element 94 (plutonium) isotopes.

Some notable isotopes

Neptunium-235

Neptunium-235 is a radioactive isotope of neptunium with 93 electrons and protons and 142 neutrons. It has a half-life of 400 days. This isotope of Neptunium either decays by:

Emitting an alpha particle - Here, the decay energy is 5.2 MeV and the decay product is Protactinium-231.
Electron capture - Here, the decay energy is 0.125 MeV and the decay product is Uranium-235

This particular isotope of neptunium has a weight of 235.0440633 grams/mole. It is not abundant in nature because it is unstable.

Neptunium-236

Neptunium-236 is a radioactive isotope of neptunium with 93 electrons and protons and 143 neutrons. It has a half-life of 154,000 years. It can decay by the following methods -

Electron capture - here, the decay energy is 0.95 MeV and the decay product is Uranium-236.
Beta emission - Here, the decay energy is 0.94 MeV and the decay product is Plutonium-236.
Alpha emission - Here, the decay energy is 5.024 MeV and the decay product is Protactinium-232

This particular isotope of neptunium has a mass of 236.04657 grams/mole. It is a fissile material with a critical mass of 7 kg. It is not found on earth because it is unstable.

possible parent nuclides: alpha from Am-240

Neptunium-237

Actinides and fission products by half-life v t e
Actinides^[1] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[2]
4n	4n + 1	4n + 2	4n + 3	Half-life range (a)	4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a		¹⁵⁵Eu^þ
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a	⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a	¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
²⁴⁸Bk^[3]	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[4]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka		⁷⁹Se^₡
				1.53 Ma	⁹³Zr
	²³⁷Np^ƒ			2.1–6.5 Ma	¹³⁵Cs^₡	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[5]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[5]
₡, has thermal neutron capture cross section in the range of 8–50 barns ƒ, fissile №, primarily a naturally occurring radioactive material (NORM) þ, neutron poison (thermal neutron capture cross section greater than 3k barns)

²³⁷
Np
decays via the neptunium series to thallium, unlike most other actinides which decay to isotopes of lead.

²³⁷
Np
was recently shown to be capable of sustaining a chain reaction with fast neutrons, as in a nuclear weapon.^[6] However, it has a low probability of fission on bombardment with thermal neutrons, which makes it unsuitable as a fuel for nuclear power plants.

²³⁷
Np
is the only neptunium isotope produced in significant quantity in the nuclear fuel cycle, both by successive neutron capture on uranium-235 (which fissions most but not all of the time) and uranium-236, or (n,2n) reactions where a fast neutron occasionally knocks a neutron loose from uranium-238 or isotopes of plutonium. Over the long term, ²³⁷
Np
also forms in spent nuclear fuel as the decay product of americium-241.

²³⁷
Np
is projected to be one of the most mobile nuclides at the Yucca Mountain nuclear waste repository.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[7]^{[n 1]}	daughter isotope(s)	nuclear spin
nuclide symbol	excitation energy			half-life	decay mode(s)^[7]^{[n 1]}	daughter isotope(s)	nuclear spin
²²⁵ Np	93	132	225.03391(8)	3# ms [>2 µs]	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-#
²²⁷ Np	93	134	227.03496(8)	510(60) ms	β⁺ (.05%)	²²⁷U	5/2-#
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+#
²²⁹ Np	93	136	229.03626(9)	4.0(2) min	β⁺ (49%)	²²⁹U	5/2+#
²³⁰ Np	93	137	230.03783(6)	4.6(3) min	β⁺ (97%)	²³⁰U
²³⁰ Np	93	137	230.03783(6)	4.6(3) min	α (3%)	²²⁶Pa
²³¹ Np	93	138	231.03825(5)	48.8(2) min	β⁺ (98%)	²³¹U	(5/2)(+#)
²³¹ Np	93	138	231.03825(5)	48.8(2) min	α (2%)	²²⁷Pa	(5/2)(+#)
²³² Np	93	139	232.04011(11)#	14.7(3) min	β⁺ (99.99%)	²³²U	(4+)
²³² Np	93	139	232.04011(11)#	14.7(3) min	α (.003%)	²²⁸Pa	(4+)
²³³ Np	93	140	233.04074(5)	36.2(1) min	β⁺ (99.99%)	²³³U	(5/2+)
²³³ Np	93	140	233.04074(5)	36.2(1) min	α (.001%)	²²⁹Pa	(5/2+)
²³⁴ Np	93	141	234.042895(9)	4.4(1) d	β⁺	²³⁴U	(0+)
²³⁵ Np	93	142	235.0440633(21)	396.1(12) d	EC	²³⁵U	5/2+
²³⁵ Np	93	142	235.0440633(21)	396.1(12) d	α (.0026%)	²³¹Pa	5/2+
²³⁶ Np	93	143	236.04657(5)	1.54(6)E+5 a	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
^236m Np	60(50) keV			22.5(4) h	β^- (48%)	²³⁶Pu	1
²³⁷ Np	93	144	237.0481734(20)	2.144(7)E+6 a	α	²³³Pa	5/2+
					SF (2E-10%)	(various)
					CD (4E-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+
²⁴⁰ Np	93	147	240.056162(16)	61.9(2) min	β^-	²⁴⁰Pu	(5+)
^240m Np	20(15) keV			7.22(2) min	1(+)	β^- (99.89%)	²⁴⁰Pu
^240m Np	20(15) keV			7.22(2) min	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-)

^ Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission

Notes

Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
^ Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
^ Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is eight quadrillion years.
^ P. Weiss (26 October 2002). "Little-studied metal goes critical - Neptunium Nukes?". Science News. Retrieved 2006-09-29.
^ http://www.nucleonica.net/unc.aspx

Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. {{cite web}}: Check date values in: |accessdate= (help)
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

[8] Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission

[1] Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.

[2] Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.

[3] Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."

[4] This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".

[5] Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is eight quadrillion years.

[critical-6] P. Weiss (26 October 2002). "Little-studied metal goes critical - Neptunium Nukes?". Science News. Retrieved 2006-09-29.

[7] ttp://www.nucleonica.net/unc.aspx

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[n 1]