Protactinium Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds, in which p ...

(₉₁Pa) has no stable

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

s. The four naturally occurring isotopes allow a standard atomic weight to be given. Thirty

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable. This excess energy can be used in one of three ...

s of protactinium have been characterized, ranging from ²¹⁰Pa to ²³⁹Pa. The most stable isotope is ²³¹Pa with a

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

of 32,760 years, ²³³Pa with a half-life of 26.967 days, and ²³⁰Pa with a half-life of 17.4 days. All of the remaining

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

isotopes have half-lives less than 1.6 days, and the majority of these have half-lives less than 1.8 seconds. This element also has five meta states, ^217mPa (t_1/2 1.15 milliseconds), ^220m1Pa (t_1/2 = 308 nanoseconds), ^220m2Pa (t_1/2 = 69 nanoseconds), ^229mPa (t_1/2 = 420 nanoseconds), and ^234mPa (t_1/2 = 1.17 minutes). The only naturally occurring isotopes are ²³¹Pa, ²³⁴Pa and ^234mPa. The former occurs as an intermediate decay product of ²³⁵U, while the latter two occur as intermediate decay products of ²³⁸U. ²³¹Pa makes up nearly all natural protactinium. The primary

decay mode Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

for isotopes of Pa lighter than (and including) the most stable isotope ²³¹Pa is

alpha decay Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus). The parent nucleus transforms or "decays" into a daughter product, with a mass number that is reduced by four and an a ...

, except for ²²⁸Pa to ²³⁰Pa, which primarily decay by electron capture to

isotopes of thorium Thorium (90Th) has seven naturally occurring isotopes but none are stable. One isotope, 232Th, is ''relatively'' stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the gen ...

. The primary mode for the heavier isotopes is beta minus (β⁻) decay. The primary

decay product In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps ( d ...

s of ²³¹Pa and isotopes of protactinium lighter than and including ²²⁷Pa are isotopes of actinium and the primary decay products for the heavier isotopes of protactinium are

isotopes of uranium Uranium (U) is a naturally occurring radioactive element (radioelement) with no stable isotopes. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in Earth's crust. The d ...

List of isotopes

, -id=Protactinium-210 , ²¹⁰Pa , , style="text-align:right" , 91 , style="text-align:right" , 119 , , , α , ²⁰⁶Ac , 3+ , , -id=Protactinium-211 , ²¹¹Pa , , style="text-align:right" , 91 , style="text-align:right" , 120 , 211.023674(75) , 6(3) ms , α , ²⁰⁷Ac , 9/2− , , -id=Protactinium-212 , ²¹²Pa , , style="text-align:right" , 91 , style="text-align:right" , 121 , 212.023185(94) , 5.8(19) ms , α , ²⁰⁸Ac , 3+# , , -id=Protactinium-213 , ²¹³Pa , , style="text-align:right" , 91 , style="text-align:right" , 122 , 213.021100(61) , 7.4(24) ms , α , ²⁰⁹Ac , 9/2− , , -id=Protactinium-214 , ²¹⁴Pa , , style="text-align:right" , 91 , style="text-align:right" , 123 , 214.020891(87) , 17(3) ms , α , ²¹⁰Ac , 7+# , , -id=Protactinium-215 , ²¹⁵Pa , , style="text-align:right" , 91 , style="text-align:right" , 124 , 215.019114(89) , 14(2) ms , α , ²¹¹Ac , 9/2− , , -id=Protactinium-216 , ²¹⁶Pa , , style="text-align:right" , 91 , style="text-align:right" , 125 , 216.019135(26) , 105(12) ms , α , ²¹²Ac , 5+# , , -id=Protactinium-217 , ²¹⁷Pa , , style="text-align:right" , 91 , style="text-align:right" , 126 , 217.018309(13) , 3.8(2) ms , α , ²¹³Ac , 9/2− , , -id=Protactinium-217m , rowspan=2 style="text-indent:1em" , ^217mPa , rowspan=2, , rowspan=2 colspan="3" style="text-indent:2em" , 1860(7) keV , rowspan=2, 1.08(3) ms , α (73%) , ²¹³Ac , rowspan=2, (23/2−) , rowspan=2, , - , IT (27%) , ²¹⁷Pa , -id=Protactinium-218 , ²¹⁸Pa , , style="text-align:right" , 91 , style="text-align:right" , 127 , 218.020021(19) , 108(5) μs , α , ²¹⁴Ac , 8−# , , -id=Protactinium-218m , style="text-indent:1em" , ^218mPa , , colspan="3" style="text-indent:2em" , 81(19) keV , 150(50) μs , α , ²¹⁴Ac , , , -id=Protactinium-219 , ²¹⁹Pa , , style="text-align:right" , 91 , style="text-align:right" , 128 , 219.019950(75) , 56(9) ns , α , ²¹⁵Ac , 9/2− , , -id=Protactinium-220 , ²²⁰Pa , , style="text-align:right" , 91 , style="text-align:right" , 129 , 220.021770(16) , 850(60) ns , α , ²¹⁶Ac , 1−# , , -id=Protactinium-220m1 , style="text-indent:1em" , ^220m1PaOrder of ground state and isomer is uncertain. , , colspan="3" style="text-indent:2em" , 26(23) keV , 410(180) ns , α , ²¹⁶Ac , , , -id=Protactinium-220m2 , style="text-indent:1em" , ^220m2Pa , , colspan="3" style="text-indent:2em" , 290(50) keV , 260(210) ns , α , ²¹⁶Ac , , , -id=Protactinium-221 , ²²¹Pa , , style="text-align:right" , 91 , style="text-align:right" , 130 , 221.021873(64) , 5.9(17) μs , α , ²¹⁷Ac , 9/2− , , -id=Protactinium-222 , ²²²Pa , , style="text-align:right" , 91 , style="text-align:right" , 131 , 222.023687(93) , 3.8(2) ms , α , ²¹⁸Ac , 1−# , , -id=Protactinium-223 , ²²³Pa , , style="text-align:right" , 91 , style="text-align:right" , 132 , 223.023980(81) , 5.3(3) ms , α , ²¹⁹Ac , 9/2− , , -id=Protactinium-224 , ²²⁴Pa , , style="text-align:right" , 91 , style="text-align:right" , 133 , 224.0256173(81) , 844(19) ms , α (99.9%) , ²²⁰Ac , (5−) , , -id=Protactinium-225 , ²²⁵Pa , , style="text-align:right" , 91 , style="text-align:right" , 134 , 225.026148(88) , 1.71(10) s , α , ²²¹Ac , 5/2−# , , -id=Protactinium-226 , rowspan=2, ²²⁶Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 135 , rowspan=2, 226.027948(12) , rowspan=2, 1.8(2) min , α (74%) , ²²²Ac , rowspan=2, 1−# , rowspan=2, , - , β⁺ (26%) , ²²⁶Th , -id=Protactinium-227 , rowspan=2, ²²⁷Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 136 , rowspan=2, 227.0288036(78) , rowspan=2, 38.3(3) min , α (85%) , ²²³Ac , rowspan=2, (5/2−) , rowspan=2, , - , EC (15%) , ²²⁷Th , -id=Protactinium-228 , rowspan=2, ²²⁸Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 137 , rowspan=2, 228.0310508(47) , rowspan=2, 22(1) h , β⁺ (98.15%) , ²²⁸Th , rowspan=2, 3+ , rowspan=2, , - , α (1.85%) , ²²⁴Ac , -id=Protactinium-229 , rowspan=2, ²²⁹Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 138 , rowspan=2, 229.0320956(35) , rowspan=2, 1.55(4) d , EC (99.51%) , ²²⁹Th , rowspan=2, 5/2+ , rowspan=2, , - , α (0.49%) , ²²⁵Ac , -id=Protactinium-229m , style="text-indent:1em" , ^229mPa , , colspan="3" style="text-indent:2em" , 12.20(4) keV , 420(30) ns , IT , ²²⁹Pa , 3/2− , , - , rowspan=3, ²³⁰Pa , rowspan=3, , rowspan=3 style="text-align:right" , 91 , rowspan=3 style="text-align:right" , 139 , rowspan=3, 230.0345397(33) , rowspan=3, 17.4(5) d , β⁺ (92.2%) , ²³⁰Th , rowspan=3, 2− , rowspan=3, , - , β⁻ (7.8%) , ²³⁰U , - , α (0.0032%) , ²²⁶Ac , - , rowspan=4, ²³¹Pa , rowspan=4, Protoactinium , rowspan=4 style="text-align:right" , 91 , rowspan=4 style="text-align:right" , 140 , rowspan=4, 231.0358825(19) , rowspan=4, 3.265(20)×10⁴ y , α , ²²⁷Ac , rowspan=4, 3/2− , rowspan=4, 1.0000Intermediate

of ²³⁵U , - , CD (1.34×10⁻¹⁰%) , ²⁰⁷Tl
²⁴Ne , - , SF (<3×10⁻¹⁰%) , (various) , - , CD (9.9×10⁻¹³%) , ''²⁰⁸Pb''
²³F , -id=Protactinium-232 , ²³²Pa , , style="text-align:right" , 91 , style="text-align:right" , 141 , 232.0385902(82) , 1.32(2) d , β⁻ , ²³²U , (2−) , , - , ²³³Pa , , style="text-align:right" , 91 , style="text-align:right" , 142 , 233.0402465(14) , 26.975(13) d , β⁻ , ²³³U , 3/2− , TraceIntermediate decay product of ²³⁷Np , - , rowspan=2, ²³⁴Pa , rowspan=2, Uranium Z , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 143 , rowspan=2, 234.0433056(44) , rowspan=2, 6.70(5) h , β⁻ , ²³⁴U , rowspan=2, 4+ , rowspan=2, TraceIntermediate decay product of ²³⁸U , - , SF (3×10⁻¹⁰%) , (various) , - , rowspan=3 style="text-indent:1em" , ^234mPa , rowspan=3, Uranium X₂
Brevium , rowspan=3 colspan="3" style="text-indent:2em" , 79(3) keV , rowspan=3, 1.159(11) min , β⁻ (99.84%) , ²³⁴U , rowspan=3, (0−) , rowspan=3, Trace , - , IT (0.16%) , ²³⁴Pa , - , SF (10⁻¹⁰%) , (various) , -id=Protactinium-235 , ²³⁵Pa , , style="text-align:right" , 91 , style="text-align:right" , 144 , 235.045399(15) , 24.4(2) min , β⁻ , ''²³⁵U'' , 3/2− , , -id=Protactinium-236 , rowspan=2, ²³⁶Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 145 , rowspan=2, 236.048668(15) , rowspan=2, 9.1(1) min , β⁻ , ²³⁶U , rowspan=2, 1(−) , rowspan=2, , - , β⁻, SF (6×10⁻⁸%) , (various) , -id=Protactinium-237 , ²³⁷Pa , , style="text-align:right" , 91 , style="text-align:right" , 146 , 237.051023(14) , 8.7(2) min , β⁻ , ²³⁷U , 1/2+ , , -id=Protactinium-238 , rowspan=2, ²³⁸Pa , rowspan=2, , rowspan=2 style="text-align:right" , 91 , rowspan=2 style="text-align:right" , 147 , rowspan=2, 238.054637(17) , rowspan=2, 2.28(9) min , β⁻ , ''²³⁸U'' , rowspan=2, 3−# , rowspan=2, , - , β⁻, SF (2.6×10⁻⁶%) , (various) , -id=Protactinium-239 , ²³⁹Pa , , style="text-align:right" , 91 , style="text-align:right" , 148 , 239.05726(21)# , 1.8(5) h , β⁻ , ²³⁹U , 1/2+# ,

Actinides and fission products

Protactinium-230

Protactinium-230 has 139 neutrons and a half-life of 17.4 days. Most of the time (92%), it undergoes beta plus decay to ²³⁰Th, with a minor (8%) beta-minus decay branch leading to ²³⁰U. It also has a very rare (.003%) alpha decay mode leading to ²²⁶Ac. It is not found in nature because its half-life is short and it is not found in the

decay chain In nuclear science a decay chain refers to the predictable series of radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radioactive isotopes do not usually decay directly to stable isotopes, but rather ...

s of ²³⁵U, ²³⁸U, or ²³²Th. It has a mass of 230.034541 u. Protactinium-230 is of interest as a progenitor of uranium-230, an isotope that has been considered for use in targeted alpha-particle therapy (TAT). It can be produced through proton or

deuteron Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen; the other is protium, or hydrogen-1, H. The deuterium atomic nucleus, nucleus (deuteron) contains one proton and ...

irradiation of natural thorium.

Protactinium-231

Protactinium-231 is the longest-lived isotope of protactinium, with a half-life of 32,760 years. In nature, it is found in trace amounts as part of the

actinium series In nuclear science a decay chain refers to the predictable series of radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radioactive isotopes do not usually decay directly to stable isotopes, but rather ...

, which starts with the primordial isotope

uranium-235 Uranium-235 ( or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nat ...

; the equilibrium concentration in uranium ore is 46.55 ²³¹Pa per million ²³⁵U. In

nuclear reactor A nuclear reactor is a device used to initiate and control a Nuclear fission, fission nuclear chain reaction. They are used for Nuclear power, commercial electricity, nuclear marine propulsion, marine propulsion, Weapons-grade plutonium, weapons ...

s, it is one of the few long-lived radioactive

actinide The actinide () or actinoid () series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. Number 103, lawrencium, is also generally included despite being part ...

s produced as a byproduct of the projected

thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural ...

, as a result of (n,2n) reactions where a fast neutron removes a

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

from ²³²Th or ²³²U, and can also be destroyed by

neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, wh ...

, though the cross section for this reaction is also low. Pa-231 solution

binding energy: 1759860 keV
beta decay energy: −382 keV spin: 3/2−
mode of decay:

alpha Alpha (uppercase , lowercase ) is the first letter of the Greek alphabet. In the system of Greek numerals, it has a value of one. Alpha is derived from the Phoenician letter ''aleph'' , whose name comes from the West Semitic word for ' ...

to ²²⁷Ac, also others possible parent nuclides:

beta Beta (, ; uppercase , lowercase , or cursive ; or ) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Ancient Greek, beta represented the voiced bilabial plosive . In Modern Greek, it represe ...

from ²³¹Th, EC from ²³¹U,

from ²³⁵Np.

Protactinium-233

Protactinium-233 is also part of the thorium fuel cycle. It is an intermediate beta decay product between thorium-233 (produced from natural thorium-232 by neutron capture) and

uranium-233 Uranium-233 ( or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a Nuclear fuel, reactor fuel. It has been used successfully ...

(the fissile fuel of the thorium cycle). Some thorium-cycle reactor designs try to protect Pa-233 from further neutron capture producing Pa-234 and U-234, which are not useful as fuel.

Protactinium-234

Protactinium-234 is a member of the

uranium series In nuclear science a decay chain refers to the predictable series of radioactive disintegrations undergone by the nuclei of certain unstable chemical elements. Radioactive isotopes do not usually decay directly to stable isotopes, but rather ...

with a half-life of 6.70 hours. It was discovered by

Otto Hahn Otto Hahn (; 8 March 1879 – 28 July 1968) was a German chemist who was a pioneer in the field of radiochemistry. He is referred to as the father of nuclear chemistry and discoverer of nuclear fission, the science behind nuclear reactors and ...

in 1921.Fry, C., and M. Thoennessen. "Discovery of the Actinium, Thorium, Protactinium, and Uranium Isotopes." January 14, 2012. Accessed May 20, 2018. https://people.nscl.msu.edu/~thoennes/2009/ac-th-pa-u-adndt.pdf.

Protactinium-234m

Protactinium-234m is a member of the uranium series with a half-life of 1.17 minutes. It was discovered in 1913 by Kazimierz Fajans and Oswald Helmuth Göhring, who named it brevium for its short half-life. About 99.8% of decays of ²³⁴Th produce this isomer instead of the

ground state The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state ...

(t_1/2 = 6.70 hours).

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Protactinium