Protactinium
Protactinium (formerly protoactinium) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds ...
(
91Pa) has no stable
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
s. The three 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 nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
s of protactinium have been characterized, with the most stable being
231Pa with a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
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 consid ...
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 state
A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ha ...
s,
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, which occurs as an intermediate decay product of
235U,
234Pa and
234mPa, both of which 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 consid ...
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) and thereby transforms or 'decays' into a different atomic nucleus, with a mass number that is reduced by four and an atom ...
, 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 gene ...
. 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 ( ...
s of
231Pa and isotopes of protactinium lighter than and including
227Pa are
isotopes of actinium
Actinium (89Ac) has no stable isotopes and no characteristic terrestrial isotopic composition, thus a standard atomic weight cannot be given. There are 33 known isotopes, from 204Ac to 236Ac, and 7 nuclear isomer, isomers. Three isotopes are found ...
and the primary decay products for the heavier isotopes of protactinium are
isotopes of uranium
Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay ...
.
List of isotopes
, -
,
211Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 120
,
, 3.8(+4.6−1.4) ms
,
α
,
207Ac
, 9/2−#
,
,
, -
,
212Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 121
, 212.02320(8)
, 8(5) ms
.1(+61−19) ms, α
,
208Ac
, 7+#
,
,
, -
,
213Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 122
, 213.02111(8)
, 7(3) ms
.3(+40−16) ms, α
,
209Ac
, 9/2−#
,
,
, -
,
214Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 123
, 214.02092(8)
, 17(3) ms
, α
,
210Ac
,
,
,
, -
,
215Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 124
, 215.01919(9)
, 14(2) ms
, α
,
211Ac
, 9/2−#
,
,
, -
, rowspan=2,
216Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 125
, rowspan=2, 216.01911(8)
, rowspan=2, 105(12) ms
, α (80%)
,
212Ac
, rowspan=2,
, rowspan=2,
, rowspan=2,
, -
,
β+ (20%)
,
216Th
, -
,
217Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 126
, 217.01832(6)
, 3.48(9) ms
, α
,
213Ac
, 9/2−#
,
,
, -
, 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
,
213Ac
, rowspan=2, 29/2+#
, rowspan=2,
, rowspan=2,
, -
,
IT (rare)
,
217Pa
, -
,
218Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 127
, 218.020042(26)
, 0.113(1) ms
, α
,
214Ac
,
,
,
, -
, rowspan=2,
219Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 128
, rowspan=2, 219.01988(6)
, rowspan=2, 53(10) ns
, α
,
215Ac
, rowspan=2, 9/2−
, rowspan=2,
, rowspan=2,
, -
, β
+ (5×10
−9%)
,
219Th
, -
,
220Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 129
, 220.02188(6)
, 780(160) ns
, α
,
216Ac
, 1−#
,
,
, -
, style="text-indent:1em" ,
220m1Pa
,
, colspan="3" style="text-indent:2em" , 34(26) keV
, 308(+250-99) ns
, α
,
216Ac
,
,
,
, -
, style="text-indent:1em" ,
220m2Pa
,
, colspan="3" style="text-indent:2em" , 297(65) keV
, 69(+330-30) ns
, α
,
216Ac
,
,
,
, -
,
221Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 130
, 221.02188(6)
, 4.9(8) μs
, α
,
217Ac
, 9/2−
,
,
, -
,
222Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 131
, 222.02374(8)#
, 3.2(3) ms
, α
,
218Ac
,
,
,
, -
, rowspan=2,
223Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 132
, rowspan=2, 223.02396(8)
, rowspan=2, 5.1(6) ms
, α
,
219Ac
, rowspan=2,
, rowspan=2,
, rowspan=2,
, -
, β
+ (.001%)
,
223Th
, -
, rowspan=2,
224Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 133
, rowspan=2, 224.025626(17)
, rowspan=2, 844(19) ms
, α (99.9%)
,
220Ac
, rowspan=2, 5−#
, rowspan=2,
, rowspan=2,
, -
, β
+ (.1%)
,
224Th
, -
,
225Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 134
, 225.02613(8)
, 1.7(2) s
, α
,
221Ac
, 5/2−#
,
,
, -
, 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,
, rowspan=2,
, rowspan=2,
, -
, β
+ (26%)
,
226Th
, -
, rowspan=2,
227Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 136
, rowspan=2, 227.028805(8)
, rowspan=2, 38.3(3) min
, α (85%)
,
223Ac
, rowspan=2, (5/2−)
, rowspan=2,
, rowspan=2,
, -
,
EC (15%)
,
227Th
, -
, rowspan=2,
228Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 137
, rowspan=2, 228.031051(5)
, rowspan=2, 22(1) h
, β
+ (98.15%)
,
228Th
, rowspan=2, 3+
, rowspan=2,
, rowspan=2,
, -
, α (1.85%)
,
224Ac
, -
, rowspan=2,
229Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 138
, rowspan=2, 229.0320968(30)
, rowspan=2, 1.50(5) d
, EC (99.52%)
,
229Th
, rowspan=2, (5/2+)
, rowspan=2,
, rowspan=2,
, -
, α (.48%)
,
225Ac
, -
, style="text-indent:1em" ,
229mPa
,
, colspan="3" style="text-indent:2em" , 11.6(3) keV
, 420(30) ns
,
,
, 3/2−
,
,
, -
, rowspan=3,
230Pa
, rowspan=3,
, rowspan=3 style="text-align:right" , 91
, rowspan=3 style="text-align:right" , 139
, rowspan=3, 230.034541(4)
, rowspan=3, 17.4(5) d
, β
+ (91.6%)
,
230Th
, rowspan=3, (2−)
, rowspan=3,
, rowspan=3,
, -
, β
− (8.4%)
,
230U
, -
, α (.00319%)
,
226Ac
, -
, rowspan=4,
231Pa
, rowspan=4, Protoactinium
, rowspan=4 style="text-align:right" , 91
, rowspan=4 style="text-align:right" , 140
, rowspan=4, 231.0358840(24)
, rowspan=4, 3.276(11)×10
4 y
, α
,
227Ac
, rowspan=4, 3/2−
, rowspan=4, 1.0000
[Intermediate ]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 ( ...
of 235U
, rowspan=4,
, -
,
CD (1.34×10
−9%)
,
207Tl
24Ne
, -
,
SF (3×10
−10%)
, (various)
, -
, CD (10
−12%)
,
208Pb
23F
, -
, rowspan=2,
232Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 141
, rowspan=2, 232.038592(8)
, rowspan=2, 1.31(2) d
, β
−
,
232U
, rowspan=2, (2−)
, rowspan=2,
, rowspan=2,
, -
, EC (.003%)
, ''
232Th''
, -
,
233Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 142
, 233.0402473(23)
, 26.975(13) d
, β
−
,
233U
, 3/2−
, Trace
[Intermediate 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, 234.043308(5)
, rowspan=2, 6.70(5) h
, β
−
,
234U
, rowspan=2, 4+
, rowspan=2, Trace
[Intermediate decay product of 238U]
, rowspan=2,
, -
, SF (3×10
−10%)
, (various)
, -
, rowspan=3 style="text-indent:1em" ,
234mPa
, rowspan=3, Uranium X
2Brevium
, rowspan=3 colspan="3" style="text-indent:2em" , 78(3) keV
, rowspan=3, 1.17(3) min
, β
− (99.83%)
,
234U
, rowspan=3, (0−)
, rowspan=3, Trace
, rowspan=3,
, -
, IT (.16%)
,
234Pa
, -
, SF (10
−10%)
, (various)
, -
,
235Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 144
, 235.04544(5)
, 24.44(11) min
, β
−
, ''
235U''
, (3/2−)
,
,
, -
, rowspan=2,
236Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 145
, rowspan=2, 236.04868(21)
, rowspan=2, 9.1(1) min
, β
−
,
236U
, rowspan=2, 1(−)
, rowspan=2,
, rowspan=2,
, -
, β
−, SF (6×10
−8%)
, (various)
, -
,
237Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 146
, 237.05115(11)
, 8.7(2) min
, β
−
,
237U
, (1/2+)
,
,
, -
, rowspan=2,
238Pa
, rowspan=2,
, rowspan=2 style="text-align:right" , 91
, rowspan=2 style="text-align:right" , 147
, rowspan=2, 238.05450(6)
, rowspan=2, 2.27(9) min
, β
−
, ''
238U''
, rowspan=2, (3−)#
, rowspan=2,
, rowspan=2,
, -
, β
−, SF (2.6×10
−6%)
, (various)
, -
,
239Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 148
, 239.05726(21)#
, 1.8(5) h
, β
−
,
239U
, (3/2)(−#)
,
,
, -
,
240Pa
,
, style="text-align:right" , 91
, style="text-align:right" , 149
, 240.06098(32)#
, 2# min
, β
−
,
240U
,
,
,
Actinides and fission products
Protactinium-230
Protactinium-230 has 139
neutrons
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...
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, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay direct ...
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 Targeted alpha-particle therapy (or TAT) is an in-development method of targeted radionuclide therapy of various cancers. It employs radioactive substances which undergo alpha decay to treat diseased tissue at close proximity. It has the potential t ...
(TAT). It can be produced through proton or
deuteron
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other being protium, or hydrogen-1). The nucleus of a deuterium atom, called a deuteron, contains one proton and one n ...
irradiation of nautral 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, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay directly ...
, which starts with the
primordial isotope
In geochemistry, geophysics and nuclear physics, primordial nuclides, also known as primordial isotopes, are nuclides found on Earth that have existed in their current form since before Earth was formed. Primordial nuclides were present in the ...
uranium-235
Uranium-235 (235U 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 exis ...
; 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 fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
s, it is one of the few long-lived radioactive
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The inform ...
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 tho ...
, as a result of (n,2n) reactions where a
fast neutron
The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium with ...
removes a
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
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, ...
, though the
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
for this reaction is also low.
![Pa-231 solution](https://upload.wikimedia.org/wikipedia/commons/6/64/Pa-231_solution.png)
binding energy: 1759860 keV
beta decay energy: −382 keV
spin: 3/2−
mode of decay:
alpha
Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) 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 , whic ...
to
227Ac, also others
possible parent nuclides:
beta
Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...
from
231Th,
EC from
231U,
alpha
Alpha (uppercase , lowercase ; grc, ἄλφα, ''álpha'', or ell, άλφα, álfa) 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 , whic ...
from
235Np.
Protactinium-233
Protactinium-233 is also part of the thorium fuel cycle. It is an intermediate beta decay product between
thorium-233
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 ...
(produced from natural thorium-232 by neutron capture) and
uranium-233
Uranium-233 (233U or U-233) is a fissile Isotopes of uranium, 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 ha ...
(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, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". Most radioisotopes do not decay direc ...
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 fields of radioactivity and radiochemistry. He is referred to as the father of nuclear chemistry and father of nuclear fission. Hahn and Lise Meitner ...
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
Kazimierz Fajans (Kasimir Fajans in many American publications; 27 May 1887 – 18 May 1975) was a Polish American physical chemist of Polish-Jewish origin, a pioneer in the science of radioactivity and the discoverer of chemical element protac ...
and
Oswald Helmuth Göhring
Oswald Helmuth Göhring, also known as Otto Göhring, (1889 - 1915) was a German chemist who, with his teacher Kasimir Fajans, co-discovered the chemical element protactinium in 1913.
Discovery of protactinium
Protactinium was first identified ...
, who named it brevium for its short half-life.
[http://hpschapters.org/northcarolina/NSDS/Protactinium.pdf ] 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
Protactinium
Protactinium (formerly protoactinium) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds ...