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ISSN: 2150-3494
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Half-Life and Decay Law of Actinide Elements

Fazal-ur-Rehman M* and Sana Akram

Department of Chemistry, University of Education Lahore-Vehari Campus, Punjab, Pakistan

*Corresponding Author:
Fazal-ur-Rehman M
Department of Chemistry, University of Education Lahore-Vehari Campus
Punjab
Pakistan
Tel: +92673362267;
E-mail: [email protected]

Received date: March 22, 2017; Accepted date: April 07, 2017; Published date: May 06, 2017

Citation: Fazal-ur-Rehman M, Akram S (2017) Half-Life and Decay Law of Actinide Elements. Chem Sci J 8: 151. doi: 10.4172/2150-3494.1000151

Copyright: © 2017 Fazal-ur-Rehman M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

All the Actinides (An) are not naturally produced elements, rather most are artificially synthesized by radioactivity (Ra) of some parental and by bombardment of alpha, beta or gamma particles. After bombardment, parental and the decayed radiations are generated or synthesized. However, the parental An are found in natural metal ores. The other An are not just synthesized by Ra of parental An, but also present in radioactive wastes of other metals.

Keywords

Actinides; Half-Life; Radioactivity; Electron capture; Radioactive decay law

Introduction

The Actinide series is consisted of 14 elements having atomic numbers from 90 to 103. The members of this series are thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr). U and Th are that An which found in the crust of earth in enough quantities, while some quantity of Np and Pu have also been found in ores of U. Ac and Pa are present in nature by the decay products of some isotopes Th and U. Rest of these have only been prepared artificially in small amounts [1]. The name of An-series is derived from its superior element named as Actinium (Ac). All of the An-elements but except one, related to the filling of the 5f-orbital, Lr which is a d-block element, is considered an An. Most of the f-block elements, An-elements show lot variability in their valences. All of them have too large atomic radii as well as ionic radii and exhibit large range variation in their physical properties. While Ac and other An (americium to onwards) react similiar to the lanthanides, while other An (from Th to Np) are too much similar to d-block elements in their chemistry [2-5].

The actinides are too much reactive and supposed to have a number of different valences in their corresponding compounds. When there is increase in their atomic numbers, addition of extra electrons is directed to 5f electron shell. Elements in this series, having atomic numbers more than U-92 are called transuranium elements, while the elements having atomic numbers more than Lr-103, are not members of the An series; element with 104 atomic number are called transactinide elements. Because all the Actinides are radioactive and they released much energy due to their radioactive decay (RaD). U and Th are naturally present abundantly on earth, while Pu is synthetically produced. These are being utilized in nuclear reactors and nuclear weapons. U and Th also have most of the historical uses, while An is utilized in the ionization chambers of most modern smoke detectors [6]. The RaD of U produces large quantities of Ac and Pa, while atoms of Np and Pu are produced from transmutation reactions in U-ores. The other An are synthesized artificially [7]. The tests of nuclear weapons have released at least six An heavier than Pu into the environment; analysis of debris from a 1952 H2-bomb explosion showed that Am, Cm, Bk, Cf, Es and Fm are present in explosion [8].

Half-Life

Half-life-t1/2 (HL) is that time which is required to reduce the quantity if a radioactive element to half from its initial quantity. The term HL is commonly used in nuclear chemistry for the description about the time of radioactive reactions of unstable atoms to become stable one. HL terminology is used more commonly to characterize the exponential as well as non-exponential decay. The medical sciences, for example, prefer the biological HL of drugs and also of the other chemicals in living bodies. The converse of HL is doubling time. HL is always constant even over the life time of an exponential decaying quantity. It is also a characterized unit for the exponential decay equation. The following Table 1 is showing the reduction in amount as HLs elapsed.

Synthesis of transuranium An
Element Years Methodology
Np 1940 With the Bombardment of neutrons on 238U
Pu 1941 With the Bombardment of deuterons on 238U
Am 1944 With the Bombardment of neutrons on 239Pu
Cm 1944 With the Bombardment of a-particles on 239Pu
Bk 1949 With the Bombardment of a-particles241Am
Cf 1950 With the Bombardment of a-particles242Cm
Es 1952 From the Nuclear Explosion products
Fm 1952 From the Nuclear Explosion products
Md 1955 With the bombardment of a-particles on253Es by
No 1965 With the bombardment of 15N on 243Am
or 22Ne on 238U
Lr 1961–1971 With the bombardment of 10B or 11B on 252Cf by
and  with 18O on 243Am

Table 1: Reduction in amount as HLs elapsed.

Radioactive decay law

Radioactivity is a process by which the nucleus of an unstable atom of a radioactive element due to its nuclear instability loses energy by emitting radiation [9-11]. Radioactivity was discovered by Henry Becquerel completely by accident. When he wrapped a sample of a U-compound within a black paper and then put it in a drawer, containing the photographic plates, he was surprised to see that U-Compound had been exposed on these plates. After this accident, he named this process as Radioactivity. In a radioactive material, it is noticed that decays per unit time are directly proportional to the total number of nuclei of radioactive compounds in the sample. Mathematically,

dN/dt ? N (or) dN/dt=?N

where number of nuclei in a sample is=N, number of radioactive decays per unit time dt is dN while ? is the proportionality constant which is called t radioactive decay constant or disintegration constant. There are many forms in RaD. The most common forms of Radioactive decay are; 1. a -Decay (Helium nuclei decayed), 2. ß - Decay (Electrons decay is done), 3. G -Decay (Highly energetic photons are decayed).

Measurement of life of radioactive element

In radioactivity, the life of a sample of radioactive element is measured using two different measurements.< /p>

• HL- T1/2: It is the time duration within which the number of nuclei, N is reduced to its half of the original value.

RaD is the conversion of unstable nuclei of any radioactive element into stable nuclei. RaD may be the any form of given; alpha emission, beta emission, positron emission, electron capture, and gamma emission. In each form of RaD, the specific particle is emitted from unstable nuclei and the specific new stable nuclei is produced or synthesized. The number of protons, electrons and neutrons is determined by the form of RaD. RaD rates are normally stated in terms of their HLs, and the HL of a given nuclear species is related to its radiation risk [12- 18]. The different types of radioactivity lead to different decay paths which transmute the nuclei into other chemical elements. Examining the amounts of the decay products makes possible radioactive dating. Radiation from nuclear sources is distributed equally in all directions, obeying the inverse square law.

Radioactivity of actinides

Radioactivity in actinides is caused by the inclusion of naturallyoccurring radioactive elements in the mineral’s composition [19]. The degree of RaD is dependent on the concentration and isotope present in the mineral. For the most part, minerals that contain potassium (K), U, and Th are radioactive. This table lists all of the naturally-occurring radioactive isotopes. a - decay is occurred when a helium nuclei is emitted from the parent isotope. It means that two protons and two neutrons are emitted. This a - particle is accomplished by ? - radiation and a daughter isotope, which is 2 protons and 2 neutrons lighter than the parent nuclei. ß - decay is occurred due to the emission of an electron from the parent nucleus. This particle is accomplished by ? - radiation and a daughter isotope which is one proton heavier and one neutron lighter than that of parent nuclei.

Electron Capture (EC) decay is very rare and is the result of the nucleus capturing one of the atom’s orbital electrons. This decay is accompanied by gamma radiation and a daughter isotope which is one neutron heavier and one proton lighter than the parent isotope. The Actinides are all radioactive elements. U, Th, Pa and Ac are the only four An that have been found in the environment. Other An are artificial, being produced through various nuclear reactions. At the creation of the universe, some amount of 244Pu could have been formed; however, with an 80 million year HL, it would have fully decayed during the past 10 billion years [20-23].

U-238, U-235 and Th-232 are starting An of “RaD chains” or “natural RaD series”. Pa was notified as isotope with short-live. In 1918, O Hahn and L Meitner (Germany), F Soddy and J Cranston (United Kingdom); renamed the “Protoactinium” as protactinium [24-26].

Synthesis of transuranium elements

In 1940, Edwin McMillan was the first person who introduced a trans uranium element. He also started to bombard deuterons on U239, but he had to leave this due to MIT to work on his radar project. Seaborg, Kennedy, Wahl and McMillan synthesized element Pu-94 in 1941.10 An elements (Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No) including element Sg-106 (named in his honor while he was still living).

RaD chains/series of an elements

The Decay Chains of the different An elements with their calculated energy and HL are given in Tables 2-4 with actual values.

U-Decay Chain
Isotope HL HL Units HL Seconds Decay N
(mole/kg)* %Abundance
Calculated Activity (Becquerel)
Kg-sec
Calculated Activity (Curie) Ci/Kg-sec Decay Energy (MeV)
238U 4.47E+09 years 1.41E+17 a 2.512E+24 1.236E+07 3.340E-04 4.270
234Th 2.41E+01 days 2.08E+06 ß- 3.713E+13 1.236E+07 3.340E-04 0.273
234Pa 1.17E+00 min 7.02E+01 ß- 1.252E+09 1.236E+07 3.340E-04 2.197
234U 2.48E+05 years 7.82E+12 a 1.395E+20 1.236E+07 3.340E-04 4.859
230Th 7.70E+04 years 2.43E+12 a 4.330E+19 1.236E+07 3.340E-04 4.770
226Ra 1.60E+03 years 5.05E+10 a 8.997E+17 1.236E+07 3.340E-04 4.871
222Rn 3.82E+00 days 3.30E+05 a 5.885E+12 1.236E+07 3.340E-04 6.681
218Po 3.05E+00 min 1.83E+02 a 3.263E+09 1.236E+07 3.340E-04 6.115
214Pb 2.68E+01 min 1.61E+03 ß- 2.867E+10 1.236E+07 3.340E-04 1.024
214Bi 1.98E+01 min 1.19E+03 ß- 2.118E+10 1.236E+07 3.340E-04 3.272
214Po 1.62E+02 µsec 1.62E-04 a 2.889E+03 1.236E+07 3.340E-04 7.833
210Pb 2.23E+01 years 7.03E+08 ß- 1.254E+16 1.236E+07 3.340E-04 3.792
210Bi 5.01E+00 days 4.33E+05 ß- 7.723E+12 1.236E+07 3.340E-04 5.037
210Po 1.38E+02 days 1.20E+07 a 2.132E+14 1.236E+07 3.340E-04 5.407
206Pb stable
Sum 238U Activity for 1 kg Natural U       172,997,240 0.00468

Table 2: Calculated energy of Uranium and HL.

Ac-Decay chain
Isotope HL HL Units HL Decay (mole/kg)* %Abundance at Equilibrium Calculated Activity (Becquerel)
Kg-sec
Calculated Activity (Curie) Ci/Kg-sec Decay Energy (MeV)
235U 7.04E+08 years 2.22E+16 a 1.845E+22 5.762E+05 1.557E-05 4.679
231Th 2.55E+01 hours 9.18E+04 ß- 7.632E+10 5.762E+05 1.557E-05 4.213
231Pa 3.25E+04 years 1.02E+12 a 8.521E+17 5.762E+05 1.557E-05 5.149
227Ac 2.18E+01 years 6.87E+08 ß- 5.716E+14 5.762E+05 1.557E-05 5.042
227Th 1.85E+01 days 1.60E+06 a 1.329E+12 5.762E+05 1.557E-05 6.146
223Ra 1.14E+01 days 9.85E+05 a 8.189E+11 5.762E+05 1.557E-05 5.979
219Rn 4.00E+00 sec 4.00E+00 a 3.326E+06 5.762E+05 1.557E-05 8.130
215Po 1.78E+00 msec 1.78E-03 a 1.480E+03 5.762E+05 1.557E-05 7.526
211Pb 3.61E+01 min 2.17E+03 ß- 1.801E+09 5.762E+05 1.557E-05 1.373
211Bi 2.13E+00 min 1.28E+02 a 1.063E+08 5.762E+05 1.557E-05 6.751
207Tl 4.77E+00 min 2.86E+02 ß- 2.380E+08 5.762E+05 1.557E-05 1.423
207Pb stable
Sum 235U Activity for 1 kg Natural U 6,337,932 1.713E-04  

Table 3: Calculated energy of Actinium and HL.

Th-Decay Chain
Isotope HL HL Units HL Seconds Decay N (kmol) Calculated Activity (Becquerel)
Kg-sec
Calculated Activity (Curie) Ci/Kg-sec Decay Energy (MeV)
232Th 1.40E+10 years 4.42E+17 a 2.596E+24 4.075E+06 1.101E-04 4.083
228Ra 5.80E+00 years 6.93E+11 ß- 4.072E+18 4.075E+06 1.101E-04 5.520
228Ac 6.10E+00 hours 2.20E+04 ß- 1.291E+11 4.075E+06 1.101E-04 2.127
228Th 1.90E+00 years 5.99E+07 a 3.523E+14 4.075E+06 1.101E-04 5.520
224Ra 3.60E+00 days 3.11E+05 a 1.829E+12 4.075E+06 1.101E-04 5.789
220Rn 5.50E+01 sec 5.50E+01 a 3.234E+08 4.075E+06 1.101E-04 0.800
216Po 1.50E-01 sec 1.50E-01 a 8.820E+05 4.075E+06 1.101E-04 6.906
212Pb 1.06E+01 hours 3.82E+04 ß- 2.244E+11 4.075E+06 1.101E-04 0.574
212Bi 6.10E+01 min 3.66E+03 ß-,a 2.152E+10 4.075E+06 1.101E-04 2.254
212Po 3.00E-01 sec 3.00E-01 a 1.764E+06 4.075E+06 1.101E-04 8.954
208Tl 3.00E+00 min 1.80E+02 ß- 1.058E+09 4.075E+06 1.101E-04 5.001
208Pb stable  
Sum 232Th Activity for 1 kg Natural Th 44,824,572 1.211E-03  

Table 4: Calculated energy of Thorium and HL.

Conclusion

From all the above discussion, it is well informed that all the An are not created naturally, rather some are naturally and others are created through the radioactivity of that An. By bombardment of Alpha, Beta or Gamma particles, the other An are generated artificially. And their HL depends upon their nature [27].

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