Artificial transmutation, Synthetic or Transuranic elements and artificial radioactivity.
(1) Artificial transmutation or nuclear transformation or nucleartransmutation:The conversion of one element into another by artificial means, i.e., by means of bombarding with some fundamental particles, is known as artificial transmutation. The phenomenon was first applied on nitrogen whose nucleus was bombarded with -particles to produce oxygen.
14 4 17 1 7 N 2 He 8 O 1 H Nitrogen isotope Alpha particle Oxygen isotope Proton
The element, which is produced, shows radioactivity, the phenomenon is known as Induced radioactivity. The fundamental particles which have been used in the bombardment of different elements are as follows:
4 (i) -particle: Helium nucleus, represented as 2 He .
1 (ii) Proton: Hydrogen nucleus, represented as 1 H .
2 2 (iii) Deutron: Deuterium nucleus, represented as 1 H or 1 D .
1 (iv) Neutron: A particle of mass number 1 but no change, represented as 0 n .
Since -particles, protons and deutron carry positive charge, they are repelled by the positively charged nucleus and hence these are not good projectiles. On the other hand, neutrons, which carry no charge at all, are the best projectiles. Further among -particles, protons and deutron; the latter two carrying single positive charge are better projectiles than the -particles. However, the positively charged -particles, protons and deutron can be made much more effective if they are imparted with high velocity. Cyclotron is the most commonly used instrument for accelerating these particles. The particles leave the instrument with a velocity of about 25,000 miles per second. A more recent accelerating instrument is called the synchrotron or bevatron. It is important to note that this instrument cannot accelerate the neutrons, being neutral.
When a target element is bombarded with neutrons, product depends upon the speed of neutrons. Slow neutrons penetrate the nucleus while a high-speed neutron passes through the nucleus.
238 1 239 238 1 237 1 92 U 0 n 92 U ; 92 U 0 n 92 U 2 0 n slow speed high speed Thus slow neutrons, also called thermal neutrons are more effective in producing nuclear reactions than high-speed neutrons.
Alchemy:The process of transforming one element into other is known as alchemyand the person involved in such experiments is called alchemist. Although, gold can be prepared from lead by alchemy, the gold obtained is radioactive and costs very high than natural gold.
Some examples are given below for different nuclear reactions: (i) Transmutation by -particles: (a) , n type
9 12 9 4 12 1 239 242 4 Be (,n) 6 C i.e. 4 Be 2 He 6 C 0 n ; 94 Pu (,n) 96 Cm i.e.
239 4 242 1 94 Pu 2 He 94 Cm 0 n (b) , p type
19 22 19 4 22 1 14 17 9 F (, p) 10 Ne i.e. 9 F 2 He 10 Ne 1 H ; 7 N (, p) 8 O i.e.,
14 4 17 1 7 N 2 He 8 O 1 H (c) , type
59 63 59 4 63 0 26 Fe (, ) 29 Cu i.e., 26 Fe 2 He 29 Cu 1e (ii) Transmutation by protons: (a) p, n type
31 31 31 1 31 1 15 P (p,n) 16 S i.e., 15 P 1 H 16 S 0 n (b) p, type
12 13 12 1 13 6 C (p, ) 7 N i.e., 6 C 1 H N (c) p, d type
9 8 9 1 8 2 4 Be (p,d) 4 Be i.e., 4 Be 1 H 4 Be 1 H (d) p, type
16 31 16 1 13 4 8 O (p,) 7 N i.e., 8 O 1 H 7 N 2 He (iii) Transmutation by neutrons: (a) n,p type
27 27 27 1 27 1 13 Al (n, p) 12 Mg i.e., 13 Al 0 n 12 Mg 1 H (b) n, type
16 27 16 1 13 4 8 O (n,) 12 Mg i.e., 8 O 0 n 6 C 2 He (c) n, type 238 239 238 1 238 92 U (n,) 92 U i.e., 92 U 0 n 92 U (d) n, type
18 19 18 1 19 0 8 O (n, ) 9 F i.e., 8 O 0 n 9 F 1e (iv) Transmutation by deutron: (a) d,p type
6 7 6 2 7 1 75 76 3 Li (d, p) 3 Li i.e., 3 Li 1 H 3 Li 1 H ; 32 As (d, p) 32 As i.e.,
75 2 76 1 32 As 1 H 32 As 1 H (v) Transmutation by -radiations: (a) , n type
9 8 9 8 1 4 Be ( ,n) 4 Be i.e., 4 Be 4 Be 0 n
(2) Synthetic elements:Elements with atomic number greater than 92 i.e. the elements beyond uranium in the periodic table are not found in nature like other elements. All these elements are prepared by artificial transmutation technique and are therefore known as transuranic elements or synthetic elements. The nuclear reactions for the preparation of some transuranic elements are cited below. Elements 93 (neptunium) and 94 (plutonium) were first discovered in 1940. Bombarding uranium-238 with neutrons produced them. 238 1 239 239 0 239 239 0 92 U 0 n 92 U 93 Np 1e ; 94 Np 94 Pu 1e (Uranium) (Neptunium ) Elements with larger atomic numbers are normally formed in small quantities in particle accelerators. For example, curium-242 is formed when a plutonium-239 target is struck with alpha particles. 239 4 242 1 94 Pu 2 He 96 Cm 0 n Plutonium curium
(3) Artificial radioactivity or induced radioactivity:In 1934, Irene Curie and F. Joliot observed that when boron and aluminum were bombarded by -particles, neutrons, protons and positrons were emitted. Curie and Joliot explained this observation by saying that during bombardment, a metastable isotope is formed which behaves as a radioactive element. This process was termed as artificial radioactivity.
“The process in which a stable isotope is converted into radioactive element by artificial transmutation is called artificial radioactivity.”
27 30 When 13 Al is bombarded by -particles, radioactive isotope 15 P is formed.
30 1 27 4 14 Si 1 H (95% of total conversion ) 13 Al 2 He 30 * 1 30 15 P 0 n (5% of total conversion half life period of 15 P is 3.2 minutes)
30 0 14 Si 1 e Positron
10 In a similar manner, the artificial radioactivity was observed when 5 B was bombarded by -particles.
13 1 10 4 6 C 1 H 5 B 2 He 13 * 1 7 N 0 n
13 0 6 C 1e The following are some of the nuclear reactions in which radioactive isotope are formed. 23 2 24 1 24 238 1 239 11 Na 1 H 11 Na * 1 H ( 11 Na radioactiv e) ; 92 U 0 n 92 U * 239 ( 92 U radioactiv e)
12 1 13 13 25 4 28 1 6 C 1 H 7 N * ( 7 N positron radioactiv e) ; 12 Mg 2 He 13 Al * 1 H 28 ( 13 Al radioactiv e)