Next – 16/3/13 Sat, early. Stable vs. Unstable. In some atoms, the binding energy is great enough to hold the nucleus together. The nucleus of this kind of atom is said to be stable .
Q: What makes the nucleus a stable one?
less stable means more radioactive
more stable means less radioactive
(b) 35/17 Cl and 36/17 Cl
(c) 20/10 Ne and 17/10 Ne
(d) 40/20 Ca and 45/20 Ca
(e) 195/80 Hg and 196/80 Hg
(a) The 16/8O contains 8 protons and 8 neutrons (even-even) and the 17/8O contains 8 protons and 9 neutrons (even-odd). Therefore, 17/8O is radioactive.
(b) The 35/17Cl has 17 protons and 18 neutrons (odd-even) and the 36/17Cl has 17 protons and 19 neutrons (odd-odd). Hence, 36/17Cl is radioactive.
(c) The 20/10Ne contains 10 protons and 10 neutrons (even-even) and the 17/10Ne contains 10 protons and 7 neutrons (even-odd). Therefore, 17/10Ne is radioactive.
(d) The 40/20Ca has even-even situation and 45/20Ca has even-odd situation. Thus, 45/20Ca is radioactive.
(d) The 195/80Hg has even number of protons and odd number of neutrons and the 196/80Hg has even number of protons and even number of neutrons. Therefore, 195/80Hg is radioactive.
Mass of 26 p = 26 x 1.007825 = 26.20345 amu
Mass of 30 n = 30 x 1.008665 = 30.25995 amu
Total 56.46340 amu
This mass is larger than 55.934942 amu (experimentally determined mass) by 0.52846 amu.
Mass defect: The difference between experimental mass of the atom and the sum of the masses of its protons, neutrons, and electrons is known as mass defect [md]
md = mass of products – mass of reactants
= experimental mass of an atom – calculated mass of an atom
= 55.934942 amu – 56.46340
= - 0.52846 amu
As a consequence, the calculated energy will also be negative because the formation of 56Fe from 26 protons and 30 neutrons is an exothermic reaction meaning that the energy is released to the surrounding.
Change in energy [Jule] = mass defect [amu]*c2
E = [mass defect] X 1.4945 x 10-10 J/amu
= -0.528458 amu x 1.4945 x 10-10 J/amu
= - 7.8978 x 10-11 J/ nucleus
This is the amount of energy released when one iron-56 nucleus is created from 26 protons and 30 neutrons.
So, the nuclear binding energy for this nucleus is 7.8978 x 10-11 J,
which is also the amount of energy required to decompose this nucleus into 26 protons and 30 neutrons.
Therefore, the nuclear binding energy for 1 mole of iron-56 is 4.7560 x 1010 kJ (this is about 48 billion of ), which is a tremendous amount of energy!
a + X Y + b
a is an incident particle,
X is a target nucleus,
Y is a residual nucleus,
b is an emitted particle.
Reactions where no ais involved are called decays [alpha, beta, gamma decays or rays].
1 Ci = 3.7 × 1010Bq
meaning that these elements have unstable nuclei and are radioactive.
The radioactive decay and transmutation process will continue until a new element is formed that has a stable nucleus and is not radioactive.
U238 Nucleus Thorium-234 + alpha decay
Alpha particle 2p + 2n
Carbon-14 nucleus –
In beta decay, a neutron from an atom will split into one positively charged proton & a negatively charged electron
C-14 [6p, 8n, 6e] ??[6+1p, 8-1n, 1e] N-14 [7p, 7n, 7e]
So, Carbon-14 Nitrogen-14 nucleus
1n 1p + 1e
Some isotopes decay very rapidly and, therefore, have a high specific activity.
Polonium-215 0.0018 seconds
Bismuth-212 60.5 seconds
Sodium-24 15 hours
Iodine-131 8.07 days
Cobalt-60 5.26 years
Radium-226 1600 years
Uranium-238 4.5 billion years
Half of the U-238 atoms have decayed to Thorium atoms!
λ = h／p
where,h is Planck’s constant
λ = 2.86×10−11E−1/ 2(m)
This energy is extremely large compared with that of a nucleus.
Nuclear fission by a thermal neutron is called thermalfission and
The only naturally-occurring elements that are useful as nuclear fuel are uranium - U and thorium - Th.
- the size of the nucleus and
- the distance that the neutron travels per unit time.
Thus, to express the quantity of neutrons, it is more convenient to use the product of the neutron number density nandthe velocity v
φ (r, E, t) = vn (r, E, t)
ionization chamber, proportional counters, Geiger-Muller counters, etc.
scintillation counter, Cerenkov counter
3. Based on the visualization of the tracks of the radiation
cloud chamber, bubble chamber, spark chamber