Devuce

1. REVIEW LECTURE-
10
UNIT-10 (ATOMIC
SPECTRA AND NUCLEAR
PHYSICS)

2. Spectrum
Spectrum means set of frequencies absorbed or emitted by a substance.
Emission spectra fall into following three categories
(a) Continuous spectra
(b) Line spectra
(c) Band spectra
ATOMIC SPECTRA / LINE SPECTRUM

3. Spectrum of Hydrogen
Number of spectral lines =
𝑛 𝑛−1
2

5. It is a mixture of classical and modern physics.
Main Points of Bohr’s Atomic Model
 An electron can revolves only in those orbits in which
their angular momentum is integral multiple of
ℎ
2𝜋
.
mv𝑛𝑟𝑛 =
nh
2𝜋
 As long as electron remains in an allowed orbit, its energy
remains constant,
 Emission of energy from atom takes place only when its
electron undergoes down transition between two allowed
orbits.
E = En-Ep = hf
BOHR’S MODEL OF THE HYDROGEN ATOM

6.  𝑟𝑛 =
𝑛2ℎ2
4𝜋2𝑚𝑒2𝑘
rn = r1 n2 Where 𝑟1 =
ℎ2
4𝜋2m e2
𝑘
= 0.53A°
Similarly, r2 = 4r1 and r3 = 9 r1 and so on.
Quantized Radii

7.  En = K.E+P.E
 𝐾. 𝐸 =
𝑘𝑒2
2𝑟𝑛
𝑃. 𝐸 =
−𝑘𝑒2
𝑟𝑛
 𝐸𝑛 = −
𝐸𝑜
𝑛2 Where 𝐸𝑜 =
2𝜋2𝑒4mk
2
ℎ2 = 13.6eV
 E1 = -13.6eV for n = 1 E2 = -3.4 eV for n = 2 and so on.
 Formula for the wavelength of nth orbit is given as;
1
𝜆𝑛
= 𝑅𝐻
1
𝑝2 −
1
𝑛2
Where n > p
RH = Rydberg’s constant =1.0974 x 107 m-1.
Quantized energies

8. In excited state the total energy is E, what is K.E with
proper sign
(a) 2E
(b) -E/2
(c) 2/E
(d) -E
QUESTION-1

9. A Balmer line is emitted when the electron in a hydrogen
atom jumps from
(a) A higher orbit to the first orbit
(b) A higher orbit to the second orbit
(c) The first orbit to a higher orbit
(d) The second orbit to a higher orbit
QUESTION-2

10. • The nucleus is very small part which exists at the center of the
atom.
• Nucleus was discovered by Rutherford through his –
scattering experiments.
• The whole positive charge and almost the whole mass of an
atom resides inside the nucleus.
• The charge on the nucleus is (+ Ze). It is due to protons
present in the nucleus.
• The radius of the nucleus is the order of 10–15 to 10–14m.
• In lighter nuclei (N = Z) e.q. 7𝑁14
etc.
In heavier nuclei (N > Z) e.g. 92𝑈238
,90 𝑇ℎ294
etc.
• The neutrons and protons present inside the nucleus taken
ATOMIC NUCLEUS

11. Isotopes
The atoms of an element having same atomic number but
different atomic mass number,
e.g. Hydrogen 1H1
,1 H2
,1 H3
an d Oxygen:8 O16
,8 O17
,8 O18
Isobars
The nuclei having same number of nucleons (A) but
different number of protons (Z). They also have different
number of neutrons. For example
(a)1H3
and2He3
(b) 6C14
and7N14
Isotones
The nuclei having equal number of neutrons are called
isotones.
7 8 3 4

12.  Nuclei having Z > 82 are unstable and they emit α,  and
𝛾 rays;
 Some radioactive elements are Po (Z=84) Rd (Z=88) and
U (Z=92) etc.
 -decay Charge no. (Z) decreases by 2 and mass no. (A)
by 4
𝑍𝑋𝐴
𝑍−2𝑌𝐴−4
+2 He4
e.g. 92𝑈238
90Th
234
+2 He4
.
RADIOACTIVITY

13.   decay 𝑧𝑋𝐴
𝑧+1𝑌𝐴
+−1 𝑒𝑜
Only charge no. (Z) increases by 1.
e.g. 11Na24
12Mg24 +−1 𝑒0
The daughter nucleus remaining after emission of -
particles is an isobar of the parent nucleus.
 -decay –rays are massless photons; their emission will
cause no change either in A or Z of the parent nuclide. -
decay is due to de-excitation of nucleus.
e.g. 𝑍𝑋𝐴 ∗
𝑍𝑋𝐴
+ 𝛾
Where  sign show excitation of atom

14.  Radioactive elements disintegrate and emit α, β and γ
radiations. This process is called transmutation by spontaneous
disintegration.
 In the natural spontaneous disintegration of a radioactive
material not all the atoms disintegrate at the same time.
 The process of disintegration takes place randomly, when a
nucleus disintegrates, nobody knows
HALF-LIFE AND RATE OF DECAY
 Radioactive decay is a random process so we get idea of half-
life.
 The half-life T1/2 of a radioactive element is that period in
which half of the atoms decay.
 Half-life (T1/2) depends on element and is not affected by any
physical change or chemical change.
SPONTANEOUS AND RANDOM NUCLEAR DECAY

15.   T1/2 = ln2 = 0.693
Where  is called decay constant depends upon nature of
material.  Decay constant of any element is equal to the
fraction of the decaying atoms per unit time. The unit of
the decay constant is s-1.
 The decay curve shows that radioactive element decay
exponentially

16. Laws of Radioactivity
 N/t  No or A  - N
 N/t = No or A = - N
𝜆 =
−𝐴
𝑁
= −
𝛥𝑁
𝛥𝑡
𝑁
=
−𝛥𝑁
𝑁𝛥𝑡
=
−𝛥𝑁
𝑁
𝛥𝑡
 Nt = etNo
𝑁𝑅 = 𝑁𝑜
1
2
𝑛
𝑁𝑑 = 𝑁𝑜
2𝑛−1
2𝑛
QUESTION-3

17. Half Life of some Radioactive Elements
QUESTION-4

18. Radiations can damage living tissues. The degree and
type of damage depend on several factor, strength and
energy of radiation as well as property of matter. Alpha
particles cause extensive damage but have small
penetration power. The neutrons penetrate deeper,
casuing significant damage.
 Incident radiations Damage to ozone layer is done
through following sources: -Chemical industry
Nuclear tests
CFC (chlorofluorocarbons)
Aerosol sprays and plastic foam industry
BIOLOGICAL EFFECTS OF RADIATION

19. Effects of radiations are of two types:
Somatic Effect:
Somatic effect is a radiation damage to any cell such
as, skin cells, lung cells. It causes of cancer or seriously
alter the characteristics of specific organisms.
Genetic Effects:
Genetic effect is a radiation damage to only
reproductive cells. Due to damage the genes in the
reproductive cells, genetic effect causes defective off
spring or mutation.

20. Absorbed Dose
 𝐷 =
𝐸
𝑚
Its SI unit is gray (Gy). 1 Gy = 1 J kg-1
An old unit is rad. 1 rad = 0.01 Gy
Equivalent Dose
It is defined as the product of absorbed dose and RBE
(relative biological effectiveness)
1 Sv = 1 Gy x RBE (SI Unit)
Old Unit 1 rem = 0.01 Sv

21. Radiations are widely used in medicine, diagnostic
examination, biological research and education for a
range of purpose. We will explain
1. Radiation therapy
2. Diagnosis of diseases
3. Tracer techniques
BIOLOGICAL AND MEDICAL USES OF RADIATION

22. Subatomic particles are divided into three groups
Photons
Leptons (electron, muons and neutrinos) Hadrons
There are two types of hadrons
Baryons (the particles equal in mass or greater than
protons are called baryons e.g. protons and neutrons)
Mesons (the particles lighter than proton e.g. 𝜋 mesons)
A pair of quark and anti-quark makes a meson and 3
quarks make a baryon.
Hadrons are composed of elementary particles called
quarks.
BUILDING BLOCKS OF
MATTER

23. Half life of radium is 1590 years. In how many years shall
the earth loss all its radium due to radioactive decay?
(a) 1590×106 years
(b) 1590×1012 years
(c) 1590×1024 years
(d) Never
QUESTION-1

24. Tungsten-176 has a half-life of 2.5 hours. After how
many hours will the disintegration rate of a tungsten-176
sample drop to
1
16
its initial value?
(a) 5
(b) 8.3
(c) 10
(d) 13
QUESTION-2

25. In which sequence the radioactive radiations are emitted
in the following nuclear reaction.
𝑧𝑋𝐴
𝑧+1𝑌𝐴
z −1𝑍𝐴−4
z −1𝑌𝐴−4
(a) ,,
(b) ,,
(c) ,, 
(d) , , 
QUESTION-3

26. Curie is a unit of
(a) Energy of -rays
(b) Half life
(c) Radioactivity
(d) Intensity of -rays
QUESTION-4

27. Various types of cancer are treated by _____________
(a) Cobalt-60
(b) Strontium-90
(c) Carbon-14
(d) Nickel-63
QUESTION-5