5Radioactivity and Nuclear transformation

📚
RADIOACTIVITY
▢ Discovery:

Table 1: Discovery of Radioactivity

Scientist
Discovery
Henri Becquerel
Radioactivity
▢ Units of Radioactivity:

Table 1: Units

Unit
Symbol
Value
Becquerel
Bq
1 disintegration per second / 1 dps
Rutherford
Rd
\(10^6\) dps / Bq
Curie
Ci
\(3.7 \times 10^{10}\) dps / Bq
▢ Nuclear Reactor Components:

Table 1: Components & Functions

Component
Function
Examples
Moderator
Slows down neutrons without absorbing them
Heavy water, graphite
Control rod
Absorbs excess neutrons
Boron, cadmium
Coolant
Removes heat from reactor core
Heavy water, He, \(CO_2\), air
❖ Coolant Note: Heavy water used in thermal reactor
▢ Nature of Radioactive Radiations:

Table 1: Alpha, Beta & Gamma Rays

Property
\(\alpha\)-rays
\(\beta\)-rays
\(\gamma\)-rays
Nature
\(_2^4He^{2+}\)
Electron / \(e^-\)
Electromagnetic radiation
Charge
Positive
Negative
Neutral
Electric field effect
Attracted toward negative plate
Deflected toward positive plate
Not deflected
Magnetic field effect
Deflected
Deflected
Not deflected
Velocity
\(\frac{1}{10}\) of velocity of light
Nearly equal to light
Velocity of light
Penetrating power
Low
Greater than \(\alpha\)
Maximum
Ionizing power
Highest
Moderate
Low
Kinetic energy
High
Moderate
Low
Photographic plate
Strong effect
Strong effect
Slight effect
ZnS screen
Strong effect
Little effect
Slight effect
❖ Order:

Table 1: Power Order

Property
Order
Penetrating power
\(\alpha < \beta < \gamma\)
Ionizing power
\(\alpha > \beta > \gamma\)
Deflection in field
\(\beta > \alpha > \gamma\)
▢ Causes of Radioactivity:
❖ Nuclear Stability: Stable nucleus → \(\frac{n}{p}\) close to 1

Table 1: n/p Ratio & Emission

Condition
Emission
\(\frac{n}{p} < 1\)
\(\alpha\)-rays
\(\frac{n}{p} > 1\)
\(\beta\)-rays
Secondary nuclear effect
\(\gamma\)-rays
▢ Important Notes:
  • •
    \(\alpha\)-decay produces isodiaphers
  • •
    No radioactive substance emits both \(\alpha\) and \(\beta\)-particles simultaneously
  • •
    \(\gamma\)-rays emitted after \(\alpha\) or \(\beta\)-emission
  • •
    \(\gamma\)-emission → no change in mass number
  • •
    \(\gamma\)-emission → no change in atomic number
  • •
    \(\gamma\)-emission → change only in nuclear energy
  • •
    Rate of decay independent of temperature
  • •
    Activation energy of radioactive decay = 0
▢ Radioactive Decay Law:
❖ Equation: \(-\frac{dN}{dt} = \lambda N\)

Table 1: Symbols

Symbol
Meaning
\(N\)
Number of radioactive nuclei present
\(-\frac{dN}{dt}\)
Rate of disintegration / activity
\(\lambda\)
Decay constant
▢ Measurement of Radioactivity:
  • •
    Geiger-Muller counter
  • •
    Wilson cloud chamber
  • •
    Electroscope
▢ High-Yield Recall:

Table 1: Radioactivity One-Liners

Fact
Answer
Radioactivity discovered by
Henri Becquerel
1 Bq
1 dps
1 Rutherford
\(10^6\) dps
1 Curie
\(3.7 \times 10^{10}\) dps
Moderator function
Slow down neutrons
Moderator examples
Heavy water, graphite
Control rod function
Absorbs excess neutrons
Control rod examples
Boron, cadmium
\(\alpha\)-particle
\(_2^4He^{2+}\)
\(\beta\)-particle
Electron / \(e^-\)
\(\gamma\)-ray
Electromagnetic radiation
Most penetrating ray
\(\gamma\)-ray
Most ionizing ray
\(\alpha\)-ray
Least penetrating ray
\(\alpha\)-ray
Least ionizing ray
\(\gamma\)-ray
Radiation not deflected by field
\(\gamma\)-ray
\(\alpha\)-decay produces
Isodiaphers
\(\gamma\)-emission changes
Energy only
Radioactive decay equation
\(-\frac{dN}{dt} = \lambda N\)
Radioactivity detector
Geiger-Muller counter
Q1.
Radioactivity was discovered by
Q2.
Radius of the nucleus is related to the mass number A by
Q3.
A device used for the measurement of radioactivity is a
Q4.
Which is not emitted by radioactive substance?
Q5.
An α-particle is identical with
Q6.
Gamma rays are
Q7.
Positron is
Q8.
Which leaves no track on Wilson cloud chamber?
Q9.
Of the following radiations, the one most easily stopped by air is
Q10.
In radioactive decay, which one of the following moves the fastest?
Q11.
Cathode rays are deflected by
Q12.
A magnet will cause the greatest deflection of
Q13.
The ratio of charge of a proton and an α-particle is
Q14.
92U238 emits an α-particle, the product has mass number and atomic number
Q15.
Loss of a β-particle is equivalent to
Q16.
Tritium undergoes radioactive decay giving
Q17.
The reaction 5B8 → 4Be8 + 1e0 takes place due to
Q18.
The number of α- and β-particles emitted in nuclear reaction 90Th228 → 83Bi212 are respectively
Q19.
Isobars are formed when emission of ___ takes place
Q20.
Radioactive disintegration differs from a chemical change in being
Q21.
Which element is the end product of natural radioactive series?
Q22.
Radioactivity decay is a reaction of
Q23.
The half-life of 92U238 is 4.5 × 109 years. After how many years, the amount of 92U238 will be reduced to half of its present amount?
Q24.
75% of a first-order reaction was completed in 32 minutes. When was 50% of the reaction completed?
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Q25.
The half-life period of a radioactive element is 30 min. One-sixteenth of the original quantity remains unchanged after
Q26.
The half-life period of a radioactive material is 15 minutes. What percent of that radioactive material will remain after 45 minutes?
Q27.
A radioisotope has a half-life of 20 hours, after 60 hours the fraction of this isotope left is
Q28.
If 2.0 g of a radioactive isotope has a half-life of 20 hr., the half-life of 0.5 g of the same substance is
Q29.
The half-life period of a radioactive element is 140 days. After 560 days, one gram of the element will reduce to
Q30.
What is the value of decay constant of a compound having half-life time, t1/2 = 95 days?
Q31.
A radioactive element has a half-life of 20 mins. How much time should elapse before the element is reduced to 1/8th of the original mass?
Q32.
After 2 hours, the radioactive substance becomes 1/16th of original amount. The t1/2 in minutes is
Q33.
The age of most ancient geological formation is estimated by
Q34.
Atoms of the same atomic number but different atomic weights are known as
Q35.
The relative abundance of two isotopes of atomic weight 85 and 87 is 75% and 25% respectively. The average atomic weight of element is
Q36.
Ordinary oxygen contains
Q37.
Two nuclei which are not identical but have the same number of nucleons represent
Q38.
Atoms with the same mass number but having different nuclear charges are called
Q39.
20Ca40 and 19K40 are
Q40.
Elements having same number of nucleons and different number of protons are
Q41.
Ca2+ is isoelectronic with
Q42.
A possible material for use in nuclear reactors as a fuel is
Q43.
In nuclear reactor the control rods are made of
Q44.
Hydrogen bomb is based on the principle of
Q45.
If an isotope of hydrogen has two neutrons in its atom, its atomic number and mass number will respectively be
Q46.
The radiation which has highest penetrating power is
Q47.
Which of the following is used as moderator in nuclear reactors?
Q48.
Which of the following is a man-made element?
Q49.
β-Particle is emitted in radioactivity
Q50.
The phenomenon of radioactivity arises from the
Q51.
The first artificial disintegration of an atomic nucleus was achieved by
Q52.
Unstable substances exhibit higher radioactivity due to
Q53.
The binding energy of 8O16 is 127 MeV. Its binding energy per nucleon is
Q54.
11Na23 is a more stable isotope of Na. Find out the process by which 11Na24 can undergo radioactive decay.
Q55.
Which one of the following radioisotopes is used in the treatment of blood cancer?
Q56.
Half-life of a radioactive substance which disintegrates by 75% in 60 minutes will be
Q57.
A sample of wood decayed to 1/16 of its original value. What is the number of T1/2?
Q58.
The compound used in enrichment of uranium for nuclear power plant is
Q59.
A radioactive substance disintegrates to 1/16th of its original mass in 160 days. Then its half-life period is
Q60.
The half life of 6C14 (if its λ is 2.31 × 10-4) is:
Q61.
The proper rays for radiocarbon dating are
Q62.
The reactor used to convert fertile form to fissible form is
Q63.
Highest ionising power is exhibited by
Q64.
In a radioactive decay, an emitted electron comes from
Q65.
90Th228 → 83Bi212 by
Q66.
Thorium (atomic mass 232 and atomic no. 90) is converted to lead isotopes (atomic mass 208 and atomic no. 82) then no. of α and β particles emitted is
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