lecture9 (chap 9)

7/28/2019 Lecture9 (Chap 9)

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Nuclear Physics and Radioactivity

Nuclear Structure

Radioactivity

Radioactivity Decay and Activity

Radiation Detectors

Nuclear Reaction


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31.1Nuclear Structu re

The atomic nucleus consistsof positively charged protons

and neutral neutrons.


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neutronsofNumber

protonsofNumber

neutronsandprotonsofNumber

NZA

atomic

number

atomic mass number/

nucleon no.

A = 27, Z = 13

N = A-Z = 14

Al27

13

Example:


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Nuclei that contain the same number of protons but a different

number of neutrons are known as isotopes.

C126

Example:

98.9% 1.1%

C136


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3115m102.1 Ar


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31.3The Mass Def ic i t of the Nucleus and Nuclear Bind ing Energy

22deficitMassenergyBinding cmc


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Example 3The Binding Energy of the Helium Nucleus Revisited

The atomic mass of helium is 4.0026u and the atomic mass of hydrogen

is 1.0078u. Using atomic mass units, instead of kilograms, obtain thebinding energy of the helium nucleus.


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u0304.0u0026.4u0330.4 m

MeV5.931u1

MeV3.28energyBinding


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31.4Radioactivi ty

A magnetic field separates three types (, , ) of particles emitted by

radioactive nuclei.

Conservative Law:

No of nucleons (proton + neutrons) before decay = No of nucleons after decay


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31.4Radioactivi ty

DECAY

HeDP 2242

A

Z

A

Z


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31.4Radioactivi ty

A smoke

detector


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31.4Radioactivi ty

DECAY

eDP 011 A

Z

A

Z


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31.4Radioactivi ty

DECAY

PP AZ

A

Z

excited energy

statelower energy

state


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31.4Radioactivi ty

Gamm a kni fe

31 6 R di t i D d A t i i t


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31.6Radioact ive Decay and Act iv i ty

The half-life of a radioactive decay is the time in which

of the radioactive nuclei disintegrate.

; t=0, N=No

When N = No, t = T1/2,

t

oeNN

2ln21 T

Activity = , no. of disintegration = -N ; unit Bq (becquerel) or Ci (curie)

time interval where is decay constantt

N

31 6 R di t i D d A t i i t


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31.6Radioact ive Decay and Act iv i ty

31 9 R di t i D t t


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31.9Radiat ion Detecto rs

A Geiger cou nter

31 9 R di t i D t t


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31.9Radiat ion Detecto rs

A scint i l lat ion

counter

32 2 Induced Nuclear Reactio ns


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32.2Induced Nuclear Reactio ns

A nuclear react ionis said to occur whenever the incident nucleus,

particle, or photon causes a change to occur in the target nucleus.



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Examp le 3An Induced Nuclear Transmutation

An alpha particle strikes an aluminum nucleus. As a result,

and unknown nucleus and a neutron are produced.

nXDHe 1027

13

4

2 A

Z

P30

15



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An induced nuclear reaction in which

uranium is transmuted into plutonium.

24, 100 yrs

lecture9 (chap 9)

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