Chapter 1 Structure of matterChapter 2 Nuclear transformation

The nucleus

isotope same Nproton, different Nneutron

isotone same Nneutron, different Nproton

isobar same (Nneutron+ Nproton), different Nproton

isomer same Nproton, same Nproton,

different nuclear energy state

XAZ

A the mass number (Nproton+ Nneutron)Z the atomic number (Nproton )

Charts of isotopes

Z=N

Isotope

Isobar

Isotone

Atomic mass and energy units

1 amu = mass of =1.6610-27 kg 1 eV =1 V1.602 10-19 C =1.602 10-19 JEinstein’s principle of equivalence of mass and energy

C12612

1

MeV0.511

m/sec103kg109.12831

2

2

cm

mcE

e

Decay constant ()

Nt

NN

t

N

or

teN

N

tNN

NC

Nt

CtN

dtN

dN

0

0

0

0

lnln

ln

ispresentnumberthe,0If

ln

teNN 0

Activity

1 Ci =3.71010 disintegrations/sec =3.71010 dps =3.71010 Bq

teAA

Nt

NA

0

The half-life (T1/2) & the mean life (T)

The half-life (T1/2) The mean life (T)

2/1

0

2ln2

12

1

2/1

T

e

NN

T

693.02ln

2/1 T

00 NNT

2/12/1 44.1

693.0

1T

TT

Radioactive equilibrium

22112

011

NNdt

dN

eNN t

teN

N )12(

12

0112 1

)(

teA

A )12(

12

112 1

Transient equilibrium

T1>T2 (1<2)

Transient equilibrium

time

activ

ity

112

22 AA

Secular equilibrium

T1>>T2 (1<<2)

A2 = A1

Secular equilibrium

time

activ

ity

particle decay

Q = the disintegration energy

= the difference in mass between the parent nucleus and product nuclei

E 510 MeV (discrete energy)

QHeYX 42

4A2Z

AZ

Negatron(-) emission

An excessive number of neutrons or a high neutron-to-proton (n/p) ratio

anti-neutrino Q = the difference in mass between and the

sum of the masses of and the particles emitted.

QνYX AZ

AZ

~011 β

~

XAZ

YAZ 1

Positron(+) emission

A deficit of neutrons or a low n/p ratio

neutrinoAnnihilation

QνYX AZ

AZ β011

ν

+positron

free electron

0.511 MeV photon

0.511 MeV photon

The -ray spectrum

The average energy of the particles is approximately Emax/3.

Electron capture

The unstable nuclei with neutron deficiency may increase their n/p ratio by EC.

An alternative process to the positron decayK capture characteristic x-rays

(L or M capture) Auger electrons

ν nep 10

01

11

QνYeX AZ

AZ 1

01

K

LM

hole

Characteristic radiation

An empty hole in a shell is filled by electron from outer shell with an emission of characteristic radiation.discrete energy

h=EK - EL

K

LM

hole

Auger Electrons

The absorption of characteristic x-rays by orbital electrons and reemission of the energy in the form of monoenergetic electronsdiscrete energy

E=h-EM=EK – EL-EM

Nuclear reactions (1)

The , p reaction– – Threshold energy– AX (, p) A+3Y

The , n reactionProton bombardmentDeuteron bombardment

QYX AZ

AZ

HHe 11

42

31

Nuclear reactions (2)

Neutron bombardment– Neutron, no electric charge effective in penetrating the nuclei and producing nuclear reactions– – n, reaction

Photon disintegrationFission– Chain reaction

Fusion

HeLinB 42

73

10

105

Activation of nuclides

The yield of a nuclear reaction– The number of bombarding particles– The number of target nuclei– The probability of the occurrence

• Cross-section– 1 barn = 10-24 cm2

The growth of activity– Saturation activity

Thank you for your attention!