PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

UNAWEZA JIPATIA NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU: 0787237719

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PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

RADIOACTIVITY

This is the emission of radiations from heavily elements such as uranium whose nuclei are unstable.

Radiations emitted are called alpha $C:\thlb\cr\tz\__i__images__i__\1we1.PNG$ , Beta (β) particles and gamma $C:\thlb\cr\tz\__i__images__i__\368.PNG$ rays.

RATE OF DISINTEGRATION

The number of atoms of radioactive elements disintegrating per second $C:\thlb\cr\tz\__i__images__i__\450.PNG$ is directly proportional to the number of atom present at that instant.

$C:\thlb\cr\tz\__i__images__i__\529.PNG$

Where λ = decay constant

The negative sign (-) indicates that N decreases as time (t) increases.

If N₀ is the number of atoms at time t= 0 and N is the number of atoms at time t. then:-

$C:\thlb\cr\tz\__i__images__i__\4468.PNG$

HALF LIFE

The half life time $C:\thlb\cr\tz\__i__images__i__\726.PNG$ of a radioactive element is the times taken for the atoms disintegrate to half their initial number.

NECTA 1994/1/19

Draw a graph of $C:\thlb\cr\tz\__i__images__i__\916.PNG$

SOLUTION:

This is the graph of radioactive decay in time.

$C:\thlb\cr\tz\__i__images__i__\109.PNG$

$C:\thlb\cr\tz\__i__images__i__\4467.PNG$

X-RAYS

X-rays are produced by bombarding a target of heavy metal with high energy electron.

NECTA 1984/2/8

The emission of X-rays may be regarded as the inverse of photo electric effect.Explain

SOLUTION

X-Rays which are waves are produced by bombarding a hard metal with electrons(particles)where as in photoelectric effect electron(particles) are liberated from ametal surface by incident radiation(waves)

MODERN X-RAY TUBE

$C:\thlb\cr\tz\__i__images__i__\x-ray3.jpg$

Electron are obtained from the filament by thermionic emission and are accelerated to the anode having small target of high melting point such as tangstem.

X-RAY QUANTITY

Refers to the intensity of X-rays which increases with the number of electrons limiting the target.This depends on the cathode temperature controlled by the heating current

X-RAY QUALITY

Refer to the penetrating power of X-ray and determined by velocity whith which electrons strikes the target.

SOFT X-RAY:
Are those which can penetrate soft objects such as flesh

HARD X-RAY
Are those which can vibrate much more solid material

PROPERTIES OF X-RAY

1.They travel in a straight line.

2.They readily penetrate matter.

3.They affect photographic plates

4.They are not deflected by electric or magnetic field,because they have no charge

They are wave of wavelength 1⁰A

X-RAY SPECTRA

$C:\thlb\cr\tz\__i__images__i__\x-ray_spectra.jpg$

CONTINUOUS SPECTRUM

Explained by electromagnetic theory.

It is due to electrical interaction between the bombarding electrons and the nuclei of the target atom

An electron approaching a positively charged nucleus is accelerated and according to electromagnetic theory accelerated motion is accompanied by emission of radiations in this case x-ray

DISCRETE SPECTRA

These are explained by quantum theory.They are produced when the incident electron interact with electron close to nucleus of the target atom.The bombarding electrons knock off electron in their orbits and the created gaps are filled by electrons in the high energy levels,when they moves in these gaps they produce x-ray photon.

The cut off wavelength or short wave limit(λ min)

This is the minimum wavelength of x-radiations which corresponds to the maximum energy of the X-rays produced by electrons which have given out all their K.Æ on a single encounter with the target nucleus

ENERGY OF X – RAY:

Energy of an electron striking the atom of the target is eV where e = electronic charge.

V = p.d across the X-ray tube.

If a direct collision is made with a target atom and the energy is absorbed then on quantum theory X-rays produced hence a maximum energy hV

Therefore

eV = 1/2mV2 = hV

eV = hc/ λ minimum

λmin = hc/eV

$C:\thlb\cr\tz\__i__images__i__\re13_edit.png$

NECTA 1989/1/18

Calculate the wavelength of most energetic X-rays produced by a tube operating at 1.0 x 10⁵V.

USES OF X – RAYS

1.in investigation of suspected bone fractures

2.Detection of lung tuber culosis (feased tissue is denser than a heatthy one).

3.Treatment of cancer (cancer cells are killed by X-rays)

4.Casting and welding joints can be inspected for internal imperfection.

5.It is used in the study of crystal structure refer to Bragg’s law.

PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

NUCLEAR FISSION FUSSION

Nuclear fission is a splitting disintegrating of heavy nucleus such as uranium into two other lighter nuclei (with several neutrons)

Example:

$C:\thlb\cr\tz\__i__images__i__\1418.PNG$

Nuclear fusion

This is the combination of light nuclei to form a heavier nucleus.

Example:

$C:\thlb\cr\tz\__i__images__i__\1613.PNG$

NECTA 1990/2/8

(1)Both fission and fusion are source of energy

Explain.

SOLUTION:

Fission-During disintegration of heavy nucleus such as uranium, energy is released which is

transformed into K.E of fragments.

Fussion-When light nuclei are fused together a large amount of energy is released in term of heat.(eg

in the sun)

PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

PHYSICS FORM 6-ATOMIC PHYSICS-NUCLEAR PHYSICS

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