Nuclear Physics

Gold Foil Experiment

Gold Foil Experiment

Alpha Particles are directed to the center of a sensitive screen. A flash is seen where alpha particles fall on the screen. Alpha source is placed in a lead shield, to get a narrow beam of alpha particles. Lead shield is also to avoid backscattering of alpha particles. A very thin gold is placed in the pathway of alpha particles. Even when the thin sheet of gold is placed in the pathway of the alpha particle beam, the flash on the screen does not disappear. More fashes are seen in different positions positions of the screen

Explain the observations

Most of the alpha particles passed straight and do not deviate. Fewer alpha particles are deflected with a small angle (acute).

explain why most of the particles passed straight forward with no deviation

Most of the atom is empty space so alpha particles are not stopped

Explain why some particles are deviated at an obtuse angle

1. There is a heavy nucleus

2. The nucleus is tiny nucleus and very small compared with the whole size of the atom

3. The nucleus is positively charged

Explain why some alpha particles are deviated with an acute angle

The nucleus of the atom is positively charged so as alpha particles carries the same charge they are repelled.

what is the old model of an atom?

the atom is a sphere with positive and negative charges evenly distributed among the sphere and this idea was incorrect

how is an ion formed?

when one or more electrons is gained or lost

what is the mass of an electron?

1840 times smaller than a proton or

1/1840 mass of a proton

what is an isotope?

atoms of the same element with the same number of protons but a different number of neutrons

OR

Atoms of the same element with same atomic number but different mass number

When does an atom emit alpha, beta, or gamma radiation? What is this process called?

When an unstable isotope is transformed into a stable one it emits radiation. The new stable atom is an isotope of a totally different element. This is called radioactive decay. This process is spontaneous and random.

Why may an isotope be radioactive?

due to excess neutrons in the nucleus and the nucleus being too heavy.

properties of alpha particles

1. What is it?

2. What does it consist of?

3. What is its symbol?

4. What is its ionisation power?

5. What is its penetration?

6. What is its shielding and screening?

7. What is its range in air?

8. What is its charge?

9. What is its mass?

10. What is its deflection with electric and magnetic fields?

1. nucleus of helium -4

2. 2 protons +2 neutrons

3. 4 He 2

4. very strong

5. very weak

6. stopped by paper

7. about 6 cm

8. +2

9. 4 times the mass of a proton

10. Slightly deflected by electric and magnetic fields

Beta particles

1. What is it?

2. What does it consist of?

3. What is its symbol?

4. What is its ionisation power?

5. What is its penetration?

6. What is its shielding and screening?

7. What is its range in air?

8. What is its charge?

9. What is its mass?

10. What is its deflection with electric and magnetic fields?

1. high speed electron emitted from the nucleus

2. An electron

3. 0 e -1

4. weak

5. moderate

6. stopped by a few mm of aluminum

7. about 100 cm

8. -1

9. 1/1800 proton mass

10. strongly deflected by electric and magnetic fields

gamma rays

1. What is it?

2. What does it consist of?

3. What is its symbol?

4. What is its ionisation power?

5. What is its penetration?

6. What is its shielding and screening?

7. What is its range in air?

8. What is its charge?

9. What is its mass?

10. What is its deflection with electric and magnetic fields?

1. high energy (short wavelength) electromagnetic radiation high frequency

2. electromagnetic radiation

3. weird ass gamma ray symbol

4. very weak nearly 0

5. very high

6. thick lead, concrete and steel

7. longer than 100 m

8. 0

9. 0

10. not deflected by electric or magnetic fields

What 3 things can be used to measure radiation?

1. Photographic

2. Geiger-Muller Detector

3. Cloud chamber

What is background radiation?

It is the normal radiation of surround with no radioactive sources present

What are natural causes of background radiation?

1. from earth and rocks

2. radioactive gases

3. space (cosmic rays)

4. the sun

What are artificial causes of background radiation?

from man like nuclear power stations and nuclear experiments

correction to the background

source reading - background reading

Unit of radiation measurement

Count/min and Count/s

What is half-life?

it is the time taken for the activity of the source to be reduced to half its original value