22 - 23 Theory

Question 1

State law of electrostatics

Answer 1

Identical charges exert a repelling force on each other

Question 2

What is nuclear force?

Answer 2

The force exits between nucleons that holds nuclear constituents together (pre- vent the repelling of identical charges, charge-independent)

Question 3

What is mass defect?

Answer 3

The mass of a nucleus is less than the mass of its constituent nucleons.

(The reason the actual mass is different from the masses of the components is because some of the mass is released as energy when protons and neutrons bind in the atomic nucleu)

Question 4

What are nucleons?

Answer 4

Protons and neutrons

Question 5

What is binding energy of nucleons

Answer 5

The energy corresponding to the mass defect

Question 6

What is Binding energy per nucleon?

Answer 6

The strength of a nuclear bond

Question 7

What are isotopes

Answer 7

Atoms of the same element with

• the same number of protons
• different numbers of neutrons
• different mass number

Question 8

Light nucleus are most stable when ____

Answer 8

N=Z

Question 9

Heavy nuclei are most stable when

Answer 9

N>Z

Question 10

Describe nuclear stability

Answer 10

As the number of protons increases, the Coulomb force increases and so more neutrons are needed to keep the nucleus stable

Question 11

3 stability rules

Answer 11

(1) There are more stable nuclei with even, than with odd number atomic num- bers
(2) There are more stable nuclei with even, than with odd number neutron numbers
(3) There are more stable nuclei with even, than with odd number mass num- bers

Question 12

What is radioactivity?

Answer 12

the spontaneous release of energy in the form of particles or electromagnetic waves

the result of decay of unstable nuclei

Question 13

What is radioactive decay?

Answer 13

Spontaneous decay of unstable parent nucleus into a more stable daughter nucleus & constituents/particles & energy

Question 14

What is activity of radioactive decay?

Answer 14

number of nuclei decayed in a unit time (characterizes the quantity and quality of radioactive substances)

Question 15

State the law of radioactive decay

Answer 15

The rate of decay is proportional to the number of radioactive nuclei present.

Question 16

What is specific activity?

Answer 16

activity in a unit mass of isotope (Bq/kg)

Question 17

Describe average lifetime of radioactive nuclei

Answer 17

The time within which the number of atomic nuclei is decreased exponentially with the decay constant and half-life

Question 18

What is half-life (T) of radioactive decay?

Answer 18

A period during which number of undecayed nuclei is decreased to half of the original number

Question 19

2 things that activity depends on

Answer 19

the type of isotope and

the size of the population of unstable (radioactive) nuclei

Question 20

Which types of radiation participate in direct ionization?

Answer 20

Question 21

Which types of radiation participate in indirect ionization?

Answer 21

Question 22

Describe alpha-decay

Answer 22

• For heavy atoms
• A parent nucleus → A daughter nucleus + alpha particle
• Alpha particle = 2 protons + 2 electrons

Question 23

Why do protons and electrons usually fall off from the parent nucleus on the edge?

Answer 23

Because that is where there is less strong nuclear force and greater electrostatic force

Question 24

Do all alpha particles have same velocity and kinetic energy? Why?

Answer 24

Yes

→ Because the decay is always the same

Question 25

Characteristics of spectrum of alpha particle

Answer 25

Line spectrum → shows that the kinetic energy of particles has an exactly determined value

Question 26

2 types of beta decay

Answer 26

* Beta minus decay * Beta positive decay

Question 27

Describe the spectrum of beta decay.

Answer 27

It is continuous → Because electrons have different energies → The spectrum shows that low number of beta particles possess the maximum number

Question 28

Do beta particles take all the energy?

Answer 28

Yes, they do not share the energy with other particles

Question 29

Describe beta minus decay

Answer 29

* When parent nucleus is unstable because there are **too many neutrons & too little protons** * Neutron → proton + electron + anti-neutrino

Question 30

Characteristics of anti-neutrino

Answer 30

* An anti particle of neutrino - has the mass of an electron but no charge * Why it appears? → Because turning a neutral particle to a positive one should should involve the production of a negative particle as well

Question 31

Does the mass number of atom stays the same after beta minus decay? Why?

Answer 31

It stays the same → No neutron or protons fall out while atomic number changes by +1 with the addition of proton (give a different chemical identity)

Question 32

Describe Beta positive decay

Answer 32

* When parent nucleus is unstable → because there are too many protons and too little neutrons * Protons → Neutron + positron + neutrino * The daughter nucleus has the atomic number -1

Question 33

what is positron?

Answer 33

* Anti-matter of electron * Having the same mass but opposite charge as

Question 34

Medical application of Beta plus decay

Answer 34

Used in POSITRON EMISSION TOMOGRAPHY (PET) SCAN

Question 35

Describe gamma decay

Answer 35

* When a nucleus loses & releases energy in the form of high frequency gamma photons * Unstable nucleus dissipates excess energy by a spontaneous electromagnetic process in the from of gamma radiation * Result → No change in atomic mass or atomic numbers

Question 36

Can alpha and beta particles escape the body easily?

Answer 36

No, only gamma

Question 37

Describe the spectrum of gamma radiation

Answer 37

* It is discrete → photons have a particular wavelength

Question 38

Describe penetration depth of alpha radiation

Answer 38

* Alpha particles are large and charged → Directly ionize atoms over a short distance → Low penetration depth and short effective range → High linear ion density (concentrated over area)

Question 39

Describe penetration depth of beta minus radiation

Answer 39

Beta particles is small and charged → Directly ionize atoms of matter but less energy loss → change the direction when they collide → The path is not linear and charge are distributed → Larger penetration depth and longer effective range

Question 40

Describe interaction of beta plus radiation

Answer 40

Undergo annihilation (not pair production) → masses of an electron and positron are converted to gamma photon energy upon collision →

Question 41

Describe interaction of gamma radiation with matter

Answer 41

Because gamma radiation is not charged → Indirectly ionizes (producing charged particles which then interaction with matter) → No effective range → Follow exponential attenuation law → Photoeffect + Compton scattering