Nuclear Physics

Question 1

What is Rutherford scattering?

Answer 1

Experiments held by Ernest Rutherford consisting of alpha particles (+ charged particles, 2 protons and 2 neutrons aka helium nuclei). These experiments proposed:

1. The positive charge of the atom is densely concentrated at the center of the atom.
2. The nucleus is responsible for most of the mass of the atom.
3. The atom is mostly empty space.

Question 2

Radioactive Elements

Answer 2

Elements that transform into other elements spontaneously, emitting particles in the process.

Question 3

Nuclide

Answer 3

A distinct kind of atom or nucleus characterized by a specific number of protons Z (Atomic number) and neutrons N (Neutron muber).

Question 4

The total number of neutrons and protons in a nucleus is called its __________.

Answer 4

Mass number, A. Such that Z+N = A.

Question 5

Neutrons and protons, when considered collectively as members of a nucleus, are called ____________.

Answer 5

Nucleons.

Question 6

Nuclides with the same atomic number Z but different neutron numbers N are called _________ of one another.

Answer 6

isotopes.

Question 7

A ____________ is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle from the nucleus.

Answer 7

radionuclide.

Question 8

___________ _______ is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha decay, beta decay, and gamma decay, all of which involve emitting one or more particles or photons.

Answer 8

Radioactive decay

Question 9

Nuclides of the same mass number.

Answer 9

Isobar (Chemistry Definition).

Question 10

A convenient unit for measuring distances on the scale of nuclei is the ________.

Answer 10

femtometer; This unit is also called the fermi.

1 femtometer = 1 fermi = 1 fm = 10^-15 m.

Question 11

Scattering experiments allow us to assign to each nuclide an effective radius given by ________. What is the limit of this equation?

Answer 11

r = r₀A^1/3. Where r₀ ≈ 1.2 fm.

This does not apply to halo nuclides, (neuton-rich nuclides).

Question 12

The approximate mass of both the nucleus and the neutral atom for ^#X is precisely the same or different?

Answer 12

Same, provided by the Rutherford experiments. The mass of an atom is concentrated at the center of the atom.

Question 13

Scientists and engineers working with atomic masses often prefer to report the mass of an atom by means of the atom’s mass excess Δ, defined as what?

Answer 13

Δ = M - A.

Where M is the actual masss of the atom in atomic mass units and A is the mass number for that atom’s nucleus.

Question 14

The difference in mass energy between a nucleus and its individual nucleons is called _______ _______of the nucleus and is defined as what?

Answer 14

binding energy;

ΔE_be = Σ(mc²) - Mc².

Mc²: Mass energy of the nucleus.

Σ(mc²): mass energy of the individual parts.

If we were able to separate a nucleus into its nucleons, we would have to transfer a total energy equal to ΔE_be.

Question 15

The average energy needed to separate a nucleus into ists individual nucleons is called _______; What is the mathematical equation.

Answer 15

binding energy per nucleuon, ΔE_ben.

ΔE_ben = ΔE_be/A.

Question 16

In nuclear physics and nuclear chemistry, ______ ______is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei.

ex. uranium nuclei

Answer 16

nuclear fission.

Question 17

_______ _______is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles. The difference in mass between the reactants and products is manifested as either the release or absorption of energy.

ex. this occurs in the sun, thermonuclear weapons.

Answer 17

Nuclear fusion

Question 18

In nuclear physics and particle physics, the ______ __________ is the mechanism responsible for the strong nuclear force, and is one of the four known fundamental interactions, with the others being electromagnetism, the weak interaction, and gravitation.

Answer 18

strong interaction

Question 19

True or False: There is absolutely no way to predict whether any given nucleus in a radioactive sample will be among the small number of nuclei that decay during any given second. All have the same chance.

Answer 19

True. The laws for subatomic processes are statistical.

Question 20

What is the SI unit for the disintegration constant (or decay constant)?

Answer 20

[λ] = [s^-1].

Question 21

Give the equation that will predict the number of radioactive decays remaining, provided how many we start with, decay constant, and time t.

Answer 21

N = N₀e^-λ​t.

Start with -dN/dt = λN.

The rate of decay is proportional to the number N of radioactive atoms present with the proportionality constant of λ.

Question 22

What is the radioactive decay in terms of the decay rate R?

Answer 22

Differentiate N.

R = R₀e^-λt.

R = -dN/dt = λN₀e^-λt = R₀e^-λt.

Question 23

The total decay rate R of a sample of one or more radionuclides is called the _________ of the sample. The SI unit is the ________, and an older unit is _______.

Answer 23

activity; becquerel; curie.

Question 24

There are two common time measures of how long any given type of radionuclides lasts. What are they?

Answer 24

Half-life, T_1/2, and mean (average) life τ.

Question 25

How is the half life, T_1/2, and mean life, τ, realted?

Answer 25

T_1/2 = ln(2)/λ = τ ln(2).

Such that 1/λ = τ.

Question 26

Explain what an alpha decay is.

Answer 26

When a nucleus undergoes an alpha decay, it transforms into a different nuclide by releasing a helium nucleus ⁴He.

Ex. ²³⁸U → ²³⁴Th + ⁴He.

Question 27

Nuclei are held together by an attractive force acting among the nucleons, part of the ______ _______ acting between the quarks that make up the nucleons.

Answer 27

Strong Force.

Question 28

Alpha decays is inhibited by a potential energy barrier that cannot be penetrated accoding to classical physics but is subject to __________ according to quantum physics.

Answer 28

tunneling.

Question 29

In ____ _____ either an electgron or a positron is emitted by a nucleus, along with a neutrino. The emitted particles share the available disintegration energy. The electrons and positrons emitted in ____ _____ have continuous spectrum of energies from near zero up to a limit K_max ( = Q = -Δmc²).

Answer 29

beta decay.

Question 30

This model assumes that the nucleons, moving around within the nucleus at random, interact strongly with each other. The central feature of the __________ ________ of a compound-nucleus concept is that the formation of the compound nucleus and its eventual decay are totally independent events.

Answer 30

collective model

Question 31

The __________ _______ ______ assumes that each nucleon remains in a well-defined quantum state within the nucleus and makes hardly any collisions at all. This is opposite of it’s rival model.

Answer 31

Independent Particle Model.

Question 32

In the independent particle model, nuclei show closed-shell effects, associated with certain _____ ________ __________. This property is similar to that of atomic electrons when they arrange themselves in shells that have a special stability when fully occupied, such that in noble gases.

Answer 32

magic nucleon numbers.

Question 33

The central idea of a ______ ____ is that a single particle outside a ______ _____ can be relatively easily removed, but considerably more energy must be expanded to remove a particle from the shell itself.

Answer 33

closed shell.

Question 34

Consider a nucleus in which a small number of neutrons (or protons) exist outside a core of closed shells that contains that contains magic numbers of neutrons or protrons. The outside nucleons occupy quantized states in a potential well established by the central core, thus preserving the central feature of the _____________-______ model. These outside nucleons also interact with the core, deforming it and setting up “tidal wave” motions of rotation or vibration within it. These collective motions of the core preserve the central feature of the _____________ _____. Overall, this is called the _______ _____.

Answer 34

independent model; collective model; combined model.