nuclear 2 Flashcards
Who proposed the idea of atoms and what was his proposal?
Democritus, in the 5th century BC, proposed the idea that all matter was made up of little, identical lumps called “atomos.”
Who proposed the atomic theory in 1804, and what were its key points?
John Dalton proposed the atomic theory in 1804, suggesting that matter was made up of tiny spheres (atoms) that couldn’t be broken up. He believed that each element was composed of a unique type of atom.
What significant discovery did J. J. Thomson make about atoms nearly 100 years after John Dalton’s proposal?
J. J. Thomson discovered that electrons could be removed from atoms, demonstrating that Dalton’s theory, which suggested that atoms were indivisible, was not entirely accurate. This discovery challenged the notion that atoms could not be broken up.
What model of the atom did J. J. Thomson propose?
J. J. Thomson proposed the “plum pudding” model of the atom, suggesting that atoms were spheres of positive charge with tiny negative electrons embedded within them, similar to fruit in a plum pudding.
Who was the first to propose the idea of the nucleus, and what was the significance of this proposal?
Ernest Rutherford was the first to suggest the idea of the nucleus. This proposal was significant because it challenged the prevailing notion that atoms had uniformly distributed charge and density, leading to a new understanding of atomic structure.
What experiment did Rutherford and Marsden conduct in 1909?
Rutherford and Marsden fired a beam of alpha particles at thin gold foil.
How did Rutherford and Marsden detect the deflection of alpha particles in their experiment?
They used a circular detector screen surrounding the gold foil and the alpha source to detect alpha particles deflected by any angle.
What did Rutherford and Marsden expect to observe in their experiment regarding the deflection of alpha particles?
They expected that the positively-charged alpha particles would be deflected by the electrons by a very small amount if the plum pudding model of the atom was true.
What unexpected observation did Rutherford and Marsden make regarding the behavior of alpha particles in their experiment?
Instead of being deflected by a small amount as expected, most of the alpha particles passed straight through the foil, while a small number were deflected by a large angle.
What particularly surprising observation did Rutherford and Marsden make about the deflection of alpha particles in their experiment?
Some alpha particles were deflected by more than 90°, sending them back in the direction they came from. This unexpected result was confusing at the time and prompted the need for a significant change to the model of the atom.
What conclusions did Rutherford draw from the results of his scattering experiment?
*Most of the atom must consist of empty space, as most alpha particles passed straight through the foil.
*The nucleus must possess a large positive charge, as some positively-charged alpha particles were repelled and deflected by a large angle.
*The nucleus must be small, as very few alpha particles were deflected back.
*Most of the mass of the atom must reside in the nucleus, since fast alpha particles (with high momentum) were deflected by the nucleus.
What approach can be used to determine how close an alpha particle can get to a gold nucleus in Rutherford scattering?
The initial kinetic energy of the alpha particle is known when it is fired at the gold nucleus.
An alpha particle that “bounces back” and is deflected through 180° reaches a point where its electric potential energy equals its initial kinetic energy.
This is based on the principle of conservation of energy and can be used to find how close the particle can get to the nucleus.
Coulomb’s law can be employed to calculate the electric potential energy.
What equation is used to calculate the electric potential energy in Rutherford scattering?
Ek = Eelec = Qgold x Qalpha/4πε0r
What does the distance of closest approach in Rutherford scattering provide an estimate of, and how does it compare to the values obtained from electron diffraction?
The distance of closest approach in Rutherford scattering provides an estimate of the nuclear radius, giving a maximum value for it
What type of particle are electrons, and how does this relate to their interaction with the strong nuclear force?
Electrons are a type of particle called a lepton. Leptons do not interact with the strong nuclear force, unlike neutrons and alpha particles. This lack of interaction allows electron diffraction to be an accurate method for estimating the nuclear radius.
What concept allows electron beams to be diffracted?
Electrons, like other particles, exhibit wave-particle duality, meaning they can exhibit both particle-like and wave-like behavior. This allows electron beams to be diffracted.
What is the equation for the de Broglie wavelength associated with a beam of moving electrons?
λ =hc/ E
Why must the wavelength of electrons be very small to investigate the nuclear radius, and what does this imply about their energy?
The wavelength of electrons must be very small to investigate the nuclear radius effectively. This implies that the electrons will have very high energy.
What happens when a beam of high-energy electrons is directed onto a thin film of material in front of a screen?
A diffraction pattern will be observed on the screen.
What is the equation for the angle at which the first minimum appears in the diffraction pattern of electrons?
sin θ = 1.22λ/2R
What does the diffraction pattern of electrons resemble?
The diffraction pattern of electrons resembles that of a light source shining through a circular aperture, with a central bright maximum (circle) containing the majority of the incident electrons, surrounded by other dimmer rings (maxima).
What does the diffraction pattern of electrons resemble?
The diffraction pattern of electrons resembles that of a light source shining through a circular aperture, with a central bright maximum (circle) containing the majority of the incident electrons, surrounded by other dimmer rings (maxima).
How does the intensity of the maxima change as the angle of diffraction increases, and what type of graph might represent this intensity?
The intensity of the maxima decreases as the angle of diffraction increases. A graph showing the relative intensity of electrons in each maximum may be presented, and it could be a logarithmic plot where the difference in peak heights is less pronounced.
What is the approximate radius of an atom?
The approximate radius of an atom is about 0.05 nm which is equivalent to 5 × 10–11 m
What are nucleons, and what is the nucleon number of an atom?
Nucleons are the particles that make up the nucleus, including protons and neutrons.
The nucleon number represented by A is the total number of nucleons in an atom.
As more nucleons are added to the nucleus, it increases in size.
What factors can contribute to the instability of a nucleus?
Having too many neutrons,
Not having enough neutrons, or
Having too much energy in the nucleus.
What process describes the transformation of an unstable nucleus into a stable form?
The process is called radioactive decay, during which the nucleus releases energy and/or particles until it reaches a stable form.
What term describes the phenomenon when a radioactive particle knocks off electrons from an atom, creating an ion?
This phenomenon is known as ionizing radiation, and radioactive emissions are also referred to as ionizing radiation because they have the ability to create ions by knocking off electrons from atoms.
Is radioactive decay predictable?
No, individual radioactive decay events are random and cannot be predicted.
What is the function of a cloud chamber in detecting ionizing particles?
A cloud chamber contains air saturated with vapor at a very low temperature. When an ionizing particle passes through, it leaves a visible track of condensed vapor droplets due to ionization of the air.
What type of tracks do alpha particles produce in a cloud chamber?
Alpha particles produce straight tracks that radiate from the source and are easily visible. The tracks are all of the same length, indicating that the alpha particles have the same range.
What type of tracks do beta particles produce in a cloud chamber?
Beta particles produce wispy tracks that are easily deflected as a result of collisions with air molecules. The tracks are not as easily visible as alpha particle tracks because beta particles are less ionizing.
What is the count rate, and how is it calculated?
The count rate is the number of counts detected per unit time. It is calculated by dividing the number of counts by the time taken.
What must be done before testing a radioactive source to measure its count rate?
Before testing a radioactive source, the count rate due to background radioactivity must be measured. This is the count rate without the source present.
What is done to determine the corrected count rate from a radioactive source?
The count rate is measured with the source at a fixed distance from the detector tube without any absorber present. Then, the background count rate is subtracted from the count rate with the source present to give the corrected (true) count rate from the source.
What is done to compare the effect of an absorber on the count rate from a radioactive source?
The count rate is measured with the absorber in a fixed position between the source and the detector tube. Then, the corrected count rates with and without the absorber present can be compared to assess the effect of the absorber.
How does paper and thin metal foil interact with alpha radiation?
Alpha radiation is absorbed completely by paper and thin metal foil.
How does about 5mm of metal interact with beta radiation?
Beta radiation is absorbed completely by about 5mm of metal.
How does several centimeters of lead interact with gamma radiation?
Gamma radiation is absorbed completely by several centimeters of lead.
What is the Geiger tube?
The Geiger tube is a sealed metal cube containing argon gas at low pressure.
What purpose does the thin mica window serve in the Geiger tube?
The thin mica window allows alpha and beta particles to enter the tube.
How does the Geiger tube detect gamma photons?
Gamma photons can enter the tube through the tube wall.
What is the function of the metal rod in the Geiger tube?
The metal rod down the middle of the tube is at a positive potential.
How is the Geiger tube connected to a power supply?
The tube wall is connected to the negative terminal of a power supply and grounded.
What does the dead time represent in a Geiger tube?
The dead time represents the time taken for the tube to regain its non-conducting state after an ionizing particle enters it.
How does the dead time affect the count rate in a Geiger tube?
During the dead time, another particle that enters the tube will not cause a voltage pulse. Therefore, the count rate should be no greater than about 5000 counts per second.
What is the range of alpha radiation in air?
The range of alpha radiation in air is fixed but depends on its energy, ranging up to about 100 mm.
What is the range of beta radiation in air?
The range of beta radiation in air can be up to about 1 meter.
How does the range of gamma radiation in air behave?
The range of gamma radiation in air follows the inverse square law
How does alpha radiation behave in a magnetic field?
Alpha radiation is deflected in a magnetic field.
How does beta radiation behave in a magnetic field compared to alpha particles?
Beta radiation is deflected in the opposite direction to alpha particles and is more easily deflected.
What is the behavior of gamma radiation in a magnetic field?
Gamma radiation is not deflected in a magnetic field.
What is the absorption capability of paper or thin metal foil for alpha particles?
What is the absorption capability of paper or thin metal foil for alpha particles?
How thick of aluminum can stop beta particles?
How thick of aluminum can stop beta particles?
What material can stop or significantly reduce gamma radiation?
Gamma radiation is stopped or significantly reduced by several centimeters of lead.
How many ions per millimeter in air does the ionization of alpha radiation produce at standard pressure?
The ionization of alpha radiation produces about 10^4 ions per millimeter in air at standard pressure.
How many ions per millimeter in air does the ionization of beta radiation produce at standard pressure?
The ionization of beta radiation produces about 100 ions per millimeter in air at standard pressure.
What is the ionization effect of gamma radiation?
Gamma radiation has a very weak ionizing effect.
How did Rutherford demonstrate the nature of alpha particles?
Rutherford devised an experiment in which alpha particles were collected as a gas in a glass tube fitted with two electrodes. When a voltage was applied to the electrodes, the gas conducted electricity and emitted light.
What did Rutherford observe when he analyzed the light emitted by the alpha particles?
Using a spectrometer, Rutherford proved that the spectrum of light from the tube was the same as from a tube filled with helium gas.
