1.2-STABLE AND UNSTABLE NUCLEI Flashcards
What does a stable isotope have?
nuclei that does not disintegrate, so there must be a force holding them together
What is the force holding the protons + neutrons together in the nuclei called?
strong nuclear force
What force does the strong nuclear force balance out?
It overcomes the electrostatic force of repulsion between the protons in the nucleus and keeps the protons and neutrons together
What is the range of the strong nuclear force?
no more than about 3-4 femtometres (fm)
What do 1 fm equal to in m?
1 fm = 10^(-15)m
What is the range of the strong nuclear force about the same as?
diameter of a small nucleus
What is the range of the electrostatic force between two charged particles like?
has an infinite range (although it decreases as the range increases)
How does the strong nuclear force effect protons and neutrons?
it has the same effect between two protons as it does between two neutrons or a proton and neutron
From what range is the strong nuclear force an attractive for?
from 3-4 fm down to about 0.5 fm
What happens to the strong nuclear force when the separation is smaller than 3-4 fm to 0.5fm?
it is repulsive force that acts to prevent neutrons and protons being pushed into each other
What do naturally occurring radioactive isotopes release?
3 different types of radiation:
alpha, beta, gamma
Which force has the larger range?
electrimagetic
What does alpha radiation consist of?
alpha particles which each comprise two protons and neutrons
What is the proton number and mass number of an alpha particle?
proton number - 2
mass number - 4
What happens to the numbers of an unstable nucleus of an element X when it emits an alpha particle?
its nucleon number decreases by 4 and its atomic number decreases by 2
What happens as a result of the alpha particle being emitted? (element)
the product nucleus belongs to a different element Y
How do you detect alpha radiation?
Tracks left by alpha alpha particles are seen in a cloud chamber.
Geiger counter of spark counters detect the ionising radiation - see the count rate drop if you slowly move it away from the source.
What does beta radiation consist of?
fast-moving electrons with electron antineutrino’s
What is the charge and mass of a beta particle like?
its charge is equal and opposite to that of the proton
its mass is much smaller than the proton’s mass
Why does an unstable nucleus of an element X emit a beta particle?
Nucleus is isotope is neutron rich.
The neutron in the nucleus changes into a proton.
What else is emitted with the beta particle?
an antiparticle with no charge, called an antineutrino
What happens in Beta radiation?
What numbers increase / stay the same?
One of the neutrons from the nucleus is changed into a proton. The beta particle is created and is emitted instantly
Proton number increases by 1, Nucleon number stays the same
Antineutrino particle is released
What does the antineutrino carry?
Some energy and momentum
What do neutrinos have / not have and why?
Needed to conserve energy
Neutral charge, zero / almost zero mass, carries momentum and energy
How does the beta particle being emitted affect the element X?
atomic number decreases by 1 but the nucleon number stays the same
What happens to the product nucleus after beta particle being emitted?
belongs to a different element W
What type of nuclei undergo beta decay?
nuclei that have too many neutrons
What is gamma radiation?
electromagnetic radiation emitted by an unstable nucleus
What can gamma radiation pass through?
thick metal plates
What is the charge and mass like of gamma radiation?
no mass and no charge
What type of nucleus emits gamma radiation and what is it followed by?
emitted by a nucleus with too much energy, following an alpha or beta emission
What was found when the energy spectrum of beta particles was first measured?
beta particles were released with kinetic energy up to a maximum that depended on the isotope
What did scientists think happened after they found out beta particles were released with K.E. up to a maximum that depends on the isotope ?
either energy was not conserved in the change or some of it was carried away by mystery particles
What did scientists think happened after they found out beta particles were released with K.E. up to a maximum that depends on the isotope ?
either energy was not conserved in the change or some of it was carried away by mystery particles
What were the mystery particles called that carried some charge away?
neutrinos and antineutrinos
How were antineutrinos detected over 20 years later?
as a result of their interaction with cadmium nuclei in a large tank of water
Where was the large tank of water where antineutrinos were discovered installed?
next to a nuclear reactor as a controllable source of these very elusive particles
