PRELIMINARY STAGE 2024
Contest 34
T.I. AMASS, Kumasi: 71 points (Winner)
Amenfiman SHS: 40 points
Tuobodom SHTS: 21 points
Contest 35
Accra Girls’ SHS: 39 points (Winner)
Notre Dame Girls’ SHS: 34 points
Aburi Girls’ SHS: 27 points
Contest 36
Anlo SHS: 69 points (Winner)
Tamale Islamic Science SHS: 34 points
Yendi SHS: 28 points
ROUND 5 - RIDDLE
RIDDLE
I am a particle.
I have both mass and electric charge.
I'm unconditionally stable when free.
However, I can participate in a weak interaction in which I am transformed into a neutron accompanied by a positron and an electron neutrino.
I'm responsible for most of the mass of protion.
Who am I?
ANSWER: PROTON
EXPLANATION:
The proton is a stable, positively charged baryon (uud).
Inside a nucleus, beta-plus decay turns a proton into a neutron, a positron and an electron neutrino.
NOTE: The fifth clue's word “protion” is a slip in the original; protons, with neutrons, carry most of the mass of an atom.
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PRACTICE QUESTIONS
1. RIDDLE:
I am a particle found in the nucleus.
I have no electric charge.
My mass is slightly greater than that of the proton.
Outside a nucleus I decay in about fifteen minutes.
Chadwick discovered me in 1932.
Nuclear reactors release me to keep a chain reaction going.
Who am I?
ANSWER: NEUTRON
EXPLANATION:
The neutron (udd) is neutral; a free one beta-decays into a proton, an electron and an antineutrino.
2. RIDDLE:
I am the antiparticle of the electron.
I have the electron's mass.
My charge is positive.
I am emitted in beta-plus decay.
When I meet an electron we annihilate into gamma rays.
Carl Anderson discovered me in cosmic rays in 1932.
Who am I?
ANSWER: POSITRON
EXPLANATION:
The positron is the antielectron; electron-positron annihilation gives two 511 keV gamma photons.
3. RIDDLE:
I am a lepton with no electric charge.
My mass is extremely small.
I pass through the Earth almost without stopping.
Pauli predicted me to save energy conservation in beta decay.
The Sun sends out vast numbers of me.
I come in three flavours.
Who am I?
ANSWER: NEUTRINO
EXPLANATION:
Neutrinos interact only by the weak force (and gravity), so they rarely interact with matter.
4. RIDDLE:
I am a lepton.
I carry the same charge as the electron.
I am about two hundred times heavier than the electron.
I am unstable and live about two microseconds.
Cosmic rays produce me high in the atmosphere.
Time dilation lets me reach the ground.
Who am I?
ANSWER: MUON
EXPLANATION:
The muon lives 2.2 μs at rest; its dilated lifetime at high speed lets it reach sea level.
5. RIDDLE:
I am the lightest meson.
I am made of up and down quarks with their antiquarks.
I can be positive, negative or neutral.
Yukawa predicted me as the carrier of the nuclear force.
I was discovered in cosmic rays in 1947.
My charged forms decay into muons.
Who am I?
ANSWER: PION
EXPLANATION:
The pion (pi meson) was predicted by Yukawa to carry the force between nucleons.
6. RIDDLE:
I am a particle of light.
I have no mass and no charge.
I always travel at the speed of light in a vacuum.
My energy equals Planck's constant times my frequency.
I carry the electromagnetic force.
Einstein used me to explain the photoelectric effect.
Who am I?
ANSWER: PHOTON
EXPLANATION:
The photon is the quantum of electromagnetic radiation, with energy $E = hf$.
7. RIDDLE:
I am a baryon made of antimatter.
My mass equals that of the proton.
My charge is negative.
I am made of two anti-up quarks and one anti-down quark.
Segrè and Chamberlain discovered me in 1955.
When I meet a proton we annihilate.
Who am I?
ANSWER: ANTIPROTON
EXPLANATION:
The antiproton ($\bar{u}\bar{u}\bar{d}$) has charge −e and the proton's mass.
8. RIDDLE:
I am the heaviest charged lepton.
I am about 3500 times heavier than the electron.
I am unstable and live less than a picosecond.
I am heavy enough to decay into hadrons.
I was discovered in 1975.
I have my own neutrino.
Who am I?
ANSWER: TAU
EXPLANATION:
The tau lepton (about 1.78 GeV/$c^2$) is the only lepton heavy enough to decay into hadrons.
9. RIDDLE:
I am a meson.
I contain a strange quark or a strange antiquark.
I decay by the weak force.
My decays revealed that nature is not perfectly symmetric between matter and antimatter.
I was found in cosmic rays in 1947.
I am also called the K meson.
Who am I?
ANSWER: KAON
EXPLANATION:
Kaons carry strangeness; CP violation was discovered in neutral-kaon decays in 1964.