Particle Physics Questions : Multiple Choice

 

Q1. What are the numbers of hadrons, baryons and mesons in an atom of ?

	hadrons	baryons	mesons
A	7	3	3
B	7	4	4
C	7	7	0
D	10	7	0

 There are 3 protons and 4 neutrons - which are baryons and hadrons

There are no mesons!

Q2. A radioactive nucleus emits a β^– particle then an α-particle and finally another β^– particle.

The final nuclide is:

A	an isotope of the original element
B	the same element with a different proton number
C	a new element of higher proton number
D	a new element of lower nucleon number

Beta emission a neutron changes to a proton - two betas so the proton number increases by two.

Alpha emission means two protons leave the nucleus (along with two neutrons) so the proton number decreases by two.

Overall effect - no change in proton number - same element!

 

Q3. The nucleus of  captures a proton and emits an α particle.

What is the product nucleus?

A         

      
B         

      
C         

      
D             

 

Capturing a proton takes the proton number to 4 + 1 = 5

Emitting and alpha particle reduces the proton number by two 5 - 2 = 3

It is therefore Lithium.

The number of neutrons is 9 - 4 = 5

Capuring a proton has no effect on the number of neutrons, but Alpha emission decreases the number by two: 5 - 2 = 3

Nucleon number = 3 + 3 = 6 - choice C

 

Q4. Electron capture can be represented by the equation:   

 p + e^- → X + Y

Which row correctly identifies X and Y?

	X	Y
A	p	K-
B	e-	e+
C	n	νe
D	n	π0

 

The nucleus captures the electron and it combines with a proton to form a neutron.

To conserve lepton number there must be a lepton on the right hand side of the equation - ν_e

 

Q5. A calcium ion is formed by removing two electrons from an atom of  .

What is the specific charge of the calcium ion?

A	3.2 × 10-19 C kg-1
B	2.9 × 10-18 C kg-1
C	4.8 × 106 C kg-1
D	4.8 × 107 C kg-1

 

Specific charge is charge per kilogram (it tells you that by giving you the unit!)

charge/mass of ion = (2e/(20m_p + 20m_n)

 

However you can see that the answer is only to 2sf.... and mass of proton and neutron are the same to 3sf....

We can therefore make the maths easier... another aoption is to use the average mass for a neutron and proton as there are equal numbers of each other.

 

charge/mass of ion = 2e/40m_p

 

charge/mass of ion = 2 x 1.6 x 10^-19/(40 x 1.67 x 10^-27)

charge/mass of ion = 4.8 × 10⁶ C kg^-1

Q6. The table below links exchange particles with nuclear processes. Select the line that does not give the correct exchange particle for the process.

	Process	Exchange Particle
A	gravitational attraction	Z boson
B	electrostatic repulsion of electrons	virtual photon
C	strong interaction	pion
D	β− decay	W boson

 

Q7. Select the line that gives the correct category and quark combination for the particle.

	Particle	Category	Quark combination
A	neutron	baryon	̅u̅ d
B	neutron	meson	u d d
C	proton	baryon	u u d
D	positive pion	meson	̅u̅ d

 

Q8. Select the incorrect statement about muons from the following.

A	A muon is a lepton
B	A muon has a greater mass than an electron.
C	If a muon and an electron each have the same de Broglie wavelength then they each have the same momentum.
D	A muon with the same momentum as an electron has a larger kinetic energy than the electron.

 

The first two are obviously true (if you know your facts).

λ_dB = h/p - so if the have the same de Broglie wavelength they will have the same momentum.

The muon with that same momentum as the electron, having more mass will have a lower velocity. Therefoe its kinetic energy will be lower than the electron because the velocity is squared for kinetic energy....

Q9. Which of the following nuclei has the smallest specific charge?

A
B
C
D

 

Specific charge is charge/mass ratio. You can just work out the nucleon number to proton number ratio to compare values.

 

Q10. is an unstable nuclide in a radioactive decay series. It decays by emitting an α particle. The next two nuclides in the series emit β⁻ particles. Determine which nuclide is formed after these three decay processes have taken place.

A
B
C
D

 

Alpha emission reduces the nucleon number by 4 - beta makes no difference to it (as a neutron changes to a proton). Therefore the nucleon number must be 232 - 4 = 228. That means the answer is either C or D.

The alpha emission will reduce the proton number by 2, but each of the beta emissions will increase it by 1, therefore the proton number will be the same as we started with and D is the answer.

Q11.

A CERN detector shows a signal only in the hadronic calorimeter. No signal is observed in the in the tracker, electromagnetic calorimeter or muon chambers). Therefore, this signal is most likely due to a:

A	pion
B	neutrino
C	photon
D	neutron

 

The only hadron is the neutron.

Q12.

The exchange particles carrying the strong nuclear force are the:

A	photons
B	gluons
C	gravitons
D	w-bosons

Q13.

Which was the first particle discovered which is still today believed to be elementary, i.e. not made up of further constituents?

A	electron
B	gluon
C	photon
D	proton

Q14. Which of the following is not true?

 

Q15. Which equation shows the process of annihilation?

See here for notes on annihilation.

Q16. Which of the following is not made of quarks?

A	kaon
B	muon
C	neutron
D	pion

 

The muon is a lepton, the others are hadrons.

Q17. What is the quark structure for antiprotons?

Q18. The equation represents the weak interaction between a negative pion and a proton.

π⁻ + p → K^o + X

What is the charge, baryon number and strangeness of particle X?

the charge of the proton is +1 and the pion -1 - therefore the left hand side of the equation has zero charge - the kaon has zero charge so X must have zero charge also.

the baryon number of the proton is 1 and the meson zero - giving total baryon number of one on the left hand side of the equation - kaon is zero so X must have a baryon number of 1

the pion and proton are not strange - kaon is - so X must be - with opposite strangeness number....K^o can be positive or negative.... therefore X might be +1 or -1.

See here for notes on strange particles.

Q19. Which diagram represents the process of beta-plus decay?

In positron decay a proton becomes a neutron:

p n + β⁺ +

so, quark change is: uud ddu

u d

Therefore it is either choice A or B

To balance leptons we need a lepton to be formed as well as the antilepton (positron) - so choice A is correct.

 

Q20. Two gamma photons are produced when a muon and an antimuon annihilate each other.

What is the minimum frequency of the gamma radiation that could be produced?

 

Sum of rest energies = 2 x 105.659 MeV

This is changed to electromagnetic energy in two identical gamma rays travelling in opposite directions.

Each gamma ray therefore has energy of 105.659 MeV

1 eV = 1.6 x 10^-19J

Therefore the energy of each gamma ray is 105.659 x 10⁶ x 1.6 x 10^-19 = 1.69 x 10^-11 J

E = hf

f = E/h

f = 1.69 x 10^-11/(6.63 x 10^-34)

f = 2.55 × 10²² Hz

Choice C