All exercise Short Questions of Detectors and Accelerators of book Nuclear Physics for BS/MSc Physics students.
Q.1 Define ionization chamber.
Answer. A partially evacuated tube provided with electrodes so that its conductivity due to the ionization of the residual gas reveals the presence of ionizing radiation
Q.2 Distinguish between chamber and counter.
Answer. Ionization chambers can be operated in current or pulse mode. In contrast, proportional counters or Geiger counters are almost always used in pulse mode.
Q.3 What are the different classes of particle accelerator?
Answer. There are two basic types of particle accelerators: linear accelerators and circular accelerators. Linear accelerators propel particles along a linear, or straight, beam line. Circular accelerators propel particles around a circular track.
Q.4 Why is the velocity of ion inside a dees of the cyclotron constant?
Answer. In a dee the force on the charge comes from the magnetic field, so the force is perpendicular to the velocity. The speed, and hence the kinetic energy, stays constant, so the change is zero.
Q.5 Why is an ordinary cyclotoron not suitable for the acceleration of electrons?
Answer. Cyclotron is not suitable for accelerating electrons. Due to the small mass, the speed of electrons increases rapidly. Likewise, due to quick relativistic variation in their mass, the electrons get out of step with the oscillating electric field.
Q.6 Distinguish between a cyclotron, synchrotron and synchrocyclotron.
Answer. In a cyclotron, the frequency of the alternating electric field between the dees and the strength of the magnetic field making the charged particles move along a circular path within the dees are kept constant. The energy to which a particle can be accelerated in a cyclotron is limited due to the change of mass with velocity.
Synchrotron;
In a synchrotron the frequency of the applied alternating electric field is kept constant by changing the value of B.
Synchrocyclotron;
It is frequency modulated cyclotron in which the magnetic field B is kept constant.
Q.7 What is the basic principle of a Betatron?
Answer.
Operation principle
In a betatron, the changing magnetic field from the primary coil accelerates electrons injected into the vacuum torus, causing them to circle around the torus in the same manner as current is induced in the secondary coil of a transformer (Faraday’s law).
Q.8 What is synchrotron radiation?
Answer. Synchrotron radiation is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity. It is produced artificially in some types of particle accelerators, or naturally by fast electrons moving through magnetic fields.
Q.9 What is the basic principle of linear accelerator?
Answer. Synchrotron radiation is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity. It is produced artificially in some types of particle accelerators, or naturally by fast electrons moving through magnetic fields.
Q.10 How does a cyclotron accelerate a proton?
Answer. In a cyclotron, protons are accelerated by a high frequency voltage. A uniform magnetic field, of flux density 200mT, causes the protons to follow a circular path that increases in radius as the protons gain kinetic energy. Immediately before the protons leave the cyclotron, the radius of their circular arc is 1.5m.
Q.11 Can we accelerate neutrons by a cyclotron?
Answer. A neutron cannot be accelerated by a cyclotron. A neutron carries no charge; it cannot be accelerated by the electric field between the two dees. It can also be not acted upon by the magnetic field so that its path within the dees cannot be regulated.
Q.12 Can a cyclotron be used to accelerate electrons? If not, why? If yes, how?
Answer. A cyclotron cannot be used to produce high energy electron beams. The reason for the same is that there is an appreciable increase in the mass of the electron at fairly low energies. For example, a 10% increase in the rest mass of the electron takes place at energy of 50 KeV only. Electron being a very light particle there is an appreciable increase in its velocity at low energies which is not the case with massive particles like the proton or the – particle.
Q.13 What are the primary functions of electric and magnetic field in a cyclotron?
Answer.
Electric field;
The basic function of the electric field is to provide a potential difference between the dees of the cyclotron to accelerate the charged particles.
Magnetic field;
The basic function of the magnetic field is to move the charged particle into a semi- circular path within the dees.
Q.14 A cyclotron is a so-called resonance device. Explain.
Answer. In a cyclotron the value of the magnetic field strength depends upon the frequency of the oscillating electric field applied between the dees. The frequency is,
$$F = \frac{1}{T} = \frac{\omega}{2\pi} = \frac{eB}{2\pi m}$$
This is the cyclotron resonance condition for a charged particle of a given value of e/m. If this condition is not satisfied there will be no resonance between the arrival of the charged particle in the gap and the reversal of the voltage between the dees. The particle will go out of step and will not be accelerated. This is why it is said that a cyclotron is a resonance device.
Q.15 A Cyclotron is a so-called resonance device. Does Betatron also depend upon resonance?
Answer. Betatron is a resonance device. The action of betatron is like that of a transformer in which an alternating current applied to a primary coil induces a similar current in the secondary windings.
Q.16 Explain the concept that the working of a betatron is like that of a transformer.
Answer. The action of the betatron depends upon the same principle as that of the transformer in which an alternating current applied to a primary coil induces a similar current in the secondary windings. The primary current produces an oscillating magnetic field which in turn induces an oscillating emf in the secondary coil. The betatron is also like a chamber takes the place of secondary winding. The chamber is placed within the pole pieces of an electromagnet energized by an alternating pulsed current and the magnet produces a strong varying field in the central place or hole of dough-nut. The electrons move in a circular orbit of constant radius within the vacuum chamber and gain energy by induction because of change with time of the magnetic flux linking the orbit. Thus the electromagnet plays the role of primary coil.
Q.17 Suppose you are able to produce a beam of protons of energy E in the laboratory ( where E>> mp c2 ) and that you have your choice of making a single- beam machine in which this beam strikes a stationary target , or dividing the beam into two parts ( each of energy E) to make a colliding beam machine. Discuss the relative merits of these two alternatives from the point of view the angular distribution of particles produced and its consequences for detector design.
Answer. With a stationary-target machine, most of the final particles are collimated in the forward direction of the beam in the laboratory. Detection of new particles must deal with this highly directional geometry of particle distribution and may have difficulty in separating them from the background of beam particles. With a colliding-beam machine the produced particles will be more uniformly distributed in the laboratory since the total momentum of the colliding system is zero. In this case the detectors must cover most of the 4 solid angle.
Q.18 Describe the main functions of alternating magnetic field in Betatron.
Answer. The main functions of alternating magnetic field in Betatron are:
- The alternating or changing magnetic field gives rise to an electric field. The increasing magnetic field produces an emf which imparts energy to the electrons.
- With the help of the magnetic field the electron is maintained in a circular orbit.
Q.19 What are the main problems of synchrotron? How synchrotrons are different from linear accelerators?
Answer. The main problems of the synchrotron are:
- A complex operation cycle
- Low average flux
Acceleration takes place in a synchrotron filled with ferrite cores to provide inductive current over a board frequency range. This cavity is similar to a linear induction accelerator cavity.
The two differences are;
- An Ac voltage is applied across the gap
- The ferrites are not driven to saturation to minimize power loss.
