LABORATORIO DI FISICA SUBNUCLEARE
INTRODUCTION ON RADIATION – MATTER INTERACTION
- Radiation sources and radioactive decays
- Neutron production via spontaneous fission processes and nuclear reactions
- Radioisotopes: discovery, production, features and medical uses
- The radioactive decay law and the decay chains
- The definition of cross section
- The interaction of photons with matter:
** photoelectric effect, Compton effect, pair production
** photon spectra as a function of the detector dimension
- The interaction of charged particles with matter:
** energy loss of heavy charged particles: the Bethe Bloch formula; medical applications: hadron therapy
** energy loss of electrons and positrons: ionization and bremsstrahlung
** Coulomb multiple scattering
INTRODUCTION ON DETECTORS
- Detector features: sensitivity, response, energy resolution, response time
- Gas detectors:
** working principles: from ionization chambers to Geiger counters
** drift and diffusion in the gas; avalanche multiplication
- Scintillating detectors:
** working principles
** organic and inorganic scintillators: mechanisms of luminescence production and features
** light readout: the photomultiplier tubes
- Semiconductor detectors:
** the pn junction and the detectors features
** silicon pin diodes
DESCRIPTION OF THE EXPERIMENTAL MEASUREMENTS WITH FINAL REPORT
1. Measurements with the Geiger counter:
- the working plateau
- the emission poissonian statistics of a radioactive source
- the deadtime measurement
2. Measurements with a X ray tube (choosing one between 2a and 2b):
- 2a. The Bragg experiment:
** measurement of X-ray diffraction with a monocrystal
** measurement of the X-ray spectrum varying the tube voltage and current
** measurement of Planck’s constant
- 2b. X ray fluorescence – XRF:
** pin diode calibration
** measurement of the X-ray beam reflected by a low Z sample positioned at the end of the tube chamber
** analysis of spectra to discover the elements contained in several samples (rocks, coins, jewels, etc)
3. Measurements of gamma spectroscopy with inorganic scintillators (NaI, LaBr):
** dependence of gain, resolution and linearity on the bias voltage
** analysis of the emission spectra of several sources
** measurement of the absorption coefficient of lead
4. Measurement of the nuclear lifetime of Co-57:
** calibration of the two NaI detectors analyzing the 2D plot obtained acquiring data in coincidence
** analysis of the region of interest in the 2D plot to fill the plot of the two gamma arrival time difference
DESCRIPTION OF THE “JOLLY” EXPERIMENTAL MEASUREMENTS
Each group has to choose one of the following experimental measurements, acquire data, analyze them and present the results to the other groups.
1. Alpha spectroscopy: the setup consists in a amplified silicon pin diode and in several alpha sources. It allows to perform measurements of absorption with the observation of the Bethe Bloch curve and of the Bragg peak and to compute the age of the Ra-226 source.
2. Gamma-gamma correlations: the coincidence technique allows to study sources that emit two gammas in coincidence such as Na-22, Co-60, Ba-133.
3. Cosmic rays: a portable system of three detectors of scintillating bars allows to perform flux measurements as a function of the altitude, the angle with respect to the vertical direction and to understand the effect of the material above the detector itself.
For the interested students and if the accelerator were available, a data taking activity at an accelerator (such as CERN or the INFN National Laboratories in Frascati) will be organized to perform measurements of energy resolution of calorimeters or spatial resolution of tracking systems.
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The reference bibliography is the following :
- W.R.Leo, ISBN 0-387-57280-5
- A.C.Melissinos, ISBN 0124898513
- dedicated seminars
Students are provided with the slides of the lessons and dedicated material when necessary (articles, notes).
The course is organized in:
- frontal lessons (for a total of 16h) each one divided in two parts:
** in the first part the theoretical topic is introduced (radiation-matter interaction, working principles of detectors, experimental measurements)
** in the second part, students start to face the analysis of typical data in order to learn how to perform it and how to obtain the info to insert and comment in the lab reports. Students will perform the analysis in the classroom on their portable PCs, on their own or in the working group that then takes data in the lab. Students can use the software they prefer, depending on what done in the previous years; this course proposes to use the python language, that students have already met and used in the Modern Physics Laboratory course.
- data taking sessions in the lab: students are organized in groups of 2 or 3. Each group participates to the data taking and analysis; each group has to deliver one single report per experiment. At the end of the theoretical lessons, a calendar of the data taking sessions will be given to the students. Each group will have an adequate number of hours to perform the experimental part. The data analysis can be performed in the lab itself or asynchronously with respect to the presence in the lab.
During the lab sessions, several tutors will be present so that each group of students is followed by an assistant. In case of an emergency such as the Covid one, the activity will be re-organized in presence and/or online in order to reach the learning outcomes.
For questions/discussion/comments, students are invited to contact the teacher via email at the following address: michela.prest@uninsubria.it