Detecting Giant Monopole
Resonances
Giant Resonances
• Discovered in the late 1940s by bombarding nuclei
with gamma rays
• Giant resonances is a collective motion of
nucleons that occurs when the nucleus becomes
excited
• Each mode has an associated multipole integer
value L to represent the angular momentum
transfer
• Classification
– Isoscalar means the protons and neutrons
move in phase and is denoted as ∆T = 0
– Isovector means the protons and neutrons do
not move out of phase and is denoted by ∆T = 1
Energy Loss
• Using SRIM, a program that computes the energy associated with scintillator thickness,
the energy loss after striking the scintillator is calculated and subtracted from the initial
energy
Peter Nguyen
Advisors: Dr. Youngblood, Dr. Lui
Texas A&M University
Stable Nuclei
Isoscalar Giant Monopole Resonances (ISGMR)

• ISGMR is the “breathing” mode where
the nucleons compress and expand
causing the nucleus’ radius to fluctuate
• ISGMR can be related to the nucleus,
denoted as Knm


Excessive studies have been made on the stable nuclei by using alpha
particles scattering
Through inelastic scattering, information of ISGMR and ISGDR have been
obtain from the stable nuclei (12C - 208Pb)
Researcher are focusing more on unstable nuclei
Proton Energy Loss (MeV)
• It is a fundamental quantity describing the ground state properties of nuclear matter  Detector on the back of spectrometer combined with decay detector
inside target chamber to measure the resonance of unstable nucleus
• Uses
– Supernova collapses

Reaction - 28Si(6Li, 6Li) 28Si*
d 2 ( E / A)
– Neutron stars
K nm  9 o
|

Inverse Reaction - 6Li (28Si, 28Si*) 6Li
d 2
– Heavy-ion collisions
– Determine the Nuclear Equation of State
• Measuring it
– Deduce information from the frequency of the compression mode of the nucleus • The detector is compose of a thick
scintillator block, and vertical and
during ISGMR and ISGDR
horizontal thin strips that are 1 mm thick
– Relate the compressibility to the centroid energy of the ISGMR
2
1
2
• The particles will go through the vertical

2
N

Z
Z


3
 AK A
K A  K nm  K surf A  K sym 
  K coul 4
strip first and then the horizontal strip.
Eo 
 A 
2
This will determine the position of the
mr 
A3
outgoing particles
• The scintillator block measures the
energy of the particles
• Difficult to detect because Giant
o
Decay Detector in Target Chamber
6
Energy Loss (MeV)
Motivation Behind Knm
To study the unstable nuclei, an inverse reaction is needed, the
unstable nuclei becomes the projectile
6
5
4
3
2
1
0
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
5
4
3
2
1
0
0.00
80.00
20.00
40.00
60.00
Initial Energy (MeV)
Tritium Energy Loss (MeV)
30
5
25
4
MDM Spectrometer
Scintillator
3
2
1
90.00
140.00
10
5
190.00
240.00
0
50
100
150
Initial Energy (MeV)
a1  1.47(1  1.00794) -0.70
a1  1.47(1 3.0160492)-0.70
a1  1.47(2  4.002602) -0.70
Identifying The Particles
Particle Identification
Energy Loss Light Output vs. Final Energy Light Output
23
18
13
Proton
Deuterons
Tritons
Alpha
8
3
0
200
Initial Energy (MeV)
Light Output
Energy Loss Light Output
• The photomultiplier absorbs the emitted light and electrons are
release via photoelectric effect at the photocathode
• The cathode, dynodes, and the anodes create a potential
“ladder” that directs the electrons
• The electrons travel from the photocathode to the first dynode
and excite more electrons in the dynode
• The excited electrons leave the dynode and travel to the next
dynode to repeat the process
• At the anode all the electrons are collected and then amplify to
create a readable current
160.00
0
40.00
Photomultiplier
• The target nuclei in the
target will excite to a
higher energy level
• α particles with different
energy will separate by
MDM spectrometer and
focus on different
position of the detector
140.00
15
a1  1.47(1 2.013553)-0.70
• A scintillator is a device that absorbs energy and
– Sensitive to Energy
emits light
• Represented as a linear
• Several kinds of scintillating material exists including:
function
organic, inorganic and plastic
– Fast Time Response
• The particle hits the scintillator which excites the
• Recovery time is short
molecules in the scintillating material to emit light
– Pulse Shape Discrimination
• The photons released is then capture by a
photomultiplier that is coupled to the scintillator via a
• Determining different
light guide or directly attached
particles
120.00
20
Detection of ISGMR
Quadrupole Resonance GQR hid the
GMR except at small scattering
angles
• Beam analysis system provides a
very clean beam which can be used
in the measurement
• Using a beam of specific MeV, the
beam will collide target nucleus
100.00
Alpha Energy Loss (MeV)
6
0
-10.00
80.00
Initial Energy (MeV)
Energy Loss (MeV)

Unstable nuclei cannot be placed in the target chamber because of its
decaying nature. The nuclei will immediately decay into another element
Energy Loss (MeV)

7
Energy Loss (MeV)
Unstable Nuclei
Deuterium Energy Loss (MeV)
500
1000
1500
2000
-2
Final Energy Light Output
2500
3000
250
300
350