Detecting Giant Monopole Resonances

Peter Nguyen

Advisors: Dr. Youngblood, Dr. Lui

Texas A&M University

Giant Resonances Discovered in the early 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

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

Motivation Behind Knm

It is a fundamental quantity describing the ground state properties of nuclear matter

Uses Supernova collapses Neutron stars Heavy-ion collisions Determine the Nuclear Equation of State

Measuring it Deduce information from the frequency of the compression

mode of the nucleus during ISGMR and ISGDR Relate the compressibility to the centroid energy of the

ISGMR

od

AEdK onm

|)/(

92

2

2

2

rm

AKE Ao

3

4

22

3

1

A

ZK

A

ZNKAKKK coulsymsurfnmA

Detection of ISGMR Difficult to detect because

Giant 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

MDM Spectrometer

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

Stable Nuclei 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

Unstable Nuclei Unstable nuclei cannot be placed in the target chamber

because of its decaying nature. The nuclei will immediately decay into another element

To study the unstable nuclei, an inverse reaction is needed, the unstable nuclei becomes the projectile

Detector on the back of spectrometer combined with decay detector inside target chamber to measure the resonance of unstable nucleus

Reaction - 28Si(6Li, 6Li) 28Si* Inverse Reaction - 6Li (28Si, 28Si*) 6Li

Decay Detector in Target Chamber The detector is compose of a

thick scintillator block, and vertical and horizontal thin strips that are 1 mm thick

The particles will go through the vertical strip first and then the horizontal strip. This will determine the position of the outgoing particles

The scintillator block measures the energy of the particles

Scintillator

Sensitive to Energy Represented as a

linear function Fast Time Response

Recovery time is short

Pulse Shape Discrimination

Determining different particles

A scintillator is a device that absorbs energy and emits light

Several kinds of scintillating material exists including: organic, inorganic and plastic

The particle hits the scintillator which excites the molecules in the scintillating material to emit light

The photons released is then capture by a photomultiplier that is coupled to the scintillator via a light guide or directly attached

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

Photomultiplier

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

Proton Energy Loss (MeV)

0

1

2

3

4

5

6

7

0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00

Initial Energy (MeV)

En

erg

y L

oss

(MeV

)

Energy Loss (cont.)

Deuterium Energy Loss (MeV)

0

1

2

3

4

5

6

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

Initial Energy (MeV)

En

erg

y L

oss

(MeV

)

Energy Loss (cont.)

Tritium Energy Loss (MeV)

0

1

2

3

4

5

6

-10.00 40.00 90.00 140.00 190.00 240.00

Initial Energy (MeV)

En

erg

y L

oss

(MeV

)

Energy Loss (cont.)

Alpha Energy Loss (MeV)

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350

Initial Energy (MeV)

Ene

rgy

Loss

(MeV

)

Light Output

-0.701 1.00794)1(47.1 a

-0.701 2.013553)1(47.1 a

-0.701 3.0160492)1(47.1 a

-0.701 4.002602)2(47.1 a

Light Output Data PointsProton

Final Energy Energy Loss

14.0445494 45.65449513

121.7725841 16.75876843

265.2827946 9.924787821

441.7524491 6.90586927

651.127854 5.121702054

890.9217898 4.062224042

1161.51625 3.310228612

1459.508539 2.89640396

1789.231921 2.450009156

2147.213482 2.119347153

2533.127937 1.863983349

2946.982321 1.648915691

3388.135887 1.472603244

4348.151763 1.272532761

Deuterium

Final Energy Energy Loss

123.3270106 19.01374922

231.1026128 12.84648608

359.8641216 9.378536605

508.2255034 7.212428237

675.2244704 5.780727277

858.1053615 4.998311244

1061.203003 4.221229134

1281.668295 3.642717902

1519.588504 3.178649471

1774.651665 2.801073083

2046.323568 2.502614581

2636.883021 2.140732853

3295.256736 1.779895568

4017.299028 1.509377271

4801.740674 1.303716468

5647.703756 1.140994357

6554.138308 1.012369008

7520.338171 0.907226759

8545.667934 0.818352334

9629.186423 0.745711981

Tritium

Final Energy Energy Loss

244.3963258 13.18231512

356.0533784 10.06235227

480.9530824 8.164524532

619.2371887 6.882279685

771.7236226 5.857644727

938.3466018 4.994116805

1116.99387 4.402916419

1309.220687 3.875750442

1514.242378 3.438651238

1958.516515 2.937909656

2454.534918 2.448657849

2998.933658 2.06758188

3590.37012 1.776982275

4227.774835 1.558597089

4911.142151 1.375439938

5639.422415 1.228612782

6412.284574 1.104784763

7228.973732 1.003203917

8089.20021 0.916022879

8992.505998 0.8406453

9938.386706 0.776116463

10926.46715 0.720301017

11956.51908 0.670081402

13027.93474 0.62749363

14141.6748 0.578068303

15295.16879 0.545017772

Alpha

Final Energy Energy Loss

41.42294465 135.6397697

110.8979309 93.82538113

186.3169591 73.28500163

270.1263004 59.42945228

360.7180493 49.73150895

457.8888839 42.55009296

561.5185097 37.01540361

790.5481019 28.43737153

1038.670959 23.65732572

1309.10599 20.47395873

1608.501269 17.38504145

1929.623412 15.18195948

2274.305667 13.37833735

2640.261746 12.04178611

3030.80488 10.76934387

3442.138413 9.804311112

3877.242976 8.869569149

4332.702042 8.150895245

4809.934145 7.515757865

5308.623791 6.955582819

5828.584993 6.457850664

6368.372455 6.066687325

6932.791627 5.566141551

7513.140365 5.296047997

8115.294364 5.006635036

8739.052539 4.70402281

9382.008357 4.46208109

10046.19639 4.208325864

10729.41354 4.00329773

11432.53184 3.814142001

12154.45195 3.663975779

12898.07895 3.475189812

Identifying The Particle

To verify the GMR, the monopole sum rule is used

Particle IdentificationEnergy Loss Light Output vs. Final Energy Light Output

-2

3

8

13

18

23

0 500 1000 1500 2000 2500 3000

Final Energy Light Output

En

erg

y L

oss

Lig

ht O

utp

ut

Proton

Deuterons

Tritons

Alpha

Particle IdentificationEnergy Loss Light Output vs. Final Energy Light Output

-2

0

2

4

6

8

10

12

0 500 1000 1500 2000

Final Energy Light Output

En

erg

y L

oss

Lig

ht O

utp

ut

Proton

Deuterons

Tritons

Alpha

Current Progress

This holds the scintillator that will be place inside the target chamber

Current Progress (cont.)

The high voltage will be control from upstairs with wire connecting from the ceiling

Current Progress (cont.)

On top of the target chamber will be a ring that will be attach. The photomultipliers are then attach from the outside of the target chamber

Acknowledgement

Dr. Youngblood Dr. Lui Xinfeng Chen Jonathan Button Robert Polis