Decay features of medium mass nuclei at high excitation and...

Simone ValdreUniversita degli studi di FirenzeandINFN — Sezione di Firenze

for the NUCL-EX collaboration

Decay features of medium mass nucleiat high excitation and spins

Comex5, Krakow

September 16th, 2015

1/13

2/13

Introduction Experimental apparatus Statistical model Results Conclusions

Introduction

The reaction

=⇒

Reaction parameters

Eb [MeV] Ecm [MeV] ε∗ [MeV/u] lgr [~] lBf=0 [~]

300 135 1.4 91 79450 203 2.2 124 79600 271 3.0 149 79

3/13


Introduction

Why 88Mo?

large fission barrier up to high spins

mass region not well explored in literature

GDR study performed here in Krakow

Michal Ciema la talkM. Ciema la et al., Phys. Rev. C 91,054313 (2015)

This talk will be focused on:

light charged particles emission in fusion-evaporation channelcheck of statistical model parametersfusion-evaporation and fusion-fission cross sectionsS. Valdre et al., submitted to Phys. Rev. C. arXiv:1509.03184

4/13


Experimental apparatus


The experiment

performed at Laboratori Nazionali di Legnaro (LNL)

beam from ALPI linac

Main detectors: Garfield and Hector

4/13




Garfield

∆E (gas)-E (CsI(Tl)) telescope array

cylindrical symmetry; divided into 24 azimuthal sectors

detects LCPs and IMFs at 29° < θ < 85°

4/13




Hector

8 BaF2 scintillators from Hector setup

detect high energy γ-rays (Eγ & 4 MeV)

not considered in the present work

4/13




Phoswiches

48 scintillator telescopes from Fiasco experiment

identify evaporation residues and fission fragments

at forward angles (5° < θ < 15°)

5/13


Evaporation residue selection

ToF [ns]20 40 60 80 100 120

gat

eA [

arb

. un

its]

500

1000

1500

2000

2500

a)

elastic scattering

HHe CN

OF

NeNaMgAlSiP

gateB [arb. units]500 1000 1500 2000

gat

eA [

arb

. un

its]

500

1000

1500

2000

2500

b)

elastic scattering

H

HeCNOFNe

NaMg

AlSi

Ptrigger threshold

Condition for the selection of fusion-evaporation events

1 particle in dotted areal gate in any phoswichno other particles in continuous areal gates

6/13


Statistical model of Compound Nucleus decay

The Gemini++ statistical model code

is a widely used statistical model code

adopts a default set of parameters obtained by fitting datafrom several previous experiments

parameters are tuned for heavy nuclei (A & 150)there aren’t many experimental data to fix parameters formedium-light nuclei

We compared experimental data with Gemini++ varyingmany parameters:

level densityCoulomb barrier distributionyrast energy parametrizationetc. . .

R. J. Charity, Phys. Rev. C 82, 014610 (2010)

7/13


From 4π to experimental geometry and vice-versa

Geometry and efficiency filter

directly compare experimental spectra with filtered simulations

correct experimental yields for the apparatus efficiency

]° [(lab)θ0 2 4 6 8 10 12 14

[a.

u.]

θdσd

-310

-210

Evaporation residue angular distribution

4π

Filtered

Gemini++

8/13


Comparison between experimental data and Gemini++

300 and 600 MeV ER angular distributions

Spectra are scaled to the same integral to compare the shape

Very good agreement

8/13



300 MeV energy spectra in coincidence with ER

Spectra are scaled to the same integral to compare the shape

Very good agreement for protons

Simulated α spectra have a correct slope, but lower energy

p α

9/13


Improvement of the agreement for α-particles

Only adopting RLDM yrast and fission barrier(instead of linearized Sierk) the agreement improves

]hJ [0 10 20 30 40 50 60 70 80

E [

MeV

]

01020304050607080 Lin. Sierk Y.

RLDM Y.fSierk B

fRLDM B

Yrast and fission barriers

10/13



proton energy spectra at 300 MeV

[MeV](c.m.)E5 10 15 20

[ar

b. u

nit

s]d

Eσd

-210

-110

(a)

exp

GEMINI++

°300MeV p 60

[MeV](c.m.)E10 20

[ar

b. u

nit

s]d

Eσd

-310

-210

-110

(b)

°300MeV p 47

[MeV](c.m.)E0 10 20

[ar

b. u

nit

s]d

Eσd

-310

-210

-110

(c)

°300MeV p 35

α-particle energy spectra at 300 MeV

[MeV](c.m.)E10 20 30 40

[ar

b. u

nit

s]d

Eσd

-210

-110

(d)

° 60α300MeV

[MeV](c.m.)E10 20 30 40

[ar

b. u

nit

s]d

Eσd -310

-210

-110

(e)

° 47α300MeV

[MeV](c.m.)E10 20 30 40

[ar

b. u

nit

s]d

Eσd -310

-210

-110

(f)

° 35α300MeV

10/13




[MeV](c.m.)E10 20

[ar

b. u

nit

s]d

Eσd -210

-110

(a)

exp

GEMINI++

°450MeV p 60

[MeV](c.m.)E10 20 30

[ar

b. u

nit

s]d

Eσd-310

-210

-110

(b)

°450MeV p 47

[MeV](c.m.)E0 10 20

[ar

b. u

nit

s]d

Eσd

-210

-110

(c)

°450MeV p 35


[MeV](c.m.)E10 20 30

[ar

b. u

nit

s]d

Eσd

-210

(d)

° 60α450MeV

[MeV](c.m.)E10 20 30 40

[ar

b. u

nit

s]d

Eσd

-210(e)

° 47α450MeV

[MeV](c.m.)E10 20 30

[ar

b. u

nit

s]d

Eσd -210 (f)

° 35α450MeV

10/13




[MeV](c.m.)E10 20 30

[ar

b. u

nit

s]d

Eσd

-210

-110

(a)

exp

GEMINI++

°600MeV p 60

[MeV](c.m.)E10 20 30

[ar

b. u

nit

s]d

Eσd

-310

-210

-110

(b)

°600MeV p 47

[MeV](c.m.)E0 10 20 30

[ar

b. u

nit

s]d

Eσd

-210

-110

(c)

°600MeV p 35


[MeV](c.m.)E10 20 30 40 50

[ar

b. u

nit

s]d

Eσd

-210 (d)

° 60α600MeV

[MeV](c.m.)E10 20 30 40 50

[ar

b. u

nit

s]d

Eσd

-210(e)

° 47α600MeV

[MeV](c.m.)E10 20 30 40

[ar

b. u

nit

s]d

Eσd

-210(f)

° 35α600MeV

10/13



proton angular distributions

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1 (a)

exp

GEMINI++

p 300MeV

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1 (b)

p 450MeV

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1 (c)

p 600MeV

α-particle angular distributions

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1

1.5(d)

300MeVα

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1

1.5(e)

450MeVα

[deg](lab)θ20 40 60

[ar

b. u

nit

s]Ωdσd

0

0.5

1

1.5(f)

600MeVα

10/13



Ebeam [MeV]200 300 400 500 600 700 800

mu

ltip

licit

y

1

2

3

4

5

6p totald total

totalαp from GARFIELDd from GARFIELD

from GARFIELDα

11/13


Cross section estimations

Rutherford cross-section normalization

It’s possible to measure cross sections via a normalization obtainedfrom a plastic scintillator at 2° that measures elastic scattering

σFE(300 MeV) = 0.89(11) b

σFE(450 MeV) = 0.55(5) b

σFE(600 MeV) = 0.46(12) b

P. Eudes et al., Europhys. Lett. 104, 22001 (2013)

σFEσR

11/13


Cross section estimations

Rutherford cross-section normalization

It’s possible to measure cross sections via a normalization obtainedfrom a plastic scintillator at 2° that measures elastic scattering

σF(300 MeV) = 1.01(11) b

σF(450 MeV) = 0.81(6) b

σF(600 MeV) = 0.88(16) b

σFσR

12/13


Conclusions

We measured the reaction 48Ti+40Ca at 300, 450 and 600 MeVto study the decay of nuclei of masses in the region A ∼ 90

Gemini++ statistical model code well describes the decay inthe evaporative channel at least in Garfield (θ > 30°)

We found an α-particle yield excess, in particular at forwardangles and increasing with energy.

It’s difficult to improve the agreement by tuning the modelparameters; indication of the onset of minor pre-equilibriumemission or contamination from other processes.

We gave an estimation of fusion-evaporation and total fusioncross section. Expecially at higher energies, there is room forDIC and quasi-fission decays.

Thanks for your attention!13/13

Decay features of medium mass nuclei at high excitation and...

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