Piotr Bednarczyk 1,2 and Adam Maj 2 for the RISING Collaboration

Piotr BednarczykPiotr Bednarczyk1,21,2 and and Adam MajAdam Maj22

forfor the RISING Collaboration the RISING Collaboration

1GSI Darmstadt, Germany2IFJ PAN Kraków, Poland

Remarks Remarks on the background on the background radiation radiation

in the RISING fast beam campaignin the RISING fast beam campaign**

HISPEC/DESPEC MEETING Valencia (Spain)

15th-16th June

*) Based on discussions with and contributions from:A.Bürger (Bonn), F.Camera (Milano), P.Doornenbal (GSI), J.Gerl (GSI), M.Górska (GSI), M.Kmiecik (Kraków), Zs. Podolyak (Surrey), M. Taylor (York), H.J.Wollersheim (GSI), Q. Zhong (Legnaro)

FRS

HECTORHECTOR8 BaF2 scintillators

CATE: CATE: Position Sensitive Position Sensitive CaCalorimeter lorimeter TeTelescopelescope

Relativistic CoulombE2 or E1 excitation of projectile, break-up

EUROBALL15 cluster Ge-detectors

POV-Ray animation: R. Maj

Layout of the fast-RISING experimentLayout of the fast-RISING experiment

HECTOR SPECTRA

Hector time spectra (100 MeV/u 84Kr beam)

142o

142o

142o142o

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90o

TotFloor

Prompt (target)

8-1

2 n

s aft

er

5 n

s b

efo

re

15 n

s aft

er

(CA

TE)

100 MeV/u 84Kr beam

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baf#1

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time4 no wall

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time2 no w all

Thick (0.2 g/cm2) Au target, 150 MeV/u 132Xe beam

At the very beginning…

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Simple wall

142o 90o

A/Q - 37Ca, CATE -K (mainly 36K)

37Ca beam @196MeV/u;

A/Q - 37Ca, CATE - Ca

ConclusionsConclusionsPrompt radiation from target, increasing with the target thickness

Early gamma radiation, coming from the beam line, caused by the light particles, ranging to very high energies (0-20 MeV)

Late gamma radiation (neutrons?)

Gamma radiation from the interaction of heavy ions in CATE

Ge Cluster detectors

BaF2 HECTOR detectors

beambeam

Target Target chamberchamber

CATE

MINIBALL detectors

Ge SPECTRA15*7 crystals

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510 596

834 846

10141040 1461

180926142211

3004

1369

• Natural radioactivity: 40K, 208Pb,…• 27Al,56Fe(n,n’) with fast neutrons, Doppler broadened • 27Al(p,2p)26Mg; with Ep~Ebeam/u• Ge n capture

A single gamma spectrum, no condition;86Kr primary beam, 100MeV/u 54Cr secondary beam on Au target

55Ni@165 MeV/uBe-target; gates on CATE

129Sn@165 MeV/uBe-target; gates on CATE

Time structure of an in-beam Ge spectrumTime structure of an in-beam Ge spectrumselection: selection: 132132Xe primary beam on Au target & Xe outgoing Xe primary beam on Au target & Xe outgoing particleparticle

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50ns

off-time, randomRadioactivity lines

prompt Coulex target, projectile 27Al(p,2p)26Mg

delayedn induced

Conclusion : A lot of high energy particles (protons) is emitted in the fragmentation reactions

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x 0.25 ns

200 s

2 V

Huge amplitude (>> 20MeV), overshooting signals due to charged particles directly hitting the Ge crystal (?)

“normal” gammas

In-beam (spill-on) pre-amplified Ge signal

In-beam Ge time distribution @ 1st EB ring

If only low amplitudes accepted(DGF filtering)

Ge multiplicity distributionGe multiplicity distribution

0

good signals (central time peak position)

bad signals (satellite time peaks )

Number of fired crystals in a cluster

Number of clusters involved

1 71 15

Conclusion: Radiation/particles of high energy irradiate several Ge detectors (mainly central) in the same time

5 clusters in the central ring

Around: 196Os 200-201Pt 206Hg

Surviving ions

Destroyed ions

Zs. Podolyak et al, Nucl. Phys. A722 (2003) 273c

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Solution: Multiplicity filtering, when the number of crystals in a cluster is 1-3(physically correct condition to detect the Compton scattering)

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A BaF2 (HECTOR) time distribution in coincidence with a cluster

BaF-GeMGe=1-3

BaF-GeMGe=5-7

BaFsingle

Radiation emitted downstream

target

neutrons

CATE

Conclusion: the source of the high multiplicity, and high amplitude signals is situated downstream in the FRS area

Some other properties of the “bad” signals:• For the outer rings the number of saturated signals is reduced• With a primary beam (no fragmentation before a target) the bad signals contribute

less • The higher beam energy and the current the bigger contribution of the bad signals• No matter if a reaction target is used or not

A general conclusion on that point:A fragmentation in the FRS area is a source of the intensive backgroundradiation seen by the Ge detectors. Its nature could be high energy particles* (protons) affecting mainly detectors close to the beam line.

*However a pileup of several hundred gammas irradiating the whole array cannot be excluded (i.e. a very intense bremsstrahlung)

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134Cs secondary beam on Au target

projectile in-fragments out

projectile in-out outTarget Coulex projectile Coulex

a few gammas, mainly elastic scattering=> enhanced background (correlated with a beam)gammas from excited fragments emitted in flight

electronbremsstrahlung ?

Low energy background in a Ge gamma spectrum

Z

A/Q

CATE

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548

~600MeV/u 68Ni secondary beam

~100MeV/u 54Cr secondary beam

~200MeV/u 132Xe primary beam

Incoming-outgoing projectile selection, Au target

197Au Cx line(~35mb)?

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•target•no target•difference

Presence of the Au target enhances the prompt low energy gammas.

Gamma-time Gamma-energy

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132Xe primary beam -single

• prompt gammas •~100ns delayed

134Cs secondary beam -single

The prompt and delayed distributions are shifted in energy

There is (almost) no prompt background bump if only a primary beam is of use

Spectra normalized according to the 400-1000 keV range

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35EB Ring#1 ~15deg

EB Ring#2,3 ~30deg

MB Ring#4,5 ~90deg

134Cs secondary beam -particle

Position of the (prompt) bump very little depends on a detector angle

At ~60 and~ 120 degrees

Zs. Podolyak et al, Nucl. Phys. A722 (2003) 273c

Bremsstrahlung componentsRadiative electron Capture of target electrons into bound states of the projectilePrimary Bremsstrahlung of target electrons produced by the collision with the projectileSecondary Bremsstrahlung of high energy knock-out electrons re-scattering in the target

atomic~ 10000 * (nuclear)

Conclusion: •The prompt background may result from the (secondary ?) bremsstrahlung of electrons slowing down in the secondary target (Au). These electrons would be produced by fragments scattered on the FRS components. (suppressed if there is no primary or secondary target) •The delayed component may be than related to the bremsstrahlung of the electrons in CATE (CsI) or in the environment. (In this case the electrons could be also emitted from the secondary target)

132132Xe (662 keV) Xe (662 keV) v/c = 0.000v/c = 0.000

What happens to the spectral shape, when one applies Doppler corrections?

„662 keV”

132132Xe (662 keV) Xe (662 keV) v/c = 0.100v/c = 0.100

132132Xe (662 keV) Xe (662 keV) v/c = 0.200v/c = 0.200

132132Xe (662 keV) Xe (662 keV) v/c = 0.300v/c = 0.300

132132Xe (662 keV) Xe (662 keV) v/c = 0.320v/c = 0.320

132132Xe (662 keV) Xe (662 keV) v/c = 0.330v/c = 0.330

132132Xe (662 keV) Xe (662 keV) v/c = 0.340v/c = 0.340

132132Xe (662 keV) Xe (662 keV) v/c = 0.345v/c = 0.345

132132Xe (662 keV) Xe (662 keV) v/c = 0.350v/c = 0.350

132132Xe (662 keV) Xe (662 keV) v/c = 0.355v/c = 0.355

132132Xe (662 keV) Xe (662 keV) v/c = 0.360v/c = 0.360

132132Xe (662 keV) Xe (662 keV) v/c = 0.370v/c = 0.370

132132Xe (662 keV) Xe (662 keV) v/c = 0.380v/c = 0.380

132132Xe (662 keV) Xe (662 keV) v/c = 0.390v/c = 0.390

132132Xe (662 keV) Xe (662 keV) v/c = 0.400v/c = 0.400

132132Xe (662 keV) Xe (662 keV) v/c = 0.410v/c = 0.410

132132Xe (662 keV) Xe (662 keV) v/c = 0.420v/c = 0.420

132132Xe (662 keV) Xe (662 keV) v/c = 0.430v/c = 0.430

132132Xe (662 keV) Xe (662 keV) v/c = 0.440v/c = 0.440

132132Xe (662 keV) Xe (662 keV) v/c = 0.450v/c = 0.450

132132Xe (662 keV) Xe (662 keV) v/c = 0.355v/c = 0.355

This is NOT bremmstrahlung!This IS compressed nearly constant background.