piotr bednarczyk 1,2 and adam maj 2 for the rising collaboration
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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
100 MeV/u 84Kr beam
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Thick (0.2 g/cm2) Au target, 150 MeV/u 132Xe beam
At the very beginning…
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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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• 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
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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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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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
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bad signals (satellite time peaks )
Number of fired crystals in a cluster
Number of clusters involved
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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
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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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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
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CATE
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~600MeV/u 68Ni secondary beam
~100MeV/u 54Cr secondary beam
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Incoming-outgoing projectile selection, Au target
197Au Cx line(~35mb)?
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Presence of the Au target enhances the prompt low energy gammas.
Gamma-time Gamma-energy
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• prompt gammas •~100ns delayed
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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
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MB Ring#4,5 ~90deg
134Cs secondary beam -particle
Position of the (prompt) bump very little depends on a detector angle
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 = 0.355v/c = 0.355
This is NOT bremmstrahlung!This IS compressed nearly constant background.
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