Positrons from Heavy Ion Collisions-Experiments at the UNILAC

Backe, H.; Bonin, W.; Kankeleit, E.; Kramer, M. A.; Krieg, R.; Metag, V.; Senger, P.; Trautmann, Ν.; Weik, P.; Wilhelmy, J. B.

doi:10.1007/978-1-4899-2139-0_5

Cited by 10 publications

(11 citation statements)

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“…Together with a series of recent studies carried out also at GSI by three independent groups, the ORANGE [8,[11][12][13][14][15][16], the EPOS [17,18,19,51 ], and the TORI collaborations [32][33][34][35], they largely establish the characteristics of positron creation in heavyion collisions predicted by theory. To accomplish it, the smooth positron background, resulting from internal pair decay of excited nuclear states having transition energies larger than 2 m o c 2, had to be determined experimentally as well by measuring the y-ray spectra in coincidence with the scattered heavy ions.…”

Section: Introductionmentioning

confidence: 76%

“…From these measurements it has been turned out that the measured positron yield can be accounted for by the nuclear process, when assuming mainly E1 nuclear transitions with a small (~ 5-10%) E2 admixture [3,32]. Note in this context that positrons, stemming from pair decay of E0 transitions, cannot be taken into account by this procedure.…”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 97%

“…In view of the rather large systematic errors expected by this procedure as well as of uncertainties in the theoretical conversion coefficients, its capability has to be checked by measurements in light collision systems (see e.g. [32]). …”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 99%

“…This empirical procedure, avoiding efficiency corrections and unfolding of the measured y-ray spectra, reduces the systematic uncertainties, and has further advantage as being based on experimentally-determined quantities only. Furthermore, additional corrections regarding the positron background due to external pair creation, caused by the interaction of the y radiation with the target material (contribution about 10% for a 1 mg/cm 2 thick target [32]), are automatically included in this method. We have used this empirical approach to determine the nuclear positron background for the collision systems Pb + Th, U + Th, and U+ U [39].…”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 99%

“…The latter, ho~vever, depend on the multipolarity M2 of the 7 radiation which is not known. To estimate the mean multipolarity, a series of measurements with lighter collision systems (Z,~ < 160) [3,32] was, therefore, necessary.…”

Section: Evahtation Of the Nuclear Positron Backgroundmentioning

confidence: 99%

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Systematic studies of positron production in heavy-ion collisions near the Coulomb barrier

Tsertos¹,

Berdermann²,

Bosch³

et al. 1992

Z. Physik A - Hadrons and Nuclei

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We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united charge Z,=Z I+Z 2 ranging from Z,= 164 (Pb+Pb) to Z,,= 184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orangefl-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasiatomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of about 0.75 can be established for the calculated spectra. In particular, the dependence on Z,, of the measured emission probabilities was found to follow a power law (ocZ,~95-+~), in fair agreement with the theoretical prediction.

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