E.Chiaveri on behalf of the n_TOF Collaboration n_TOF Collaboration/Collaboration Board Lisbon, 13/15 December 2011 Proposal for Experimental Area 2(EAR-2)

E.Chiaveri on behalf of the n_TOF Collaboration

n_TOF Collaboration/Collaboration Board Lisbon, 13/15 December 2011

Proposal for Experimental Area 2(EAR-2)

Scientific Motivation


2

Scientific Case for EAR-2

• Astrophysical Research

• Nuclear Technology Application

• Basic Nuclear Research

• List of Examples of EAR-2 Proposals


EAR-2 Experiments

Experiments in EAR-2 can be performed :

on very small samples (important to reduce mass of unstable samples and in cases where sample material is limited)

on isotopes with very small cross sections (where signal/background ratio is crucial)

in much shorter time (measurements can be eventualy repeated to reduce systematic uncertainties)

Measurements of neutron-induced cross sections at high energies (En>10-100 MeV), which are not possible in the existing EAR-1, will benefit from largely reduced the -flash.

EAR-2 Nuclear Transmutation

From the transmutation projects (or future generation nuclear energy systems), the EAR2 would allow to measure the fission cross-section of Pu isotopes and minor actinides with half lives of a few tens of years.

Although short lived, it may be convenient to burn those actinides in future systems (either ADS or Gen IV fast reactors), together with their neighboring long-lived isotopes.

Important Candidates: Fission Cross Section :238Pu (87.7 y)/241Pu (14.1 y) 244Cm(18.1 y) 242mAm(141y) 243Cm (29.1y) Capture Cross Section : 242Am (141 y)/ 243Cm (29.1 y) 231Pa(32400 y)

N.Colonna

n_TOF Collaboration/Collaboration

Board Lisbon, 13/15 December 2011


EAR-2: Nuclear Astrophysics Nucleosynthesis by the slow neutron capture process represents a unique tool for studying the related abundances through the tight correlation with the experimental (n, g) cross sections.

The EAR-2 options for measurements of so farinaccessible reaction rates will provide a boost for ourunderstanding of neutron capture nucleosynthesis during theHe burning phases of stellar evolution, which played a crucialrole in the history of the Universe, because they contributed half of the abundances between Fe and Bi.

important candidates for EAR-2: 79Se, 90Sr, 93Zr, 107Pd, 135Cs, 147Pm, 163Ho,171Tm, 182Hf, 204Tl

F. Kaeppeler


very small samples unstable isotopes along the reaction path of the slow neutron capture process (s process*), which give rise to local branchings in the reaction path; (n, g) cross sections of branch point isotopes are needed for analysis of abundance pattern to deduce information on neutron flux, pressure, and temperature of stellar plasma * responsible for half of the abundances between Fe and Bi.

important candidates for EAR-2: 79Se, 90Sr, 93Zr, 107Pd, 135Cs, 147Pm, 163Ho,171Tm, 182Hf, 204Tl

The EAR-2 window to stellar nucleosynthesis: s-process branchings

F. Kaeppeler


very small cross sections neutron magic isotopes exhibit particularly small (n,g) cross sections and act therefore as bottle necks for the reaction flow; present data are too uncertain and need significant improvement

isotopes between C and Si represent crucial neutron poisons because their small cross sections are balanced by their high abundances; present data by far not sufficient

important candidates for EAR-2: 86Kr, 88Sr, 138Ba, 140Ce, 208Pb; isotopes of C, O, Ne, Mg

The EAR-2 window to stellar nucleosynthesis: neutron magic isotopes

F. Kaeppeler


short measuring times isotopes of pure s-process origin (which are shielded by stable isobars against contributions from the r process) are important constraints for model predictions of the s-abundance distribution and have, therefore, to be known with an accuracy of less than 2% (so far achieved only for about half of the s-only isotopes); to reach this accuracy, systematic effects have to be studied in repeated measurements with different experimental conditions

important candidates for EAR-2: 64Zn, 70Ge, 76Ge, 80,82Kr, 86,87Sr, 95,96Mo, 104Pd, 164,166Er, 198Hg

The EAR-2 window to stellar nucleosynthesis: s-only isotopes

F. Kaeppeler


Basic Nuclear Research Neutron-induced reactions measured with the time-

of-flight technique form a unique tool to investigate nuclear structure at high excitation energies by observing resolved nuclear levels that are revealed by resonances in the reaction yields

Neutron resonance spectroscopy is used to obtain crucial information on level densities in the vicinity of the neutron binding energy, i.e. at several MeV above the ground state

A large number of level density models exist which are all calibrated by the level density observed with neutron resonances

Basic Nuclear Research


Example of the observation of nuclear levels in neutron-induced experiments.

Tthe total cross section is shown as a function of neutron energy for several nuclei with increasing mass ranging from 6Li to 241Am


LIST OF EXAMPLES OF EAR-2 PROPOSALS

Simultaneous measurements of capture and fission cross

sections of fissile Pu isotopes 239,240Pu (n,g), (n,f) isotopes

Measurement of the 25Mg(n,α)22Ne cross section Simultaneous measurements of capture and fission cross

sections of 238Pu and 244Cm Simultaneous measurements of capture and fission cross

sections of 245Cm Measurements of (n,xn) reaction cross sections for heavy

target nuclei Fission cross section of the 230Th(n,f) reaction Neutron capture measurement of the s-process branching

point 79Se Cross section and angular distribution of fragments from

neutron-induced fission of 232U


EAR-2 proposal 1


EAR-2 proposal 2


EAR-2 proposal 3


EAR-2 proposal 4


EAR-2 proposal 5


EAR-2 proposal 6


EAR-2 proposal 7


EAR-2 proposal 8

Documents

E.Chiaveri on behalf of the n_TOF Collaboration n_TOF Collaboration/Collaboration Board Lisbon, 13/15 December 2011 Proposal for Experimental Area 2(EAR-2)