排序方式: 共有46条查询结果,搜索用时 31 毫秒
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G Viesti M Lunardon D Fabris G Nebbia M Cinausero E Fioretto G Prete JB Natowitz K Hagel R Wada 《Pramana》1999,53(3):395-404
The transition of the level density parameter a
off from the low excitation energy value a
off=A/8 MeV−1 to the Fermi gas value a
FG ∼ A/15 MeV−1 was discovered a few years ago studying particle spectra evaporated from hot compound systems of A∼ 160. A number of experiments have been recently performed to confirm the earlier findings and extend the investigation to
other mass regions and to higher excitation energies. Furthermore, precision coincidence experiments have been done in the
lead region in which evaporation residues are tagged by low energy gammarays. Those experiments open the possibility of a
detailed study of the level densities in nuclei where the shell effects are important. 相似文献
44.
Knoop M. Champenois C. Hagel G. Houssin M. Lisowski C. Vedel M. Vedel F. 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,29(2):163-171
The lifetime of the
-level in singly-ionized calcium has been measured by the electron-shelving technique on different samples of rf trapped ions. The metastable state has been directly populated by exciting the dipole-forbidden
transition. In ion clouds, the natural lifetime of this metastable level has been measured to be (
) ms. For the single-ion case, we determined a lifetime of (
) ms. The
-error bars at the 2%-level have different origins for the two kinds of experiments: data fitting methods for lifetime measurements in an ion cloud and control of experimental parameters for a single ion. De-shelving effects are extensively discussed. The influence of differing approaches for the processing of the single-ion quantum jump data on the lifetime values is shown. Comparison with recent measurements shows excellent agreement when evaluated from a given method.Received: 14 November 2003, Published online: 24 February 2004PACS:
32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Pj Optical cooling of atoms, trapping 相似文献
45.
Bearden IG Beavis D Besliu C Budick B Bøggild H Chasman C Christensen CH Christiansen P Cibor J Debbe R Enger E Gaardhøje JJ Germinario M Hagel K Hansen O Holm A Holme AK Ito H Jipa A Jundt F Jørdre JI Jørgensen CE Karabowicz R Kim EJ Kozik T Larsen TM Lee JH Lee YK Løvhøiden G Majka Z Makeev A Mikelsen M Murray M Natowitz J Nielsen BS Norris J Olchanski K Ouerdane D Płaneta R Rami F Ristea C Röhrich D Samset BH Sandberg D Sanders SJ Scheetz RA Staszel P Tveter TS Videbaek F Wada R Yin Z 《Physical review letters》2004,93(10):102301
Transverse momentum spectra and rapidity densities, dN/dy, of protons, antiprotons, and net protons (p-p) from central (0%-5%) Au+Au collisions at square root of S(NN)=200 GeV were measured with the BRAHMS experiment within the rapidity range 0=y=3. The proton and antiproton dN/dy decrease from midrapidity to y=3. The net-proton yield is roughly constant for y<1 at dN/dy approximately 7, and increases to dN/dy approximately 12 at y approximately 3. The data show that collisions at this energy exhibit a high degree of transparency and that the linear scaling of rapidity loss with rapidity observed at lower energies is broken. The energy loss per participant nucleon is estimated to be 73+/-6 GeV. 相似文献
46.
Bearden IG Beavis D Besliu C Blyakhman Y Brzychczyk J Budick B Bøggild H Chasman C Christensen CH Christiansen P Cibor J Debbe R Gaardhøje JJ Grotowski K Hagel K Hansen O Holm A Holme AK Ito H Jakobsen E Jipa A Jørdre JI Jundt F Jørgensen CE Keutgen T Kim EJ Kozik T Larsen TM Lee JH Lee YK Løvhøiden GL Majka Z Makeev A McBreen B Murray M Natowitz J Nielsen BS Olchanski K Olness J Ouerdane D Planeta R Rami F Röhrich D Samset BH Sanders SJ Sheetz RA Sosin Z Staszel P Thorsteinsen TF Tveter TS 《Physical review letters》2001,87(11):112305
Measurements, with the BRAHMS detector, of the antiproton-to-proton ratio at midrapidities and forward rapidities, are presented for Au+Au reactions at square root of [s(NN)] = 130 GeV, and for three different collision centralities. For collisions in the 0%-40% centrality range, we find N(&pmacr;)/N(p) = 0.64+/-0.04((stat))+/-0.06((syst)) at y approximately 0, 0.66+/-0.03+/-0.06 at y approximately 0.7, and 0.41+/-0.04+/-0.06 at y approximately 2. The ratios are found to be nearly independent of collision centrality and transverse momentum. The antiproton and proton rapidity densities vary differently with rapidity, and indicate a significant degree of collision transparency, although a net-baryon free midrapidity plateau (Bjorken limit) is not yet reached. 相似文献