The 2H (),, p ) n cross section was measured absolutely at 0 ° for the outgoing proton, for photon energies between 8 and 18 MeV. The rising trend observed in the cross section in this energy region indicates the existence of the theoretically predicted minimum. Our results at Ev..~ 10 MeV are well described by recent relativistic calculations, the data around 15 MeV, on the contrary, are commonly underestimated.
Excitation energy spectra resulting from the '2C, '60, and vCa(y, p) reactions at 90' have been measured with tagged photons of about 61 and 77 MeV. Decay to several discrete states is discussed. Evidence is shown for an absorption process where the photon interacts with a T 1 proton-neutron pair, instead of the T 0 p-n pair implicit in the quasideuteron model.A long time ago it was suggested' that a real photon with energy between 40 and 140 MeV predominantly interacts with correlated proton-neutron pairs in the nucleus, which have a relative wave function similar to the free deuteron wave function. Models based upon this quasideuteron picture yield a satisfactory description of total absorption cross sections2 and provide a natural framework for (y,pn) reactions. Also, only such models seem to be able to account for the near equality of (y,p) and (y, n) cross sections in light nuclei. Only recently, clear experimental indications for a reaction mechanism other than a pure single-particle knockout have been found in the (y,p) reaction. In ' C, a large transition probability was observed' towards states in "B at an excitation energy of =6.8 MeV, which are only very weakly excited in the quasifree (e, e'p) reaction. It was pro-
The total deuteron photodisintegration cross section has been determined in an alternative way, based on the absolute measurement of the 90' cross section and, to a lesser extent, the 0' and 180' cross sections. The accuracy of the deduced total cross sections amounts to 3%, including systematic errors. The agreement of our data with the results from recent theoretical calculations is very good.PACS number(s): 25.20. -x, 27.10.+h For a number of reasons, the study of the characteristics of the deuteron photodisintegration process has continuously attracted a lot of attention, from both the experimental and the theoretical side. More specifically, this reaction has been considered as a fundamental testing ground for the details of the nucleon-nucleon interaction. At present, the correspondence between the experimental photodisintegration data and the results from conventional theoretical approaches (including mesonexchange currents, isobaric configurations, and relativistic spin-orbit terms) seems to have reached a satisfying level. In particular, the magnitude of the total photoabsorption cross section in the low-energy region (here arbitrarily defined as the interval between the reaction threshold and, say, 25 MeV) can be extremely well described by theory. This agreement is accentuated by the high accuracy (3 -5% total uncertainty, i.e. , the sum of statistical and systematic errors) of the results from the total absorption measurements [1,2]. Such accuracy is necessary as the predictions from the various theoretical calculations are in accordance with each other within the 2%%uo level.Results from direct H(y, p) measurements [3] have a somewhat larger uncertainty (about 7%), while the data deduced from the neutron-proton radiative capture experiments [4 -9] generally show a 5 -10% total error. A balanced review of all data in the relevant energy range has been given in Refs. [2] and [8], while the general status of the theoretical as well as the experimental situation for the deuteron photodisintegration is extensively described in a recent review by Arenhovel and Sanzone [10]. However, there also exists an indirect way to determine the total photodisintegration cross section with good accuracy. This is based on an adequate knowledge of the Now at Master Foods, +d sin Ocos0+e sin 0, with 0 the c.m. proton emission angle; the so-called "Partovi coefficients" a up to e contain the information concerning the e.m. multipolarity of the involved transition(s). Consequently, one obtains (0') = a +c, do o (2) (180')=a -c, do (3) (90') =a +b +e, der (4) while the total absorption photodisintegration cross section O. T reads cr r = 4m (a + , ' b + , ', e) . --Alternately, the latter can be written as (5) cr r = 4ir -a + -( 90') -e 1 2 do, 2 3The knowledge of o. T now solely depends on the magnitude of the various terms entering the above expression; in principle, these should all be taken from experiment.In previous papers [12], we have described our results for the forward, backward, and 90' deuteron photodisintegra...
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