Measurement of the total cross section for 238U photofission in the nucleon resonance region

Bianchi, N.; Deppman, A.; Sanctis, E. De; Fantoni, A.; Sandri, P. Levi; Lucherini, V.; Muccifora, V.; Polli, E.; Reolon, A. R.; Rossi, P.; Anghinolfi, M.; Corvisiero, P.; Gervino, G.; Mazzaschi, L.; Mokeev, V.; Ricco, G.; Ripani, M.; Sanzone, M.; Taiuti, M.; Zucchiatti, A.; Bergère, R.; Carlos, P.; Garganne, P.; Leprêtre, A.

doi:10.1016/0370-2693(93)90251-c

Cited by 90 publications

(27 citation statements)

References 16 publications

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“…[6,7]. Our 238 U data agree well with the average of the Mainz [11] and the Frascati [12] data from the ∆-resonance region up to about 800 MeV. In the same energy region our 232 Th data agree with the Frascati [13] data.…”

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confidence: 86%

Photofission of Heavy Nuclei at Energies up to 4 GeV

et al. 2000

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Total photofission cross sections for 238 U, 235 U, 233 U, 237 Np, 232 Th, and nat Pb have been measured simultaneously, using tagged photons in the energy range Eγ =0. 17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238 U relative to that for 237 Np is about 80%, implying the presence of important processes that compete with fission. We also observe that the relative photofission cross sections do not depend strongly on the incident photon energy over this entire energy range. If we assume that for 237 Np the photofission probability is equal to unity, we observe a significant shadowing effect, starting below 1.5 GeV.PACS numbers: 25.85. Jg, 25.20.Dc It has long been assumed [1,2] that the photofission cross section σ γF for the uranium and transuranic isotopes should exhaust the total nuclear photoabsorption cross section σ γA for incident photon energies above 50 MeV, so that the fission probability of these nuclei at these energies was generally assumed to be unity. If this were the case, the photofission method would provide a very convenient way to determine the total photoabsorption cross section. This interesting quantity [3], not easily determined by other methods for heavy nuclei, would yield information on the intrinsic properties of nucleons inside the nuclear medium, as well as on the hadronic nature of the photon.One might assume the total photoabsorption cross section per nucleon σ γA /A to be independent of A. In the ∆-resonance region, this has been shown to be plausible by various measurements for several complex nuclei ranging from Li to U, leading to the concept of the "universal curve" [4]. For several nuclei, recent measurements have been performed up to 2.6 GeV [5]. If we define the photofissility W F of a nucleus as the probability that this nucleus undergoes fission, then we can express W F as the ratio σ γF /σ γA . A constant σ γA /A implies that, for two nuclei, the ratio of their photofissilities is given by the ratio of their photofission cross sections per nucleon σ γF /A.The assumption W F ≃ 1 had to be reconsidered after a Novosibirsk group [6] reported that the fission probability for 237 Np is about 30% higher than that for 238 U in the photon energy range 60-240 MeV. Subsequent measurements performed at the Saskatchewan Accelerator Laboratory (SAL) [7] corroborated these results for the same energy range. We now observe this trend to be true up to 4 GeV.This experiment was the first measurement performed in Hall B at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) using the photon-tagging facility [8]. An electron beam is passed through a thin radiator to produce bremsstrahlung. The residual energy of an electron after bremsstrahlung emission is deduced from its measured position in the focal plane of the tagger bending magnet. The two-layer focal-plane detector array has an energy resolution of 0.1% provided by the highly segmented ...

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confidence: 86%

Photofission of Heavy Nuclei at Energies up to 4 GeV

et al. 2000

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“…17 we show our results for the photoabsorption on nuclei together with the experimental data for uranium [31,32,33]. The calculations have been done using Λ = 550 MeV, g ′ 11 = 0.6 and g ′ 12 = g ′ 22 = 0.25.…”

Section: The ρ Meson In Nuclear Mattermentioning

confidence: 95%

Momentum dependence of the pion cloud for ϱ-mesons in nuclear matter

et al. 1998

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“…We have applied the present, phenomenological, semiempirical photofission approach to analyse the photofissility data obtained at 1 GeV for a number of pre-actinide, intermediate-mass, and less massive nuclei [3,[11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Some data for actinide targets [3,11,14,[25][26][27][28] are also presented. Photofissility is defined as the ratio of the photofission cross section, σ f , to the total nuclear photoabsorption cross section, from data reported in [3,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”

Section: The Very Interesting Results Reported Above Suggest Parametrmentioning

confidence: 99%

“…Some data for actinide targets [3,11,14,[25][26][27][28] are also presented. Photofissility is defined as the ratio of the photofission cross section, σ f , to the total nuclear photoabsorption cross section, from data reported in [3,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The calculated trend from the present model (f c ) is shown by the full line.…”

Section: The Very Interesting Results Reported Above Suggest Parametrmentioning

confidence: 99%

Photofissility at 1 GeV for nuclei throughout the periodic table

Tavares¹,

Duarte²,

Morcelle³

et al. 2005

Braz. J. Phys.

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A new approach to evaluate nuclear photofissilities at incident photon energies above the pion photoproduction threshold has been recently developed and proved to describe successfully the fissilities of nat Pb and 232 Th target nuclei at energies ∼ 0.2 − 4.0 GeV. The method is merely a simple, semiempirical description of the photofission reactions in which fissility, f , is governed by two basic quantities, namely, i) the first-chance fission probability,f 1 , for the average cascade residual, and ii) the slope,s, of the chance-fission probability associated with the average evaporative sequence of fissionable residuals. In the present work we have extended this approach to analyse photofissity data that have been accumulated over the past fourty years or so, measured at 1 GeV, for nearly fourty target nuclei extending from Ti up to Np. Results have shown that the variation of fissility with Z 2 /A could be described quite satisfactorily by the proposed model.Recently, a new approach to evaluate nuclear photofissilities at incident photon energies E γ 200 MeV has been developed to overcome the calculational difficulties imposed by the available Monte Carlo codes when the target nuclei are expected to exhibit low, or very low, fissility-values ( 1%), as is the case for pre-actinide, intermediate-mass, and less massive nuclei [1]. The method is a simple, semiempirical approach that has proved to work quite well in describing the fissilities of nat Pb and 232 Th target nuclei induced by ∼ 0.2 − 4.0 GeV photons, which have been measured at the Thomas Jefferson Laboratory by Cetina et al [2,3].Since photofissility values for actinide targets have been already analysed to some detail in the framework of Monte Carlo calculations [3,4] we decided, in the present work, to extend this approach [1] to analyze photofissility data that have been accumulated over the past fourty years or so, measured at 1 GeV, for nearly fourty target nuclei extending from Ti up to Np. Results have shown that the variation of fissility with Z 2 /A can be described quite satisfactorily by the proposed model. We remark that the trend of fissility is seen as an inverse reflection of the behaviour of the height of the fission barrier with Z 2 /A [5,6].Monte Carlo calculations are, at present, the main tool to describe quantitatively both the cascade and fissionevaporation competition processes, as well as to obtain the total fission probabilities (photofissility values) for a number of photofission reaction cases. However, for cases where the target nucleus is expected to have low fissility-values (pre-actinide, intermediate-mass, and less massive nuclei), the available codes may reveal themselves very time-consuming in obtaining a calculated fissility-curve of acceptable uncertainty over a large energy-interval such as ∼ 0.2 − 4.0 GeV. This fact led us to develop an alternative method to calculate nuclear photofissility-values semiempirically. This approach is based on the current, two-step model for intermediateenergy photonuclear reactions...

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Measurement of the total cross section for 238U photofission in the nucleon resonance region

Cited by 90 publications

References 16 publications

Photofission of Heavy Nuclei at Energies up to 4 GeV

Photofission of Heavy Nuclei at Energies up to 4 GeV

Momentum dependence of the pion cloud for ϱ-mesons in nuclear matter

Photofissility at 1 GeV for nuclei throughout the periodic table

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