Photofissility of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Th</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>232</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>measured with tagged photons from 250 to 1200 MeV

Bianchi, N.; Deppman, A.; Sanctis, E. De; Fantoni, A.; Sandri, P. Levi; Lucherini, V.; Muccifora, V.; Polli, E.; Reolon, A. R.; Rossi, P.; Iljinov, A. S.; Mebel, M. V.; Arruda‐Neto, J. D. T.; 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:10.1103/physrevc.48.1785

Cited by 25 publications

(12 citation statements)

References 25 publications

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“…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.…”

supporting

confidence: 81%

“…The D 13 and F 15 resonances, clearly seen in the photoabsorption on the proton and the deuteron [19], and still seen in 3 He [20], are not observed in the total cross sections for A ≥ 4 nuclei. Photoabsorption measurements have been done for Li, C, Al, Cu, Sn, and Pb [15], and photofission measurements for Th [13] and U [11,12]. As expected from most previous data, the present photofission cross sections exhibit no prominent resonance structure above the ∆ resonance.…”

supporting

confidence: 58%

“…3 we present a comparison between the photofission data for 237 Np, 238 U, and 232 Th and the existing Pb photoabsorption data [5,[14][15][16]. The photofission data include the data presented in this paper as well as previous data from [6,7,[11][12][13]. Both σ γF and σ γA data were fitted using a modified Breit-Wigner formula.…”

mentioning

confidence: 99%

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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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supporting

confidence: 81%

supporting

confidence: 58%

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Photofission of Heavy Nuclei at Energies up to 4 GeV

et al. 2000

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“…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%

“…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%

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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Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

Frommhold

Steiper

Henkel

et al. 1994

Z. Physik A - Hadrons and Nuclei

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Abstract. The total photofission cross section c%,F for Z35U and 238U has been measured in the energy range 50< E.y < 800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 47r arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section c%,F, which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections c%,F normalized to the atomic number A for both isotopes coincide, and agree in the A-resonance region, within the systematic errors, with the socalled "Universal Curve" C%,T/A of the total photon absorption cross section crT,T. At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there is n__0o resonancelike shape near the D13 resonance (at ~ 710 MeV) as observed for the free proton. This complete suppression of the DI3 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.

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Photofissility ofTh232measured with tagged photons from 250 to 1200 MeV

Cited by 25 publications

References 25 publications

Photofission of Heavy Nuclei at Energies up to 4 GeV

Photofission of Heavy Nuclei at Energies up to 4 GeV

Photofissility at 1 GeV for nuclei throughout the periodic table

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

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