Thick-target Recoil Properties Research Articles

Recoil properties of deep spallation and fragmentation products in the interaction of tantalum with 3.65 AGeV 12C-ions and protons

Thick-target recoil properties of deep spallation and fragmentation products of the interaction of tantalum with 3.65 AGeV 12C-ions and 3.65 GeV protons have been studied. The kinematic parameters such as mean product kinetic energies and velocities of the remnant have been deduced from the data by means of the two-step vector velocity model of high-energy reactions. The results have also been used to test the applicability of the factorization hypothesis to the kinematic properties.

Systematics of thick-target recoil properties of deep spallation and fragmentation productions of high-energy proton reactions

Abstract Thick-target recoil properties of deep spallation and fragmentation products of the interaction of lanthanum, terbium, and lutetium with 800 GeV protons have been measured. The results yield the values of the mean product kinetic energies and, combined with previously reported angular distributions, those of the velocity of the remnant, β ∥ . The systematics of these quantities are examined both for these and other targets, ranging from silver to uranium.

Production of Kr and Xe isotopes by interaction of197Au with 0.15–24 GeV protons

Cross sections and thick-target recoil properties of several Kr and Xe isotopes formed in the interaction of197Au with 0.15–24 GeV protons have been determined in order to study their variations with mass product and incident energy. Noble gas isotopic composition and concentration have been obtained by using high sensitivity mass-spectrometry. The measurement of the experimental range, 2W(F+B), and of the forward-to-backward ratio,F/B, permits (with the help of a mathematical formalism based on the two-step model) the determination of some characteristics of nuclear reactions. The results are discussed in terms of fission and spallation mechanisms.

Recoil properties of fragments emitted in the interaction of complex nuclei with relativisticC12ions and protons

Thick-target recoil properties of seven fragments ranging from /sup 24/Na to /sup 52/Mn produced in the interaction of 18.5 GeV /sup 12/C ions and 400 GeV protons with Cu, Ag, Gd, Ta, Au, and U have been measured. After correction for the difference in bombarding energy, the results were used to test the factorization hypothesis. While the properties associated with the ablation step (range and kinetic energy) obey the hypothesis, those associated with abrasion (F/B, ..beta../sub vertical-barvertical-bar/) do not, there being a approx.30% enhancement in these values in reaction induced by /sup 12/C ions. The scaling power of various energy related variables is examined and the systematics of the recoil parameters are developed. The implications of these results for the reaction mechanism are considered.

Production of Kr and Xe isotopes by interaction ofTh232with 0.15-24 GeV protons

Cross sections and thick-target recoil properties of several Kr and Xe isotopes formed in the interaction of $^{232}\mathrm{Th}$ with 0.15-24 GeV protons have been determined in order to study their variations with mass product and incident energy. High sensitivity mass spectrometry has been used to measure noble gas isotopic composition and concentration. The recoil technique, combined with a mathematical formalism based on the two-step model, permits the determination of some characteristics of the nuclear reactions; i.e., the range $R$, the mean kinetic energy $〈T〉$, the observed products and the excitation energy ${E}^{*}$, and the residual nucleus after intranuclear cascade. The results are discussed in terms of fission and deep spallation mechanism. Fission contributes noticeably to the formation of neutron-excess products at all incident energies, while deep spallation concerns the most neutron-deficient isotopes at energies beyond 1 GeV. This last mechanism is described in terms of coherent interaction between incident protons and target nucleus.

Production ofAr38andAr39in the interaction of gold and thorium with 1, 2.5, and 24 GeV protons

Cross sections and thick-target recoil properties of $^{38}\mathrm{Ar}$ and $^{39}\mathrm{Ar}$, formed in the interaction of Au and Th with 1, 2.5, and 24 GeV protons, have been determined in order to study their variations with incident energy. The measurement of the experimental range, $2W(F+B)$, and of the forward-to-backward ratio $\frac{F}{B}$ permits (with the help of a mathematical formalism based on the two-step model) the determination of some characteristics of nuclear reactions; i.e., the mean kinetic energy of the observed products $〈T〉$, the mean forward component of the velocity imparted to the struck nucleus in the first step, $〈{v}_{\ensuremath{\parallel}}〉$, and the excitation energy ${E}^{*}$ of the residual nucleus after cascade. The results are discussed in terms of very asymmetric fission (at 1 GeV) and deep spallation (at 2.5 and 24 GeV) mechanisms. These results are very similar to those obtained for neutron-deficient krypton and xenon isotopes formed in thorium and presented in a previous publication from this laboratory.NUCLEAR REACTIONS Measured $\ensuremath{\sigma}$, $2W(F+B)$, and $\frac{F}{B}$ of $^{38}\mathrm{Ar}$ and $^{39}\mathrm{Ar}$ isotopes formed in interaction of Au and Th with 1, 2.5, and 24 GeV protons.

Formation of isobaric nuclides withA=131in the interaction ofU238with 0.8-11.5 GeV protons

Cross sections and thick-target recoil properties of $^{131}\mathrm{Ce}$, $^{131}\mathrm{La}$, $^{131}\mathrm{Ba}$, and several neighboring Ba nuclides formed in the interaction of $^{238}\mathrm{U}$ with 0.8-11.5 GeV protons have been determined. The results reveal a dichotomy between $^{131}\mathrm{Ba}$ and the more neutron-rich products on the one hand, and the more neutron-deficient ones on the other. The latter have rising excitation functions, forward-to-backward ratios (F/B) that peak at 3 GeV, and ranges that decrease abruptly just below this energy. The former have decreasing excitation functions as well as F/B and ranges that decrease slowly and featurelessly with increasing proton energy. The energy dependence of F/B as well as the changes in the angular distributions of the very neutron deficient products observed between 3 and 11.5 GeV are explained in terms of a change in the nature of near-central proton-nucleus interactions. At the lower energies the interaction consists of a series of nucleon-nucleon collisions while at high energies the proton interacts collectively with all the nucleons lying in its path. The dropoff in the mean ranges of these same nuclides and the accompanying broadening of the spectra indicate a transition between fission and deep spallation. The possible connection between these two effects is discussed. Several experiments to test the proposed model are suggested.NUCLEAR REACTIONS Measured $\ensuremath{\sigma}$, range, and F/B of $^{131}\mathrm{Ce}$, $^{131}\mathrm{La}$, $^{131}\mathrm{Ba}$, $^{128}\mathrm{Ba}$, $^{133}\mathrm{Ba}^{m}$, $^{135}\mathrm{Ba}^{m}$, and $^{140}\mathrm{Ba}$ formed in interaction of $^{238}\mathrm{U}$ with 0.8-11.5 GeV protons. Proposed explanation for change in properties of very neutron deficient products.

Recoil properties of radionuclides formed in the interaction of 1-300-GeV protons with gold

The thick-target recoil properties of a number of nuclides, varying from $^{22}\mathrm{Na}$ to $^{196}\mathrm{Au}$, formed in the interaction of 1-300-GeV protons with $^{197}\mathrm{Au}$ have been measured in order to study the systematics of their variation with product mass and incident energy. The forward-to-backward ratios ($\frac{F}{B}$) of many of the products have a peak at 3 GeV and decrease at higher energies, with products in the mass region $46\ensuremath{\le}A\ensuremath{\le}65$ having $\frac{F}{B}=1.0$ at 300 GeV. The $\frac{F}{B}$ values of products with $A\ensuremath{\gtrsim}140$ decrease monotonically between 1 and 300 GeV. The results are analyzed by the two-step model of high-energy reactions and discussed in terms of the different reaction mechanisms, spallation, fission and fragmentation. Fission contributes appreciably to the formation of products in the mass region $46\ensuremath{\le}A\ensuremath{\le}103$ at 1 GeV bombarding energy, but other mechanisms predominate at and above 11.5 GeV. The results are compared to the predictions of intranuclear cascade-evaporation calculations, and are in reasonable agreement at 1 and 3 GeV, although the calculations predict more forward momentum transfer than is observed. At higher energies the relation between forward momentum and mean deposition energy derived from the calculations must break down, because nuclides requiring high deposition energies for their formation have little or no forward momentum. Some possible explanations for this phenomenon are discussed.NUCLEAR REACTIONS $^{197}\mathrm{Au}(p, x)^{22}\mathrm{Na}$-$^{196}\mathrm{Au}$, ${E}_{p}=1\ensuremath{-}300$ GeV; measured thick-target recoil properties; derived momenta and deposition energies.

Evidence for sideward emission of Sc fragments in the interaction ofU238with 400 GeV protons

Thick-target recoil properties of Sc fragments produced in the interaction of $^{238}\mathrm{U}$ with 400 GeV protons have been determined. The anisotropy parameter $\frac{b}{a}$ was obtained from measurements on targets oriented either parallel or perpendicular to the proton beam on the assumption that the angular distribution of the fragments in the moving system has the form $a+b{cos}^{2}\ensuremath{\theta}$. The weighted average value of $\frac{b}{a}$ for four Sc nuclides is -0.67 \ifmmode\pm\else\textpm\fi{} 0.12 indicating that the angular distribution must show strong sideways peaking.NUCLEAR REACTIONS $^{238}\mathrm{U}(p,f)^{44}\mathrm{Sc}^{m}$, $^{46}\mathrm{Sc}$, $^{47}\mathrm{Sc}$, $^{48}\mathrm{Sc}$, ${E}_{p}=400$ GeV. Measured thick-target recoil properties; deduced anisotropy parameter.

Production of Sc nuclides in the interaction ofU238with 1-300 GeV protons

Cross sections and thick-target recoil properties of several Sc nuclides formed in the interaction of /sup 238/U with 1 to 300 GeV protons have been determined. The ranges of all the products decrease markedly between 1 and 10 GeV and only slightly thereafter. The forward-to-backward emission ratios peak at 3 GeV and decrease to a value of unity at 300 GeV. The excitation functions increase sharply up to approx. 10 GeV and go through a very shallow peak at this energy. The results are analyzed within the context of the two-step model of high-energy reactions and found to require a larger ratio of transverse to forward momentum transfer than expected on this basis. The systematics of fragment momenta are developed. (AIP)

Charge dispersion and recoil properties atA=131from the interaction ofAu197with 11.5- and 300-GeV protons

Cross sections and thick-target recoil properties of five nuclides with A=131 as well as those of a number of neighboring nuclides have been determined for the interaction of $sup 197$Au with 11.5-GeV protons. The charge dispersion at A=131 has a single peak at Z/subA/-Z=-3.5 and the total isobaric cross section is 8.9plus-or-minus0.8 mb. The ranges indicate that only approx.2% of this value can be ascribed to fission, the bulk of the cross section involving a deep spallation process. Similar data have been obtained at 300 GeV. Within the limits of error the results are the same at both energies. The systematics of deep spallation reactions are examined.

γ-γ coincidence spectrometry of high-energy nuclear reaction targets

The application of Ge(Li) γ−γ coincidence spectrometry to the assay of a uranium foil irradiated by 300 GeV protons is described. Digital gates were set on γ-rays from a number of possible reaction products and coincidence spectra were recorded. The technique was applied to the determination of both cross sections and thick-target recoil properties, and results are presented and compared with those obtained by conventional techniques.

Interaction of 300-GeV protons with uranium

The cross sections and thick-target recoil properties of 30 nuclides produced in the interaction of 300-GeV protons with a $^{238}\mathrm{U}$ target have been measured. The cross sections were determined relative to the monitor reaction $^{27}\mathrm{Al}(p,3\mathrm{pn})^{24}\mathrm{Na}$, whose cross section was assumed to be constant above 10 GeV. The average cross section of all products is found to be \ensuremath{\sim}10% lower at 300 GeV than at 11.5 GeV. The recoil ranges of observed nuclides are \ensuremath{\sim}8% shorter than at lower proton energy and $\frac{F}{B}$ values are closer to unity. A preliminary study of the effect of secondary particles is presented.[NUCLEAR REACTIONS $^{238}\mathrm{U}(p,f, \mathrm{and}\mathrm{spallation})$, $E=300$ GeV; measured $\ensuremath{\sigma}$ and thick-target recoil properties of 30 product nuclides.]

Cross Sections and Recoil Properties of Xenon Isotopes Formed in 11.5-GeV Proton Bombardment ofU238

Partial cumulativc yields and thick-target recoil properties of 14 xenon nuclides formed in the interaction of /sup 238/U with 11.5-GeV protons and ranging from /sup 122/Xe to /sup 136/Xe have been measured. Independent yields and recoil ranges were deduced with the aid of reported data. The isotopic-yield distribution consists of two peaks with a broad region of near-constant yields between them. The recoil ranges exhibit the charactcristic dropoff on the near neutron-deficient side of stability. Comparisons with other isotopic- and isobaric-yield distributions and ranges of products in the same mass region are presented. (auth)

Cross Section and Recoil Properties of Copper Isotopes from Uranium Bombarded with 11.5-GeV Protons

Cross sections and thick-target recoil properties have been measured for $^{61}\mathrm{Cu}$, $^{64}\mathrm{Cu}$, and $^{67}\mathrm{Cu}$ from the interaction of $^{238}\mathrm{U}$ with 11.5-GeV protons. The kinetic energies are much smaller than expected from a conventional fission process, even for the neutron-rich $^{67}\mathrm{Cu}$. It is proposed that these Cu nuclides are produced at proton energies above 3 GeV by the fission of low mass nuclei which are the residues of an intranuclear cascade process involving high deposition energy and the emission of fragments prior to fission both in the fast cascade and the evaporation stage.

Charge Dispersion and Recoil Properties atA=131from the Interaction ofU238with 11.5-GeV Protons

Independent and cumulative yields have been measured for eight $A=131$ nuclides formed in the interaction of $^{238}\mathrm{U}$ with 11.5-GeV protons. A good fit to the cross sections was obtained with a charge dispersion consisting of two overlapping Gaussians peaking at $Z=52.2 \mathrm{and} 56.5$. The neutron-excessive curve accounts for about 40% of the total isobaric yield of 23.3\ifmmode\pm\else\textpm\fi{}0.4 mb. Thick-target recoil properties were determined for all the nuclides. The recoil ranges are characteristic of fission fragments for $^{131}\mathrm{Sb}$ through $^{131}\mathrm{Cs}$ but decrease by a factor of 2 between $^{131}\mathrm{Cs}$ and $^{131}\mathrm{La}$. This decrease occurs some two $Z$ units beyond the minimum between the two humps in the charge dispersion. The deposition energies derived from the recoil data exhibit a similar trend as the ranges, increasing in the manner expected for fission products up to barium but not beyond. The transformation of isotopic to isobaric yield distributions is considered and it is concluded that the use of $\frac{N}{Z}$ as the composition variable gives the best agreement with experiment.

Charge distribution and recoil properties in the fission of 208Pb by 11·5 GeV protons

Cross-sections and thick-target recoil properties have been determined for a number of products in the mass region 100–113 from the interaction of 208Pb with 11·5 GeV protons. The recoil ranges of the neutron deficient products are approximately a factor of two smaller than those of the neutron excessive products are approximately a factor of two smaller than those of result a charge dispersion curve consisting of two gaussians, peaking at N Z = 1·24 and 1·34 , was constructed to fit the measured cross-sections of the A = 111 isobars. The resulting curve is single-peaked but has a pronounced shoulder on the neutron excessive side. The curve for the neutron excessive products is very similar to that obtained in the fission of 208Pb by 450 MeV protons except for a reduction in the value of the integrated cross-section. The values of the average deposition energy, average total kinetic energy of the primary fragments, and average separation distance at scission obtained for these products from their recoil properties are nearly equal to the corresponding values at 450 MeV. Integration of the charge dispersion curve for the neutron deficient products indicates a 82 per cent contribution to the total isobaric cross section at A = 111. Comparison of the properties of the neutron deficient products with similar results previously obtained for a 238U target as well as with evaporation calculations indicates that only a fragmentation mechanism can explain all the experimental results.

Charge distribution and recoil properties in the fission of 238U by 11·5 GeV protons

Cross-sections and thick-target recoil properties have been determined for a number of products in the mass region 100–115 from the interaction of 238U with 11·5 GeV protons. The recoil ranges of the neutron deficient products are nearly a factor of two smaller than those of the neutron excessive products suggesting a difference in reaction mechanisms. On the basis of this finding a charge dispersion curve consisting of two separate gaussians, peaking at N Z = 1·26 and 1·40, was constructed to fit the measured cross-sections. The resulting curve is single-peaked but has a pronounced shoulder on the neutron deficient side. The isobaric yield at A = 111 is 35·0 ± 3·5 mb and the curve associated with the neutron excessive products contributes 80 per cent of the total yield. This curve is very similar to that obtained in the fission of 238U by 450 MeV protons except for a reduction in the fission cross-section by a factor of 2·4. The values of the average deposition energy, average total kinetic energy of the primary fragments, and average separation distance at scission obtained for the neutron excessive fragments from their recoil properties are nearly equal to the corresponding values at 450 MeV. Many of the properties of the neutron deficient products are consistent with either spallation or fission of a nucleus in the heavy rare earth region but neither mechanism can explain all the results.

Yields and recoil properties of scandium isotopes produced in the interaction of 590 MeV and 18 GeV protons with uranium

Absolute cross-sections and some thick target recoil properties have been measured for the production of 43–49Sc in uranium bombarded with protons of 590 MeV and 18 GeV, using radiochemical and electromagnetic isotope separation techniques. The yield of the neutron-deficient isotopes 43Sc and 44Sc increased by about a factor of 10 relative to 49Sc when the proton energy was increased from 590 MeV to 18 GeV. The average kinetic energy of the products calculated from the recoil results was 79 ± 4 MeV for both neutron-rich and neutron-deficient products at 590 MeV proton energy. At 18 GeV, the average kinetic energy of the neutron-rich products was 52·7 ± 1·0 MeV, whereas the kinetic energy of the most neutron-deficient product observed, 43Sc, had decreased to only 34·6 ± 1·0 MeV. New determinations of the half-lives of seven scandium isotopes were made on isotopically separated samples.

Recoil properties and charge distribution in the fission of 208Pb by 450 MeV protons

Cross-sections and thick-target recoil properties have been determined for three isobaric nuclides with A = 111 as well as for several other palladium and silver nuclides formed in the fission of 208Pb by 450 MeV protons. The cross-sections have been used to construct a Gaussian charge distribution. The analysis indicates that the neutron-to-proton ratio of the most probable product, N Zp , has a value of 1·337 ± 0·008 for A = 103–111; the full width at half maximum of the distribution is 1·88 ± 0·04 Z units; the isobaric fission cross-section for A = 111 is 6·1 ± 0·4 mb. The recoil data have been used to derive, for a given mass chain, the dependence on atomic number of the average cascade deposition energy, the average total kinetic energy release, and the average separation distance between the primary fragment charge centers. The results are compared with similar data previously obtained for 238U.