Nuclear Data Sheets for A=40☆

https://escholarship.org/content/qt1mg151pc/qt1mg151pc.pdf?t=pgp78k

Nuclear Data Sheets for A=40 ☆

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range E
 γ
 ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E
 γ
 ≳ 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the 40,48Ca, 90Zr, 139La, 142Nd, and 181Ta nuclei, as well as difference (E
 γmax = 85–55 MeV) bremsstrahlung photoneutron spectra for the 63Cu, 115In, 118Sn, 181Ta, 207Pb, 209Bi, and 235U nuclei and bremsstrahlung photoproton spectra for the 90Zr nucleus at the energies of E
 γmax = 22, 25, and 34 MeV.

Combined model of photonucleon reactions

The absorbed dose due to photonuclear reactions in soft tissue, lung, breast, adipose tissue and cortical bone has been evaluated for a scanned bremsstrahlung beam of end point 50 MeV from a racetrack accelerator. The Monte Carlo code MCNP4B was used to determine the photon source spectrum from the bremsstrahlung target and to simulate the transport of photons through the treatment head and the patient. Photonuclear particle production in tissue was calculated numerically using the energy distributions of photons derived from the Monte Carlo simulations. The transport of photoneutrons in the patient and the photoneutron absorbed dose to tissue were determined using MCNP4B; the absorbed dose due to charged photonuclear particles was calculated numerically assuming total energy absorption in tissue voxels of 1 cm3. The photonuclear absorbed dose to soft tissue, lung, breast and adipose tissue is about (0.11-0.12)±0.05% of the maximum photon dose at a depth of 5.5 cm. The absorbed dose to cortical bone is about 45% larger than that to soft tissue. If the contributions from all photoparticles (n, p, 3He and 4He particles and recoils of the residual nuclei) produced in the soft tissue and the accelerator, and from positron radiation and gammas due to induced radioactivity and excited states of the nuclei, are taken into account the total photonuclear absorbed dose delivered to soft tissue is about 0.15±0.08% of the maximum photon dose. It has been estimated that the RBE of the photon beam of 50 MV acceleration potential is approximately 2% higher than that of conventional 60Co radiation.

https://iopscience.iop.org/article/10.1088/0031-9155/44/9/301/pdf

Calculation of absorbed dose and biological effectiveness from photonuclear reactions in a bremsstrahlung beam of end point 50 MeV

Neutrons play a dominant role in the stellar nucleosynthesis of heavy elements and the quest for accurate experimental determinations of neutron-induced reaction cross sections becomes more stringent with the refinement of nuclear and astrophysical models. We review here an experimental nuclear-astrophysics program using a high-intensity neutron source based on the 7Li(p, n)7Be reaction with a Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF) Phase I. The quasi-Maxwellian neutron spectrum with effective thermal energy $ kT \approx 30$ keV, characteristic of the thick-target 7Li(p, n) yield at proton energy $ E_p \approx 1.92$ MeV close to its neutron threshold, is well suited for laboratory measurements of neutron capture reactions along the astrophysical s -process path. The high-intensity proton beam (in the mA range) of SARAF and the high power (few kW) dissipation of LiLiT result in the most intense source of neutrons available today at stellar-like energies. The principle, design and properties of the LiLiT device and recent measurements of Maxwellian Averaged Cross Sections (MACS) based on activation of targets of astrophysical interest are described. Decay counting or atom counting methods (accelerator mass spectrometry, atom-trap trace analysis) are used for the detection of short-lived or long-lived activation products, respectively. In a different realm of applications, the 7Li(p, n) reaction is a leading candidate as an accelerator-based neutron source for Boron Neutron Capture Therapy (BNCT). The high neutron yield achievable from a liquid-lithium target, its sustainability of operation under kW-power incident beams and the recent availability of small-size high-intensity accelerators are compatible with a hospital-based clinical facility. An effort towards the characterization and realization of a liquid-lithium target for BNCT is reviewed. Perspectives of pending and future developments towards SARAF Phase II, based on a 40MeV, 5mA CW proton/deuteron superconducting linear accelerator, are summarized.

Reactions along the astrophysical s-process path and prospects for neutron radiotherapy with the Liquid-Lithium Target (LiLiT) at the Soreq Applied Research Accelerator Facility (SARAF)

Photonuclear reactions in $^{90}\mathrm{Zr}$ were studied in the excitation region of the giant dipole resonance. Experimental results which include all the most important reaction channels consist of cross sections integrated over angles, and for photoprotons, of additional data on angular distributions. Photoproton cross sections were determined by a least-squares-fit analysis of proton spectra resulting from a series of irradiations with bremsstrahlung of different end-point energies. In addition to the ground state $^{90}\mathrm{Zr}(\ensuremath{\gamma},{p}_{0})^{89}\mathrm{Y}_{\mathrm{g}.\mathrm{s}.}$, photoproton cross-section data for three groups of $^{89}\mathrm{Y}$ excited states are presented. Other results which consist of cross sections for reactions ($\ensuremath{\gamma},{p}_{1}$), ($\ensuremath{\gamma},{n}_{1}$), ($\ensuremath{\gamma}, 2n$), ($\ensuremath{\gamma},\mathrm{np}$), and ($\ensuremath{\gamma},n$) were obtained through different techniques based on the measurement of activation yields. It is shown that 70% of the total photoproton cross section is due to the transition to the ground, the 1.74 MeV, and possibly the 1.51 MeV states of $^{89}\mathrm{Y}$. The photoneutron cross section is dominated by the contribution involving the first excited state and all those states of $^{89}\mathrm{Zr}$ which subsequently decay to it. Experimental data are interpreted in terms of isospin splitting of the giant dipole resonance. In the total photoproton cross section, apart from a broad resonance at 16 MeV similar to the dominant structure of the ($\ensuremath{\gamma},n$) reaction, an additional resonance of approximately the same magnitude appears at 20.5 MeV. The latter resonance is attributed to the ${T}_{g}$ part of the giant dipole resonance. Its integrated cross section of about 8% of the total photonuclear cross section accounts for the main part of the expected ${T}_{g}$ strength. Neutron channels do not seem to contribute significantly to the decay of the ${T}_{g}$ resonance. It is concluded from ($\ensuremath{\gamma},\mathrm{np}$) and ($\ensuremath{\gamma},2n$) reactions that the ${T}_{g}$ resonance is superimposed on a ${T}_{l}$ background extending to higher energies.NUCLEAR REACTIONS $^{90}\mathrm{Zr}(\ensuremath{\gamma},p)$, ($\ensuremath{\gamma},n$), ($\ensuremath{\gamma},np$) and ($\ensuremath{\gamma},2n$), ${E}_{\ensuremath{\gamma}}=12\ensuremath{-}30$ MeV; measured photoproton spectra and bremsstrahlung activation yields; deduced $\ensuremath{\sigma}(E,\ensuremath{\vartheta})$ and $\ensuremath{\sigma}(E)$.

A. Stanovnik

Papers

Photonuclear reactions in Zr-90

Photonuclear reactions inCa40