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The intense, nearly monoenergetic, 100% polarized ȳ-ray beams available at the HIȳS facility, along with the realization that the E1-E2 interference term that appears in the Compton scattering polarization observable has opposite signs in the forward and backward angles, make it possible to obtain an order-of magnitude improvement in the determination of the parameters of the isovector giant quadrupole resonance (IVGQR). Accurate IVGQR parameters will lead to a more detailed knowledge of the symmetry energy in the nuclear equation of state which is important for understanding nuclear matter under extreme conditions such as those present in neutron stars. Our new method is demonstrated for the case of 209Bi. [ABSTRACT FROM AUTHOR]

Differential cross sections for elastic scattering of photons from the deuteron have recently been measured at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. These first new measurements in more than a decade further constrain the isoscalar electromagnetic polarizabilities of the nucleon and provide the first-ever results above 100 MeV, where the sensitivity to the polarizabilities is increased. We add 23 points between 70 and 112 MeV, at angles 60◦ , 120◦ and 150◦ . Analysis of these data using a Chiral Effective Field Theory indicates that the cross sections are both self-consistent and consistent with previous measurements. Extracted values of αs = [12.1 ± 0.8(stat) ± 0.2(BSR) ± 0.8(th)] × 10−4 fm3 and βs = [2.4 ± 0.8(stat) ± 0.2(BSR) ± 0.8(th)] × 10−4 fm3 are obtained from a fit to these 23 new data points. This paper presents in detail the experimental conditions and the data analysis used to extract the cross sections., Physics

The absolute differential cross sections for the 3He(γ,n)pp reaction were measured as a function of outgoing neutron scattering angle and energy at the incident γ-ray energies of 12.8, 13.5, and 14.7 MeV to within a precision better than ±6%. Both the absolute cross sections and the neutron energy distributions at each incident γ-ray energy agree with the state-of-the-art theoretical results when the Coulomb interaction in the final state is included. [ABSTRACT FROM AUTHOR]

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical A(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn = [11.55+1.25(stat)+0.2(BSR)+ 0.8(th)] x 10-4 fm3 and βn = [3.65≠ 1.25(stat) +0.2(BSR) ≠ 0.8(th)] x 10-4 fm3, with X2 = 45.2 for 44 degrees of freedom. [ABSTRACT FROM AUTHOR]

The second Jπ=2+ state of 12C, predicted over 50 years ago as an excitation of the Hoyle state, has been unambiguously identified using the 12C(γ, α0)8Be reaction. The alpha particles produced by the photodisintegration of 12C were detected using an optical time projection chamber. Data were collected at beam energies between 9.1 and 10.7 MeV using the intense nearly monoenergetic gamma-ray beams at the HIγS facility. The measured angular distributions determine the cross section and the E1-E2 relative phases as a function of energy leading to an unambiguous identification of the second 2+ state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground state gamma-decay width of 60(10) meV; B(E2:22+→01+)=0.73(13)e2 fm4 [or 0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more extended than the ground state of 12C presents a challenge and constraints for models attempting to reveal the nature of three alpha-particle states in 12C. Specifically, it challenges the ab initio lattice effective field theory calculations that predict similar rms radii for the ground state and the Hoyle state. [ABSTRACT FROM AUTHOR]

Compton scattering cross sections from 6Li have been measured at scattering angles of 40°-160° using a nearly monoenergetic 60-MeV photon beam at the High Intensity Gamma-Ray Source. A phenomenological model provides an estimate of the sensitivity of the 6Li(y, y)6Li cross section to the nucléon isoscalar electromagnetic polarizabilities αs and βs. [ABSTRACT FROM AUTHOR]

A photofission experiment was performed on targets of 235U, 238U, 239Pu, and 232Th using nearly 100% linearly polarized, high-intensity (∼107 &ggr;/s), and nearly monoenergetic &ggr;-ray beams having energies between 5.6 and 7.3 MeV at the High Intensity &ggr;-ray Source (Hl&ggr;S). An array of 18 liquid scintillator detectors was used to measure prompt fission neutron polarization asymmetries. An asymmetry close to zero was found for 235U and 239Pu while a significant asymmetry (∼0.5) was found for 238U and 232Th. A simplified model of near-threshold photofission has been developed in an attempt to explain the systematic difference between the even-even and even-odd targets. The results of a simulation, based on this model and using previous measurements of fission fragment angular distributions, are shown to accurately reproduce the essential features of the data. [ABSTRACT FROM AUTHOR]

The second J(π)=2+ state of 12C, predicted over 50 years ago as an excitation of the Hoyle state, has been unambiguously identified using the 12C(γ,α0)(8)Be reaction. The alpha particles produced by the photodisintegration of 12C were detected using an optical time projection chamber. Data were collected at beam energies between 9.1 and 10.7 MeV using the intense nearly monoenergetic gamma-ray beams at the HIγS facility. The measured angular distributions determine the cross section and the E1-E2 relative phases as a function of energy leading to an unambiguous identification of the second 2+ state in 12C at 10.03(11) MeV, with a total width of 800(130) keV and a ground state gamma-decay width of 60(10) meV; B(E2:2(2)+→0(1)+)=0.73(13)e(2)  fm(4) [or 0.45(8) W.u.]. The Hoyle state and its rotational 2+ state that are more extended than the ground state of 12C presents a challenge and constraints for models attempting to reveal the nature of three alpha-particle states in 12C. Specifically, it challenges the ab initio lattice effective field theory calculations that predict similar rms radii for the ground state and the Hoyle state.