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In this paper, we present results of initial measurements and calculations of prompt gamma ray spectra (produced by proton-nucleus interactions) emitted from tissue equivalent phantoms during irradiations with proton beams. Measurements of prompt gamma ray spectra were made using a high-purity germanium detector shielded either with lead (passive shielding), or a Compton suppression system (active shielding). Calculations of the spectra were performed using a model of both the passive and active shielding experimental setups developed using the Geant4 Monte Carlo toolkit. From the measured spectra it was shown that it is possible to distinguish the characteristic emission lines from the major elemental constituent atoms (C, O, Ca) in the irradiated phantoms during delivery of proton doses similar to those delivered during patient treatment. Also, the Monte Carlo spectra were found to be in very good agreement with the measured spectra providing an initial validation of our model for use in further studies of prompt gamma ray emission during proton therapy.

The β-delayed γ and proton decay of 23 Al has been studied with a novel detector setup at the focal plane of the MARS separator at Texas A&M University. We could detect protons down to an energy of 200 keV and determine the corresponding branching ratios. Contrary to results of previous β-decay studies, no strong proton intensity from the decay of the isobaric analog state (IAS) of the 23 Al ground state at Ex = 7803 keV in 23 Mg, was observed. Instead we assign the observed low energy group Ep,cm = 206 keV to the decay from a state 16 keV below the IAS. We measured both proton and gamma branches from the decay of this state at Ex = 7787 keV in 23 Mg, a very rare case in the literature. Combining our data with its measured lifetime, we determine its resonance strength to be ωγ = 1.4 +0.5 −0.4 meV. The value is in agreement with older direct measurements, but disagrees with a new direct measurement. This state is the most important resonance for the radiative proton capture 22 Na(p,γ) 23 Mg in some astrophysical environments, such as novae.

The γ -ray spectroscopy of 25 Si and 29 S has been performed using single neutron knockout reactions with intermediate energy beams of the exotic isotopes 26 Si and 30 S. Two γ rays have been observed in 25 Si and three in 29 S. These are the first γ rays observed in these two isotopes. These two nuclei appear to be well deformed, and possible future intermediate-energy Coulomb excitation measurements would confirm their rotational nature.

Intermediate-energy Coulomb excitation is a key method to investigate collectivity in exotic nuclei far from ␤ stability. We report on the measurement of the absolute B(E2;0 1 ϩ →2 1 ϩ ) excitation strength in 46 Ar for five different minimum impact parameters. Our findings underline the validity, feasibility, and perspective of this technique for the study of exotic nuclei also in the regime of higher beam energy.

The 9 Be 32 Ar; 31 ArX reaction, leading to the 5 2 ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65:1 MeV=nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state. DOI: 10.1103/PhysRevLett.93.042501 PACS numbers: 24.50.+g, 21.10.Jx, 27.30.+t The nuclear shell model pictures deeply bound nucleons as being in fully occupied states. At and above the surface of the Fermi sea, configuration mixing then leads to occupancies that gradually decrease to zero. This picture is modified in an important way by several correlation effects that are absent from or are described only approximately by effective-interaction theories, such as the shell model. These correlations arise from shortrange, soft-core, and tensor nucleon-nucleon (NN) interactions and from longer-range couplings involving low-lying and giant resonance collective excitations [1]. They result in the physical nucleon occupancies of deeply bound states being reduced and the strength shifted into states up to quite high energies; see Pandharipande et al. [2]. Absolute measurements of nucleon occupancies may therefore quantify these correlation effects. It should be pointed out that nuclear reaction observables probing the spatial behavior of the nucleonic wave functions agree well with the shell model picture. Examples are the characteristic angular distributions of transfer reactions and the longitudinal momentum distributions of the residues in knockout reactions, which identify the orbital angular momentum l of the nucleon states involved.The main body of evidence on nucleon occupancies has come from studies of the e; e 0 p reaction [2,3]. These have shown that in stable nuclei over a broad mass region, the valence proton states have their occupancies quenched by factors of order 0.6 -0.7 relative to the extreme singleparticle values. Recently, evidence has emerged that nucleon knockout reactions with heavy ions, at intermediate energies and in inverse kinematics, offer new possibilities for studying these effects by extending measurements to rare radioactive species and to neutron states. In general, the occupancy is not directly observable, but it is reflected in the spectroscopic factor C 2 S j that measures the overlap of the initial and final states with quantum numbers (l; j) [4]. The reduction factor R s is defined as the ratio of the experimental and theoretical value for the spectroscopic factor, the latter obtained when the valence nucleons are confined to a single major oscillator shell, the sd shell for the cases discussed here. This is consistent with how the reduction factors are defined in the analysis of e; e 0 p ...

Two-neutron knockout reactions from nuclei in the proximity of the proton dripline have been studied using intermediate-energy beams of neutron-deficient 34 Ar, 30 S, and 26 Si. The inclusive cross sections, and also the partial cross sections for the population of individual bound final states of the 32 Ar, 28 S and 24 Si knockout residues, have been determined using the combination of particle and γ -ray spectroscopy. Similar to the two-proton knockout mechanism on the neutron-rich side of the nuclear chart, these two-neutron removal reactions from already neutron-deficient nuclei are also shown to be consistent with a direct reaction mechanism.