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There is an ongoing challenge with STEM education: making physics, math, and science, in general, interesting, understandable, and retentive for college science and non-science majors, K-12 students, and the public. If not imparting detailed knowledge, at least one would like to introduce important concepts that will be remembered, appreciated, and hopefully would be pursued in more detail by audience members. One solution: as noted by Socrates, “Wisdom begins in wonder.” Indeed, magic as a form of wonderment dates back to Socrates and even earlier. One of the first magic books, The Discoverie of Witchcraft by Reginald Scot, was published in 1584, predating publication of many science texts. In this paper the author, based on recent research, advocates using special forms of magic to both amaze and teach, and in particular to illustrate the wonders of modern physics, i.e., Nature’s magic, but with connections also to classical physics.

We have experimentally characterized the light-output response of a deuterated trans-stilbene (stilbene-d12 ) crystal to quasi-monoenergetic neutrons in the 0.8 to 4.4 MeV energy range. These data allowed us to perform neutron spectroscopy measurements of a DT 14.1 MeV source and a 239PuBe source by unfolding the impinging neutron spectrum from the measured light-output response. The stilbene-d12 outperforms a 1 H − stilbene of similar size when comparing the shape of the unfolded spectra and the reference ones. These results confirm the viability of non-hygroscopic stilbene-d12 crystal for direct neutron spectroscopy without need for time-of-flight measurements. This capability makes stilbene-d12 a well suited detector for fast-neutron spectroscopy in many applications including nuclear reaction studies, radiation protection, nuclear non-proliferation, and space travel.

Precise antineutrino measurements are very sensitive to proper background characterization. We present an improved measurement of the $^{13}\mathrm{C}(\ensuremath{\alpha},n)^{16}\mathrm{O}$ reaction cross section which constitutes significant background for large $\overline{\ensuremath{\nu}}$ detectors. We greatly improve the precision and accuracy by utilizing a setup that is sensitive to the neutron energies while making measurements of the excited state transitions via secondary $\ensuremath{\gamma}$-ray detection. Our results shows a 54% reduction in the background contributions from the $^{16}\mathrm{O}({3}^{\ensuremath{-}},6.13\text{ }\mathrm{MeV})$ state used in the KamLAND analysis.

The $^{7}\mathrm{Li}(\ensuremath{\gamma},t)^{4}\mathrm{He}$ ground state cross section was measured for the first time using monoenergetic $\ensuremath{\gamma}$ rays with energies between 4.4 and 10 MeV at the High Intensity Gamma-ray Source. The reaction is important for the primordial Li problem and for testing our understanding of the mirror $\ensuremath{\alpha}$-capture reactions $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Li}$ and $^{3}\mathrm{He}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Be}$. Although over the last 30 years most measurements of the $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})^{7}\mathrm{Li}$ reaction have concentrated in an energy range below ${E}_{\ensuremath{\gamma}}=3.65$ MeV, measurements at higher energies could potentially restrict the extrapolation to astrophysically important energies. The experimental arrangement for measuring the $^{7}\mathrm{Li}(\ensuremath{\gamma},t)^{4}\mathrm{He}$ reaction included a large-area silicon detector array and several beam characterization instruments. The experimental astrophysical $S$ factor of $^{3}\mathrm{H}(\ensuremath{\alpha},\ensuremath{\gamma})$ calculated from the present data was fitted using the $R$-matrix formalism. The results are in disagreement with previous experimental measurements in the same energy range but the extrapolated $S$ factor agrees with the potential model calculation and lower energy experimental data.

The half-life of $^{15}\mathrm{O}$ was measured using the $\ensuremath{\beta}$-Counting Station at the University of Notre Dame's Nuclear Science Laboratory. Our new result, ${t}_{1/2}=122.308(49)$ s, is the most precise determination to date for $^{15}\mathrm{O}$, and improves the world average by a factor of 4, yielding ${t}_{1/2}^{\text{world}}=122.27(6)$ s. This more precise value will be important for future determinations of ${V}_{\text{ud}}$ using superallowed $T=1/2$ mirror transitions.

A new precision half-life measurement of $^{29}\mathrm{P}$ was conducted using the TwinSol $\ensuremath{\beta}$-counting station at the University of Notre Dame Nuclear Science Laboratory. The resulting value of ${t}_{1/2}^{\mathrm{new}}=4.1055(44)\phantom{\rule{0.28em}{0ex}}\mathrm{s}$ is the most precise $^{29}\mathrm{P}$ half-life measurement to date. Utilizing this measurement and reevaluating the world data leads to a new world average of ${t}_{1/2}^{\mathrm{world}}=4.1031(58)\phantom{\rule{0.28em}{0ex}}\mathrm{s}$, which improves the Birge ratio from 3.11 to 1.45 and is 2.3 times more precise than the previous world value. The new Cabibbo-Kobayashi-Maskawa matrix element ${V}_{\mathrm{ud}}$ for $^{29}\mathrm{P}$ shifts closer into agreement with the superallowed pure Fermi value. The uncertainty in the mixed transition value of ${V}_{\mathrm{ud}}$, however, is still dominated by the Fermi to Gamow-Teller mixing ratio $\ensuremath{\rho}$. Using the new world half-life and assuming the validity of the standard model, a new predicted value for $\ensuremath{\rho}$ and its associated correlation parameters have been evaluated in order to guide future determination of $\ensuremath{\rho}$.

We have developed and evaluated two prototype fast neutron deuterated-stilbene scintillators. The largest scintillator is hexagonal in shape with volume 32 cm3, comprised of deuterated crystalline trans-stilbene (stilbene-d12). These samples were grown using a solution-based crystal growing method developed at Lawrence Livermore Laboratory to grow conventional 1H-based stilbene scintillator crystals. The stilbene-d12 prototype detectors show excellent neutron/gamma discrimination, noticeably better than 1H-stilbene, and appear to have less asymmetry in the response to neutrons incident from different directions. Like other deuterated scintillators, the stilbene-d12 detectors in many applications can provide incident neutron energy spectra, without time of flight, by suitably unfolding the neutron light-output spectra.

The 14O(α,p)17F reaction is an important trigger reaction to the α-p process in X-ray bursts. The most stringent experimental constraints on its astrophysical rate come from measurements of the time-inverse reaction, 17F(p,α)14O. Previous studies of this inverse reaction have sufficiently characterized the high-energy dependence of the cross section but there are still significant uncertainties at lower energies. A new measurement of the 17F(p,α)14O cross section is underway at the Twin Solenoid (TwinSol) facility at the University of Notre Dame using an in-flight secondary 17F beam. The initial results are promising but improvements are needed to complete the measurement. The initial data and plans for an improved measurement are presented in this manuscript.

Precise antineutrino measurements are very sensitive to proper background characterization. We present an improved measurement of the ^{13}C(α,n)^{16}O reaction cross section which constitutes significant background for large ν[over ¯] detectors. We greatly improve the precision and accuracy by utilizing a setup that is sensitive to the neutron energies while making measurements of the excited state transitions via secondary γ-ray detection. Our results shows a 54% reduction in the background contributions from the ^{16}O(3^{-},6.13 MeV) state used in the KamLAND analysis.

We report a new precision half-life measurement of $^{20}\mathrm{F}$, performed using the $\ensuremath{\beta}$-counting station of the University of Notre Dame's Nuclear Science Laboratory. The measured half-life of $11.0160{(41)}_{\text{stat}}{(155)}_{\text{sys}}$ s resulting from this work will help resolve the longstanding discrepancy between two earlier sets of high-precision half-life measurements.

Much effort has been made to understand the origins of 18F in novae. Due to its relatively long half-life (~2 hours), 18F can survive until the nova envelope is transparent, and therefore can provide a sensitive diagnostic of nova nucleosynthesis. It is likely produced through the beta decay of 18Ne, which is itself produced (primarily) through the 17F(p,γ) reaction. Understanding the direct capture contribution to the 17F(p,γ) reaction is important to accurately calculate it. As such, the proton spectroscopic strengths of low-lying states in 18Ne are needed. At the University of Notre Dame a measurement of the 17F(d,n) reaction has been performed using a beam produced by the TwinSol low energy radioactive beam facility. Preliminary data analysis is presented.

The total fusion excitation function for 10 Be+ 40 Ar has been measured over the center-of-momentum (c.m.) energy range from 12 to 24 MeV using a time-projection chamber (TPC). The main purpose of this experiment, which was carried out in a single run of duration 90 h using a ≈100 particle per second (pps) 10 Be beam, was to demonstrate the capability of an active-target TPC to determine fusion excitation functions for extremely weak radioactive ion beams. Cross sections as low as 12 mb were measured with acceptable (50%) statistical accuracy. It also proved to be possible to separate events in which charged particles were emitted from the fusion residue from those in which only neutrons were evaporated. The method permits simultaneous measurement of incomplete fusion, break-up, scattering, and transfer reactions, and therefore fully exploits the opportunities presented by the very exotic beams that will be available from the new generation of radioactive beam facilities.

We report on some of the recent developments and experimental work done at the twin-solenoid low-energy radioactive-ion-beam (RIB) facility TwinSol installed at the U Notre Dame 10 MV FN tandem accelerator. The TwinSol facility is a joint project of the University of Michigan (UM) and the University of Notre Dame (UND), and includes several U.S. and foreign collaborators. A number of significant experiments including RIB-induced transfer reactions, elastic scattering, resonant scattering, and fusion at energies near and well below the Coulomb barrier have been performed with this facility. Several of these as well as future work and upgrades planned will be described.

Background: The precise determination of the $\mathcal{F}t$ value in $T=1/2$ mixed mirror decays is an important avenue for testing the standard model of the electroweak interaction through the determination of ${V}_{ud}$ in nuclear $\ensuremath{\beta}$ decays. $^{11}\mathrm{C}$ is an interesting case, as its low mass and small ${Q}_{EC}$ value make it particularly sensitive to violations of the conserved vector current hypothesis. The present dominant source of uncertainty in the $^{11}\mathrm{C}\phantom{\rule{4pt}{0ex}}\mathcal{F}t$ value is the half-life.Purpose: A high-precision measurement of the $^{11}\mathrm{C}$ half-life was performed, and a new world average half-life was calculated.Method: $^{11}\mathrm{C}$ was created by transfer reactions and separated using the TwinSol facility at the Nuclear Science Laboratory at the University of Notre Dame. It was then implanted into a tantalum foil, and $\ensuremath{\beta}$ counting was used to determine the half-life.Results: The new half-life, ${t}_{1/2}=1220.27(26)$ s, is consistent with the previous values but significantly more precise. A new world average was calculated, ${t}_{1/2}^{\text{world}}=1220.41(32)$ s, and a new estimate for the Gamow-Teller to Fermi mixing ratio $\ensuremath{\rho}$ is presented along with standard model correlation parameters.Conclusions: The new $^{11}\mathrm{C}$ world average half-life allows the calculation of a $\mathcal{F}{t}^{\text{mirror}}$ value that is now the most precise value for all superallowed mixed mirror transitions. This gives a strong impetus for an experimental determination of $\ensuremath{\rho}$, to allow for the determination of ${V}_{ud}$ from this decay.

TwinSol , a pair of coupled, superconducting solenoids, was one of the first devices capable of producing beams of radioactive nuclei at energies near the Coulomb barrier. A primary beam from University of Notre Dame (UND) tandem accelerator is used to bombard a primary target producing a secondary beam in flight. TwinSol is used to gather, separate, and focus the recoils. Since it was commissioned at the UND in 1997, at least 58 publications have reported data from its use and there have been hundreds of collaborators from many different countries that use this device. Currently, plans are in place at the UND to provide several upgrades to TwinSol , including a multi-cell gas production target and the possible addition of a third solenoid. Upgrades currently in progress will be discussed along with future plans.

Evaporation-proton yields were measured for the fusion of the weakly bound nucleus $^{6}\mathrm{Li}$ on a $^{58}\mathrm{Ni}$ target at six near- or sub-barrier bombarding energies. Effects of the one-neutron transfer reaction were estimated and corrections made. Total-fusion cross sections were deduced using calculated proton multiplicities. The resulting fusion excitation function shows a considerable enhancement with respect to calculations for a bare potential. Inelastic couplings are estimated to have insignificant effects on such fusion. The sum of total fusion plus one-neutron transfer cross sections nearly saturates the total reaction cross section in the energy region measured. Comparison with previous results appropriately scaled for the $^{6}\mathrm{Li}+(^{59}\mathrm{Co}, ^{64}\mathrm{Ni}, ^{64}\mathrm{Zn})$ systems shows good consistency except for some data spread at the lower energies.

A new precision half-life measurement of $^{25}\mathrm{Al}$ was conducted using the TwinSol $\ensuremath{\beta}$-counting station at the University of Notre Dame. The new measured value of ${t}_{1/2}^{\mathrm{new}}=7.1657(24)$ s is in good agreement with the most recent measurement, while being 3 times more precise. Using these new measurements, an evaluation of the $^{25}\mathrm{Al}$ half-life has been performed, leading to an average half-life of ${t}_{1/2}^{\mathrm{world}}=7.1665(26)$ s, which is 5 times more precise than it's predecessor and has a more satisfactory Birge ratio of 1.1. To aid in future measurements of correlation parameters, a new Fermi to Gamow-Teller mixing ratio $\ensuremath{\rho}$ and correlation parameters for this mixed transition have been calculated assuming the standard model validity using the new world half-life.

We present $^{8}\mathrm{B}+^{27}\mathrm{Al}$ elastic scattering angular distributions for the proton-halo nucleus $^{8}\mathrm{B}$ at two energies above the Coulomb barrier, namely ${E}_{\mathrm{lab}}=15.3$ and 21.7 MeV. The experiments were performed in the Radioactive Ion Beams in Brasil facility (RIBRAS) in S\~ao Paulo, and in the TwinSol facility at the University of Notre Dame, USA. The angular distributions were measured in the angular range of 15--80 degrees. Optical model and continuum discretized coupled channels calculations were performed, and the total reaction cross sections were derived. A comparison of the $^{8}\mathrm{B}+^{27}\mathrm{Al}$ total reaction cross sections with similar systems including exotic, weakly bound, and tightly bound projectiles impinging on the same target is presented.

Organic scintillation detectors have shown promise as neutron detectors for characterizing special nuclear materials in various arms-control and homeland-security applications. Recent advances have yielded a new plastic scintillator – EJ299-33 – with pulse-shape-discrimination (PSD) capability. Plastic scintillators would have a much-expanded range of deployment relative to liquids and crystals. Here, we present a full characterization of pulse-height response to fission-energy neutrons for an EJ299-33 detector with 7.62-by-7.62-cm cylindrical active volume, and compare with an EJ309 liquid scintillator in the same assembly. Scintillation light-output relations, energy resolutions, and response matrices are presented for both detectors. A continuous-spectrum neutron source, obtained via the bombardment of 27Al with 7.44-MeV deuterons at the Edwards Accelerator Facility at Ohio University, was used for the measurement. A new procedure for evaluating and comparing PSD performance is presented which accounts for the effect of the light-output relation on the ability to detect low-energy neutrons. The EJ299-33 is shown to have considerable deficit in matrix condition, and in PSD figure of merit when compared to EJ309, especially when neutron energy is taken into account. Nevertheless the EJ299 is likely to bring a modest PSD capability into a array of field applications that are not accessible to liquids or crystals.

Development and evaluation of a large-volume multi-element digital-signal-processing (DSP)-based deuterated (C6D6) liquid scintillator array for the study of reactions involving neutrons without the need for measurement of neutron time-of-flight (ToF) is described. In-beam testing was conducted at the University of Notre Dame (UND) 10 MV FN tandem Van de Graaff accelerator using a deuteron beam at Ed=16.0 MeV. The energy response and detector efficiency of 100 mm dia. ×; 150 mm long cylindrical deuterated liquid scintillator (Eljen 315) detectors was determined in the range En=4.8 to 8.7 MeV and En=6.8 to 21.2 MeV, respectively. In addition, we determined that optimized digital pulse-shape discrimination (DPSD) in liquid scintillator detectors using enhanced liquid (Eljen 315MOD) and other methods can yield improved recoil-particle tagging. As we demonstrate, this is particularly important in deuterated scintillators at neutron energies above 15 MeV. This is especially advantageous for study of nuclear reactions involving radioactive beams, since these often have large, positive reaction Q values.

An elastic backscattering experiment has been performed at energies below the Coulomb barrier to investigate static and dynamic effects in the interaction of He6 with Bi209. The measured cross sections are presented in terms of the dσ/dσRuth ratio, as a function of the distance of closest approach on a Rutherford trajectory. The data are compared with a three-body CDCC calculation and good agreement is observed. In addition, the critical distance of interaction was extracted. A larger value was obtained for the exotic He6 nucleus as compared with the weakly bound Li6 and Be9 nuclei and the tightly bound He4, C12, and O16 nuclei.

The clustering of $\ensuremath{\alpha}$ particles in atomic nuclei results in the self-organization of various geometrical arrangements at the femtometer scale. The one-dimensional alignment of multiple $\ensuremath{\alpha}$ particles is known as linear-chain structure, evidence of which has been highly elusive. We show via resonant elastic and inelastic $\ensuremath{\alpha}$ scattering of a radioactive $^{10}\mathrm{Be}$ beam that excited states in the neutron-rich nucleus $^{14}\mathrm{C}$ agree with recent predictions of linear-chain structure based on an antisymmetrized molecular dynamics model.

A highly portable high-speed CAMAC data acquisition system has been developed using Kmax software (Sparrow, Inc.) for Macintosh laptop and tower computers. It uses a USB-2 interface to the CAMAC crate controller with custom-written software drivers. Kmax permits 2D parameter gating and specific algorithms have been developed to facilitate the rapid evaluation of various multi-element nuclear detectors for energy and time-of-flight measurements. This includes tests using neutrons from 252Cf and a 2.5 MeV neutron generator as well as standard gamma calibration sources such as 60Co and 137Cs. In addition, the system has been used to measure gamma–gamma coincidences over extended time periods using radioactive sources (e.g., Ra-228, Pa-233, Np-237, and Am-243).

Improved time-of-flight (ToF) capability has been added to the University of Michigan (UM)–University of Notre Dame (UND) TwinSol low-energy dual 6T solenoid-based radioactive nuclear-beam (RNB) facility at the UND FN tandem Van de Graaff accelerator. An extended low-background beam line has been combined with a newly-constructed ca.1 meter diameter ISO-250 based scattering chamber capable of sub-ns ToF of RNBs. These together with the intrinsic, low ToF spread in the TwinSol ion-optical system yields improved ToF information for low-energy RNB nuclear reaction studies. Using either the intrinsic accelerator bunched and pulsed-selected beams with RF timing, or with the addition of an MCP+foil timing system (or similar) detector at the dual-solenoid cross-over region allows for reduction of the energy spread inherent in these low-energy RNB reactions. As an example, using the ToF information reduces the FWHM energy spread in a high-intensity 28 MeV 8Li beam from about 1 MeV to

A modified version of Gafchromic ® EBT radiochromic medical imaging film, which is light insensitive and requires no special development or processing, is shown to be useful for imaging low-energy (few MeV) ion beams and radioactive sources. It appears especially well suited for use with low-intensity short-lived (radioactive) secondary beams (RNB). The film can assist in optimizing the collimation needed to minimize unwanted background ions, and to accurately determine the ion-optical alignment of RNB production and transport systems. It allows for effective imaging of beam profiles and relative intensities throughout the beam-transport system and especially at locations not readily accessible to electronic imaging detectors. The special advantages of using the film for RNBs, which often are spatially extended and contaminated with unwanted ions, are demonstrated.

The reaction 12C(7Be,3He) has been studied at E(7Be) = 34 MeV. Angular distributions to levels with excitation energies up to 21 MeV in the residual 16O have been measured at θlab = 13–50 degrees. This reaction selectively populates states known to have a large 12C+α component in their structure, implying that direct processes dominates at this energy.

Intermediate-energy projectile Coulomb excitation of the unstable nucleus 18 F g.s. and its short-lived E x =1.1 MeV ( J π =5 + ) isomeric state ( t 1/2 =162 ns) 18 F m have been studied at 30 MeV per nucleon. Radioactive beams of 18 F g.s. and 18 F m nuclei were produced by nucleon transfer on a carbon production target and delivered to a secondary 197 Au target for Coulomb excitation. Photons emitted in the vicinity of the 197 Au target were detected in a large-solid-angle position-sensitive NaI(Tl) array, which allowed for the identification of the beam and target excited states populated by intermediate-energy Coulomb excitation. Two possible 18 F ground-state excitations were identified, and B (E λ ↑) values were deduced. Upper limits were established for reduced transition probabilities B (E1↑) and B (E2↑) of several predicted transitions from the 18 F m isomeric state, 5 + →4 + , 4 − , 3 + , and compared with values inferred from γ-decay lifetimes. An indication of an enhanced in-flight isomer decay, possibly due to the Coulomb interaction with the target is observed and discussed. The special detector configurations and analytical techniques needed for these types of measurements are described together with suggested improvements.

The heavy helium isotopes 7,9 He were studied via their isobaric analog states (IAS) in 7,9 Li. The IAS were populated via resonance reactions of protons with radioactive beams of 6,8 He. The isospin-conserving neutron decay of T=3/2 resonances in 7 Li and proton decay of T=5/2 resonances in 9 Li were measured. New spectroscopic information on these states were obtained, and compared with the properties of levels in 7,9 He.

Resonances in 6Be and 5Li have been investigated by deuteron transfer reactions with radioactive ion beams, 2H(8B,α)6Be, 2H(7Be,α)5Li, respectively. There is an indication of a possible resonance at excitation energy of 9.6 MeV in 6Be, just below the 3He+3He threshold. The structure of the 6Li nucleus has been also investigated by the neutron transfer reaction 3He(7Li,α)6Li. In 6Li, a new resonance is observed at about 12.4 MeV in excitation energy and the presence of a resonance at 15.2 MeV is confirmed. The data are preliminary and a detailed analysis is in progress. The instalation of a Radioactive Ion Beam facility in Brazil (RIBRAS) is also reported.

A gamma-ray spectroscopy program has been established at the University of Notre Dame using a low-energy radioactive beam of 6 He for fusion–evaporation reactions. There are many experimental difficulties to overcome in the design of any such facility, most notably the large neutron flux associated with producing the secondary beam. Solutions to the problems are discussed and illustrated with the reaction 6 He + 63 Cu .

The response of large deuterated liquid scintillators (up to 10 cm diameter by 15 cm) to neutrons 0.5–20 MeV has been studied using the 2.5 MeV neutron generator at the University of Michigan, and the d(d,n), 13C(d,n), 27Al(d,n) and other reactions at the University of Notre Dame FN tandem accelerator. The latter utilize 9 and 16 MeV deuteron beams including a pulsed beam, which permitted time-of-flight measurements. Combining pulse-shape discrimination and time-of-flight allows gating on specific neutron energy groups to determine the detector response to specific neutron energies. This will permit accurate simulation of the detector response functions for applications of these detectors in nuclear research and homeland security applications.

Elastic scattering angular distributions of the radioactive weakly bound $^{7}\mathrm{Be}$ on $^{27}\mathrm{Al}$ have been measured at energies near the Coulomb barrier. The interaction optical potential is investigated by using different potentials. Total reaction cross sections have also been obtained.

Protonradiotherapy is a powerful tool in the local control of cancer. The advantages of protonradiotherapy over gamma-ray therapy arise from the phenomenon known as the Bragg peak. This phenomenon enables large doses to be delivered to well-defined volumes while sparing surrounding healthy tissue. To fully realize the potential of this technique the location of the high-dose volume must be controlled very accurately. An imagingsystem was designed and tested to monitor the positron-emitting activity created by the beam as a means of verifying the beam’s range, monitoring dose, and determining tissue composition. The prototype imagingsystem consists of 12 pairs of cylindrical BGO detectors shielded in lead. Each crystal was 1.9 cm in diameter, 5.0 cm long, and separated by 0.5 cm from other detectors in the row. These are arranged in two rows, 60 cm apart, with the proton beam and tissue phantoms half-way between and parallel to the detector rows. Experiments were conducted with 150 MeV continuous and macro-pulsed proton beams which had beam currents ranging from 0.14 nA to 1.75 nA. The production and decay of short-lived isotopes, 15 O and 14 O , was studied using 1 min irradiations with a continuous beam. These isotopes provide a significant signal on short time scales, making on-line imaging possible. Macro-pulsed beams, having a period of 10 s, were used to study on-line imaging and the production and decay of long-lived isotopes, 13 N , 11 C , and 18 F . Decay data were acquired and on-line images were obtained between beam pulses and indicate that range verification is possible, for a 150 MeV beam, after one beam pulse, to within the 1.2 cm resolution limit of the imagingsystem. The dose delivered to the patient may also be monitored by observing the increase in the number of coincidence events detected between successive beam pulses. Over 80% of the initial positron-emitting activity is from 15 O while the remainder is primarily 11 C , 13 N , 14 O with traces of 18 F , and 10 C . Radioisotopic imaging may also be performed along the beam path by fitting decay data collected after the treatment is complete. Using this technique, it is shown that variations in elemental composition in inhomogenous treatment volumes may be identified and used to locate anatomic landmarks. Radioisotopic imaging also reveals that 14 O is created well beyond the Bragg peak, apparently by secondary neutrons.

Yields of neutron-rich and other ions in the region of 10≤ Z ≤30, produced by a 30 MeV/u 136 Xe 24+ beam on a thick nat C target, are presented. The ions were collected and identified with the University of Michigan 7-Tesla solenoid device `BigSol' at 1.36 Tm. The yields are sufficient to make feasible gamma- and/or beta-decay studies of lifetimes and nuclear structure at the solenoid's focal position, or alternately with the fragments transported away for low-background studies. Small but usable amounts of ions close to or including the most n-rich ions produced anywhere to-date are produced and it is shown that if particle-by-particle identification is not continuously required, that the yields may be increased by over two orders of magnitude.

The fusion of ${}^{6}\mathrm{He}$ with a ${}^{209}\mathrm{Bi}$ target has been studied at energies near to and below the Coulomb barrier. Despite the weak binding of the valence neutrons in ${}^{6}\mathrm{He}$, little evidence is found for suppression of fusion due to projectile breakup. Instead, a large enhancement of sub-barrier fusion is observed. It is suggested that this enhancement may arise from coupling to positive $Q$ value neutron transfer channels, resulting in ``neutron flow'' between the projectile and the target.

Total reaction cross sections, σ R , on Si were measured near 40 A MeV for the proton-halo candidate 12 N and the two-proton-halo candidate 17 Ne, and were compared with σ R for other light proton-rich nuclei. The A -dependence shows enhanced σ R 's for 12 N and 17 Ne, relative to their neighbors, but the effect is smaller than for 8 B which has been argued to have a proton halo. In general, nuclei with loosely bound last protons ( S p ⩽ 1.5 MeV) have significantly larger σ R 's than their neighbors. Cross sections for charge-removal from 12 N and 17 Ne also were obtained.

Fission following the fusion of {sup 6}He with a {sup 209}Bi target has been studied near the Coulomb barrier, at excitation energies of 32 and 34 MeV in the compound system. These new experimental data are in disagreement with previous work which reported an anomalously large fusion-fission yield, when compared with {sup 4}He-induced fission of {sup 209}Bi at similar excitation energies. In fact, the {sup 6}He-induced fusion-fission yield appears to be smaller than that for {sup 4}He, in qualitative agreement with conventional statistical model calculations. {copyright} {ital 1998} {ital The American Physical Society}

Proton pair correlations relevant for the neutrinoless double-$\ensuremath{\beta}$ decay of ${}^{76}$Ge have been probed via the ${}^{74,76}$Ge(${}^{3}$He,$n$) reactions at 16 MeV. No evidence for pairing vibrations in either nucleus is observed at sensitivity limits of $\ensuremath{\sim}$6$%$ and $\ensuremath{\sim}$19$%$ of the ground-state strength in ${}^{76}$Se and ${}^{78}$Se, respectively. These results are relevant for the understanding of matrix elements for neutrinoless double-$\ensuremath{\beta}$ decay. The lack of pairing vibrations is consistent with a simple BCS structure for the ground states of ${}^{76}$Ge and ${}^{76}$Se, assumed in quasiparticle random phase approximation (QRPA) models of the process.

The structure of ${}^{10}$Be was studied via resonant $\ensuremath{\alpha}$-particle scattering of a neutron-rich ${}^{6}$He beam. A time projection chamber, PAT-TPC, was operated in an active-target mode to provide a gaseous ${}^{4}$He target and trace the beam and reaction products traversing its active tracking volume. This significantly lowered the detection threshold of reaction products at low energies. Elastic scattering, inelastic scattering to the ${}^{6}$He 2${}^{+}$ state, and the ${}^{6}$He($\ensuremath{\alpha}$, 2$n$)${}^{8}$Be reaction were measured below an energy of 6 MeV in the center-of-mass frame. Continuous spectra of excitation functions and angular distributions were obtained from unambiguously-identified recoiling $\ensuremath{\alpha}$ particles for the elastic and inelastic channels. While a resonance of the 4${}^{+}$ state at 10.15 MeV in ${}^{10}$Be previously reported was confirmed, no other resonances were identified in the elastic channel over the measured energy region. The results are in line with antisymmetric molecular dynamics calculations that predict the limits of $\ensuremath{\alpha}$ clustering in high-spin states due to a spin-orbit force.

Total reaction cross sections, ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$, of 20--60A MeV $^{4,6,8}\mathrm{He}$, $^{6--9,11}\mathrm{Li}$, and $^{10}\mathrm{Be}$ were measured by injecting magnetically separated, focused, monoenergetic, identified secondary beams of those projectiles into a Si detector telescope and measuring their energy-deposition spectra. These ${\mathrm{\ensuremath{\sigma}}}_{\mathit{R}}$'s, accurate to about 3%, were compared with predictions of optical, strong absorption, and microscopic models. The latter gave the best overall fit to the data, providing long-tailed matter densities were assumed. The best available optical potentials generally overpredicted the data by about 10%. Strong absorption calculations, in which the isospin-dependent term is quite important, were often unsuccessful, especially for projectiles with large neutron excess. Two-neutron removal cross sections were measured for $^{6}\mathrm{He}$ and $^{11}\mathrm{Li}$; the $^{11}\mathrm{Li}$ data were slightly overpredicted by a microscopic model which includes correlation effects for the $^{11}\mathrm{Li}$ valence neutrons. Both 2n and 4n removal from $^{8}\mathrm{He}$ were observed, in about a 2:1 ratio. Subtraction analysis of the data indicates that $^{4}\mathrm{He}$ is a good core within $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$, as is $^{9}\mathrm{Li}$ within $^{11}\mathrm{Li}$. \textcopyright{} 1996 The American Physical Society.

Differential cross sections for the elastic scattering of 350 MeV $^{7}\mathrm{Li}$ from $^{12}\mathrm{C}$ and $^{28}\mathrm{Si}$ have been measured. The characteristics of the angular distributions are very similar to those of 318 MeV $^{6}\mathrm{Li}$ scattering from the same targets, with diffractive oscillations at the forward angles and smooth exponential falloff, attributed to the dominance of far-side scattering, at the larger angles. The peak-to-valley ratios of the oscillatory structure are similar to those for $^{6}\mathrm{Li}$, indicating that the $^{7}\mathrm{Li}$ ground-state quadrupole moment has no discernible effect on the cross sections. Like the $^{6}\mathrm{Li}$ data, the $^{7}\mathrm{Li}$ data define unique phenomenological optical-model potentials. Double-folding model potentials calculated from fundamental nucleon-nucleon interactions also provide reasonably good fits to the experimental data.

The Sn-120(He-3,t)Sb-120 charge-exchange reaction has been investigated at E(He-3) = 200 MeV and theta approximate to 0 degrees to study neutron decay from the isobaric analog state at E(x)=10.20 MeV in Sb-120. The low-energy neutrons (average energy similar to 0.85 MeV) were detected in coincidence with tritons observed in the focal plane of a high-resolution magnet spectrometer. Four small deuterated NE230 scintillation detectors were mounted at distances of 9.5 cm from the target resulting in an overall neutron detection efficiency including solid angle of >1%. This efficiency was obtained by combining the measured dependence on neutron energy with a calculated neutron evaporation spectrum. From the measured ratio of coincidence to singles events a branching ratio of >86% was deduced for neutron decay. The observation of isospin-violating neutron decay with a branching ratio close to 100% is in agreement with the expectation that the escape width (Gamma up arrow) of the isobaric analog state in Sb-120 is small compared to its spreading-width (Gamma down arrow). Triton spectra measured in coincidence with gamma rays from the deexcitation of the final nucleus display pronounced structures related to the thresholds for neutron emission, in agreement with the characteristics of calculated evaporation spectra.

Many astrophysical events, such as novae and X-ray bursts, are powered by reactions with radioactive nuclei. Studying the properties of these nuclei in the laboratory can therefore further our understanding of these astrophysical explosions. The TwinSol separator at the University of Notre Dame has recently been used to produce intense (~106 pps) beams of 17F. In this article, some of the first measurements with these beams are discussed.