[en] In the astrophysically important reaction ¹⁹Ne(p,γ)²⁰Na, the rate is dominated by a single key resonance at 450 keV above the proton-emission threshold in ²⁰Na. Throughout the last few decades many experiments have been performed aimed at finding the identity of this state. Despite this, the spin-parity of the key resonant state is still up for debate. The present paper describes a new experiment studying the β-delayed proton decay of ²⁰Mg aimed at solving this issue.

[en] ¹⁴C(n,γ)¹⁵C is being used as a test case in the development of an indirect method to determine neutron capture cross sections on neutron-rich unstable nuclei at astrophysical energies. Our approach makes use of two reactions: one peripheral used to find the asymptotic normalization coefficient (ANC) and a second non-peripheral reaction to determine the spectroscopic factor. The ANC for ¹⁵C has been determined using a HI neutron transfer reaction with a 12 MeV/nucleon ¹⁴C beam on a ¹³C target. The spectroscopic factor will be determined using ¹⁴C(d,p) in forward kinematics with an incident deuteron energy of 60 MeV. Both experiments were performed using the MDM high-resolution spectrometer at Texas A and M University.

[en] ¹⁴C(n,γ)¹⁵C is being used as a test case in the development of an indirect method to determine neutron capture cross sections on neutron-rich unstable nuclei at astrophysical energies. Our approach makes use of two reactions: one peripheral used to find the asymptotic normalization coefficient (ANC) and a second non-peripheral reaction to determine the spectroscopic factor. The ANC for ¹⁵C has been determined using a HI neutron transfer reaction with a 12 MeV/nucleon ¹⁴C beam on a ¹³C target. The spectroscopic factor will be determined using ¹⁴C(d,p) in forward kinematics with an incident deuteron energy of 60 MeV. Both experiments were performed using the MDM high-resolution spectrometer at Texas A and M University.

[en] 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. (note)

[en] We have developed a new experimental technique to measure very low energy protons from β-delayed p-decay of proton-rich nuclei produced and separated with the MARS recoil spectrometer at TAMU. Recently we have investigated the β-delayed p-decays of ²³Al and ³¹Cl and obtained information on the resonances in the reactions ²²Na(p,γ)²³Mg and ³⁰P(p,γ)³¹S, respectively. These reactions are important in explosive H-burning in Novae. A simple setup consisting of a telescope made of a thin double sided Si strip detector (p-detector) backed or sandwiched between two thick Si detectors (β-detectors) was designed. We studied two different p-detectors and found that the thinner detectors with a small cell size are best to measure proton energies as low as 2-300 keV.

[en] Purpose: Recent studies have suggested that the characteristics of prompt gammas (PG) emitted during proton beam irradiation are advantageous for determining beam range during treatment delivery. The purpose of this work was to determine the feasibility of determining the proton beam range from PG data measured with a prototype Compton camera (CC) during proton beam irradiation. Methods: Using a prototype multi-stage CC the PG emission from a water phantom was measured during irradiation with clinical proton therapy beams. The measured PG emission data was used to reconstruct an image of the PG emission using a backprojection reconstruction algorithm. One dimensional (1D) profiles extracted from the PG images were compared to: 1) PG emission data measured at fixed depths using collimated high purity Germanium and Lanthanum Bromide detectors, and 2) the measured depth dose profiles of the proton beams. Results: Comparisons showed that the PG emission profiles reconstructed from CC measurements agreed very well with the measurements of PG emission as a function of depth made with the collimated detectors. The distal falloff of the measured PG profile was between 1 mm to 4 mm proximal to the distal edge of the Bragg peak for proton beam ranges from 4 cm to 16 cm in water. Doses of at least 5 Gy were needed for the CC to measure sufficient data to image the PG profile and localize the distal PG falloff. Conclusion: Initial tests of a prototype CC for imaging PG emission during proton beam irradiation indicated that measurement and reconstruction of the PG profile was possible. However, due to limitations of the operational parameters (energy range and count rate) of the current CC prototype, doses of greater than a typical treatment dose (∼2 Gy) were needed to measure adequate PG signal to reconstruct viable images. Funding support for this project provided by a grant from DoD

[en] The creation site of ²⁶Al is still under debate. It is thought to be produced in hydrogen burning and in explosive helium burning in novae and supernovae, and possibly also in the H-burning in outer shells of red giant stars. Also, the reactions for its creation or destruction are not completely known. When ²⁶Al is created in novae, the reaction chain is: ²⁴Mg(p,γ)²⁵AI(β⁺v)²⁵ Mg(p,γ)²⁶Al, but this chain can be by-passed by another chain, ²⁵Al(p, γ)²⁶Si(p, γ)²⁷P and it can also be destroyed directly. The reaction ^26m Al (p, γ)²⁷ Si* is another avenue to bypass the production of ²⁶Al and it is dominated by resonant capture. We find and study these resonances by an indirect method, through the beta-decay of ²⁷P. A clean and abundant source of ²⁷P was produced for the first time and separated with MARS. A new implantation-decay station which allows increased efficiency for low energy protons and for high-energy gamma-rays was used. We measured gamma-rays and beta-delayed protons emitted from states above the proton threshold in the daughter nucleus ²⁷Si to identify and characterize the resonances. The lifetime of ²⁷P was also measured with accuracy under 2%.

[en] In several radiative proton capture reactions important in novae and XRBs, the resonant parts play the capital role. We use decay spectroscopy techniques to find these resonances and study their properties. We have developed techniques to measure beta- and beta-delayed proton decay of sd-shell, proton-rich nuclei produced and separated with the MARS recoil spectrometer of Texas A and M University. The short-lived radioactive species are produced in-flight, separated, then slowed down (from about 40 MeV/u) and implanted in the middle of very thin Si detectors. This allows us to measure protons with energies as low as 200 keV from nuclei with lifetimes of 100 ms or less. At the same time we measure gamma-rays up to 8 MeV with high resolution HPGe detectors. We have studied the decay of ²³Al, ²⁷P, ³¹Cl, all important for understanding explosive H-burning in novae. The technique has shown a remarkable selectivity to beta-delayed charged-particle emission and works even at radioactive beam rates of a few pps. The states populated are resonances for the radiative proton capture reactions ²²Na(p,γ)²³Mg (crucial for the depletion of ²²Na in novae), ^26mAl(p,γ)²⁷Si and ³⁰P(p,γ)³¹S (bottleneck in novae and XRB burning), respectively. Lastly, results with a new detector that allowed us to measure down to about 80 keV proton energy are announced.

[en] The reaction cross section of the radiative proton capture on the drip line nucleus ¹²N was studied at the Cyclotron Institute at Texas A and M University. We have employed the indirect Asymptotic Normalization Coefficient method to determine the direct radiative component of the astrophysical S-factor of the ¹²N(p,γ)¹³O reaction. A value of 0.31(5) keV·b was found at zero energy. Interference between direct and resonant captures leads to a further enhancement of a factor of two. The reaction was investigated in relation to the evolution of hydrogen-rich massive objects, Population III stars, because of the role that it may play in the hot pp chain nuclear burning processes occurring in such stars

[en] The MARS group at TAMU has developed a new experimental technique to measure very low energy protons from β-delayed proton-decay of proton-rich nuclei produced and separated with the MARS recoil spectrometer at TAMU. Recently we have investigated the β-delayed p-decays of ²³Al, and ³¹Cl, and obtained information on the resonances in the ²²Na(p,γ)²³Mg and ³⁰P(p,γ)³¹S reactions, respectively. These reactions are important in explosive H-burning in Novae. Recently an experiment looking at the β-delayed p-decay of ²⁰Mg was also done in order to obtain information on resonances in the ¹⁹Ne(p,γ)²⁰Na reaction. A simple setup consisting of a telescope made of a thin double sided Si strip detector (p-detector) backed or sandwiched between two thick Si detectors (β-detectors) was designed. We studied different W1 and BB2 p-detectors made by MSL, and found that the thinner detectors with a small cell size are best to measure proton energies as low as 2-300 keV.