M.A.C. Hotchkis

The mass of 18C from a heavy ion double-charge-exchange reaction

Abstract The mass of 18 C has been measured using the double-charge-exchange reaction 48 Ca( 18 O, 18 C) 48 Ti at an 18 O energy of 112 MeV. The 18 C ions were detected at the focal plane of a magnetic spectrometer. The mass excess of 18 C was found to be 24.923 ± 0.030 MeV, and the first excited state was observed at an excitation energy of 1.62 ± 0.02 MeV. At the same time, an independent measurement of the mass excess of 17 C was obtained from the 48 Ca( 18 O, 17 C) 49 Ti reaction, and the value 21.039 ± 0.020 MeV is in excellent agreement with an earlier measurement. The first excited state of 17 C is at 295 ± 10 keV.

Masses and level schemes of 33Si and 34Si

Abstract The mass excesses of 33Si and 34Si have been measured using the 36S(11B, 14, 13N)33, 34Si; reactions. Values of −20.550 ± 0.030 MeV ( 33 Si) and −20.017 ± 0.025 MeV ( 34 Si) were obtained. In addition, an excited state of 34Si was observed at 5.33 ± 0.05 MeV, and excited levels of 33Si were observed at 1.06 ± 0.02 and 4.32 ± 0.03 MeV. These results are compared with recent shell-model calculations.

The 26Mg(18O, 17F)27Na and 26Mg(18O, 15O)29Mg reactions and the level schemes of 27Na and 29Mg

Abstract The 26 Mg( 18 O, 17 F) 27 Na and 26 Mg( 18 O, 15 O) 29 Mg reactions have been used to determine the ground-state masses and partial level schemes of 27 Na and 29 Mg. Values of −5514 ± 60 keV and −10600 ± 45 keV were determined for the mass excesses of 27 Na and 29 Mg, respectively. The probable structure of some of the levels observed was deduced from a comparison with shell-model calculations and with previous experimental information. A number of other 18 O- and 16 O-induced reactions on magnesium targets were also studied in order to obtain information on the reaction mechanisms of the ( 18 O, 17 F) and ( 18 O, 15 O) reactions.

Ground-state mass excesses and low-lying levels of the neutron-rich nuclei 36P, 35P and 34P

Abstract The ground-state masses and the excitation energies of low-lying levels of the nuclei 36P, 35P and 34P have been measured using the 36,34S(7Li,7Be)36,34P charge-exchange reactions, and the one-nucleon-transfer reaction 36S(6Li, 7Be)35P. Mass-excess values of −20.251 ± 0.027 MeV ( 36 P ), −24.828 ± 0.017 MeV ( 35 P ) , and −24.569 ± 0.040 MeV ( 34 P ) were obtained. A single excited state is observed at 252 ± 10 keV in 36 P , and a number of new levels are observed in the nuclei 35P and 34P. The 36,34S(11B, 11C)36,34P reactions were also studied in order to remove ambiguities associated with the 429 keV level in 7Be.

New measurements of the masses of 15B and 19N

Abstract The neutron-rich nuclei 15 B and 19 N have been produced in reactions between 18 O and 48 Ca. Mass excesses of 28.968 ± 0.025 MeV and 15.872 ± 0.020 MeV respectively were deduced from the reaction Q -values. These results are compared with previous measurements and theoretical predictions. Updated predictions using two different mass formulae are presented.

Time-of-flight system for a heavy ion magnetic spectrometer

Abstract A system to measure the time of flight for heavy ions around an Enge split-pole magnetic spectrometer has been developed. The system consists of a parallel plate avalanche counter at the focal plane and either a microchannel plate detector or a silicon recoil detector in the target chamber. In-beam tests under experimental conditions have demonstrated a typical resolution of 1.0 to 1.5 ns, compared to a total flight time of ∼ 100 ns. Resolution figures approaching these have been recovered, when using the 4.5° angular acceptance of the spectrometer, by applying calculated corrections to the raw data according to the angle and focal plane position. A description of the detectors is followed by the results of the in-beam tests. An example of an application to the study of a heavy ion reaction is also described.

The mass of 18N

Abstract States in 18 N have been populated with the 18 O( 7 Li, 7 Be) 18 N reaction at 52 MeV. The single ground-state peak observed in previous measurements using charge-exchange reactions is shown to be at least a doublet, which leads to a substantial revision of the ground-state mass of 18 N. The revised value of the mass excess is 13.116 ± 0.020 MeV. Several excited states of 18 N are also observed.

The mass and low-lying levels of 40Cl

Abstract The mass excess of the T z = 3 nucleus 40 Cl has been determined using the 40 Ar( 7 Li, 7 Be) 40 Cl reaction. A value −27.527 ± 0.035 MeV was obtained. A number of excited states of 40 Cl were a1so observed. In addition, the 40 Ar( 11 B, 11 C) 40 Cl and 40 Ar( 11 B, 13 N) 38 S reactions were investigated. Excited states of 38 S were observed at 1.28 ± 0.04 and 3.38 ± 0.10 MeV.

The 40Ar(13C, 14O)39S reaction and the ground-state mass of 39S

Abstract The ground-state mass excess of 39 S has been determined from a measurement of the Q - value of the 40 Ar( 13 C, 14 O) 39 S reaction using a gas target. A value of −23.164±0.050 MeV was obtained in good agreement with the predictions of standard mass equations. In addition, a single excited state was observed at 1.469 ±0.025 MeV. The reaction mechanism of the ( 13 C, 140 O) reaction is discussed in terms of a two-step reaction model based on the second-order Born approximation. The degree of angular-momentum matching appears to be an important factor in determining the degree of participation of a possible reaction channel. Calculations indicate that in the case of the 40 Ar( 13 C, 14 O) 39 S reaction, the reaction is dominated by a single path because of poor matching in competing channels.

Observations of 20n via the heavy-ion transfer reaction 48Ca(18O, 20N)46Sc

Abstract The Q -values for groups observed in the multinucleon transfer reaction 48 Ca( 18 O, 20 N) 46 Sc have been measured using a variety of heavy-ion spectrographic techniques. The group at lowest excitation energy has a Q -value of −25.87 ± 0.02 MeV, corresponding to a mass excess of 22.63 ± 0.06 MeV for 20 N. This is in significant disagreement with earlier determinations, being ∼1 MeV less bound. Possible explanations are discussed.