Doug Cline

Doug Cline, who made major contributions to our understanding of nuclear structure, died on 20 June 2025 at age 90.

Multiple Coulomb excitation (Coulex) was first observed in Berkeley by John Newton and Frank Stephens in 1958. In 1965, Winther and de Boer developed the semiclassical Coulomb excitation computer code COULEX, which enabled quantitative analysis of multiple Coulex data. That development provided the first viable way to fully exploit the phenomenon in nuclear physics.

In 1966, Doug initiated a program to use heavy-ion beams from the new Rochester MP tandem accelerator to exploit the reorientation effect of multiple Coulex to measure static electric quadrupole moments of excited states. In 1969, he developed a heavy-ion gamma-ray coincidence technique to achieve greater sensitivity than that obtained using a magnetic spectrometer, which was used initially, and modified the COULEX code to calculate the gamma-ray yields from those experiments. That eventually led to the construction of the series of CHICO heavy-ion detector arrays of parallel-plate gas avalanche detectors that have been used in Gammasphere, GRETINA, and soon GRETA.

A major development to the data analysis came in 1979, when Doug demonstrated that it is possible to make a least-squares fit of the electromagnetic matrix elements to the experimental data and hence obtain their values in a model-independent way. That led to the development of the GOSIA code, which is now used by every research group worldwide to analyze Coulex data. Earlier, in 1971, Kumar had pointed out that scalar products of the deformation tensor are scalars under rotation. Doug immediately realized that this has broader implications in that scalar products of the E2 spherical tensors are rotational invariants, so that evaluation of the rotational scalar invariants in the laboratory frame will directly give the expectation values of the quadrupole tensor in the intrinsic frame. The rotational invariants can be used to determine the centroids, variance, etc., of the E2 distribution in the intrinsic frame for each state. Assumption of a geometrical collective model allows extraction of the model-dependent shape parameters (β, γ) from the model-independent E2 parameters if so desired.

The method has been applied to several nuclei, such as ¹⁶⁸Er, determined to have a prolate deformed shape (published in 1990), and ¹⁹²Os, found to be a triaxial rotor with fairly constant deformation (published in 1996). Those measurements are unique in that they provide a model-independent determination of the collective charge distribution in a nucleus. In particular, they are the only reliable probe of axial asymmetry of the nuclear shape.

Coulomb excitation also provides a unique measure of reflection asymmetry in a nucleus, in particular its octupole deformation that is related to the E3 transition moment. Doug’s group studied the octupole collectivity of ¹⁴⁸Nd in collaboration with Liverpool, showing that the collectivity corresponds to octupole vibrations of a prolate quadrupole deformed rotor. It was the first time that a comprehensive set of E2 and E3 matrix elements was determined for the ground-state rotational band and the couplings to the low-lying b- and g-bands. In the same year (1993), the measurements of E2 and E3 moments in ²²⁶Ra were published by a GSI-led collaboration that also made use of the GOSIA code.

The measurements that Doug and his group carried out in the 1980s and 1990s were tours de force that required significant amounts of experimental beam time and very complex data analysis. During this period, the main focus of the low-energy gamma-ray community was on high-spin physics, following the discovery of backbending in 1971 and superdeformation in 1986. The Coulex techniques developed at Rochester were widely admired but remained a niche area of research. That changed dramatically with the availability of low-energy accelerated radioactive beams in the early 2000s, as now many more radioisotopes became available for measurements using Coulex, which has many advantages for studying exotic nuclei using low-intensity beams. An early successful application of the “Rochester method” was the measurement of the coexisting shapes in ^74,74Kr carried out by a Saclay-led collaboration at the SPIRAL facility, GANIL in 2007, followed by measurements of the shapes of ^94,96Kr by a Cologne-led collaboration at the REX-ISOLDE facility, CERN, in 2012. A well-publicized measurement of E3 moments in ²²⁰Rn and ²²⁴Ra was carried out by a Liverpool-led collaboration in 2013. Octupole collectivity was also probed in the medium-mass region, where E3 moments were measured in ^144,146Ba using radioactive beams from the ATLAS-CARIBU facility at Argonne by a Livermore-led collaboration in 2016 and 2017.

Doug was born in York, England, on 28 August 1934. He received his BSc 1st Class Honors in physics (1957) and his PhD in physics (1963) from the University of Manchester. He joined the University of Rochester in 1963 as a research associate and was appointed as full professor in 1977. He was director of the University of Rochester Nuclear Structure Research Laboratory for the period 1988–99. He held visiting appointments at Laval University (1965), Niels Bohr Institute in Copenhagen (1973), Lawrence Berkeley Laboratory (1975–76), Australian National University (1978), and the University of Uppsala (1981). He was a fellow of the American Physical Society (1981) and a recipient of both the Lawrence Berkeley Laboratory Gammasphere Dedication Award (1995) and the 2013 Marian Smoluchowski Medal from the Polish Physical Society.

Doug was a passionate teacher and taught undergraduate and graduate physics courses from 1965 to 2015. He received the Award for Excellence in Teaching from the department of physics and astronomy in 2007 and 2009. He published more than 250 peer reviewed articles, and his book Variational Principles in Classical Mechanics is still used and downloaded by university classes around the world. There are many PhD students whom Doug has supervised, including the late Tomek Czosnyka (who wrote the GOSIA code), Danek Kotlinski (who measured ¹⁶⁸Er), Ching-Yen Wu (who measured ^186-192Os, ¹⁹⁴Pt and developed the CHICO detectors), Rich Ibbotson (who analyzed the ¹⁴⁸Nd data), and Adam Hayes (who analyzed ¹⁷⁸Hf isomeric data).

Doug served on many program, executive, and advisory committees, including the DOE/NSF Nuclear Science Advisory Committee. He served as associate editor of Physical Review C (1988–92). He was a founding member (1987–91) and chair (1989–91) of the Gammasphere Steering Committee and a founding member of the GRETA/GRETINA Steering Committee (1998–2013).

Doug had many interests outside of nuclear physics. He shared his love of canoeing, running, camping, cycling, and skiing with his family, and he was an accomplished classical pianist. He learned to fly power planes in 1965, but his real passion was for flying sailplanes, which he started in 1966, becoming a flight instructor for the Finger Lakes Soaring Club. He leaves behind his wife of nearly 50 years, Lorraine, and their children Julia (an electronic engineer), Geoff (a United Airlines pilot), and three grandchildren.

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