SECTIONAL TRANSACTIONS. 
SECTION A. 
MATHEMATICAL AND PHYSICAL SCIENCES. 
Thursday, September 5. 
Discussion on Nuclear physics (10.0). 
Rt. Hon. Lord RuTHERFORD oF NELson, O.M., F.R.S.—Recent 
advances in nuclear physics. 
Dr. C. D. ELtis— Some problems in induced radio-activity. 
Dr. J. D. Cocxcrorr.—The production of induced radio-activity on 
protons and deuterons. 
Mr. M. L. OvipHant.—The masses of the light elements as deduced 
from transmutation data. 
Mr. M. GotpuaBer.— The nuclear photo-electric effect. 
The paper deals with the nuclear photo-electric effect, the disintegration 
of nuclei by y-rays, which Dr. Chadwick and the author have been studying 
during the last year. Observations of such an effect were first made with 
heavy hydrogen, D, the nucleus of which can be split by high energy y-rays 
according to the equation 
DBs oie gee eS ce 
The photo-protons and neutrons have been observed. From the energy 
of the photo-protons the binding energy of the deuteron can be determined 
and the mass of the neutron linked up with the masses of H and D. The 
experimental value for the probability of this photo-electric disintegration 
of D agrees satisfactorily with quantum theoretical calculations. 
Investigations have also been made of the photo-disintegration of beryl- 
lium, first reported by Szilard and Chalmers. The energy necessary to 
remove a neutron from beryllium has been determined and a lower limit 
for the cross-section of disintegration of Be® by y-rays of radiothorium has 
been found. 
Dr. N. FeatHEer.—Photo-disintegration of the deuteron. 
A mixture of heavy methane and helium was introduced into an expansion 
chamber and photographs were taken with a source of radiothorium, of 
