Answer by taking a quote from the following article:

Slotin was the first of three children born to Israel and Sonia Slotin, Yiddish-speaking refugees who had fled the pogroms of Russia to Winnipeg, Manitoba. He grew up in the North End neighborhood of Winnipeg, an area with a large concentration of Eastern European immigrants. From his early days at Machray Elementary School through his teenage years at St. John's High School, Slotin was academically exceptional. His younger brother, Sam, later remarked that his brother "had an extreme intensity that enabled him to study long hours."

The radiation doses received in these two accidents are not known with any semblance of accuracy. A large part of the dose was due to neutron radiation, which could not be measured by dosimetry equipment of the day. The available equipment, film badges, were not worn by personnel during the accident, and badges that were supposed to be planted under tables in case of disasters like these were not found. Disaster badges hung on the walls did provide some useful data about gamma radiation.  A "tentative" estimate of the doses involved was made in 1948, based on dozens of assumptions, some of which are now known to be grossly incorrect. In the absence of personal dosimetry badges, the study authors relied on measurements of sodium activation in the victims' blood and urine samples as their primary source of data. This activation would have been caused by neutron radiation, but they converted all doses to equivalent doses of gamma or X-ray radiation. They concluded that Daghlian and Slotin had probably received doses equivalent to 290 and 880 rem (respectively) of gamma rays. Minimum and maximum estimates varied from about 50% to 200% of these values. The authors also calculated doses equivalent to a mix of soft 80 keV X-rays and gamma rays, which they believed gave a more realistic picture of the exposure than the gamma equivalent. In this model the equivalent X-ray doses were much higher, but would be concentrated in the tissues facing the source, whereas the gamma component penetrated the whole body. Slotin's equivalent dose was estimated to be 1930 R (roentgen) of X-ray with 114 R of gamma, while Daghlian's equivalent dose was estimated to be 480 R of X-ray with 110 R of gamma. Five hundred rem is usually a fatal dose for humans.  In modern times dosimetry is done very differently. Equivalent doses would not be reported in roentgen; they would be calculated with different weighting factors, and they are not considered as relevant to acute radiation syndrome as absorbed doses. Recent documents have made various interpretations of Slotin's dose, ranging from 287 rad to 21 sievert. Based on citations and supporting reasoning, the most reliable estimate may be a 1978 Los Alamos memo which suggested 10 Gy(n) + 1.14 Gy(g) for Slotin and 2 Gy(n) + 1.1 Gy(g) for Daghlian. These doses are consistent with the symptoms they experienced.

When did Slotin perform this experiment?
1948,